Revision Flashcards
1
Q
Explain why the formation of sea ice is important for global ocean circulation.
A
When sea ice is formed, the salt in the water is rejected.
This makes the surface waters more dense than the surrounding ice-free waters.
Because the surface waters are dense they sink away from the surface.
As the dense waters sink they are replaced with less dense water, and this process drives a three-dimensional circulation which contributes to the global ocean circulation.
2
Q
Briefly explain what turbidity is and describe one method of measuring it in a water body.
Which of the following will present greater turbidity values: drinking water or untreated waste water?
A
Turbidity is a physical parameter used for assessing water quality. It gives a rough indication of the quantity of undissolved matter in water.
(Use one of the following methods for measuring the clarity of water).
The Secchi disk is a flat circular plate (20 – 30 cm diameter) with two quadrants painted black and two painted white.
The disk is lowered into the water until such a depth that it cannot be seen, which provides an indication of the waters turbidity.
The nephelometer is a device that measures the scattering of light at an angle of 90 degrees to the light source.
Light scattering is caused by suspended solids in water and occurs in all directions, however measurements at this angle are able to see smaller particles.
3
Q
Briefly state two relative advantages for each of the following methods of measuring a minor atmospheric constituent in the troposphere and stratosphere:
(a) Using a balloon.
(b) Using a polar-orbiting satellite.
A
(a) Relative advantages of a balloon measurement (any two from):
- Cheap and/or quick to build, launch and operate.
- Can measure more easily under cloud cover or close to the surface.
- The atmosphere can be sampled directly, in contrast to a remote indirect measurement.
- Measurements can be made as the balloon ascends, giving a more detailed vertical profile.
- Not necessarily restricted to a gas that has distinct absorption features at wavelengths in atmospheric spectral windows.
(b) Advantages to a polar-orbiting satellite measurement (any two from):
- Global coverage with a single instrument.
- May operate for periods of several years, giving better coverage in time.
- Provide access to regions where it is difficult to launce balloons, for either geographical or political reasons.
- Can potentially measure over a larger altitude range.
4
Q
Chlorofluorocarbons CFCs, are anthropogenic compounds, which add to the normal background level of stratospheric chlorine and have been linked to ozone depletion in this region.
(a) Chloromethane CH3Cl, is a natural source gas for chlorine atoms in the stratosphere.
Give one origin of this gas at the Earth’s surface.
(b) One CFC linked to stratospheric ozone depletion is CFC-113 which has an atmospheric lifetime T of 90 years.
To the nearest whole year, determine how long it will take for the atmospheric concentration of CFC-113 to fall to quarter of the level reached when all emissions cease.
(The lifetime of an atmospheric gas is related to the half like, t1/2 as t1/2 = 0.693 T.)
A
Natural sources at the Earth’s surface of CH3Cl are (any one of the following origins):
Formed by natural processes from the oceans. Burning of biomass. Volcanic activity. It will take two half-lives to reduce to a quarter of the atmospheric concentration, so one half-life is: t_(1/2)= 0.693 X 90=62 So two half-lives are: 62 X 2=124
It will take 124 years for the concentration of CFC-113 to fall to quarter of the level reached when all emissions cease.
5
Q
Briefly describe two major properties of soil organic matter that can enhance plant growth.
A
Any two of the following properties which can all enhance plant growth:
- Nutrient supply: the breakdown of soil organic matter releases nitrogen, phosphorus and sulfur (among other nutrients) that can be used by plants.
- Ion adsorption and desorption: through its high cation exchange capacity, organic matter can hold and release large amounts of nutrient cations in a form readily available to plants.
- Structure: humus binds soil particles together, stabilising the structure and allowing water and air to pass through to lower layers, as well as enabling easier root penetration and seedling emergence.
- Water holding capacity: organic matter has a high capacity to retain water, and the structure of soil that is rich in organic matter allows for easier water infiltration and reduced runoff.
- Colour: the dark colours characteristic of humus-rich soils absorb more sunlight at the surface than those of a lighter colour and, therefore give rise to warmer soils.
6
Q
Briefly describe the mechanism by which beach sediment is transported along a coastline.
A
Most waves strike the shore at an oblique angle. When oblique-angled waves hit a shoreline, they are reflected and generate a longshore current which flows parallel to the shore.
Because waves strike the beach at an angle, the swash of the wave travels obliquely up the beach, but the backwash flows straight down the beach.
The result is beach drift, a zigzag movement of sand and pebbles along the shore.
Beach sediment transport along the coastline results from the longshore current and beach drift. This transport is called longshore drift.
7
Q
Briefly describe the main factors determining the physical structure of habitats.
A
Physical structure of habitats is generally defined in terms of the dominant vegetation, such as trees or grasses.
Vegetation influences physical factors, for example habitat height, exposure, light regime and humidity.
Vegetation structure is affected by both abiotic growing conditions (climate, geology, soil), biotic factors (e.g. activity of organisms within the habitat: grazing, trampling, competition for light), and human activity.
The physical structure of aquatic environments is linked to the water depth, speed and turbidity.
Some habitats – such as caves, cliffs, glaciers, rock exposures, urban developments – do not have vegetation as the dominant structural factor.
8
Q
(a) Define species richness and species diversity.
(b) Two ecological communities may have the same number of species but score differently for measures of diversity.
Explain why this is the case.
A
(a) Species richness is the number of species in a site.
Species diversity is the number of species weighted by their relative abundance
(b) If one community is dominated by one or a small number of species and the other has a more even distribution of species the second community should be expected to score higher for diversity.
9
Q
Give one example of how sulfur may move naturally from the terrestrial crust into the atmosphere or oceans.
Explain how anthropogenic activities are increasing the flux of sulfur from the crust.
A
Sulfur-containing rocks (including shales and evaporites) eventually move into the oceans vai natural weathering and erosion.
Humans are increasing the flux of sulfur from the crust by mining and extraction of fossil fuels that contain sulfur.
Combustion of fossil fuels results in emission of sulfur to the atmosphere, much of which will be redeposited on land, or into the oceans through riverine flow or by directly being deposited on the oceans.
10
Q
Describe the causes and symptoms of eutrophication in aquatic environments.
A
Eutrophication is caused by an excess of nutrients in the water.
It usually causes explosive growth of algae or bacteria.
The volume of material can block sunlight, preventing autotrophs from photosynthesising, so oxygen levels in the water decline.
This can lead to increased mortality of animal life.
11
Q
Exhaust emissions from the internal combustion engine of motor vehicles can give rise to several primary pollutants in addition to H2O and CO2.
(a) Name one of these primary pollutants and describe how, and under what conditions, it is formed.
(b) The action of sunlight and the mixing of primary exhaust emissions gives rise to various secondary pollutants, such as ozone.
What is the term used to describe this type of pollution, which often occurs in urban areas?
A
(a) There are a total of four primary pollutants emitted from a vehicle (only one is required)
- Carbon monoxide (CO) and unburnt hydrocarbons (HCs), which are produced by incomplete combustion of fuel during traffic idling (and deceleration) when insufficient air is taken in for complete combustion to occur.
- Nitric oxide (NO), which is generated by the fixation of nitrogen from the air at the high temperatures in the engine.
- Particulate matter (PM), which again comes from the incomplete combustion of the fuel in the engine and is dependent on the type of fuel and engine conditions.
(b) This type of pollution is referred to as photochemical smog
12
Q
A sample of the mineral Almandite has the formula:
Fe3Al2Si3O12
What is the formal charge on iron (Fe) in this mineral, i.e. is the iron Fe(II) or Fe(III)?
Explain how you reached your answer, showing your calculations.
A
All the components of this mineral have fixed formal charges except Fe.
The other components are Al3+; Si4+; O2-
The sum of the positive charges must equal the sum of the negative charges.
Sum of positive charges
=[3 x (Fe)]+[2 x (Al)]+[3 x (Si)
=[3 x (Fe)]+[2 x 3]+[3 x 4]
=[3 x (Fe)]+6+12
=[3 x (Fe)+18
Sum of negative charge
=12 x (O)
=12 x 2
=24
Therefore, charge on Fe
= ((24-18))/([3 x (Fe)])
= 6/3=2
The iron is in the Fe(II) form
13
Q
Seed size varies greatly between different species of plant.
Describe any ecological trade-offs that exist with the respect to this attribute and the colonization of new habitats.
A
Small seeds can be efficiently dispersed, but have poor survival in hostile environments.
Large seeds have a better chance of survival, but may not be able to reach the new environment.
14
Q
Describe the time-scales on which the carbon cycle operates.
A
The carbon cycle involves a hierarchy of subcycles that operate on different timescales, stretching from years to millions of years.
The terrestrial carbon cycle is the shortest term subcycle, with residence times of tens of years.
The marine carbon cycle is the intermediate-term subcycle, with residence times of thousands of years.
The geological carbon cycle is the long-term subcycle, with residence times of millions f years.
15
Q
The sea surface in the centre of a North Atlantic gyre, which is rotating in a clockwise direction, is raised by about 1 meter.
Briefly describe the reason for this.
You should include a sketch as part of your answer.
A
The sea surface is raised (in the Northern Hemisphere) because Ekman pumping results in water flow at 90° to the right of the current direction, i.e. towards the centre of the gyre.
Water piles up in the centre of the gyre, raising the sea surface, see sketch below
16
Q
Describe and account for differences in the annual variation in runoff from a river in southwest England and a glacier fed stream in western Greenland.
A
In southwest England, runoff is likely to be highest in the winter months when rainfall is relatively high and evapotranspiration is at its lowest rate.
In western Greenland, the glacier is frozen during the winter and does not feed into the river, so runoff is low to zero at this time. However, in the summer the glacier melts so runoff will be highest at this time.
17
Q
Briefly Describe the difference between porosity and permeability in rocks, and use these concepts to explain why chalk is a good aquifer.
A
A rock is permeable when water can flow easily through it, whereas the percentage of a rock that is comprised of space is its porosity.
Chalk has both high permeability and high porosity, and thus is a good aquifer.
The high permeability means that water can flow through it easily and the high porosity means that it can retain a lot of water.
18
Q
Outline two ground surface features that act to reduce rainwater infiltration
A
(any two including the mechanism)
Dense vegetation, through the interception of rainfall
Steep slopes, as water runs off rapidly reducing time for infiltration to occur
Concrete / Roofs / Covered surfaces all of which prevent water passing through
19
Q
Saturated ground can become frozen and form permafrost in polar regions or at high altitudes.
(i) Why is there very little permafrost in the Southern Hemisphere?
(ii) Why is widespread flooding common in permafrost regions?
(iii) Why is the progressive thawing of permafrost of concern?
A
Most of the land where permafrost could form in the Southern Hemisphere is already covered with glacial ice.
(ii)
In winter rivers are frozen and their flow is minimal. As the thaw occurs, ice dams are common features and the rivers become blocked and flood their banks. In addition, the permafrost is relatively impermeable.
(iii)
Progressive thawing of permafrost is a concern because
Many buildings are constructed on permafrost. As the permafrost retreats their foundations may become unstable and cause buildings (and other structures and trees) to collapse. It can release methane, which is a greenhouse gas so will likely cause increased atmospheric warming.
20
Q
A researcher is interested in assessing how flow rate in a small river changes seasonally and over several years. Describe the equipment they could use and the data they might collect using this method. Explain some of the disadvantages of using your suggested method.
A
Since the researcher is interested in looking at change over several years as well as with the seasons, they could look to build a v-notch weir with a stilling well
Providing the weir can be built on an impermeable bedrock, so that there is no groundwater flow, or throughflow via the soil, out of the catchment.
If the weir is not on an impermeable bed, an allowance must be made for these other pathways.
This equipment is suitable for assessing flow rate over long periods of time and does not require frequent visits to the site. The stilling well would contain a logger or chart recorder which would continuously record the height of the water: the more water flowing down the stream the higher the water level recorded by the logger or chart recorder.
Flow rate can be calculated directly from the water height.
The disadvantages of this method are that it is expensive to install and involves some disturbance of the system. It may therefore not be suitable for all sites or purposes.
21
Q
Briefly describe the processes that allow the climate system to maintain an equilibrium temperature on average, despite the difference between the two curves in Figure 2.
A
Polewards heat transfer in the atmosphere is required to maintain an equilibrium temperature.
This is largely accomplished by the Hadley circulation at low latitudes, and by frontal cyclones at mid latitudes, which develop on fronts separating warm and cold air masses and transport heat and moisture poleward and upwards.
Heat is transported by the movement of warm air polewards, or in the form of latent heat transport by evaporation at lower latitudes
22
Q
Describe how incoming and outgoing radiation vary with latitude for typical July conditions compared to the annually averaged conditions illustrated in Figure 2.
Explain how this change in radiation will change the Hadley cells, compared to their annual average form.
A
In July, the incoming radiation is shifted towards the Northern Hemisphere as a result of the seasonal variation of insolation, peaking at around 23° N.
It drops to zero south of around 67° S (the Antarctic Circle) because of the Earths tilt.
The outgoing radiation curve is less strongly affected, as this depends fundamentally on the absolute temperature of the atmosphere, but compared to the annual average it would be slightly lower in the Southern Hemisphere and slightly higher in the Northern Hemisphere.
In the annual average, the Hadley cells are symmetrical about the equator, with rising branches at the Equator, the point of maximum net heating.
In July, the rising branches will move north with the point of maximum incoming radiation (and so maximum net heating), resulting in rising motion north of the Equator and a larger, weaker cell crossing the Equator into the Southern Hemisphere.
23
Q
Stratospheric ozone is created and destroyed in the cycling of reactions known as the Chapman mechanism
Figure 3 A reaction cycle showing the creation and destruction of Stratospheric ozone
(i) The first reaction in the cycle involves the photolysis of an oxygen molecule, O2 Write out this reaction and define what is meant by ‘photolysis’
(ii) From Figure 3, Write out the other three reactions in the cycle.
Briefly indicate the processes involved in each reaction with respect to the production and destruction of ozone in the stratosphere.
(iii) Stratospheric ozone is an important filter of UVB radiation.
If ozone is destroyed in the stratosphere what effect will this have on the absorption of UVB radiation and potential consequences at the Earth’s surface?
A
(i) The reaction at the top of the cycle is
O2 + hv → O + O (R1)
In Reaction 1, photolysis is the fragmentation of a molecule of O2 initiated by the absorption of ultraviolet radiation (hv) at a wavelength of about 240 nm, generating highly reactive free atoms and/or radicals of O.
(ii) From the reaction cycle:
Free O atoms generated from Reaction 1 combine with O2 molecules to form ozone
O2 + O → O3 (R2)
Ozone adsorbs ultraviolet radiation (hv) itself, which leads to photolysis in:
O3 + hv → O2 + O (R3)
Ozone encounters a free O atom and is converted back into O2
O3 + O → 2O2 (R4)
Hence, ozone is being created and destroyed in the cycle by Reactions 2 and 3, and finally removed from the cycle by Reaction 4.
(iii) Ozone destruction would increase UVB radiation reaching the Earth’s surface and potentially cause an increase in its harmful effects, such as damaging DNA, proteins, lipids and membranes in plants and animals at the Earth’s surface as well as sunburn, eye damage and skin cancer in humans.
24
Q
Explain any five functions of soil on the Earth’s land surface.
A
(A) Any five of the following functions of soil:
• Water storage for vegetation and life forms:
Soils retain water which is available to a variety of organisms in different ways.
Soils differ in their capacity to store water and organisms which use soil water vary in their ability to extract water stored in soil.
• Habitat:
Soils are home for many organisms which live exclusively or predominantly in them.
• Nutrient storage and retention:
Macro-nutrients such as Carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulfur, calcium and magnesium as well as a range of micro-nutrients including iron, manganese, boron, zinc, copper, chlorine, molybdenum, cobalt and nickel are stored in soils
Different soils have different capacities for nutrient storage and retention.
• Nutrient recycling:
Carbon, oxygen, nitrogen and other nutrients are recycled through the action of plants, fungi and microbes in the soil.
• Structural support to plants:
Soil gives plants a medium to grow into.
Different soils are able to support plants differently.
• Filtration and purification of toxins:
Toxins may be broken down or filtered out by biotic or abiotic processes in soil.
25
Briefly outline the role that naturally acidic rain plays in rock weathering.
Rainwater dissolves carbon dioxide from the air and so is naturally slightly acidic.
This has a particular effect on the chemical weathering of carbonite rocks and leads, for example to underground cave systems in limestone areas.
This weak acid is also the initiator of the chemical reaction between silicate rocks and water, known as hydrolysis.
Feldspar exposed to an acidic aqueous solution of carbon dioxide reacts, releasing metal ions and dissolved silica into solution and leaving behind a solid clay mineral, kaolinite.
26
{12 marks} Discuss the causes of soil acidification that occur:
(i) Naturally with time, and
(ii) As a consequence of human action.
Soils may acidify naturally as plants take up positively charged nutrients which are exchanged for acidifying hydrogen ions.
However, basic cations are normally returned to the soil, which should counteract this acidification, as broad-leaved trees shed their leaves and, eventually, die.
This is why the development of coniferous forests over time leads to greater soil acidification. (unless the underlying geology means that the soil is well buffered against this.)
(ii)
Acid deposition may occur as a consequence of atmospheric pollution, with atmospheric sulfur being the main acidifying agent. (Nitrogen deposition is also important for acidification.)
Afforestation by humans may also lead to soil acidification, as this often involves extensive coniferous plantations.
Also, as trees are harvested, basic cations are exported from the ecosystem resulting in acidification.
27
Explain with reference to Figure 4, the distinction between population extinctions due to chance (random) variations in population size and extinctions due to a consistent reduction in the size of the population.
Name one cause of chance variation and one cause of consistent reduction
The figure contrasts extinction due to chance (random) events with no long-term change in average size (Figure 4a) with extinction due to consistent reduction in population size with little variation around the mean (Figure 4b).
Extinction may also be due to a combination of the two processes, as shown in Figure 4c.
Chance events may be due to annual climate variation causing direct mortality or affecting food supply, while consistent reduction may be due to continuous habitat loss, possibly through direct anthropogenic activity, or long-term trends in climate (rising sea levels, increased mean temperature).
28
Explain how Population Viability Analysis can be used to inform the conservation of threatened species.
Population Viability Analysis (PVA) is the application of population dynamics theory to the conservation of rare species.
It aims to help estimate the probability that a population or a species will go extinct within a certain timeframe.
This allows a risk of extinction to be estimated.
Population Viability Analysis has been used to estimate the minimum viable population required for a species to persist.
29
How does the International Union for the Conservation of Nature (IUCN) Red List use information on population size, population change and extinction risk to categorise threatened species?
```
The IUCN Red List categories threatened species as follows:
Extinct (+ extinct in the wild)
Critically Endangered
Endangered
Vulnerable
```
Based on different factors
Species with small populations are given higher threatened status than those with large populations.
Species which are experiencing rapid population declines are given higher threatened status that those with stable populations.
Species where PVA has identified a high risk of extinction are given higher threatened status than those with low risk.
30
A group of conservation biologists were concerned about the effect of woodland management on population of a rare butterfly in Britain.
They wanted to compare population density of the butterfly in ten woodlands which were being managed with coppicing with ten woodlands which were not coppiced.
(i) Explain what coppicing is and how it affects woodlands.
(ii) Describe a study that conservation biologists could carry out to answer their question.
Write down a suitable study hypothesis and null hypothesis.
State an appropriate statistical test foe the comparison between woodlands and explain why you have chosen that test.
Coppicing is the cutting of trees at their base periodically to encourage new growth.
It opens up areas of woodland, and forms a mosaic of conditions allowing light from the canopy to reach the forest floor and creating structural diversity which provides increased niches for a range of species.
It can benefit a range of woodland species
(ii)
The conservation biologists could carry out visual surveys of butterflies using a walk and count method in each woodland.
They would need to ensure that they walked the same survey line/ transect length in each woodland to make it a fair comparison between sites.
They should do several transects in each woodland to account for habitat variation in each woodland.
They should do their surveys in similar weather conditions and at similar times of day to make them comparable.
A suitable study hypothesis would be:
Coppicing has a significant effect on butterfly population density
A suitable null hypothesis would be:
There is no significant difference between butterfly population density in coppiced and un-coppiced woodlands
Because the study is looking at differences between two samples the Mann-Whitney U-test would be appropriate for a statistical analysis,
31
Describe how population size can be assessed in insects and elephants
Assessment of population size generally requires sampling of the population rather than counting all the individuals in a population.
Sampling involves counting part of the population or using indirect estimates of numbers of individuals and then scaling up to the whole population.
Examples relevant to insects include walk-and-count with mark-release-recapture.
Elephant numbers can be assessed by sampling density of dung.
32
Explain using appropriate examples, how information on variation in population size from year to year could be included in a plan to conserve a species of woodland butterfly.
Variation in population size is an important factor to consider when assessing the likelihood of population extinction (see answer to part ‘a’ of this question).
This variation can be quantified as standard deviation around the mean.
A population with higher variation around the mean and a lower mean population size is likely to be more vulnerable, i.e., more likely to go extinct.
This information can be included in population viability analysis and combined with other information, such as geographic range in Red List criteria.
A plan to conserve woodland butterfly species should respond to information on population variation, e.g., high variation may be due to seasonal changes in host plant availability for breeding butterflies.
Management, such as thinning the canopy to maintain a suitable light environment for the host plant, could help reduce the variation in population size.
33
Briefly explain how an ecosystem services assessment might benefit the conservation of African elephants.
Ecosystem services provide a way of valuing different components and functions of an ecosystem.
African elephants, as large and iconic herbivores, may provide a cultural services (both to local people and more widely to visitors, with possible benefits of ecotourism income).
Maintenance of large grassland or savannah ecosystems may also contribute to other ecosystem services (provisioning, regulating or supporting).
34
Describe the different ways in which dinitrogen gas (N2) may be transferred from the atmosphere to terrestrial nitrogen reservoirs.
Pay particular attention to the different fluxes and processes in your answer.
Nitrogen in the form of dinitrogen (N2) is chemically stable, and so is not useful to terrestrial ecosystems in this form. The nitrogen must therefore be “fixed” into a form that is biologically available. N2 can be fixed naturally and artificially, as explained below.
A small natural component of the total amount of bioavailable nitrogen is fixed by lightening, which converts N2 to NO. The NO then reacts to form NO2 and subsequently HNO2 and HNO3, which are deposited on land in rain water.
However, overwhelmingly, the majority of nitrogen fixed directly from the atmosphere is vai nitrogen-fixing organisms.
Such as certain species of free living cyanobacteria, and bacteria that exist in a symbiotic relationship with plants such Rhizobium bacteria which lives in the root nodules of legumes.
Dinitrogen may also be fixed through an industrial process known as the Haber-Bosch process. Here N2 is reacted with H2 under high temperatures and pressure in the presence of a catalyst to form ammonia (NH3). This ammonia is then used in the production of fertiliser, which is available for plants so can enter the terrestrial reservoir.
35
Briefly explain how nitrogen in terrestrial reservoirs may be transferred to the atmosphere.
Ammonia (NH4) can be volatilised from soil.
| Nitrate (NO2) can be denitrified in oxygen-poor soils to form N2 N2O or NO
36
(i) What is the main anthropogenic source of atmospheric nitrogen?
Explain how anthropogenic nitrogen in the atmosphere affects the amount of biologically active nitrogen in terrestrial ecosystems.
(ii) Describe how an increased amount of biologically active nitrogen affects the composition of a terrestrial plant community.
(i)
The main anthropogenic source of nitrogen within the atmosphere is produced by the combustion of fossil fuels, for example from vehicles and powerplants.
The burning of fossil fuels releases NO into the atmosphere, which will react further with O2 to form NO2.
Both NO and NO2 are highly soluble in rain/cloud water to form HNO2 and HNO3 is deposited in rain and dissociates to release biologically active NO2- and NO3-
(ii)
An increased amount of biologically active nitrogen can change the plant species within a terrestrial community, which will impact the community composition.
The biomass of species that can respond to the elevated nitrogen by increasing growth or productivity will increase; whereas, in contrast plant species that are unable to adapt to the high concentration of nitrogen by increasing their growth will be eliminated through competition. Therefore, overall it is likely that the species richness will decline.
37
Figure 5 is a Hjulstrőm diagram. Using this diagram as a guide, describe the erosion process and the processes of detachment, entrainment and deposition
The process of erosion can be seen as a sequence of three events: detachment, entrainment, and transport.
Erosion begins with detachment, where a piece of rock is released from the rock around it, to become an unattached rock fragment.
Physical weathering leads to detachment by purely mechanical means which can occur in many different ways.
Chemical weathering breaks down minerals formed at higher temperatures and pressures and transforms them into new minerals that are more stable at the Earth’s surface.
Biological weathering can facilitate detachment by providing cracks and fissures that may be exploited by physical and chemical weathering.
Entrainment is the process which lifts particles off the bed or ground and sets them in motion.
Entrainment is resisted by friction between the particle and its neighbours and the force of gravity.
If the drag created by the fluid is sufficient to overcome the horizontal resistance of friction and vertical resistance gravity, the particle will begin to move.
The critical speed at which entrainment occurs is related to grain size.
The largest (heavy) and smallest (cohesive) particles are entrained at higher speeds.
Transport can occur in four different ways: solution, suspension, saltation and traction.
Transport will continue until there is a reduction in the speed of the medium or an increase in the resistance of the particles (i.e. flocculation).
If either of these occurs, the ability of the medium to transport will be reduced and deposition is the result.
38
Explain how rates of glacial erosion are inferred using glacial meltwater and list the variables that can affect the reliability of this technique.
Rates of erosion for glaciers are frequently inferred by the sediment yield of a glacier, i.e. the mass of sediment per unit area by melt water.
This is relatively easy to measure and should reflect the rate at which sediment is produced by erosion beneath the glacier.
It is not yet possible to define a constant relationship between glacier formation and sediment yield because of several variables:
* Variations in glacier mass balance and flow rate.
* Nature of the bed rock.
* Stability of the channels.
* The relaxation time of the previous glaciations, i.e. the abundance of transportable sediment exposed during glacial retreat.
* Variations in meltwater discharge.
39
Using your knowledge both of energy flow through ecosystems and of habitat fragmentation, explain why populations of large carnivores are now particularly susceptible to extinction.
Your answer should address:
(a) {7 marks} Food chains, including energy transfer and efficiency;
(b) {7 marks} range and energy requirements;
(c) {6 marks} habitat requirements and habitat changes.
Large carnivores will tend to be at or near the top of the food chain. Probably secondary or tertiary consumers.
There are therefore three or four steps in the food chain between the original energy source, sunlight, and these large consumers.
The potential for energy to enter an ecosystem is determined by the amount of solar radiation it receives, which in turn is determined by its area and position on the globe.
The transfer of energy from one trophic level to the next is inefficient.
Typically, only 0.1% of solar radiation becomes stored in the tissues of primary producers.
Less than 1% of this would be expected to become incorporated into the tissue of a primary consumer in many ecosystems. And each additional step of the food chain would result in a further 90% loss of available energy.
Therefore, tertiary consumers would have only 0.001 x 0.01 x 0.1 = 1 x 10-6 of the energy entering the system potentially available to them as prey, whilst in contrast a primary consumer would have 10-3 of this amount of potentially available to them as food, a difference of 1000. {NB these values are dimensionless in the model answer!!}
One could therefore estimate that for a tertiary consumer to sustain a population as large as that of a primary consumer of similar body size, it would require a land area 1000 times larger. Even if the large carnivore were a secondary consumer (e.g. a lion), this figure would still be 100.
The result is that large carnivores need a very large range to support their energy requirements.
Examples of large carnivores: bears, wolves, tigers, eagles and sharks.
These are highly mobile animals moving over large distances to locate and kill prey.
Habitat fragmentation has two effects on the range of large carnivores.
First, it reduces the total area of habitat and therefore reduces the amount of energy entering the ecosystem (for example the fragmentation of woodland in Britain has reduced its total area by more than 95%).
Second, it may introduce barriers to movement of these animals within their range. Dissection of forest with tracts of open grassland may confine predators to small blocks of woodland because they are unwilling to cross unfamiliar. {NB the model answer just stops there! I would add territory or ground to finish the sentence}
In summary, large carnivores require large tracts of suitable habitat to sustain them because of the inefficiency of energy transfer up the food chain.
Fragmentation of the habitat may confine populations to areas too small to sustain them in the long term. Putting them at risk of extinction.
In addition to its effect on area, habitat fragmentation causes other changes to the environment which may place large carnivores at greater risk of extinction.
Disturbance from human activity (logging, ranching, fishing, etc.) may impact on the behaviour of both the carnivores themselves and that of their prey, upsetting the predator / prey balance.
Opening up a habitat such as a forest during its fragmentation provides routes such as logging tracks along which {human} hunters can travel. Large carnivores are often targets for such hunters and so there could be a top-down control on their population size.
40
(ii) {2 marks} Some researchers have argued that the changes in the pH of the lake are not due to acid rain but to other processes.
Briefly outline two processes other than acid rain that are thought to lead to acidification of lake waters.
(iii) {2 marks} Name the gas that is primarily responsible for causing acid rain.
What is the principal source of this gas?
(iv) {2 marks} In the introduction to part (b) of the question, it is stated that the fish population of Big Moose Lake has declined.
Why does acidification of lake waters lead to a decline in fish populations?
(v) {2 marks} Indicate the two principal approaches taken to manage the problem of lake acidification.
(ii) Natural acidification (e.g. respiration by plant roots)
Change in land use (e.g. conifer afforestation / heathland regeneration / decline in upland agriculture)
(iii) Sulfur dioxide
Burning fossil fuels
(iv) Acidification leads to an increase in dissolved aluminium (Al3+) in lake waters and this is thought to lead to fish kills.
(v) Liming of lake waters to counteract acidity
Reduction in sulfur emissions
41
How can water content of soil be determined?
By drying the soil in an oven
```
Soil is weighed
Then put in an oven at 105 degrees where it is dried for 24 hours
The soil is then weighed after
The mass loss represent water
1L = 1kg
```
42
What are held in the pores of soil?
Water and air
43
How big is a micropore?
<0.08mm
44
How big is a macro pore?
>0.08mm
45
What is porosity?
The ratio of the volume of void spaces in a rock or sediment to its total volume
46
What is secondary porosity?
Porosity that has been caused by fractures or weathering in a rock or sediment after it has been formed
47
What is air filled porosity?
The proportion of a soils volume that is occupied by air
48
What type of soil do macropores generally dominate?
Sandy soils
49
What type of soil does micropores generally dominate?
Fine textured soils eg clay silt
50
What can macropores be created by?
Crack opening by clay that has been wet and then dried
Soil freezing and thawing
Living organisms roots, worms, termites
51
What is considered unavailable water in terms of soil moisture?
There is still water in the soil below the PWP, but it cannot be extracted by plants and is therefore called unavailable water.
52
Are micropores usually filled?
Yes they are most of the time filled with water
53
What type of soils have greater water holding capacity and why?
Fine textured soils dominated but clay or silt have better water holding capacity because they are made of micropores which are mostly filled with water all the time and are poorly drained so are prone to flooding
54
Do sandy soils have good water holding capacity?
No they are made of macropores so the rapid movement of water and air occurs
Larger pores may be filled with roots
55
What does the rate of percolation depend on?
The rate of percolation is highly dependent on soil structure and texture. The rate of water movement is greatest in sandy soils or very well-structured soils.
56
How can you determine the porosity of soil?
```
Take an undisturbed core of soil
Saturate the soil with water
Weigh it
Then completely dry out the soil
Weigh it again
```
Porosity % = saturated mass - dry mass(coverted to volume)/volume of core
57
A soil is sampled, using a soil core of volume 100 cm3, and the difference between saturated mass and dry mass is determined to be 50 g.
Given that the density of water is 1 g cm−3 at room temperature, calculate the porosity of the soil.
Because 50 g of water occupies 50 cm3 in total:
Porosity = 50 cm3/100 cm3 x 100
Thus the porosity of this soil is 50 cm3 of pores in 100 cm3 of undisturbed soil, or 50%.
58
In addition to total pore space, what is it important to know for estimating important properties of soils, such as ease of drainage?
It is important to know the proportions of different sizes of pore, particularly the relative proportions of macropores to micropores, and how the pores are connected together.
59
Does clay give plants good availability to water?
despite its high porosity, much of the water in a clay-textured soil (pores < 0.0002 mm or < 0.2 µm in size) may be held with such strength that it is not available to plants. Such a soil may have a high water content but poor water availability.
60
What type of soil can plants get better water availability?
On the other hand, free-draining sandy soils, with large pores, may contain little water in those pores. Most of them may be filled with air. Usually, it is the intermediate-sized pores (0.2–80 µm) which store water that is available for plants to use
61
What is permeability?
The permeability of a soil is the ease with which water passes through the soil.
62
How is permeability related to porosity?
Permeability is related to porosity, pore size distribution and how well the pores are interconnected. Pores must be large enough for water flow to occur; so clay soils have high porosity but low permeability.
63
Describe the porosity and permeability of clay
clay soils have high porosity but low permeability.
64
What is field capacity?
When the last drop of water has fallen from the pot, the drainable water has drained away and the soil is said to be at field capacity (FC). In this condition, the soil is holding as much water as it can against the force of gravity
65
What is available water in terms of soil moisture?
The amount of water held between field capacity and permanent wilting point is called the available water.
66
What is permanent wilting point?
When the plant will be unable to extract sufficient moisture to survive.
At this point, the soil is said to be at its permanent wilting point (PWP)
67
What is considered unavailable water in terms of soil moisture?
There is still water in the soil below the PWP, but it cannot be extracted by plants and is therefore called unavailable water.
68
How does soil water content at field capacity differe from different textures of soil
The soil water content at field capacity differs greatly for different textures of soil. In general, the finer the texture of the soil, the more water it can hold at field capacity. Soils with a high clay content can hold several times more water at field capacity than very sandy soils
69
What is infiltration?
Infiltration is the process whereby water from rainfall, irrigation or snowmelt enters the soil pores and becomes soil water.
70
What is percolation?
Once it has infiltrated, water moves through the soil by percolation. If the soil is wet, or the rainfall intensity is high, the water will move rapidly through the larger pores
71
What is the water cycle and what is it driven by?
• The water cycle involves the movement of water, in all its forms, over, on and through the soil and rocks near the surface of the Earth and in the atmosphere. This cycle is driven by the Sun’s energy and the Earth’s gravity.
72
What are the three mechanisms for soil water movement?
There are three mechanisms of soil water movement:
saturated flow
unsaturated flow
as water vapour.
73
What does the movement of water into and through a soil have implications on?
The movement of water into and through a soil has implications for soil formation, plant growth, surface runoff and erosion. It also has implications for the transport of nutrients and pollutants.
74
How will water percolate through soil if it is dry and the rain intensity is low?
If the soil is dry, or the rainfall intensity is low, water will move more slowly than in wetter soils, and it will move through the finest pores. These differences are important because water moving more slowly through finer pores has more time to react chemically and physically with organic matter, clay particles, soil minerals and the soil biota.
75
What are the major components of soil solution?
The major components of the soil solution include:
ions derived from atmospheric deposition
carbon dioxide from root respiration
dissolved nutrient ions from the decomposition of organic matter
dissolved inorganic ions from weathering.
76
What ions from atmospheric deposition (rain and snow) are found in soil solution?
Rain and snow typically contain:
basic cations (Ca2+, Mg2+, K+, Na+) from dust, sea spray and volcanoes
anions, for example Cl− from sea spray, NO3− and SO42− from car exhaust gases and power stations
ammonium (NH4+) from the agricultural emission of ammonia (NH3)
CO2 from the atmosphere and H+ from acids.
77
How do ions from atmospheric deposition affect the soil and plants?
Dust particles which have been filtered out by leaves (conifers are particularly effective at this), atmospheric chemicals adsorbed on leaves or bark, or aerosols absorbed into leaves can all be washed to the soil surface in rain or snowfall. This precipitation, with its dilute chemicals, percolates through the soil.
The cations are often vital nutrients for vegetation. They also play an important role in maintaining a high soil pH.
The anions, particularly nitrate, are also plant nutrients. Sulfate is a plant nutrient but is usually not required in large amounts. The excess either washes through the soil solution or is adsorbed by hydrous oxides or organic matter. Chloride is barely used by most plants and washes away through the soil.
78
Explain how root respiration create CO2?
Levels of dissolved CO2 in soil solution can easily exceed atmospheric CO2 concentrations by a factor of 10 or more. This is because of root and microbial respiration, especially in warm, wet climates where respiration is high.
By creating high concentrations of CO2 in the soil, living organisms strongly influence the geochemical process of rock weathering.
79
What dissolved nutrient ions from the decomposition of organic matter are found in soil?
Organic material is rich in carbon and nitrogen. It also contains phosphorus and other elements. These nutrients are released into the soil solution during decomposition, making them available for use by plants and microbes. Dissolved C, N and P compounds are often rapidly recycled back into living matter.
80
What dissolved inorganic ions in soil come from weathering?
The basic cations Ca2+, Mg2+, K+ and Na+ are made available to the soil solution through cation exchange with clays and organic matter. But their primary source is usually rock weathering.
Phosphorus is also supplied to the soil from the weathering of rocks, in particular those containing the mineral apatite.
The concentration of dissolved silica in the soil solution is also regulated by the rates of chemical weathering of the silicate matrices in clays, and the minerals in silicate rocks.
81
What percentage of soil is air and what pore does air usually occupy?
It may not be immediately obvious that soil contains air. In fact, most soils contain about 25% air by volume. Whereas most soil water is held in the smallest pores, soil air is usually held in larger pores.
82
What type of soil have more pore space?
Sandy soils generally have a higher dry bulk density than clayey soils. In other words, sandy soils have less pore space than clayey soils. At first, this may seem difficult to believe, because sandy soils usually appear more porous than clayey soils.
However, sandy soils have only a relatively few very large pores and almost no small pores, whereas clayey soils have many extremely small pores. In other words, the total pore space is greater in clayey soils.
83
How is the oxygen that plants receive controlled mainly by?
The amount of oxygen is controlled mainly by macropore space, soil water content and oxygen consumption by soil biota.
84
What is the hydraulic head determined by?
The speed of water movement down a slope through saturated soil between two points in a catchment is determined by the hydraulic head, the hydraulic conductivity of the soil and the distance between the two points (Darcy’s law).
85
What are the chemical constituents of soil air?
Soil air is held in larger pores. The chemical constituents of soil air include oxygen, carbon dioxide, methane and nitrous oxide.
86
What is dry bulk density?
Dry bulk density is the mass of a specific volume of dry soil and, therefore, includes pore space as well as solids.
87
What is the water cycle and what is it driven by?
• The water cycle involves the movement of water, in all its forms, over, on and through the soil and rocks near the surface of the Earth and in the atmosphere. This cycle is driven by the Sun’s energy and the Earth’s gravity.
88
What does the depth of saline water under a land at the coast depend on?
There is usually saline groundwater under the land at a coast, with a wedge of denser saline groundwater under the fresh groundwater. The depth to the saline groundwater depends on the height of the water table above sea level and the densities of the fresh and saline water.
89
What is residence time of water?
• Residence time is also a measure of the rate at which water in different parts of the cycle is renewed: it is fastest in the atmosphere (about 11 days) and rivers (a few weeks).
90
How to calculate residence time for water?
• The residence time for water in a reservoir is the average length of time that water remains in that reservoir. It is calculated by dividing the mass in a particular reservoir by the rate of transfer to or from the reservoir.
91
What is interception?
Interception is the process by which precipitation is prevented from reaching the ground by vegetation.
92
Where is precipitation the greatest?
• Precipitation has a very uneven global distribution, but is greatest near the Equator. On a smaller scale, precipitation is greatest over mountainous areas on land.
93
How is water returned to the atmosphere?
Water is returned to the atmosphere by evaporation and transpiration
94
What is transpiration?
Transpiration is the process by which plants draw water from the soil, transfer it to their leaves and it then evaporates
95
What is evapotranspiration?
The combination or evaporation and transpiration
96
What can ecosystem services be classified as?
Ecosystem services can be classified as cultural, provisioning, regulating and supporting, each of which can be applied to water.
97
What does the rate at which water infiltrates the ground depend on?
The rate at which water infiltrates into the ground depends on the permeability of the rocks and the state of the ground surface. Below the ground surface is an unsaturated zone which has air in the pore spaces, and a saturated zone which has all the pores filled with water.
98
What is an unconfined aquifer?
Unconfined aquifers outcrop at the ground surface; water normally has to be pumped to the surface from the water table in these aquifers.
99
What is water below the water table known as?
Water below the water table is called groundwater. The
100
Does the water table follow the topography?
The water table follows the topography of the ground surface but with gentler gradients.
101
What does darcys law relate?
Groundwater will flow in response to differences in elevation and pressure. Darcy’s law relates the rate of the groundwater movement (Q) to the hydraulic conductivity (K), the cross-sectional area (A) and the hydraulic gradient or slope of the water table (h/l):
102
What does hydraulic conductivity depend on?
The hydraulic conductivity depends on the permeability of the rock and the properties of the water. Water generally flows in the direction of the hydraulic gradient and the slope of the water table.
103
Pumping water from wells or boreholes lowers the water level (or potentiometric surface) in the surrounding area. Water flows into the borehole, and this creates a cone of depression around it. The difference in height between the water table before pumping and the water level in the well during pumping is called the drawdown.
What is the drawdown?
104
What does the depth of saline water under a land at the coast depend on?
There is usually saline groundwater under the land at a coast, with a wedge of denser saline groundwater under the fresh groundwater. The depth to the saline groundwater depends on the height of the water table above sea level and the densities of the fresh and saline water.
105
What is porosity a measure of?
Porosity is a measure of how much water a rock can store
106
What is permeability a measure of?
The permeability of a rock is a measure of the properties of the rock which determine how easily water can flow through it.
107
What type of rocks are porosity and permeability generally greater in?
The porosity and permeability are generally greater in unconsolidated sedimentary rocks, particularly sands and gravels, than in consolidated sedimentary, igneous or metamorphic rocks.
108
What processes can increase porosity and permeability and what is this known as?
Both porosity and permeability can be increased by processes that occur after the formation of the rock, such as solution or fracturing. These are called secondary porosity and secondary permeability.
109
What is an aquifer?
An aquifer is a body of rock that can store water, and through which water can flow.
110
What qualities must a rock have to be a good aquifer?
For a rock to be an aquifer it must be sufficiently porous and it must be permeable.
111
What type of rocks do not make good aquifers?
Igneous and metamorphic rocks seldom make good aquifers unless they have both secondary porosity and secondary permeability.
112
What is specific yield?
The proportion of water that can be recovered from a saturated aquifer is known as the specific yield
113
What will flood alleviation around a river depend on?
Flood alleviation will depend on individual river characteristics.
114
What is an unconfined aquifer?
Unconfined aquifers outcrop at the ground surface; water normally has to be pumped to the surface from the water table in these aquifers.
115
What is a confined aquifer?
Confined aquifers are separated from the ground surface by an impermeable layer.
116
What is artesian water?
Water in confined aquifers is called artesian water, and wells that penetrate confined aquifers are called artesian wells.
117
What is the potentiometric surface?
The potentiometric surface is an imaginary surface joining the heights to which water will rise. For an unconfined aquifer, the potentiometric surface is the water table. If the potentiometric surface lies above ground level then water will naturally flow from a well.
118
What is the safe yield of an aquifer?
| What would happen if you exceed the safe yield?
The safe yield of an aquifer is the maximum rate of extraction of water that does not produce a long-term decline in the average water table level or have any other adverse effect, such as a significant reduction in the flow to springs and rivers. Exceeding the safe yield (i.e. ‘mining’ groundwater) would necessitate pumping from progressively greater depths to obtain water, and might lead to a reduced flow to springs and rivers, and a deterioration in water quality.
119
What does the effectiveness of an aquifer as a water supply depend on?
The effectiveness of an aquifer as a water supply depends on the hydraulic conductivity, K and also on the thickness of the aquifer.
120
What is the transmissivity of an aquifer?
• The effectiveness of an aquifer as a water supply depends on the hydraulic conductivity, K and also on the thickness of the aquifer. The product K × b, where b is the aquifer thickness, is called the transmissivity of the aquifer.
121
How can aquifers be characterised?
Aquifers can be characterised in terms of their geological, hydrological and hydraulic properties. Measurements of these properties can be conducted in the field and in the laboratory.
122
How can you age groundwater?
Groundwaters move very slowly, particularly where they are confined. The age of a groundwater sample can be determined from levels of the radioactive isotopes, and also other tracers (such as CFCs) present in groundwaters.
123
What are the 4 main routes for precipitation to travel through a catchment?
The four main routes for precipitation to travel through a catchment are: channel precipitation, Qp; overland flow, Qo; groundwater flow, Qg; and throughflow, Qt.
124
What factors determine the relative importance of precipitation through a catchment?
• The factors determining the relative importance of the routes include: the nature of the ground surface, vegetation, and underlying soil and rock; topography; the duration of a rainstorm; and the existing water content of the ground.
125
What is a catchment area?
The area in which rainfall flows in to a river, lake or reservoir
126
What are hydrographs useful for?
• Hydrographs are useful for understanding river discharge patterns and predicting peak river flows. They can be used to link rainstorm and river flow rate with time and to estimate flood frequencies from discharge data.
127
What does the shape of a short period and long period hydrograph depend on?
• The shape of a short-period hydrograph (the record for a few days) depends on the size, shape, geology, vegetation and land use of the river catchment. The shape of a long-period hydrograph (e.g. for a year) depends primarily on the type of climate in the river catchment.
128
What is river flooding the result of?
River flooding is the result of a complex series of factors including precipitation, infiltration rates and routes of water flow
129
What will flood alleviation around a river depend on?
Flood alleviation will depend on individual river characteristics.
130
Where does the journey of a river begin?
The journey of a river begins at the source, which is often a spring or seepage, which occur at points where groundwater reaches the surface
131
Which part of a river has the most speed?
•The speed of water in a river channel is not uniform over a cross-section, being slower where the water is in contact with the riverbed and faster nearer the centre of the channel
132
What affects the speed of the river?
The nature of the riverbed also affects the water speed, as does the gradient.
133
What indicates the efficiency of the river flow?
The hydraulic radius of a river channel indicates the efficiency of the river flow.
134
Explain what a river is like with a low hydraulic radius?
Rivers with a low hydraulic radius are less efficient and have greater friction with the riverbed and banks
135
How can river speed be estimated?
• River speed can be estimated using a float, a flow rate meter, a V-notch weir, the Manning equation or dilution gauging.
136
What are the 2 major factors controlling the characteristics of estuaries?
Two major factors controlling the characteristics of an estuary are water flows (tides and currents) and depositional processes.
137
Where are the deep passages to the northern sea?
The deep passages to the northern seas are only in the Atlantic Ocean and they are relatively shallow.
138
What is deposition of fine estuarine sediments assisted by?
Deposition of fine estuarine sediments is assisted by flocculation and slack water at high tide.
139
What can colours or changes in smell of sediment detect?
• Changes in the colour and/or smell of a sediment can be used to detect the presence or absence of oxygen.
140
What can reservoirs be used for?
• Reservoirs increase the amount of water stored on the land surface. They can be used for water supply, river regulation, hydroelectricity generation or flood prevention.
141
What are the negative impacts of human built dams?
Reservoir projects involving large dams are increasingly subject to scrutiny, particularly on the grounds of sustainable development. The negative impacts of constructing a reservoir include the loss of a large area of land, human resettlement, ecological changes, dam failure, sediment filling, sediment loss to agriculture, soil salinisation and induced earthquakes.
142
What is pollution of water?
Pollution is the deterioration of water quality caused by human agencies that makes the water less suitable for use than it was originally. Water does not have to be completely pure to be considered unpolluted.
143
Why is rainwater slightly acidic?
Rainwater contains a greater relative proportion of dissolved gases, particularly carbon dioxide, than seawater, and this makes it slightly acidic.
144
What different sources can pollution come from?
domestic sewage, farms, industry, mining, quarrying and cooling.
145
Name some different types of pollutants?
There are many types of pollutants, including natural organic materials, living organisms, plant nutrients, organic and inorganic chemicals, sediments and heat.
146
What other parameters might be measured when measuring water quality?
In monitoring water quality several different chemical parameters might be measured (such as pH, water hardness, oxygen demand, nitrogen compounds, metals and pesticides).
147
How are most pathogens introduced in to the water?
Most pathogens are introduced into water as a result of animal or human faecal contamination.
148
What are routine microbial indicators of water quality?
Routine microbial indicators of water quality are coliforms, E. coli and enterococci.
149
What happens to sewage? Where does it end up?
Sewage treatment aims to reduce the amount of organic and suspended solid material present, remove toxic materials and eliminate pathogenic bacteria, mainly by settlement of biological processes. The effluent is discharged into rivers, lakes or the sea, and the remaining sludge may be dumped at sea (but not in the EU), disposed of on farmland, dumped in landfills or incinerated.
150
Explain the hydrology of permafrost affected regions?
The hydrology of permafrost-affected regions is typically highly seasonal with runoff restricted to a few weeks in spring/summer, and is influenced by unfrozen groundwaters circulating in taliks, river freezing/thawing and consequent flooding, and by the formation of icings, which provide an important redistribution of water between winter and summer.
151
How is heat moved around the planet?
Heat is moved around the planet by the oceans and can affect regional climate
152
What are typical features of the oceanic floor?
Typical features of the oceanic sea floor include the continental shelf, abyssal plains and mid-ocean ridges.
153
Where are the deep passages to the northern sea?
The deep passages to the northern seas are only in the Atlantic Ocean and they are relatively shallow.
154
What makes the salt ions in seawater constant?
• The constancy of composition means that the ratio of many different dissolved salt ions in seawater is constant.
155
What heats the surface of seawater?
• Seawater is heated at the surface by solar radiation and the salinity of seawater is controlled by the balance between evaporation and precipitation, E–P.
156
What is the effect of wind stress on the surface of the ocean passed through?
• The effect of the wind stress on the surface of the ocean is passed down through the water column through eddy viscosity and energy is transferred into the water column.
157
What is the net result of the ekman spiral in the north and south hemisphere?
• The net result of the Ekman spiral in the Northern Hemisphere is to cause a slow transport of moving water to the right of the wind. In the Southern Hemisphere it causes a slow transport of moving water to the left.
158
What drives the ocean conveyor belt? What does it also do?
• The processes that drive a circulation pattern throughout the Atlantic Ocean also operate in the other oceans of the world. The differing densities of water have set up a global circulation pattern which is drawn
schematically as an ‘oceanic conveyor belt’ that redistributes large amounts of heat around the Earth.
159
What is the crysophere?
• The majority of fresh water on the surface of the Earth is in the form of snow and ice, and is known as the cryosphere
160
What is the state of health of an ice massed expressed through?
• The state of ‘health’ of an ice mass is expressed through its mass balance: the sum of mass gain (accumulation) and mass loss (ablation). When an ice mass is in a state of equilibrium with the climate, the annual net mass balance is zero; this rarely occurs in practice.
161
Explain the run off of snow and ice?
Snow and ice assume great importance in the hydrology of catchments. Runoff is low or even absent in winter, increases greatly with the onset of spring/summer, then dwindles again as the snow cover diminishes. This is the opposite of typical catchments.
162
How can glaciers have a dramatic impact on the landscape?
• Glaciers erode, transport and deposit rock debris and can have a dramatic impact on the landscape.
163
What percentage of earth is affected by periglacial conditions?
• As much as 25% of the Earth’s surface is affected by periglacial conditions, characterised by intense frost weathering and permafrost.
164
What is permafrost?
Generally regarded as permanently frozen ground, but more correctly perennially cryotic ground.
165
Name some perglacial landscape processes?
• Periglacial environments exhibit many distinctive landscape processes, including frost weathering, frost heaving, frost creep, frost cracking and gelifluction.
166
Explain the hydrology of permafrost affected regions?
The hydrology of permafrost-affected regions is typically highly seasonal with runoff restricted to a few weeks in spring/summer, and is influenced by unfrozen groundwaters circulating in taliks, river freezing/thawing and consequent flooding, and by the formation of icings, which provide an important redistribution of water between winter and summer.
167
What are hazards of the cryosphere?
Hazards include glacier advances and unstable glaciers, ice avalanches, glacier floods, glacier–volcano interactions and snow avalanches. Some of these have caused great loss of life in mountain regions around the world.
168
What is the oceanic conveyor belt?
Global oceanic circulation through a series of strong currents, driven by deep water formation in the polar seas and heating of water in the tropical seas; an effect of temperature and salinity differences. Also called thermohaline circulation.
169
What are the layers of thin gas that surround the earth called?
• The Earth’s atmosphere is a thin layer of gas surrounding the planet. It has several distinct layers, including the troposphere, stratosphere and mesosphere.
170
Which layer of the atmosphere does most of the mass lye within?
Most of the mass of the atmosphere lies within the troposphere, within 8 - 15 km of the Earth’s surface. The troposphere is deeper at the Equator than at the poles.
171
Explain what happens to the temperature in the diffferent layers of the atmosphere?
The temperature falls with height within the troposphere, but increases within the stratosphere, then falls again in the mesosphere.
172
What gases is the atmosphere mainly made up of and to what ratio?
The atmosphere is made up of a mixture of gases but is mainly nitrogen and oxygen in a ratio of roughly
4 : 1.
173
What does the amount of solar radation that a location on the earth depend on?
The amount of solar radiation that a location on Earth receives depends strongly on its latitude and the season of the year.
174
Which part of earth receives the most radiation and which part radiates the most?
The Earth receives an excess of solar radiation at the Equator but radiates more than it receives at the poles.
175
What does the motion of the atmosphere play a large part in?
• The motion of the atmosphere plays a large part in moving heat from the Equator to the poles and gives rise to the weather.
176
What is the stability of the atmosphere to vertical motions determined by?
• The stability of the atmosphere to vertical motions is determined by the rate of decrease of temperature with height.
177
What does the rotation of the earth play a crucial role in in terms of weather?
• The rotation of the Earth plays a crucial role in determining the large-scale circulation in the atmosphere of the Earth, constraining the circulation cells and resulting in mid-latitude weather systems. The rotation direction is opposite in each hemisphere.
178
What is pressure in the atmosphere related to?
Pressure is a fundamental variable which describes the atmosphere and is related to the total mass of air above any point.
179
What happens to pressure with increasing height?
• Pressure falls exponentially with increasing height above the surface.
180
What are horizontal pressure gradients closely related to?
• Horizontal pressure gradients are closely related to winds;
181
How can precipitation occur?
• Precipitation can occur as rain, snow or hail, but largely forms initially in clouds as ice crystals.
182
Why do winds tend to follow pressure contours?
• Winds tend to follow pressure contours as a result of the Coriolis Effect largely balancing the pressure gradient force.
183
What is the coriolis effect?
The influence of the Earth's rotation on the motion of air across its surface which produces an apparent deflection of air to the right of the direction of motion in the Northern Hemisphere, and to the left of the direction of motion in the Southern Hemisphere.
184
What is the coriolis force?
An apparent force invented to explain the deflection of bodies moving over the surface of the Earth without being frictionally bound to it. It acts 90° to the right of the direction of motion in the Northern Hemisphere, and 90° to the left in the Southern Hemisphere.
185
what is the Ekman Spiral?
The vertical spiral pattern of water velocities that develops in the upper ocean as a result of the Coriolis force acting on moving water. The pattern develops to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere.
186
Which direction do winds circle in the northern and southern hemisphere?
Winds circle low pressure systems anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The rotation is opposite for high pressure systems.
187
What is temperature related to?
• Temperature is related to the mean speed of molecules in a gas and has a major impact on both the environment and human life.
188
What does the ideal gas equation of state link?
• The ideal gas equation of state links the pressure, temperature and density of air. If any two of these variables are known, the third can be determined.
189
what is specific humidity?
The specific humidity is a measure of the total amount of water in the air.
190
What is relative humidity?
The relative humidity indicates how close the air is to the condensation temperature and so how dry the air will feel.
191
What can a psychrometric chart be used to convert?
A psychrometric chart can be used to convert between drybulb temperature, wetbulb temperature, partial pressure of water vapour and relative humidity.
192
How does water condensation play a large role in determining the stability of the troposphere?
• Water condensation plays a large role in determining the stability of the troposphere. Conditionally unstable air is stable to a dry ascent but unstable to the ascent of a parcel of air which is saturated and warmed by the condensation of water.
193
When do clouds, mists and fogs form?
Clouds, mists and fogs form when the air reaches its dewpoint temperature.
194
What is the dewpoint temperature?
The temperature to which the drybulb temperature of an air sample must fall to produce saturation, at constant barometric pressure and absolute humidity.
195
What do the ten genera of clouds indicate?
• The ten genera of clouds indicate their formation mechanism and the type of precipitation, if any, that they are likely to form.
196
What are dews and frost a result of?
Dews and frosts result from the condensation of water or ice directly on the surface.
197
How can precipitation occur?
• Precipitation can occur as rain, snow or hail, but largely forms initially in clouds as ice crystals.
198
What type of radiation is the most important in atmospheric energy?
The most important for atmospheric energy transfers are ultraviolet, visible and infrared radiation.
199
What type of waves are solar radiation and which part of the electromagnetic spectrum are they on?
Solar radiation is mainly in the ultraviolet and visible parts of the electromagnetic spectrum.
200
What part of the electromagnetic spectrum is terrestrial radiation mainly on?
Terrestrial radiation is mainly in the infrared part of the spectrum.
201
What happens to electromagnetic radiation by gases and particles as it passes through the atmosphere?
Electromagnetic radiation is scattered and absorbed by both gases and particles in the atmosphere.
202
What is the bulk composition of the atmosphere and what percentage are trace gases? What is the most abundent trace gas?
The bulk composition of the atmosphere is a mixture of nitrogen (N2) and oxygen (O2) gases. Trace gases make up less than 0.1% by volume, the most abundant being methane (CH4).
203
What is meteorology and what does it measure?
• Meteorology is an observational science and a wide variety of instruments are used to measure atmospheric variables, including pressure, temperature, wind, humidity, clouds, precipitation, sunshine and constituent gases.
204
What is weather a result of on a global scale?
The weather is a result of global-scale processes which move heat from the Equator to the poles.
205
What cells dominate in low latitudes?
At low latitudes, the circulation is dominated by longitudinally symmetrical Hadley cells.
206
What type of weather systems dominate in mid latitude?
At mid-latitudes, waves take over most of the heat transport, which manifests at the surface as low-pressure and high-pressure weather systems.
207
What cells dominate at high latitudes?
At high latitudes, polar cells form, associated with a polar high and subpolar low and a polar vortex in the upper winter troposphere.
208
Why does the northern and southern hemispheres have different weather patterns?
The Northern and Southern Hemispheres do not behave as mirror images of each other, largely as a result of the different distribution of land in each hemisphere.
209
What happens when colder and warmer air masses meet?
Where colder and warmer air masses meet at the polar front, instabilities can develop which then form mid-latitude depressions.
210
What are fronts in terms of weather?
The borders between air masses are called fronts. They behave differently according to whether warm air is advancing into cold air, or vice versa.
211
How can large mountain ranges change the weather?
The presence of large mountain ranges can enhance precipitation on the upwind side and form rain shadows on the downwind side.
212
Define the term climate?
Climate is a time average of weather statistics, formally taken over a period of 30 years.
213
What are hurricanes and typhoons examples of?
• Hurricanes and typhoons are examples of intense, low-pressure weather systems, more generally known as tropical cyclones.
214
What 5 conditions does a tropical cyclone require?
• The development of a tropical cyclone requires five conditions:
o a warm ocean surface (temperature above about 26 °C)
o a moist troposphere
o an atmosphere which is not too stable, to allow the development of deep cumulonimbus clouds
o light winds, which will not disrupt the developing structure
o initial development at least 5° latitude away from the Equator.
215
What hemisphere are tropical cyclones more common in?
• Tropical cyclones are more common in the Northern Hemisphere than in the Southern Hemisphere. The existence of any storms in the South Atlantic Ocean strong enough to be classed as tropical cyclones is in dispute.
216
What type of surfaces causes tropical cyclones to grow and weaken?
Tropical cyclones tend to grow in strength over warm tropical sea surfaces and to weaken over land surfaces and when they move to colder seas.
217
How are humans mainly affected by topical cyclones?
The impact of tropical cyclones on human life can depend more on the associated flooding and landslides than on the direct effects of the wind.
218
What is the bulk composition of the atmosphere and what percentage are trace gases? What is the most abundent trace gas?
The bulk composition of the atmosphere is a mixture of nitrogen (N2) and oxygen (O2) gases. Trace gases make up less than 0.1% by volume, the most abundant being methane (CH4).
219
Hoe does the wavelength affect the energy associated with it?
The shorter the wavelength (λ) of electromagnetic radiation, the higher the energy of the associated photons.
220
What happens to incoming solar UV radiation when passing through the atmosphere? What is photolysis?
Different atmospheric constituents absorb different wavelengths in the incoming solar UV radiation, leading to photolysis, splitting molecules into highly reactive fragments (free atoms and radicals), and hence initiating chemical change.
221
What layer in the atmosphere is ozone most abundent?
• Ozone (O3) occurs in trace amounts throughout the atmosphere, but its concentration varies markedly with altitude. Concentrations peak in the ozone layer in the stratosphere
222
How is ozone in the atmosphere formed?
All ozone in the atmosphere is formed photochemically – from the photolysis of O2 (at λ < 240 nm) in the stratosphere.
223
Why does the temperature increase in the stratosphere?
• Absorption of solar UV radiation during the ozone cycle heats the stratosphere and is responsible for the temperature inversion at the tropopause (the boundary between the troposphere and stratosphere).
224
How is ozone formed in the stratosphere?
• All ozone in the atmosphere is formed photochemically – from the photolysis of O2 (at λ < 240 nm) in the stratosphere
225
How is ozone formed in the troposphere?
from the photolysis of NO2 (at λ < 400 nm) in the troposphere
226
How has background ozone in the troposphere formed?
• Background levels of tropospheric ozone have increased over the past century, alongside the growth in anthropogenic sources of the main precursor gases (CH4, CO and NOx). These sources include enhanced biogenic emissions (linked to food production, waste management and biomass burning) and emissions related to the extraction or distribution and the combustion of fossil fuels
227
What primary pollutants are emitted from a vehicle?
The classes of primary pollutants emitted from a vehicle with an internal combustion engine (in addition to H2O and CO2) are carbon monoxide (CO) and a wide range of unburnt hydrocarbons (HCs), accompanied by other partial oxidation products. In addition, nitric oxide (NO) is generated by the fixation of nitrogen from the air at the high temperatures involved in the combustion reaction. On leaving the exhaust system, NO can be oxidised to NO2, so that, overall, NOx is a pollutant.
228
What particulate matter is emitted from the internal combustion engine?
A further important emission arising from the internal combustion engine is particulate matter (PM). Typically, this is made up of carbonaceous material with volatile organic compounds (VOCs) either sorbed on the solid matter or present as hydrocarbon droplets. Sulfates and nitrates can also be present.
229
What causes acid rain?
one of the primary pollutants, including PM, are desirable additions to the atmosphere, causing significant health problems and contributing to environmental hazards such as acid rain.
230
What is the major factor in the build-up of NOx and hydrocarbons in the atmosphere?
Emissions from motor vehicles are a major factor in the build-up of NOx and hydrocarbons in the atmosphere, and hence the problem of photochemical smog.
231
What systems are in place to cut motor vehicle emissions?
Pollution abatement measures designed to drastically cut motor vehicle emissions involve various catalytic systems. • A three-way catalytic converter in petrol driven vehicles is fitted into the exhaust system.
232
How do catalyst converters achieve control of exhause emissions?
Control of exhaust emissions is achieved by promoting reactions that have the net effect of simultaneously oxidising CO and HCs (to CO2 and CO2 + H2O, respectively) and reducing NO (to harmless N2).
233
What main elements are the earths crust formed of?
• The rocks of the Earth’s crust are composed of minerals, principally formed from the elements oxygen and silicon
234
What is the rock cycle?
• The rock cycle, in which any rock may be converted into other rock types, is a cycle in which rocks are continually formed and destroyed.
235
How are igneous rocks formed?
Igneous rocks are formed by the cooling and crystallisation of magma. Examples are ocean-floor basalts, and andesite and granite of the continental crust.
236
How are sedimentary rocks formed?
• Weathering and erosion of pre-existing rocks, resulting from interaction with water and the atmosphere, lead to the formation of sediments. Subsequent compression and cementation (the lithification process) give rise to sedimentary (or fragmentary) rocks, which include sandstones and shales (or mudstones). Limestones are usually formed from fragments of ancient life forms. ?
237
What are metamorphic rocks?
Metamorphic rocks – gneiss, schist and slate – are former igneous or sedimentary rocks, transformed by heat and pressure. They frequently contain minerals which differ from those in the source rock, often distributed in layers.
238
What can igneous rocks in the earths crust be divided in to?
Igneous rocks in the Earth’s crust can be divided into coarse-grained (intrusive) and fine-grained (extrusive) groups.
239
What does grain size of a rock depend on?
Grain size depends on the rate of cooling.
240
What do MAfic rocks contain a high proportion of?
• Mafic rocks contain a high proportion of the mafic (ferromagnesian) minerals olivine and pyroxene, so they have high levels of iron, magnesium and calcium. Felsic
241
What do felsic rock contain a high proportion of?
Felsic rocks have a high proportion of the felsic minerals feldspars and quartz (silica), so they have more sodium, potassium and silicon.
242
what do intermediate rocks mainly contain?
Intermediate rocks have mainly feldspar and amphibole.
243
As magma cools which minerals crystallise first?
As magma cools, mafic minerals crystallise first, then pyroxene and amphibole, then feldspars and mica and, finally, quartz
244
What causes metamorphic rocks?
• Heat from cooling magma, or heat and pressure from deep burial or tectonic activity, bring about contact and regional metamorphism, respectively. More intense metamorphism results in larger crystals.
245
How are metamorphic rocks different from the original rock
• Metamorphic minerals have closer packed crystal structures than the original rock.
246
What are the three main clay minerals? and how are they structured?
• The three main clay minerals are kaolinite (aluminium-rich), illite (potassium-rich) and montmorillonite (iron/magnesium-rich). They have a layered structure of 1 : 1 or 2 : 1 sheets of silicate tetrahedra and aluminium (or magnesium) octahedra with metal ions between the layers.
247
What do limestone consist mainly of?
• Limestones consist mainly of calcium carbonate, generated by chemical precipitation (e.g. oolitic limestone) or from fossil fragments, and cemented by calcite.
248
What are the three main silicate sedimentary rocks?
• Silicate-based sedimentary rocks – conglomerates (breccias), sandstones and mudstones (shales) – are classified according to size, sorting and fragment shape.
249
What interacts to to result in physical and chemical weathering?
• The interaction between the atmosphere, water and rock-forming minerals results in physical and chemical weathering.
250
What are the different types of physical weathering?
• Physical weathering is a mechanical process, breaking rocks into smaller fragments through frost shattering, crystal formation, heating and cooling, root growth, and attrition during transport.
251
Why does chemical weathering occur?
• Chemical weathering occurs because minerals formed at depth are unstable at the Earth’s surface, in the presence of oxygen and aqueous acid (especially CO2 in water). Silicate rocks disintegrate, forming new minerals, an aqueous solution of metal ions and ‘silicic acid’ (sometimes called ‘soluble silica’), and residual resistant material.
252
What does calcium in limestone dissolve in to?
• Calcium carbonate in limestone dissolves to form calcium and hydrogen carbonate ions.
253
When a primary mineral weather to a clay mineral what does it become deficient in?
When a primary mineral weathers to a clay mineral, it becomes deficient in potassium, sodium, calcium, magnesium and silicon, which weather out more easily than aluminium or iron.
254
What are all clays enriched and depleted of?
All clays are enriched in aluminium compared with the original mineral, but depleted in silicon.
255
What are the highly weathered soils of the tropics dominated by?
• The highly weathered soils of the tropics are dominated by hydrated oxide clays, oxides and hydroxides of iron, aluminium or manganese, which are formed by hydrolysis and oxidation reactions.
256
What can the rocks beneath your feet be?
The rocks beneath your feet can be either the bedrock geology (the solid rocks – igneous, Hi sedimentary or metamorphic) or, where they occur, the superficial deposits (recent unconsolidated sediments) overlying the bedrock, or a combination of both.
257
What three sources does the energy for transporting material into and out of the landform system come from?
The energy for transporting material into and out of the landform system comes from three sources: the Earth’s internal heat, solar radiation and gravity.
258
What 4 steps in the process of erosion divided in to?
• The process of erosion is divided into four steps: detachment, entrainment, transport and deposition
259
What are fluvial processes driven by?
• Fluvial processes are driven by the potential energy of water, evaporated from the sea and precipitated at higher elevations.
260
What does fluvial mean?
of or found in a river.
261
What can material transported by streams be divided in to?
• Material transported by streams can be divided into three fractions: dissolved load, suspended load and bedload.
262
What can be calculated to determine the extent at which a stream is straight, meandering or braided
• The extent to which a stream is straight, meandering or braided is determined by calculating the sinuosity and braiding index.
263
What is the height of a wave determined by?
• The height of a wave is determined by the fetch and the wind speed.
264
How can a wave contribute to a beach?
• Depending on the height and wavelength, a wave may be constructive and build up a beach, or destructive and remove material from a beach.
265
What is longshore drift?
• Wave action erodes material from the coastline and transports it along the beach by longshore drift.
266
How can glaciers physically shape landscape?
• Glaciers and ice sheets can physically shape landscapes by the erosion, transportation and deposition of material through the landscape.
267
What physical actions lift material into ice?
• The physical actions of scooping, plucking and scouring lift material into the ice.
268
What erosive features indicate that glacial action has removed material locally?
• Erosive features, such as cirques, arêtes, horns and glacial trough valleys, indicate that glacial action has removed material locally.
269
What depositional features indicate that material has accumulated locally as a result of glacial action?
• Depositional features, such as moraines, eskers and erratics, indicate that material has accumulated locally as a result of glacial action.
270
How does wind erode material?
• Wind erodes material by deflation and abrasion.
271
How does wind transport eroded material?
• Wind transports eroded material by suspension, saltation and traction (surface creep).
272
What are dunes
• Dunes are asymmetrical with a gentle windward slope and a steep leeward slope. The movement of grains up and over the dune causes the slope to migrate downwind.
273
dunes occur in a number of forms depending on....?
• Dunes occur in a number of forms, depending on wind strength, wind direction, sediment supply and vegetation cover.
274
What are soils
• Soils are naturally occurring, unconsolidated materials consisting of mineral and organic components that are potentially capable of supporting plant growth.
275
What are soils composed of?
• Soils are composed of inorganic matter, organic matter, water and air.
276
What are important basic soil qualities?
• Soil structure (the organisation of the soil) and soil texture (the proportions of different particle size fractions) are important basic soil properties.
277
What does carrying out a risk assessment involve?
• Carrying out a risk assessment involves:
o identifying the hazards
o identifying the possible harm and seriousness of that harm
o assessing the likelihood of the hazard occurring.
The risk is the product of the likelihood that a hazard will cause harm and the seriousness of the harm.
278
What are the 5 formation factors of soil?
• There are five soil formation factors: parent material, climate, biota, topography and time.
279
What are the 4 soil forming processes?
• The four soil-forming processes are:
o addition of materials such as organic matter from leaves and roots, or atmospheric dust
o loss of components, such as leaching of soluble salts or erosion of particulate matter from the soil surface
o transformation, such as organic matter breakdown or mineral weathering
o translocation of material from one depth of the soil to another.
280
How do soils develop?
• Soils often develop a distinct vertical profile through the long-term accumulation of organic material at the surface, leaching of water and weathering of minerals.
281
What do the horizons within a soil profile reflect?
• The horizons within a soil profile may be different colours or textures. This reflects the sum total of the processes of organic matter deposition and decomposition, water movement, rock weathering and biological activity that have formed the soil so far.
282
What are soil classification systems based on?
• Soil classification systems group soils on the basis of chemical, physical and biological properties. National soil classification schemes are often used in addition to international systems because they are well suited to the particular types of soils found in a particular country.
283
What are the 6 major soil groups in the UK system?
• The UK system contains six major soil groups: lithomorphic soils, brown soils, podzols, gley soils, peat soils and man-made soils.
284
What is the international soil classification system?
• International soil classification systems include the World Reference Base for Soil Resources (WRB). This aims to correlate across systems and contains 32 major soil groups.
285
What can be assessed using the Munsell chart?
• Soil colour, which is assessed using the Munsell chart, can indicate differences in soil characteristics.
286
What makes a soils texture?
• The mineral fraction of soils comprises sands, silts and clays. The proportions of these components make the soil’s texture.
287
What contributes to a soils physical and chemical properties?
• Sand and silt contribute mainly to a soil’s physical properties, whereas clays contribute to both the physical and the chemical properties.
288
What is organic material in a soil composed of?
• Organic material in soil is composed of matter that is, or was, living. The non-living organic matter is ultimately degraded to humus. This consists of dark-coloured, highly degraded organic compounds that are resistant to further decay.
289
What does soil organic matter influence?
• Soil organic matter influences such fundamental soil properties as nutrient supply, ion exchange, structure, water-holding capacity and soil colour.
290
What is cation exchange capacity
• Cation exchange capacity (CEC) is the ability of a soil to adsorb and exchange cations with the surrounding soil solution. The CEC of a soil depends primarily on the amount of organic matter and the amount and type of clays in the soil.
291
What is anion exchange capacity?
• A soil’s capacity to retain anions is called its anion exchange capacity. Soils with a low pH and a high proportion of hydrous oxide clays can have a substantial anion exchange capacity (e.g. highly weathered tropical or semi-tropical soils).
292
What is base saturation?
• Base saturation is the ratio of the basic cations (Ca2+, Mg2+, K+ and Na+) to the total CEC. In general, soils with a high base saturation have a higher pH and are more fertile than soils with a low base saturation. Base saturation can be increased by adding lime to soils.
293
What is soil structure in an arrangement of?
• Soil structure is the arrangement of sand, silt, clay and organic matter into a series of stable units or aggregates.
294
What can good soil structure facilitate?
• Good soil structure facilitates water infiltration, root penetration and seedling emergence and minimises erosion. Poor cultivation practices can damage soil structure.
295
Explain what darcys law is?
• The speed of water movement down a slope through saturated soil between two points in a catchment is determined by the hydraulic head, the hydraulic conductivity of the soil, and the distance between the two points (Darcy’s law).
296
What are major components found in soil solution?
• The major components found in the soil solution include ions derived from atmospheric deposition, carbon dioxide from root respiration, dissolved organic nutrient ions, and dissolved inorganic ions from weathering.
297
What are the chemical components in soil air?
• Soil air is held in larger pores. The chemical constituents of soil air include oxygen, carbon dioxide, methane and nitrous oxide.
298
What does the level of aeration influence in soil?
• The level of aeration of a soil influences organic matter decomposition, soil colour, plant growth, and the form and concentration of many nutrients and pollutants.
299
What is particle density and dry bulk density?
• Particle density is the mass per volume of the different particles in the soil. Dry bulk density is the mass of a specific volume of dry soil and, therefore, includes pore space as well as solids.
300
What influence does the distribution of micropores and macropores have on soil? What type of soil does each tend to dominate in?
• The distribution of micropores and macropores in a soil influences such fundamental soil properties as ease of drainage, aeration and root penetration. Generally, macropores dominate in sandy soils, while micropores are most abundant in fine-textured soils.
301
What can texture, structure and organic matter affect in soil?
• Texture, structure and organic matter affect soil porosity and dry bulk density.
302
What type of correlation test can be used to find statistical differences in environmental data?
• Differences in environmental data can be assessed statistically using the Mann–Whitney U-test.
303
How can soils resist changes in PH?
• Soils can resist changes in pH through chemical buffering reactions between hydrogen ions in the soil solution and certain key chemical constituents in the soil.
304
What are the 18 elements essential for plant growth?
• The 18 elements essential for plant growth are divided into nine macronutrients (carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulfur, calcium and magnesium) and nine micronutrients (iron, manganese, boron, zinc, copper, chlorine, molybdenum, cobalt and nickel).
305
What are the limiting nutrients or limiting factors with plant growth?
• A plant’s development can be no greater than is allowed by the limiting nutrient (usually nitrogen or phosphorus) or other limiting factor (often water, sometimes sunlight or heat).
306
What is erosion
• Erosion is the removal of soil by the action of wind or water. Disruption of vegetation or the soil surface by humans or animals can greatly increase the rate of erosion.
307
Why si erosion destructive to soil?
• Erosion is destructive not only because it may remove vast amounts of soil but also because it preferentially removes the most valuable components: organic material and fine mineral particles.
308
How can erosion cause problems far away?
• Erosion also causes effects far from the erosion site. Loess soils are the results of accumulation of wind-blown sediment. Deposition of eroded sediments can also be damaging as sediments enter water bodies, causing pollution and flooding, and wind-blown dust hazards.
309
What ecosystem services does soil provide?
Soil provides a range of ecosystem services including: soil quality regulation, water/soil purification, flood regulation/water storage, greenhouse gas regulation, soil formation, nutrient cycling, carbon storage, a platform for human activity, heritage/archaeological protection and soil materials.
310
What are communities?
• Species are not distributed evenly. Groups of organisms tend to occur together in particular environments to give characteristic assemblages called communities.
311
What makes plant autotrophs?
• Plants are autotrophs. They take carbon dioxide, water and light energy from the Sun and convert them into sugars, by a series of reactions called photosynthesis. Oxygen is a by-product.
312
What do all organisms rely on?
• Nearly all organisms rely on the carbon and energy from sugars originally produced by photosynthesis for the growth and maintenance of their tissues. They obtain their energy by respiration, which is essentially the reverse of photosynthesis.
313
What resources are plants adapted to exploit?
Plants are differentially adapted to exploit the varying availability of resources, such as light, which occur at contrasting positions within a particular environment.
314
What does the term habitat refer to?
• The term ‘habitat’ strictly refers to the range of environments in which a given species occurs. However, in practice, it usually describes a distinct unit in the landscape which supports a particular group of organisms.
315
On a global scale what determines the vegetation type?
• On a global scale, climate determines the dominant, terrestrial vegetation types (biomes).
316
What PH level are most plants adapted to grow?
Most plants are adapted to grow in soils with a pH of around 6. At this pH, all of the essential nutrients are readily available to plants.
317
What are plants called that thrive at a PH above 7?
• However, some plants, called calcicoles, thrive at a pH above 7
318
What are plants called that thrive at a PH below 5?
Others, called calcifuges, thrive at a pH below 5.
319
What is a biotic factor?
• A biotic factor may be: a food source, a predator, a beneficial partner or a competitor.
320
What is the distribution and abundance of species affected by?
• The distribution and abundance of a species is affected by the availability of key resources and conditions (bottom-up controls) and the intensity of factors such as predation (top-down controls).
321
What do plants convert sunlight in to?
• Plants use the light and dark reactions of photosynthesis to convert light energy and atmospheric carbon dioxide into sugars (gross primary production or GPP). Sugars act as a source of carbon and energy for all
living tissues.
322
What do plants use sugars for? what is this called? what do they do with the remaining sugars?
• Some sugars are used to provide the energy for maintenance, growth and reproduction. Their energy is lost from the plant as heat during biochemical processes such as respiration. • The remaining sugars are deposited in cells as stored dry mass (net primary production or NPP).
323
How have plants evolved to protect themselves from the damage caused by light?
• Light can seriously damage plants. They have evolved several mechanisms of protection, including photorespiration, CO2 concentration, shiny leaves and ‘sacrificial molecules’.
324
Where do heterotrophs get their energy from?
• Heterotrophs obtain energy and carbon in the form of complex organic molecules that have been synthesised by other organisms.
325
What is plant respiration?
• Respiration is the process that releases energy from organic molecules.
326
What are heterotrophs classified as ?
• Heterotrophs can be classified as consumers and decomposers.
327
What do consumers include?
• Consumers include carnivores, herbivores and detritivores, according to whether they eat animals, plants or dead organic remains.
328
What are decomposers and what do they do?•
• Decomposers, such as fungi and bacteria, digest detritus externally, using enzymes which they secrete.
329
What does the efficiency of primary production converted in to secondary production depend on?
• The efficiency with which primary production is converted into secondary production (i.e. consumer biomass) depends on several factors. These include feeding preference and whether the consumer is an endotherm or an ectotherm.
330
What is an ecosystem?
• An ecosystem is a community of organisms, interacting with one another and their abiotic environment, to form a unit with its own characteristic pattern of energy flow and nutrient cycling.
331
How can ecosystems be studied?
• Ecosystems can be studied using pyramids of numbers, biomass or energy, which represent the relative sizes of the trophic levels. Each type of pyramid has advantages and disadvantages.
332
Using energy budgets how can three main types of ecosystem be recognised?
• Using energy budgets, three main types of ecosystem can be recognised. They are based on whether the bulk of the primary production is consumed, stored or decomposed.
333
What is Water movement through the soil–plant–atmosphere continuum is dictated by?
• Water movement through the soil–plant–atmosphere continuum is dictated by gradients in water potential. This quantity and the flux of water through the system can both be measured.
334
Where is resistance in water flow considered the greatest in a plant?
• Resistances to water flow can be calculated. They are considered greatest at the soil/root interface and at the leaf surface.
335
What can happen if a plant is water logged?
• Oxygen is an essential resource for all plant tissues. Underground organs can experience difficulty acquiring oxygen, especially if the soil is waterlogged.
336
What is the plumbing system in a plant known as and what does it do?
• The main adaptation to this environmental stress is an internal plumbing system, called aerenchym, which can transport oxygen from the atmosphere to the roots.
337
What impacts on vegetation does the soil water status have?
• Soil-water status can have two independent impacts on vegetation: it influences both the water supply for growth and the oxygen supply for root respiration.
338
What is the single most important nutrient for plants?
• Nitrogen is the single most important mineral nutrient for plants and often the growth-limiting one.
339
Why do some plants form a mutualistic relationship with bacteria?
• Some species have overcome this restriction by forming mutualistic relationships with bacteria which can use the vast resource of atmospheric nitrogen gas
340
How do plants survive nutrient poor soils?
• Plants can survive in nutrient-poor soils by several mechanisms. Mutualistic fungi called mycorrhizas can assist with nutrient acquisition. Capturing and digesting insects is an extreme adaptation to the unavailability of soil minerals.
341
What is a function of plant behavious in nutrient recycling?
• The availability of plant nutrients, especially basic cations, is a function of plant behaviour in nutrient recycling. The soil pH and its development are heavily influenced by this behaviour.
342
What are natural barriers to plant dispersal?
• Patterns of species occurrence are strongly influenced by natural barriers to dispersal, such as oceans and mountain ranges
343
Why are large bodied organisms under threat of extinction?
• Large-bodied organisms are under particular conservation threat because of their low rate of population increase and requirement for large foraging area.
344
What three subcycles can the global carbon cycle be divided in to?
• The global carbon cycle can be divided into three subcycles, each of which operates on a different timescale.
o The terrestrial carbon cycle operates on a timescale of months to decades.
o The marine carbon cycle operates over hundreds of thousands of years.
o The geological carbon cycle operates over millions of years.
345
Describe the terrestrial carbon cycle?
• The terrestrial carbon cycle operates on short timescales. Carbon dioxide is removed from the atmosphere and photosynthesis transforms it into organic compounds. Some carbon is returned to the atmosphere quickly via respiration, while the rest becomes organic matter. When a plant dies, the carbon is incorporated into the soil and microbial degradation releases it as CO2. A small amount of carbon escapes respiration and decomposition and is buried on land or transported by runoff to the oceans.
346
Describe the marine carbon cycle?
• The marine carbon cycle operates on intermediate timescales. Marine phytoplankton utilise dissolved CO2 in surface waters to generate organic matter, which eventually sinks down through the water column. The CO2 in surface waters is replenished from the atmosphere and this transport of carbon to the deep ocean constitutes the biological pump. As with the terrestrial carbon cycle, small amounts of organic matter escape degradation and are buried in sediments.
347
Desribe the geological carbon cycle?
• The small but steady leak of carbon from the terrestrial and marine carbon cycles due to burial allows carbon to enter the geological carbon cycle. This cycle operates on long timescales and the rock reservoirs contain most of the carbon in the carbon cycle. This carbon is returned to the atmosphere and ocean when tectonic processes expose buried carbon to be weathered or directly oxidised to CO2.
348
Why is the CO2 in the atmosphere rising?
• Over the last 100 years, the concentration of CO2 in the atmosphere has been rising. This rise is caused primarily by the burning of fossil fuels. Fossil fuel use short-circuits the geological carbon cycle by increasing the rate of transfer between the geospheric and atmospheric carbon reservoirs
349
How can agricultural practices disrupt all aspects of the nitrogen cycle?
• Agricultural practices disrupt all aspects of the nitrogen cycle of a temperate grassland, enhancing the losses of fixed nitrogen, and fertilizers may have to be used to maintain the fertility of the soil. Biogeochemical cycling of fertilizers in the soil leads to significant losses of fertilizer nitrogen, which can result in the pollution of the atmosphere and aquatic environments.
350
Where does sulfur occur naturally?
• Sulfur occurs naturally in all parts of the environment, including the atmosphere, oceans, soils, rocks and living organisms. Natural sources of sulfur include sulfides of metals in rocks, sea spray, biogenic gases and volcanic activity.
351
What does all of the sulfur in the atmosphere occur as?
• Almost all the sulfur in the atmosphere occurs as SO2. Natural and anthropogenic emissions are fairly evenly balanced.
352
Where is most of the earths phosphorus?
• Most of the Earth’s phosphorus is present in the crust as the mineral apatite.
353
What is eutrophication?
• Eutrophication is a process in which an ecosystem accumulates mineral nutrients. It can occur naturally but is usually associated with human activity which releases nutrients into the environment.
354
How can eutrophication have an effect on aqautic environments?
• The symptoms of eutrophication are most readily seen in aquatic systems, where the additional nutrients lead to the explosive growth of algal or bacterial populations. The large biomass produced excludes light from the water which can result in the deoxygenation of the water, killing fish and other animals.
355
How does eutrophication decrease species richness?
• In terrestrial systems, additional nutrients boost the productivity of competitive plant species. These then exclude less competitive species by shading them, leading to a decrease in species richness. The ‘humped-back’ curve describes the relationship between biomass and species richness.
356
What type of environment is particularly prone to eutrophication?
• Estuaries are particularly prone to eutrophication. Like other aquatic environments, they can experience algal blooms which eliminate other species. The loss of key species, such as seagrass, can result in the disappearance of an entire habitat type and its dependent species.
357
What elements are the main agents of eutrophication?
• The main agents of eutrophication are compounds containing the elements phosphorus and nitrogen. Under natural conditions, these elements usually limit the primary production in ecosystems. Increasing their supply therefore increases productivity.
358
What are the sources of anthropogenic phosphorus?
• The sources of anthropogenic phosphorus entering the environment include sewage discharges, intensive livestock farms and spreading artificial fertilisers and animal manures on agricultural land. The majority of phosphorus comes from point sources.
359
What are the sources of anthropogenic nitrogen?
• The sources of anthropogenic nitrogen entering the environment include gaseous emissions from vehicle exhausts and power stations and artificial fertilisers applied to agricultural land. The majority of nitrogen comes from diffuse sources.
360
How does european legislation try to limit eutrophication?
• European legislation tries to limit further eutrophication of the environment by measures such as stripping phosphorus from wastewater and controlling nitrogen fertiliser applications in sensitive zones.
361
Living organisms are systems that?
Living organisms are systems that:
require a constant input of energy
grow and reproduce
respond to their environment.
362
Where are all living organisms found and what is this called?
They are found throughout the atmosphere, oceans, land surface and deep within the Earth’s crust. The range of environments they inhabit is called the biosphere.
363
What is the word to describe a wide array of different types of living organisms?
There is a vast array of different types of living organism. This variety is often referred to as biodiversity.
364
What is a community?
Biologists regard species that often occur together as a community. This word is often used to refer to organisms of a particular kind, such as the plant community on a heath or the insect community inside a cowpat. Communities are made up of several populations of different species.
365
How is population defined?
A population is defined as all the members of the same species that occur in the same place at the same time.
366
What is an ecotone?
The boundary between two distinct communities is called an ecotone. However, ecotones do not have to be abrupt. They can also be diffuse, where one community grades smoothly into another.
367
What do plants need to build their tissues?
they can build their tissues using light energy from the Sun and simple inorganic substances from the environment, such as water, carbon dioxide and mineral salts.
368
How do animals and fungi obtain energy?
Animals and fungi cannot do this. They have to obtain the energy and materials for building their bodies in a ready-to-use, prefabricated form. That is, they have to obtain them by consuming other living things or things that were once living.
369
Are plants autotrophs or heterotrophs
Plants are termed autotrophs (from the Greek words auto, meaning ‘self’, and troph, meaning ‘feed’)
370
Are animals autotrophs or heterotrophs?
In contrast, animals and fungi are termed heterotrophs (hetero, from the Greek word for ‘different’). Therefore, all heterotrophs ultimately depend on autotrophs for the energy and materials needed to build and maintain their bodies.
371
Explain what happens with photosynthesis?
Plants take in carbon dioxide (CO2), water (H2O) and light energy from the Sun. Then, through a series of chemical reactions, they turn them into the sugar glucose (C6H12O6). Oxygen gas (O2) is a by-product of photosynthesis.
light energy + carbon dioxide + water → glucose + oxygen
372
What is the chemical notation of photosynthesis?
light energy + 6CO2(g) + 6H2O(l) → C6H12O6(s) + 6O2(g)
373
What happens to the glucose after it has been produced through photosynthesis?
The glucose then undergoes a multitude of chemical reactions. It can be combined with other elements, such as nitrogen (N), sulfur (S), phosphorus (P) and iron (Fe), and/or it can be converted into many different organic (i.e. carbon-based) substances, such as proteins, fats and storage carbohydrates, such as starch.
374
How do plants capture sunlight?
sunlight is captured by a special green pigment called chlorophyll present in leaves.
375
What is the term used to describe the processes that lead to the growth of plants?
The growth of plants resulting from these processes is termed primary production.
376
What is the other product of photosynthesis besides energy-rich sugar?
oxygen
377
What is the term used that leads to animal and fungal tissue resulting from the consumption of plants?
The animal and fungal tissue resulting from the consumption of plants is called secondary production. Animals and fungi also depend on plants for another essential resource.
378
Why do all multicellular organisms require oxygen?
They use oxygen in respiration.
379
What is the chemical notation of aerobic respiration in multicellular organisms and how is it different to photosynthesis?
Aerobic respiration is the dominant pathway in multicellular organisms. It can be summarised as:
C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(l) + energy
It is very similar to that for photosynthesis, but it operates in the opposite direction.
380
How do shade tolerant plants maximise photosynthesis?
Shade-tolerant plants usually have intrinsically slow growth rates and can maximise photosynthesis at low light intensities. Some of the woodland plants are evergreen, for example holly (Ilex aquifolium, Figure 4.1.5b). This feature enables plants to make the best use of the light available during the parts of the year when the canopy trees are leafless.
381
What are meristems?
Perennating tissue contains meristems (points capable of growth), which may remain inactive during cold or dry seasons and then resume growth when favourable conditions return. Meristems are found in buds, which are condensed, embryonic shoots in a protective covering of bud scales (Figure 4.1.6).
382
How many plant growth classification does the Raunkiaer system have?
5
383
What are the names of the 5 different Raunkiaer plant growth classification?
```
Phanerophyte
Chamaephyte
Hemicryptophyte
Geophyte
Therophyte
```
384
What is a phanerophyte?
Raunkiaer’s five plant life forms: perennating tissues are shown in dark green, woody tissues in brown and deciduous tissues in pale green. (a) Phanerophyte: tree or tall shrub with buds more than 25 cm above
Phanerophytes include trees and shrubs that are predominantly taller than an arbitrary minimum height of 25 cm. They also include the plants growing on other plants, such as the climber honeysuckle (Figure 4.1.8a) and the fern western polypode (Polypodium interjectum, Figure 4.1.8b), which often grows on the trunks and branches of established trees as well as on the ground.the ground
385
What is a chamephyte?
Raunkiaer’s five plant life forms: perennating tissues are shown in dark green, woody tissues in brown and deciduous tissues in pale green. ((b) Chamaephyte: low shrubs with buds less than 25 cm above the ground
The buds are less exposed to cold or drying winds than those of phanerophytes. They may be protected by a covering of snow in winter. Chamaephytes include dwarf shrubs and succulents. Many of the popular rock-garden plants and culinary herbs are chamaephytes, such as dwarf willows, thyme, marjoram and saxifrages.
386
What is a hemicryptophyte?
Raunkiaer’s five plant life forms: perennating tissues are shown in dark green, woody tissues in brown and deciduous tissues in pale green. (Hemicryptophyte: perennial herb with buds at ground surface.
Hemicryptophytes (hemi = partly, crypto = hidden) are perennial herbs with their perennating tissues at the soil surface. (Perennial plants live for several years.) At the soil surface, the buds can be protected by leaf litter as well as snow.
Hemicryptophytes include many of the garden plants grown in herbaceous borders, such as delphiniums (Figure 4.1.10) and lupins.
387
What is a geophyte?
Raunkiaer’s five plant life forms: perennating tissues are shown in dark green, woody tissues in brown and deciduous tissues in pale green. (Geophyte: perennial herb with a bulb or other perennating organ below the ground surface.
Geophytes (geo = ground) are perennial herbs with underground perennating tissues that are better protected from the climate. These include bulbs, corms, tubers and rhizomes:
bluebells overwinter as bulbs, formed from swollen leaf bases (Figure 4.1.11a)
crocuses grow from corms, which look like bulbs but are formed from a swollen stem base (Figure 4.1.11b)
irises (Figure 4.1.12) survive the winter as rhizomes, a horizontal stem (Figure 4.1.11c)
potatoes perennate as a tuber, which is also anatomically a swollen underground stem (Figure 4.1.11d).
In each case, the tissues are swollen with food reserves, enabling the plants to grow rapidly as soon as conditions permit. They can then flower and complete their growth and reproduction within a short growing season.
388
What is a therophyte
Raunkiaer’s five plant life forms: perennating tissues are shown in dark green, woody tissues in brown and deciduous tissues in pale green. (Therophyte: annual plant surviving unfavourable periods only as a seed
Therophytes (thero = summer) are annual or short-lived herbs that survive unfavourable seasons (or, in some cases, several unfavourable years) as seeds. The shoots and roots die after seed production. (Annual plants complete their life cycle within a single year.)
Examples of therophytes include petunias and marigolds (Tagetes spp.), as well as many weeds, such as groundsel (Senecio vulgaris, Figure 4.1.13), and chickweed (Stellaria media)..
389
What is a life form spectrum?
It is used to identify Differences in a life-form spectrum reflect the effects of environment, especially climate, on plant adaptation in communities and is expressed as a percentage
390
What vegetation type dominates a rainforest according to the Rankiaer life form classification?
For example, tropical rainforest is characterised by a predominance of phanerophyte species.
391
What is taxonomy?
taxonomy (naming and classification of organisms
392
Name the taxonomy hierarchy from closest to increasingly distant relationship?
```
Organisms are grouped into the following hierarchy of categories that are thought to have increasingly distant relationships.
Species
Genus
Family
order
Class
Phylum
Kingdom
```
sam goes for orderly coffee
393
Explain species as a hierarchical taxonomy classification?
Species: the smallest, least inclusive category. It only includes organisms that are so closely related they can freely interbreed and produce fertile offspring. For example, humans all belong to the species Homo sapiens.
394
Explain Genus as a hierarchical taxonomy classification?
Genus (plural genera): includes species that have many features in common and can sometimes interbreed to form hybrids, which have variable levels of fertility. For example, the genus Homo contains only a single species now. However, there used to be others, such as Homo erectus, who lived in Asia and died out more than 100 000 years ago.
395
Explain family as a hierarchical taxonomy classification?
Family: includes genera with broadly similar traits. Humans are in the family Hominidae, which now has only a single genus, Homo.
396
Explain order as a hierarchical taxonomy classification?
Order: includes a range of related families. Humans are one of the primates, which includes all apes and monkeys.
397
Explain class as a hierarchical taxonomy classification?
Class: a broad term encompassing a range of organisms that may share only a few features in common. In our case, humans are mammals, which all have hair and suckle their young.
398
Explain phylum as a hierarchical taxonomy classification?
Phylum (plural phyla): an even broader group. Humans are in the phylum Chordata, which includes all animals with a backbone.
399
Explain kingdom as a hierarchical taxonomy classification?
Kingdom: the highest level of organisation. Humans are in Animalia, which includes all animals. There are currently six recognised kingdoms
400
What are the 6 kingdoms of organisations
bacteria, archaea, protista, animals, fungi
401
Which two kingdoms can be described as single cells and which ones multi cellular?
Two of the kingdoms – bacteria and archaea – lack nuclei in their cells and are classed as prokaryotes (meaning before nuclei). These usually exist as single cells and have a very simple cellular structure. The other four kingdoms comprise organisms with a much more elaborate cellular structure, including having membrane-bound nuclei and are classed as eukaryotes.
402
What is a prokaryote? and which kingdoms are known as this?
Two of the kingdoms – bacteria and archaea – lack nuclei in their cells and are classed as prokaryotes (meaning before nuclei). These usually exist as single cells and have a very simple cellular structure.
403
What kingdoms are known as eukaryotes and why?
```
animals
fungi
plants
protista
The other four kingdoms comprise organisms with a much more elaborate cellular structure, including having membrane-bound nuclei and are classed as eukaryotes.
```
404
What does the first word in a binomial latin name denote?
Genus
405
What does the second word in the binomial latin name denote?
species
406
What are the raw materials that plants need to build and maintain their tissues?
Carbon dioxide, water and light for photosynthesis, and mineral nutrients (such as nitrogen, phosphorus and potassium).
407
What are rhizoids?
Consequently, virtually all land plants have a green, photosynthetic shoot, which must be exposed to light, and a non-photosynthetic part, which provides anchorage and absorbs mineral nutrients and water. In recently evolved plants, these structures are the roots, but in more primitive plants, e.g. mosses, they may be modified shoots or simple hair-like processes called rhizoids.
408
What are the three categories of species that can be distinguished to determine a community label?
constants
preferentials
associates
409
Describe the category 'constant' to determine a community label?
Constants are those species that almost always occur within a stand of the particular community type and usually are found frequently within it.
410
Describe the category 'preferentials' to determine a community label?
Preferentials are the species that define one of the subcommunities within the broader community type. These species occur frequently within a particular subcommunity, but rather infrequently, if at all, in the other subcommunities
411
Describe the category 'associates' to determine a community label?
Associates are species that are found within stands of the community, but at a lower frequency. They may not be particularly characteristic of that community and occur more commonly in others.
412
How are frequencies expressed when determining community plant labels?
Frequencies are conventionally expressed on a five-point scale denoted by the Roman numerals I–V, where I is a frequency of < 20%, II is 21–40%, etc., up to V, a frequency of >80%.
413
What is a habitat?
The term habitat as applied to wildlife can be defined in several ways. Essentially, it means the place where an organism lives. The common definitions are described below.
The range of environments in which a given species occurs
This definition is perhaps the truest to the original derivation of the term, as the place where something lives. However, when applied in practice the set of environments defined can be very varied, depending on the species chosen.
A distinct unit in the landscape, supporting a distinct community of organisms
The term ‘habitat’ strictly refers to the range of environments in which a given species occurs. However, in practice it usually describes a distinct unit in the landscape which supports a particular group of organisms.
414
What is a community?
Groups of plant species consistently co-occur, allowing them to be labelled as communities.
415
What is the most relevant published accounts of plant community classification in Great Britain?
There are published accounts of plant community classification. In Great Britain, the NVC is the most relevant. (national vegetation classification)
416
What does carrying out a national vegetation stand identify?
Carrying out an NVC survey requires identifying stands of uniform plant communities, surveying the plants in them and comparing the results of those surveys to published accounts of the variety of plant communities in the UK.
417
What are epiphytes?
Plants living on the branches are called epiphytes. They do not damage the host plant, unlike parasitic species such as mistletoe. The epiphytes, in turn, create habitats and provide resources for other species.
418
What causes variation in tree dominated habitats?
Variation in tree-dominated habitats is due primarily to changing conditions in light, temperature and moisture
419
What can be the temperature difference from the canopy to the forest floor?
The shaded forest floor may be 10–20 °C cooler and much darker than above the canopy. These are two extremes of a vertical gradient of change.
420
What is vertical stratification?
Many forest-dwelling species prefer different vertical positions through the canopy. This is called vertical stratification.
421
What is a decomposer?
decomposers
Organisms, primarily bacteria and fungi, that feeds on dead organic matter by secreting enzymes which digest it externally, releasing simple inorganic compounds such as CO2, water, NO3-, NH4+ and PO43-.
422
Recalling the water cycle in Block 1, why is the similarity in annual average rainfall between the Pacific coast and England and Wales misleading in terms of its effect on plants?
It does not take account of temperature which, in turn, influences rates of evapotranspiration. Recall from Block 1 that the key variable determining vegetation (habitat) type is evapotranspiration.
423
What is holdridges analysis of life zones?
The different habitats and the underlying environmental conditions are summarised in Holdridge’s analysis of life zones. The system classifies habitats in terms of its dominant vegetation with respect to annual precipitation, mean annual temperature and evapotranspiration. It takes into account how the variables change with altitude and latitude.
424
What types of conditions are grasslands formed in?
Natural grasslands are formed without human intervention. Extensive natural grasslands occur where the climate is generally hot (at least during the summer) and dry, although not to the extremes that result in the formation of deserts (Figure 4.1.35).
425
On the basis of climate what are the two types that natural grasslands can be generally classified in to?
On the basis of climate, natural grasslands are generally classified into two main types:
tropical
temperate.
426
where do tropical grasslands occur?
Tropical grasslands occur across Central and South America, Africa and in Australia. (Some of them might be considered subtropical, e.g. in southern Brazil.)
427
Where do temperate grasslands occur and what local names are they known as?
Temperate grasslands mainly occur in North America, Argentina and South Africa, and in a wide belt from the Ukraine to China. They have many different local names, respectively prairie, pampas, veld and steppe
428
Naturally temperate grasslands include the North American prairie, the Russian steppe, and those in Argentina and Australia. Why do you think they have also become the main centres of world wheat production?
Wheat is a species of temperate grass, so it performs well in the climates which support this biome.
429
What percentage of the world is covered by natural grassland?
Grasslands are the potential natural vegetation on 33 × 106 km2 (approximately 25%) of the land surface of the Earth. However, the world’s actual area of grassland is almost twice that. This is because of large areas that are maintained as grassland through human intervention. This figure is remarkably close to that estimated for grassland extent in 1700 AD, suggesting that the factors affecting the global area of grassland have maintained a rough balance over the past 300 years.
430
What features lead to the success of grasses?
The success of grasses is due to the following features.
Their growing points are close to the ground, which means that they can withstand close grazing.
Many species are resistant to trampling and have a variety of vegetative growth options (which also helps with resistance to fire).
The photosynthetic pathways (known as C3 or C4) vary, which represents adaptations to cooler and warmer conditions, respectively.
431
How do you estimate periods of relative drought?
You need to double the monthly temperature values and then subtract them from the rainfall totals. From Table 4.1.6 you can see that the periods of relative drought (highlighted in yellow) are when the values are negative (i.e. the rainfall is less than double the temperature). You will see this occurs from November to April in Managua, but never in Bluefields.
432
What type of grasses have evolved to complete their reproductive cycle during a limited growing season
Perennial grasses have evolved the ability to complete their reproductive cycle rapidly during a limited growing season. Their subterranean perennating roots and rhizomes enable them to survive periods of drought or cold, and also to recover from the effects of fire.
433
What type of plant form according to the Rankiaer classification is Tussock grass and why?
Tussock grasses are generally hemicryptophytes with persistent underground or close-to-ground perennating structures. These allow the tussocks to survive through long periods of cold and/or dry conditions.
434
What type of species dominate waterlogged areas?
Seasonal flooding or waterlogging may prevent the growth of woody species, favouring the predominance of grass species. (Conversely, some trees, such as mangrove, thrive in waterlogged habitats.) This tends to occur in the subtropics where there is considerable meteorological variation between the seasons.
435
Natural grasslands occur where the temperatures are too low, or where conditions become seasonally too dry or wet for tree growth. What do you think would happen to grasslands if the climate became warmer or the patterns of precipitation became less extreme?
The grasslands would gradually change to woodland. This is because, where environmental conditions permit tree growth, trees are stronger competitors for light than grassland species.
436
What is the criteria for determining virgin forest?
There are several criteria for determining virgin forest, in addition to vegetation structure and species composition. They were listed by the woodland ecologist George Peterken and include:
no sign of direct human interference
full range of large animals, including carnivores, which are not significantly affected by events outside the site
historical records going back to the origins of settlement in the neighbourhood and showing past interference is unlikely
surrounding events not significantly affecting the site.
437
What must a bat habitat include?
There are several criteria for determining virgin forest, in addition to vegetation structure and species composition. They were listed by the woodland ecologist George Peterken and include:
no sign of direct human interference
full range of large animals, including carnivores, which are not significantly affected by events outside the site
historical records going back to the origins of settlement in the neighbourhood and showing past interference is unlikely
surrounding events not significantly affecting the site.
438
What does an organism require from a habitat?
From an organism’s point of view, essential requirements can be divided into:
resources, i.e. something which an organism uses and can be in short supply, e.g. food, nest sites
conditions, which influence the external environment in ways that affect how the organism functions but are not actually used by it, e.g. temperature, humidity, salinity.
439
Name some physical and chemical abiotic factors?
Physical Chemical
light nutrient availability
temperature oxygen availability
humidity carbon dioxide availability
wind (exposure) water availability
water movements
(waves and currents) salinity
fire concentration of toxins
soil strength pH of solution
water tension in soil ozone concentration
440
Identify one physical factor that is both a resource and a condition as an abiotic factor
Light is a resource for photosynthesis, and a condition affecting day length (because this influences growing season, breeding season, etc.).
441
How can plant growth be sensitive to temperature?
Plant growth is extremely sensitive to temperature. Often a difference of a few degrees leads to a noticeable change in growth rate. Temperature is a key determinant of rates of reaction. However, increasing temperature also results in an increased rate of damage to enzymes, which are protein molecules that catalyse specific biochemical reactions. The net result is that enzymes have an optimum temperature at which their function is maximal
442
Most of the enzymes in a single organism tend to have broadly the same temperature optimum. If an organism is consistently exposed to temperatures away from this optimum, the enzymes can be damaged to the extent that the organism functions inefficiently or not at all.
What do you think would happen if the plant from which the enzyme in Figure 4.2.4 came was maintained at a temperature above 40 °C?
The plant would die if kept above 40 °C for very long. This is because its enzymes would be damaged or destroyed.
443
What species are endothermic?
In contrast, birds, mammals and a few specialised plant tissues are endothermic, i.e. they can maintain an internal temperature that differs from the temperature of their environment.
444
What species are ectothermic?
Plants, in common with many animals, are described as ectothermic, i.e. the temperature of the organism’s tissues is determined by the temperature of the environment.
445
Given the temperature tolerances of enzymes, what implications does this difference in temperature regulation have for the global distribution of ectotherms and endotherms?
Generally, ectotherms are restricted to a narrower range of habitats than endotherms.
446
What advantage do swallows gain from such long and hazardous journeys?
They can spend all of the time in environments with high productivity – the long days of summer in Europe and the warm wet days in Africa during the rainy season.
447
How do plant cells differ from animal cells?
Plant cells differ from animal cells in several ways. They possess a large, fluid-filled, membrane-bound space (vacuole). Freshwater tends to enter all cells, which makes them swell. Under these conditions, having no cell wall, an animal cell may eventually burst.
In contrast, a plant cell starts by swelling, but it does not burst because expansion is restricted by the cell wall. The cell becomes quite stiff (like a fully inflated football). En masse, plant tissues can be rigid enough to stand erect, like a fully inflated bouncy castle. Also like a bouncy castle, the whole structure sags if the inflation is not complete
448
What can affect plant water relationships?
Aspect, exposure and altitude can also affect plants’ water relationships. High temperatures and winds dry out both the soil and the plant. However, topography can also affect soil moisture significantly. The rain shadow effect is caused by clouds tending to deposit their load of moisture as they start to rise over hills and mountains. This means that land on the leeward side of high land tends to be relatively drier than that on the windward side
449
How can topography affect soil moisture?
Topography can also influence soil moisture in that water tends to flow downhill and accumulate in valley bottoms. This phenomenon can also have important consequences for soil fertility.
450
After temperature and precipitation, soil type is one of the major factors affecting plant distribution for obvious reasons.
Which resources do plants obtain from soils?
Water and mineral nutrients.
451
Where do the mineral elements in soil come from?
Mineral elements are acquired from the soil. All of them except nitrogen (which is derived from the air) are ultimately derived from the underlying rocks. Because rocks differ in their chemical composition, the proportions of the different mineral elements in the soils derived from them also vary. Furthermore, aluminium-rich rocks (e.g. granite) can cause aluminium toxicity problems under acid conditions.
452
What is soil texture defined by?
Soil texture is determined by the size of the rock particles. The bigger the average size of the particles, the coarser the texture and the more free-draining a soil tends to be. The smaller the particle size, the finer the texture and the more water-retentive the soil tends to be.
453
What does it mean if soil has a course texture and how does this affect water retention
Soil texture is determined by the size of the rock particles. The bigger the average size of the particles, the coarser the texture and the more free-draining a soil tends to be. The smaller the particle size, the finer the texture and the more water-retentive the soil tends to be.
454
From an agricultural point of view, is a sandy or a clayey soil better in a dry climate?
A clayey soil is better because it will retain moisture during dry periods.
455
How does geology have an important influence on soil PH?
Geology also has an important influence on soil pH. Soils derived from base-rich and, especially, calcareous rocks tend to produce soils of high pH. In contrast, soils derived from base-poor rocks tend to be more acidic.
456
How does soil PH affect plants?
In turn, pH has an enormous influence on plant distribution. This is because the solubility, and therefore the availability, of soil mineral nutrients varies with pH, as Figure 4.2.11 shows.
457
what PH are most plants adapted to thrive in?
Most plants are adapted to thrive in soils around pH 6.5. At this pH, all of the nutrients are readily available to plants. (slightly acidic)
458
What is the most common mineral toxicity in soil that affects plants?
Iron toxicity is the most commonly encountered. However, high levels of dissolved aluminium may also cause toxicity in acid soils. The limited agricultural potential of acid soils is due largely to the presence of aluminium in solution. This situation is exacerbated by acid precipitation.
459
What are plants called that are adapted to live in alkaline soils?
calcicoles
460
What are plants known as that are adapted to live in acidic soils?
calcifuges
461
What effect does increasing the temperature have on the oxygen content of the water?
it lowers it
462
What can affect the oxygen concentration in water?
Whereas the concentration of oxygen in the air is fairly stable, oxygen concentrations in water can vary widely. This depends not only on temperature, but also on turbulence (moving water can replenish oxygen from the atmosphere more effectively than stagnant water). It also depends on the amount of oxygen being removed from, or added to, the water by biological processes.
463
What organisms can produce oxygen in water?
Photosynthesis by aquatic plants and algae increases the oxygen concentration,
464
What organisms can use oxygen in water?
oxygen is removed by the respiration of all organisms. The conversion of ammonia (NH3) to nitrate (NO3−) by microscopic organisms also uses up dissolved oxygen. The sum total of the oxygen-requiring activities of organisms is called the biological oxygen demand (BOD). This is an important factor in determining the oxygen availability in freshwater habitats.
465
What do microscopic organisms convert ammonia NH3 that uses up all of the oxygen?
The conversion of ammonia (NH3) to nitrate (NO3−) by microscopic organisms also uses up dissolved oxygen.
466
What sorts of substances are likely to enter a watercourse that contains significant quantities of ammonia and/or complex organic molecules?
Dead vegetation, such as leaf litter, sewage effluent, farmyard slurry, some fertilisers and the waste products of some industrial processes.
467
Describe the relationship between:
a. oxygen concentration and BOD
b. the concentration of ammonium ions (NH4+) and nitrate ions (NO3−), downstream of the outfall pipe.
a. There is an inverse relationship between oxygen concentration and BOD.
b. There is an inverse relationship between the concentration of ammonium ions (NH4+) and nitrate ions (NO3−) downstream of the outfall pipe.
468
Describe how the bmwp biological monitoring working party system works?
biological indicators: the BMWP system
The Biological Monitoring Working Party (BMWP) has developed a system for assessing water quality based on invertebrates.
Under the BMWP system invertebrate families are awarded a score. 10 indicates a very pollution-sensitive creature and 1 indicates the most pollution-tolerant organisms.
After sampling, the scores for each family present are summed to give an overall BMWP score.
Note that a low BMWP score by itself does not indicate pollution.
469
What is the fundamental niche of a plant defined by?
The fundamental niche of a plant species is defined in terms of:
```
the range of environments that can supply its required resources (light, water, oxygen, carbon dioxide, mineral nutrients)
other abiotic factors (temperature regime, shelter from wind, anchorage)
biotic factors (e.g. the presence of pollinators and mutualistic fungi).
```
470
What is ecological dynamics?
vegetation is not static. Patterns of distribution change with time. The description and study of these changes is called ecological dynamics.
471
However, a species rarely fills its fundamental niche. One aspect that may limit its occupation of this potential niche is the presence of competitors.
What is the other factor that may limit a species’ ability to occupy a potential niche?
Dispersal, i.e. the movement of an organism within space. A niche cannot be filled if the organism is unable to reach it.
472
What are several species are confined to a single ocean island or mountain top known as?
endemic
473
The prairie lupin, which does colonise successfully, is a member of the legume family (Fabaceae).
What does this information imply about the species’ impact on the newly developing soil?
Legumes can fix atmospheric nitrogen through their mutualistic relationship with specialist bacteria.
Therefore, the lupins will enrich the soil with nitrogen as their tissues die and are recycled.
474
What advantages and disadvantages do light and heavy seeds have?
Lighter seeds favour wide dispersal, but tend to require favourable conditions at new sites.
Species with heavier seeds, although often lacking in dispersal ability, can tolerate a wider range of conditions during establishment. For example, they can establish better in dense leaf litter. This is because they can develop a tall shoot, while living on their stored reserves, without the need for light as an energy source. They can also tolerate drought-prone soils, by sending down a deep root very quickly after germination. The latter ability gave them the advantage on Mount St Helens, making them the first successful colonists.
475
What type of species have the most developed adaptations to aid dispersal and give some examples?
Species of disturbed habitats (i.e. ruderals) have the most developed adaptations to aid dispersal. Some examples are:
The field poppy (Papaver rhoeas) has tens of thousands of very small seeds, shaken from a ‘pepper dispenser’ by the wind.
Seeds of cleavers (Galium aparine) have curved hooks to attach themselves to the fur of passing animals.
Corn chamomile (Anthemis arvensis) seeds survive the digestive tracts of birds, which then scatter them widely in their droppings.
The exploding pods of the tiny plant called hairy cress (Cardamine hirsuta) can throw their seeds more than a metre away from the parent.
The dandelion (Taraxacum spp.) has a feathery parachute attached to each of its seeds, allowing a seed to catch the slightest breeze and often travel hundreds of metres.
476
What is a dispersal of a species often limited by?
The dispersal of a species is often limited by the presence of barriers. On a global scale, these may be oceans or mountain ranges.
477
Why are woodland species poor dispersers?
However, the development of a woodland ground flora is often disappointing with very few species colonising the new habitat. Woodland species are often poor dispersers because they are adapted to a stable habitat. More importantly, if the woodland is isolated from other woods, the species are unlikely to colonise the intervening arable areas. They therefore need to ‘jump’ from one wood to the next because the intervening area is outside their realised niche because of competition from non-woodland species. This would be a very infrequent event for non-specialist dispersers.
478
How does a woodland get an ancient woodland status?
‘Ancient woodland’ is a term applied to areas in the UK that are known from documentary evidence to have been continuously wooded since AD 1600.
479
What is a stress tolerater?
The probability is that they have never been ploughed and their ground flora has some continuity with the wildwood, which was at its zenith 4000 BP. Such woodland can now often be recognised by the presence of species that are stress tolerators. These are adapted to living in a shaded environment and so cannot compete in open habitats
480
Why were the species in Figure 4.3.16 such competent dispersers in former times compared with today?
The most likely reason is that in extensive forest (i.e. when the whole of England was predominantly deciduous woodland), the suitable niche for the species was continuous. In such a situation, the chance dispersal of seeds on the feet of animals would have often been successful. This is because the point where the seed was subsequently dropped would have a high probability of being a suitable habitat for the species.
In contrast, in the modern fragmented landscape, less than 1% of the land surface is likely to be a suitable habitat. So such instances of ‘jump’ dispersal will probably fail. So the species spreads mainly by very short-range seed scatter within the parent plant’s habitat.
481
What are the main factors limiting the colonisation by specialised woodland-floor species of newly planted woodland in which only the tree species had been introduced into previously arable land?
The species’ dispersal abilities would be a major factor. The isolation of the new woodland from other established woodlands is important here. A source of seeds for the ground flora is needed that is close enough to enable dispersal mechanisms to transfer them to the site.
Other factors, such as the former arable soil lacking organic matter and having an overabundance of available nutrients, would favour competitive species such as bramble (Rubus spp.) over more typical woodland species such as bluebell (Hyacinthoides non-scripta).
482
What are photoautotrophs?
Green plants are photoautotrophs – ‘photo’ because they use light energy and ‘autotroph’ because they can feed themselves by synthesising organic molecules from simple inorganic molecules (carbon dioxide and water). This process is photosynthesis.
483
What are chemoautotrophs?
In contrast, chemoautotrophs obtain energy by oxidising simple inorganic molecules; these tend to be bacteria (e.g. Nitrobacter) in the soil.
484
Recall the chemical equation summarising photosynthesis.
light energy + 6CO2(g) + 6H2O(l) = C6H12O6(s) + 6O2(g)
485
What energy rich molecules can plants convert from chemical energy?
There are two main sets of reactions involved in photosynthesis. In the so-called light reactions, energy from the Sun is converted to chemical energy in the form of complex energy-rich molecules such as adenosine triphosphate (ATP). These molecules can be thought of as an ‘energy currency’.
486
What gas is a bi product of photosynthesis?
As the name suggests, these reactions take place in the light, and involve light-harvesting pigments such as chlorophyll. During these reactions, water is split, separating hydrogen from oxygen:
2H2O(l) = 4H + O2(g)
487
What are dark reactions?
The chemical energy is then used to drive the dark reactions. These reactions reduce carbon dioxide to sugars, using the hydrogen atoms obtained from the light reactions. The second part of photosynthesis
488
What is light reactions?
The first stage of photosynthesis. There are two main sets of reactions involved in photosynthesis. In the so-called light reactions, energy from the Sun is converted to chemical energy in the form of complex energy-rich molecules such as adenosine triphosphate (ATP). These molecules can be thought of as an ‘energy currency’.
As the name suggests, these reactions take place in the light, and involve light-harvesting pigments such as chlorophyll. During these reactions, water is split, separating hydrogen from oxygen:
2H2O(l) = 4H + O2(g)
Equation label: (Eqn 4.5.2)
The oxygen is lost as a waste product and the hydrogen atoms are held by carrier molecules.
489
Where do all of the reactions of photosynthesis take place?
All of these reactions take place in the chloroplast (Figure 4.5.1), a specialised organelle. Several chloroplasts are found in all of the photosynthetic cells of plants.
490
What is net primary production?
The net primary production (NPP) is the rate at which plants accumulate dry mass, or biomass. NPP is measured in units of kg m−2 y−1 (dry mass per unit area per unit time).
491
What happens to the sugar produced in photosynthesis?
The sugar molecules produced in photosynthesis have two main fates. Some are used to provide the energy for maintenance, growth and reproduction. Their energy is lost from the plant as heat during processes such as respiration. The rest are deposited in various forms in and around cells. They represent stored dry mass.
492
What percentage of solar energy reaches plants?
Only 0.1% of the total solar energy entering the Earth’s atmosphere is stored in plant mass in this way
493
What can happen to plants if they suddenly were exposed to increased sunlight when they are not used to having sunlight?
Sudden changes in the intensity can lead to over-excitation of the photosynthetic system. This results in photo-inhibition – a reversible inhibition of photosynthesis. More extensive exposure to intense sunlight can lead to more serious and irreversible damage
494
What happens when leaves are bleached?
Sudden changes in the intensity can lead to over-excitation of the photosynthetic system. This results in photo-inhibition – a reversible inhibition of photosynthesis. More extensive exposure to intense sunlight can lead to more serious and irreversible damage
495
How do free radicals occur in plants?
Free radicals can be produced whenever the photosynthetic apparatus is capturing more energy than it can use to fix carbon. The free radicals will react with almost anything they come in contact with. So they have the potential to be very destructive within a cell. The problem is particularly acute for plants growing in shade. This is because, to make the most of the small amount of light they receive, they tend to be very efficient light-harvesters.
496
What is photorespiration?
Photorespiration is a process that acts as a safety valve. It protects against photo-inhibition and photo-oxidation, when light energy is readily available but the supply of CO2 is limiting the rate of photosynthesis.
Photorespiration got its name because of its apparent similarity to true respiration. Around 1970, it was observed that the rate of respiration in the light, as measured by oxygen consumption and carbon dioxide liberation, could be twice that in the dark. However, the similarity ends there. Photorespiration does not liberate useful energy and, when discovered, did not appear to provide any beneficial function.
497
What do some tropical species of plants that are at risk from light induced damage develop?
Almost all temperate plants use photorespiration as a protective mechanism. However, some tropical species, which are at even higher risk from light-induced damage, have developed an alternative to it.
They concentrate CO2 in the cells that are photosynthesising, to ensure a constant supply. The process of concentration is itself very energy-demanding. Therefore, it is only a viable option when there is excess light energy available
498
What are c3 species?
Plants using the C2 cycle safeguard are called C3 species. This is because the carbon they fix first appears in an organic molecule with three carbon atoms.
499
What are C4 species?
Plants using the concentrating mechanism are called C4 species. This is because they first fix carbon into a molecule with four carbon atoms.
500
How do carotenoids protect a plant?
Plants can produce chemicals which react very readily with free radicals, for example special pigments, such as carotenoids, and other molecules, such as ascorbic acid (commonly known as vitamin C). Such molecules can be viewed as ‘sacrificial’. They are made with the purpose of being destroyed in order to protect the more valuable photosynthetic structures.
501
How are plants that are habitually exposed to high light intensities protect themselves?
Plants that are habitually exposed to high light intensities are often protected by:
a thicker layer of wax on the leaf surface
a layer of fine silvery hairs over the leaf surface
vertically orientated leaves.
These adaptations not only reduce the amount of light entering the leaf, thereby reducing the potential damage to its photosynthetic machinery, but they also reduce the heat load from infrared radiation, thereby reducing the driver for water loss.
502
Why do shade plants tend not to use adaptations that protect them from light?
Shade plants need to be able to absorb as much light as possible when the intensity is low. So, adaptations that reduce their light absorption would reduce their fitness.
503
Which of the following strategies appears to have been promoted during evolution?
a. Using all of the available light for photosynthesis but risking damage to sensitive molecules.
b. Wasting light but protecting sensitive molecules from damage.
Strategy (b): plants seem to have evolved strategies that prioritise protecting sensitive molecules, even if the light available for photosynthesis is wasted.
504
What happens if there is not a constant input of energy and materials into organisms?
Unless there is a constant input of energy and materials, organisms break down into their component parts and the energy stored within them is dispersed.
505
What is the sugar that plants produce used for?
Some sugars are used to provide the energy for maintenance, growth and reproduction. Their energy is lost from the plant as heat during biochemical processes such as respiration.
The remaining sugars are deposited in cells as stored dry mass (net primary production or NPP).
506
What mechanisms do plants used to protect them from light?
Light can seriously damage plants. They have evolved several mechanisms of protection, including photorespiration, CO2 concentration, shiny leaves and ‘sacrificial molecules’.
507
What organisms are considered heterotrophs and why?
All animals and fungi, most microbes and even some plants are heterotrophs. They obtain energy and carbon in the form of complex organic molecules (food) synthesised by other organisms.
508
In respiration, the chemical energy released from these complex molecules is used to synthesise ATP. This powers a wide range of energy-requiring processes and reactions, ultimately releasing the energy as heat.
What is the chemical equation summarising aerobic respiration?
6O2(g) + C6H12O6(s) = 6CO2(g) + 6H2O(g) + energy
509
Energy is stored within organisms predominantly in the form of carbohydrates and fats. You have already seen some plant structures which are largely composed of storage tissues.
Recall from Part 1 some plant structures that are rich in storage tissues.
Structures such as bulbs, corms, tubers, rhizomes and seeds contain large reserves of energy-rich molecules.
510
What 2 phases is digestion broken down in to?
This initial phase of digestion combines physical digestion (i.e. through the grinding action of teeth, or the crop in birds) and chemical digestion (enzymes breaking up large molecules).
511
How does starch, fat, glucose and ATP differ in terms of energy access?
Complex biological molecules, such as starch and fat, store lots of chemical energy in a very stable form, which can be difficult to access. They are like monetary deposit accounts which require a period of notice before withdrawals can be made.
Simple carbohydrates such as glucose also contain lots of energy. This molecule is stable enough to be transported easily inside an organism. However, it can be readily metabolised when required, rather like a current account with instant access from a wide variety of outlets.
Small amounts of energy are carried by molecules such as ATP. They move energy over very short distances, such as those involved in biochemical pathways. These ‘energy currency’ molecules are like the small change you keep in your pocket for instant small transactions.
512
What two groups are heterotrophs divided into?
Heterotrophs are divided into two groups:
consumers (animals), which ingest organic matter and break it down internally
decomposers (primarily fungi and bacteria), which break down organic matter externally and absorb the soluble products through their membranes.
513
What 2 groups can consumers be further subdivided in to?
Consumers are further subdivided into those which eat relatively fresh, organic matter that has normally been ‘harvested’ in some way:
herbivores, which eat plants
carnivores, which eat animals
and those which consume dead organic matter:
detritivores (pronounced ‘de-try-tea-vores’).
514
What is secondary production?
Secondary production is the rate at which heterotrophs accumulate dry mass (biomass). Animals do not eat all of the biomass available to them. Cows eat only the tender shoots of grass, not the bases of the leaves or the roots. Birds may eat just the berries from trees but not the shoots or leaves. Therefore, just a fraction of NPP is actually consumed.
515
What is the proportion of food that is absorbed across the wall of the gut known as?
Furthermore, only a small proportion of the energy that an animal eats becomes deposited in the mass of its tissues. Of the food consumed (C), some will pass through an animal’s gut and out at the anus without having been absorbed through the gut wall (faeces, F). The proportion of the food that is absorbed across the wall of the gut is said to be assimilated (A).
516
What is the equation that can be expressed in units of dry mass?
Furthermore, only a small proportion of the energy that an animal eats becomes deposited in the mass of its tissues. Of the food consumed (C), some will pass through an animal’s gut and out at the anus without having been absorbed through the gut wall (faeces, F). The proportion of the food that is absorbed across the wall of the gut is said to be assimilated (A).
This relationship can be expressed in terms of an equation written in units of dry mass:
C = F + A
517
What is assimilated food used for?
Some of the assimilated food is used in cellular respiration (R) to provide energy for movement and making new chemical compounds. Some is removed in the nitrogenous waste which is excreted, known as urine in many animals (U). The rest is stored in the dry mass of new tissues as secondary production (P). This relationship is summarised in the equation:
A = U + R + P
518
What do ruminents hvae to help them digest cellulose?
Being a ruminant herbivore, bullocks rely on microorganisms to assist with digesting cellulose. Cellulose is a large, complex carbohydrate molecule. It is the major component of plant cell walls and is very difficult to digest. The digestive enzymes in animal guts cannot break down cellulose effectively. So some animals, including termites and all ruminants (sheep, cattle, goats, deer, antelope), rely on fungal or bacterial partners to do the digestion for them.
519
What is detritus?
detritus (dead organic matter).
520
Explain how detrivores and decomposers interact with each other? Are any of the 6 kingdoms not represented?
First, the dead material is attacked by detritivores such as worms, springtails and mites. They use some of the energy and materials as food. However, their activities also break up the detritus into smaller particles, which increases the surface area available for chemical decomposition. The decomposer fungi and bacteria secrete enzymes, which break down the organic compounds in the detritus. Released from the remains of the cells by the action of these enzymes, the decomposers absorb the soluble organic subunits and nutrient ions.
The nutrient ions, which are essential for plant growth, are eventually released to the soil. But some particularly intractable organic compounds remain in the soil as humus. Most of the chemical energy within dead organic matter is converted to heat when this material is decomposed by microbes. Because organisms cannot recapture this energy, it is lost to the environment.
No, all six kingdoms are represented, illustrating the complexity of environmental energy flows.
521
What set of pattern do food chains generally tend to follow?
plant → herbivore → carnivore1 → carnivore2 → carnivoren
522
What word describes animals which live in upland streams and pools that are often low in nutrients?
oligotrophic
523
In what direction does energy flow through living organisms?
radiant energy (sunlight) → chemical energy (biomass) → heat energy (from respiration)
524
Is this also true of the carbon involved, i.e. does carbon flow in one direction through ecosystems?
No, the carbon released during respiration as carbon dioxide can be recaptured and reused, by plants during photosynthesis.
525
How is an ecosystem defined?
An ecosystem is defined as a community of organisms, interacting with one another and their abiotic environment (e.g. atmosphere, soil), which exhibits energy flow and nutrient cycling.
526
Describe how ecosystems can be opened and closed?
The original concept of ecosystems envisaged that they would be self-supporting, i.e. that they would be closed. The autotrophs would capture energy and minerals from the environment, and the heterotrophs would then take some for themselves. However, experience has shown that most ecosystems exchange energy and materials with a wider environment. As such, they can be considered to be open systems to some degree.
527
Which of the following ecosystems do you think is more ‘closed’?
a. A small island located in the Pacific Ocean.
b. A stream flowing through lowland Britain.
.The small island is more closed. It probably receives limited inputs from the surrounding air and ocean, and makes few outputs.
b.A lowland stream would receive many inputs from runoff, effluents and organic matter, for example leaves from neighbouring trees. Outputs include the removal of fish and invertebrates by terrestrial predators and the ultimate discharge to the sea.
528
What are essential and non essential parts of an ecosystem?
The essential components of an ecosystem are producers, decomposers and inorganic compounds such as water, carbon dioxide and nutrients. The primary producers (algae and plants) capture the inorganic compounds from their environment. The decomposers (bacteria and fungi) return these materials to the environment. Animals, as consumers, are not an essential component of the system.
529
What is the pyramid of numbers in an ecosystem?
In the 1920s, a famous Oxford ecologist, Charles Elton (1900–1991), noted that ‘the animals at the base of a food chain are relatively abundant, while those at the end are relatively few in numbers, and there is a progressive decrease in between the two extremes’ (Elton, 1927, p. 69). This pyramid of numbers is a common feature of ecosystems worldwide.
530
What is each successive layer in an ecosystem pyramid of numbers called?
trophic level
531
What usually represent the first. second and third levels in ecosystem pyramid of numbers?
. Primary producers usually represent the first trophic level. Herbivores and then the secondary consumers occupy the second and third trophic levels, etc.
532
What alternative parameter would overcome this inherent problem in comparing differing sizes of organisms?
Using the mass of organisms rather than their numbers might permit more sensible comparisons between different ecosystems.
533
How is a pyramid of biomass constructed?
A pyramid of biomass is constructed by taking samples of the flora and fauna in an ecosystem and drying and weighing them. The results are then expressed as mass per unit area, for example grams per square metre or tonnes per hectare.
534
What word defines The amount of biomass (and litter) present in an ecosystem at a point in time?
standing crop
535
What is the disadvantage of the pyramid of biomass?
It gives no indication of the rate at which that material is being produced (productivity).
536
What three possible fates does energy assimilated by plants have?
The energy assimilated by autotrophs has one of three possible fates:
Eaten by consumers while alive.
Stored (e.g. as wood or soil organic matter).
Eaten by decomposers once dead.
537
What happens typically to much of the net primary production in grasslands, freshwater and sea?
In grasslands, freshwater and the sea, much of the net primary production is eaten by herbivores (Figure 4.5.17). The rest enters the detritus food chain when the plants die. Over the whole year, the ecosystem is in balance. The energy entering it equals the energy leaving it.
538
What is a storage ecosystem?
In the early stages of the development of peat bogs and forest, the energy entering the system each year exceeds the energy leaving it (Figure 4.5.18). The balance of the energy is stored. Little of the biomass is eaten because there are few herbivores. Much of the rest is stored either as dead organic matter or as biomass in the form of soil organic matter, peat, or in the trunks, roots and branches of woody plants.
539
What is a detritus ecosystem?
Once the plants in forests have matured, a high proportion of the net primary production enters the detritus food chain. This is sometimes called the decomposer subsystem
540
Typically, decomposers account for 90% of the energy flow through these ecosystems. In a temperate forest, much of the detritus is dead leaves.
What would happen if there was no decomposition?
The leaves would accumulate and eventually smother the wood.
541
What term defines an ecosystem when inputs of energy and materials match outputs, resulting in no net change and with the system showing a high resilience to disturbance?
stable equilibrium
542
What type of ecosystems can be recognised with energy budgets?
Using energy budgets, three main types of ecosystem can be recognised. They are based on whether the bulk of the primary production is consumed, stored or decomposed.
grazing ecosystems
detritus ecosystems
storage ecosystems
543
What 16 elements are common in a ll plant tissue?
```
carbon
oxygen
hydrogen
nitrogen
potassium
calcium
sulfur
phosphorus
magnesium
chlorine
zinc
boron
manganese
copper
iron
molybdenum
others
```
544
select the names of:
a.two macronutrients
b.two micronutrients.
in plant tissue
a. N, K, Ca, S, P, Mg
| b. Cl, Zn, B, Mn, Cu, Fe, Mo.
545
What term defines If a mineral is readily available in the soil, plants will often take the opportunity to absorb it, even though it may not be used immediately in new growth?
luxury consumption
546
Carbon, hydrogen and oxygen are all more abundant constituents of plant tissue than nitrogen. Why does their availability not limit growth more frequently?
Hydrogen and oxygen are available from water; carbon and oxygen are obtained from gaseous CO2. New supplies of both these compounds are regularly delivered to the plant by the atmosphere.
547
Nitrogen is the most abundant gas on the planet. Why then should this element be limiting for growth? The answer lies in the chemical stability of nitrogen gas.
Nitrogen is composed of molecules each containing two nitrogen atoms joined by a triple bond (N2). Plants, like animals, cannot cleave this very strong bond. The gaseous pool of nitrogen is therefore completely unavailable to them.
548
What term defines Some species of bacteria produce enzymes capable of cleaving the strong triple bond of gaseous nitrogen. These bacteria can convert gaseous nitrogen from the atmosphere into organic compounds within their cells?
nitrogen fixation
549
What do plants give bacteria in return for nitrogen fixing?
In return for a nitrogen supply, the plant provides the bacterium with a home in knobbly nodules on the sides of the plant’s roots (Figure 4.5.23), with sugars for energy and an almost oxygen-free atmosphere. This third item is important because the essential nitrogen-cleaving enzyme is poisoned by oxygen.
550
Do all bacteria need to be provided with an enclosed nodule in order to carry out nitrogen fixing?
Some other plants such as the alder tree (Figure 4.5.24) have formed similar mutualistic relationships with other bacteria. Lichens are not plants, but are an important group of nitrogen fixers, and some free-living bacteria such as Azobacter and Azospirillum can fix nitrogen without being enclosed in a nodule.
551
In aquatic systems, the free-living blue–green bacteria (cyanobacteria) can fix nitrogen. Sometimes they are so successful, they create what are misnamed as ‘algal’ blooms.
What aspect of waterlogged soils has caused several species of plant growing in them to develop mutualistic relationships with nitrogen-fixing bacteria?
In waterlogged soils, other bacteria use nitrate as part of their respiratory process (denitrification). This breaks the nitrogen cycle between the plant and the soil and nitrogen is lost from the system to the atmosphere as nitrogen gas. By becoming a nitrogen-fixer, a plant can replace this lost nitrogen.
552
What is a limiting nutrient?
Plants require a cocktail of nutrients from the soil to sustain active growth. The one which most restricts growth rate is called the limiting nutrient.
553
What is the disadvantage of a plant having a huge root system
Sustaining such a huge length of living root is a great drain on the plant. Roots, which cannot photosynthesise, rely on sugars being delivered from the shoot. Root respiration and exudation may account for up to half of the carbon assimilated by the shoot. Plants would benefit from being able to increase their nutrient uptake efficiency.
554
What term defines It is a mutualistic relationship between a species of fungus and a plant. The fungus receives sugars from the plant and, in return, facilitates the plant’s uptake of mineral nutrients?
mycorrhiza
555
What type of relationship can bacteria and fungus have with a plant?
mutualistic
556
How many times longer are fungal hyphae than plant roots, per gram of tissue?
Assume that 1 g corresponds to 1000 mm3 of tissue, for both types. Also assume that both tissues are cylindrical with a volume, V, of πr2h. Here π (pi) is a constant equal to 3.14, r is the radius (half the diameter) and h is the height of the cylinder – in this case, the length of hypha or root.
557
How does fungus benefit plants?
he fungus is composed of very fine threads called hyphae (about 4 µm in diameter). These can explore the soil much more extensively than plant roots (typically 400 µm in diameter).
Because the fungus can be in close contact with more of the soil, it is better at absorbing non-mobile minerals. Fungi also appear to be better at releasing minerals (especially phosphorus) from tightly bound forms within the soil so have access to a much larger supply of phosphorus than a corresponding mass of root.
The fungus is often not host-specific. It can form partnerships with many different species of plants. As a result, a single fungus may form a link between several plants of different species through which minerals and organic compounds can move from one plant to another (Figure 4.5.29 and Table 4.5.3). This phenomenon may have important ecological consequences in terms of a stand of vegetation truly behaving as a community.
558
Mycorrhizal fungi in forests are some of the biggest living organisms on Earth. Why are they so seldom seen?
Mycorrhizal fungi live below ground for almost their entire life. The only time they emerge is to reproduce by spores. The toadstools we see are simply structures for spore distribution.
559
Trees may pass more than a quarter of the total carbon they fix by photosynthesis to mycorrhizal fungi. How can they ‘justify’ such a large expense?
Trees can justify the large expenditure on carbon when they are ‘paying’ for an enhanced supply of a growth-limiting nutrient such as phosphorus. Without the phosphorus, they cannot grow and therefore they would have excess carbohydrate from photosynthesis and nothing to do with it, so in this situation, paying the fungus is not really a hardship for the plant.
560
Why are soils that have high rainfall deficient in nutrients?
Some soils are so deficient in nutrients (particularly nitrogen and phosphorus) that not even mycorrhizas can supply the quantities required for growth by most plants. Such soils tend to be in high-rainfall areas, where most of the soluble nutrients are leached out of the soil and carried away by the excess water. These soils are often waterlogged for much of the year and oxygen availability is low. Therefore, plant litter breaks down very slowly and nitrate may be lost through denitrification. In these conditions peat soils can develop, composed of plant remains. Because of the lack of oxygen for microbial metabolism, nutrients are not released back into the soil. This becomes a self-perpetuating cycle, with the lack of nutrients inhibiting microbial activity further. Plants which can tolerate these conditions adopt an extreme stress-tolerant strategy, in which nutrients are very strongly conserved.
561
Why can very few species co exist with mosses in peat bogs?
The mosses in the genus Sphagnum form a major component of peat-forming communities on permanently wet, nutrient-poor soils. Very few species can coexist with the Sphagnum mosses. Some that do are insectivorous: for example, the sundews (Drosera spp., Figure 4.5.33). They trap insects on their sticky leaves and then digest them, extracting the minerals contained in their tissues.
562
Mycorrhizal fungi in forests are some of the biggest living organisms on Earth. Why are they so seldom seen?
Mycorrhizal fungi live below ground for almost their entire life. The only time they emerge is to reproduce by spores. The toadstools we see are simply structures for spore distribution.
563
Trees may pass more than a quarter of the total carbon they fix by photosynthesis to mycorrhizal fungi. How can they ‘justify’ such a large expense?
Trees can justify the large expenditure on carbon when they are ‘paying’ for an enhanced supply of a growth-limiting nutrient such as phosphorus. Without the phosphorus, they cannot grow and therefore they would have excess carbohydrate from photosynthesis and nothing to do with it, so in this situation, paying the fungus is not really a hardship for the plant.
564
Why is the environment on Mount Roraima in eastern Venezuela so poor in nutrients?
The huge amount of excess rainfall received by Mount Roraima, which flows so spectacularly over its cliffs, carries away most of the soluble nutrients. Weathering of the rock will supply some new ones, but this is a very slow process compared with the rate of loss.
565
What do deciduous trees in nutrient poor habitats do to recycle nutrients?
In contrast to species of nutrient-poor habitats, many species of deciduous tree shed large amounts of basic minerals with the autumn leaves. The term ‘basic’ means a mineral element like calcium (Ca) and magnesium (Mg) that can neutralise acids.
The fallen leaves decompose rapidly because fungi and other microbes can metabolise base-rich substrates quickly. The trees can then reabsorb the cations from the soil
566
What term defines Over a period of centuries or millennia, this rapid decomposition of organic matter and constant mixing creates a deep, relatively uniform soil?
brown earth
567
What effects do deciduous trees have from recycling nutrients?
The constant cycling of these elements through the soil profile makes them more readily available than if they were static. This increased availability encourages microbial activity. It also sets up a complex food web in the soil, sustaining a macrofauna of worms and moles, which mix the soil.
568
What type of soil do evergreen trees produce?
This type of soil is a podzol
569
What effects do evergreen trees have from recycling nutrients?
As a result, fungi and microbes decompose the needle litter less rapidly. The net result of this system, with very limited recycling of cations, is an acidic soil with a reduced soil fauna. In profile, it is very stratified because of the build-up of partially decomposed litter on the surface (black). Beneath this there is pale sand from which the coloured components have been degraded under the acid conditions and washed downwards into a lower, hard, coloured layer called a pan. This type of soil is a podzol
570
what relationship do plants and soil have
Vegetation type is, therefore, an important factor in soil formation. It is a two-way process: the soil type determines which plant species are successful in an area and the plants, in turn, influence the development of the soil.
571
What is often the growth limiting nutrient a plant requires?
Nitrogen is the single most important mineral nutrient for plants and often the growth-limiting one.
572
How have some species of plants overcome a restriction in nitrogen?
Some species have overcome this restriction by forming mutualistic relationships with bacteria which can use the vast resource of atmospheric nitrogen gas.
573
What mechanisms do plants have to help them overcome nutrient poor soils?
Plants can survive in nutrient-poor soils by several mechanisms. Mutualistic fungi called mycorrhizas can assist with nutrient acquisition. Capturing and digesting insects is an extreme adaptation to the unavailability of soil minerals.
574
In terrestrial systems how does 75% of the water entering the atmosphere get there?
In terrestrial systems, typically 75% of the water entering the atmosphere does so through plants.
575
What is darcys law?
Darcy’s law states that the rate of flow is proportional to the driving force and to the conductivity of the pathway:
```
where
v=h/l x k
v is the flow rate (or flux)
is the force driving the flow (hydraulic gradient),
where h is the change in height and
l is distance
K is the conductivity of the pathway.
Darcy’s law is, in fact, just a form of the general flux equation:
```
flux = driving force × conductivity
576
In soils, plants and atmosphere how is water most often held?
In soils, plants and the atmosphere, water is most often held under tension. This equates to a negative water pressure (sometimes called a suction).
577
What measures a plants water potential?
pressure bomb
Compressed gas is fed into a chamber containing a piece of plant tissue until the pressure is sufficient to push water out of the cut stalk
578
What is a typical value that water is held in a plant?
The pressure is read from a gauge and gives you a direct measure of how strongly the water was being held within the plant. A gauge reading of 100 kPa would indicate that the plant tissue’s water potential was −100 kPa. This is a typical value for water held in a plant.
579
Aside from fine bore tubes in plants how else is water retained?
Water is held tightly by the leaf partly because it adheres to the fine-bore tubes containing it. But it is also retained within cells by the presence of solutes. ‘Solute’ describes a substance such as a salt or a sugar, when it is dissolved in water to form a solution. Solutes have the effect of lowering the water potential of the solution in comparison with pure water.
580
What are the three components of water potential?
There are two other components of water potential. Hydrostatic pressure (P) corresponds to pressure in the everyday sense. For example, the water in a bottle of sparkling mineral water is under positive hydrostatic pressure, because of the pressure of gas in the bottle acting on it. If you made a hole in the bottom of the bottle, water would spurt out much faster than by gravity alone.
It is also possible to have negative hydrostatic pressure (sometimes called tension). For example, when you suck water up a straw, the water inside the straw is under negative hydrostatic pressure. If you made a hole in the side of the straw, air would rush in and the water would fall back.
The third component of water potential is matric pressure (m). This accounts for the tendency of water to ‘cling’ to solid surfaces by adhesion. Matric pressure is what you were considering in the example of the sponge
581
If the air is saturated, is there likely to be any movement of water in the soil–plant–atmosphere system?
Yes: water could be absorbed from the atmosphere by plants and even conceivably be released back to the soil if it is dry. (This is transpiration in reverse!) The reason is that the gradient in water potential could run from the air (0 kPa) to the plant (e.g. −50 kPa) to the soil (e.g. −100 kPa).
582
inside the plant, water can move relatively freely within a plumbing system of water-filled tubes, what are these tubes called?
xylem vessels
583
How does a plant protect itself from dehydration?
This driving force for water movement is very high, but so is the resistance to flow at this step. Water exits the leaf predominantly through small pores in its surface called stomata (singular ‘stoma’). This is because the rest of the leaf surface is covered by a waxy layer, or cuticle, which forms a barrier to water loss (Figures 4.5.44 and 4.5.45). By opening or closing the stomata, the plant can influence the rate of water loss and thereby protect itself from dehydration.
584
Which phase change inside a plant requires the most energy?
The movement of water from the soil through the plant to the atmosphere involves energy. The process that demands most energy is the phase change, from liquid water to water vapour, which occurs inside the leaf.
585
What is the flux of water from gaining it from the roots to loosing it from the leaf called?
Transpiration stream
586
Therefore, why do plants have stomata, which provide holes in the cuticle through which water escapes?
Plants have stomata to absorb carbon dioxide from the atmosphere. The simultaneous loss of water vapour from within the leaf is an unavoidable by-product of carbon acquisition.
The plant can be regarded as ‘paying for’ the carbon dioxide it gains from the atmosphere with the water vapour it loses. Carbon dioxide is ‘expensive’. Typically, for each molecule of CO2 entering the leaf, 50 molecules of water leave
587
What creates the gradient in CO2 concentration between the leaf and the atmosphere?
The consumption of CO2 by photosynthesis within the leaf.
588
What is water movement through soil-plant-atmosphere dictated by?
Water movement through the soil–plant–atmosphere continuum is dictated by gradients in water potential. This quantity and the flux of water through the system can both be measured.
589
How do plants pay for carbon dioxide?
Plants must take in carbon dioxide for photosynthesis, but in doing so they also release water vapour. Plants therefore ‘pay for’ carbon dioxide by losing water.
590
What does the C-S-R strategy by grime assign species too?
This approach considers how plants survive and exploit their environment during the mature phase of their life cycle. At its broadest level, the system assigns species to one of three groups:
competitors
stress tolerators
ruderals.
591
What is the competitive approach of a plant?
This approach maximises the amount of water taken up. To extract all of the available moisture from throughout the rooting volume, this involves:
sending roots deeper into the profile
growing a more extensive root system to gather water from a greater area
a denser network of roots to explore the soil more thoroughly.
592
What is the stress tolerant approach of a plant?
This approach minimises the water loss. The waterproof, waxy cuticle over the leaf surface is often thicker. Leaves may also grow a dense network of hairs to reflect radiation, keeping the leaf cool. Hairs trap a layer of moist air around the leaf, increasing the resistance of the pathway for water vapour to diffuse out of the leaf.
These adaptations involve an investment by the plant and may compromise its growth rate. However, the benefit is they allow plants to grow in soils that become dry
593
What is the ruderal approach by plants?
‘Ruderal’ approach
This approach is to grow rapidly while the soil is moist (usually in spring), set seed by mid-summer, then remain dormant in the soil seed bank during the late summer, when soils are most prone to dry out. These ruderals behave like desert annuals. Their life cycle allows them to avoid Idrought.
An example of a species that completes its life cycle very early in the year, allowing it to colonise drought-prone sandy soils, is the whitlow grass (Erophila verna, Figure 4.5.50). It is actually a member of the cabbage family and not a grass.
594
Some plants can improve their efficiency by opening stomata at night instead of during the day.
Why would this behaviour result in less water loss?
Relative humidity tends to be higher at night. Therefore, the atmosphere’s demand for water is lower. There is no solar radiation at night, so the energy driving transpiration is much reduced.
Night-opening plants can be more than 10 times as efficient in using water than plants which open their stomata during the day
Cacti and other succulent species growing in deserts use this mode of carbon dioxide uptake. The CO2 is taken up at night while the stomata are open
595
What term defines A photosynthetic pathway that allows plants in arid environments to harvest CO2 from the atmosphere during the night and store it for use during the day, thereby reducing water loss (e.g. many cacti and succulents).
Crassulacean acid metabolism
596
Why do cacti retain so much water in their tissues?
The reason why cacti contain so much water in their tissues per unit of photosynthetic area (Figure 4.5.53) is not purely to store water for use during droughts. It also creates a larger reservoir in which to temporarily store CO2 over the night/day cycle. The CO2 is stored as an acid and requires Hi large volumes of water within the cells to dilute it. In deserts, plants are generally not limited in terms of light availability, so it is often the plant’s capacity to store CO2 that limits the amount of carbon it can fix. All CAM plants are succulent (i.e. have a high water content).
597
So why don’t all plants take in their carbon dioxide at night to conserve water?
To use the carbon dioxide, plants need energy in the form of sunlight. If the CO2 is absorbed at night, it has to be stored within the leaf until the Sun rises. Then it has to be released so that it is available for photosynthesis.
CAM metabolism allows plants to overcome periods of drought. Responses to water shortage in other plants allow them to cope with water shortages, but few of these plants can survive if they are completely cut off from water even just for a day. They require a supply on a daily timescale, not an annual one. An excess of water on a whole-year basis is irrelevant to plants. Therefore, most plants rely on the water storage capacity of the soil.
598
What are the specialised breathing pores called that allow gas to diffuse freely into shoots?
lenticels
599
What will happen to plants if the roots are not supplied with oxygen?
In these situations, plant roots are at risk of suffocation. The root tissue of many plant species will die within a few days of the soil exhausting its reserves of oxygen.
600
How do wetland plant species survive in waterlogged soil?
Wetland plants use air-filled tissue in their roots and stems, which allows oxygen to diffuse along an internal gaseous pathway from the atmosphere to the root surface (Figure 4.5.57). This tissue is called aerenchyma
Although oxygen molecules have to diffuse over a distance of a metre or more through relatively narrow tubes, they provide a much more plentiful supply to the roots than could be obtained via diffusion through just a few millimetres of waterlogged soil. Much of the plant’s root is dedicated to oxygen transport
601
What is the advantage of Arenchyma?
A further advantage of air-filled tubes is that the oxygen is not ‘intercepted’ by soil bacteria on its way to the roots. The supply from the aerenchyma can be sufficient, not only to meet all the respiratory demands of the plant’s roots, but also to allow oxygen to ‘leak’ out into the surrounding soil (the rhizosphere). There it favours bacteria which use oxygen for their respiration. These displace the anaerobic bacteria and halt the reactions described above, thereby making the soil less hostile for plant growth. This can sometimes be seen in the soil profile by red-stained lines in an otherwise dark matrix. The red colouration is caused by Fe2+ ions being re-oxidised to their Fe3+ state.
602
How many water-value categories can species be assigned to according to the Ellenberg indicator values?
12
603
What other 6 environmental variables did Ellenberg assign rankings to species?
The other six variables for which Ellenberg assigned rankings to species are:
```
light
soil reaction (pH)
soil nutrient status
temperature
continentality of climate
salinity.
```
604
What disadvantages does a competitor have?
Plants have a limited amount of energy and building materials for new tissues. The cost of adopting this strategy is that reproduction by seed must be delayed because all available resources are required for rapid growth. These plants tend only to reproduce (flower) once they have gained a secure place in the canopy and can afford to divert resources to reproduction.
The other drawback of this strategy is the need for a plentiful supply of nutrients to support this rapid growth. Because growth is rapid and a dense shade is cast, older leaves soon become redundant and are discarded. Similarly with roots, because they are extensively exploring and depleting the soil resources, many of them also become redundant. Therefore, the plant loses a proportion of the mineral resources it has captured in these discarded tissues, and so needs to capture more.
605
What are the advantages of being a competitor?
Competitors (C) are species that survive by outgrowing their neighbours. To do this, they need rapid growth rates and a tall upright habit. By growing taller than their neighbours, competitor species shade them and inhibit their growth. Competitive species also tend to have deep and extensive root systems that capture the soil resources of water and nutrients effectively.
606
What are the disadvantages of being a stress tolerator?
The price of this ability is a slow growth rate compared with the competitors.
Stress tolerators cannot compete for resources effectively when conditions permit more competitive species to grow. Their only similarity to competitors is that they also delay reproduction until the parent plant is well established. A plant may be two or more years old before it takes the risk of using some of its precious resources to make flowers and fruit.
An example of a stress-tolerant species is the cowslip (Primula veris, Figure 4.2.27), which grows in old grasslands that have not been fertilised.
607
What are the advantages of being a stress tolerator?
Stress tolerators (S) are plants that have become adapted to harsh environments. One of the important resources for growth (light, water, mineral nutrients) may be in short supply. Alternatively, other adverse factors, such as temperature extremes, exposure to wind or the presence of toxic chemicals, may create stressful conditions for plant growth.
The strategy adopted by stress tolerators is to use the resource in short supply in an efficient and conservative manner. These plants have a very low turnover of organs such as leaves and roots.
Once they have invested resources in growing a leaf, they often retain it for more than one year, increasing the return on their investment. This contrasts with the stinging nettle, which may use an individual leaf for only a few weeks.
Stress tolerators therefore have a much lower demand for resources than competitors and are more efficient at obtaining scarce nutrients. They also tend to rely much more on mycorrhizal relationships with fungi than competitors do. They can inhabit environments that are very poor in terms of nutrient availability, such as bogs or sand dunes.
608
What are the advantages of ruderals?
Ruderals (R) are short-lived species that flower just once, then die. Gardeners refer to them as annuals. The essential difference between ruderals and plants in the other two categories is that they devote their resources to reproduction as soon as they can. They do not maximise their resource capture as competitors do, nor use resources most efficiently like stress tolerators.
Ruderals are ‘built for speed’. They produce their flowers and seeds in as short a timespan as possible. Some can race through their entire life cycle in six weeks, with the potential to have several generations during a single growing season
In non-agricultural environments, ruderals are found in areas such as deserts, which have unpredictable rainfall. Again, the seeds lie dormant for long periods until the rains finally arrive. The plant will then grow, flower and set seed in the few weeks before the soil water is completely exhausted.
The huge numbers of new seeds produced will then lie dormant, awaiting the next rain, which may not be for several years. In areas of such extreme unpredictability, ruderals may be the only effective strategy
609
What are the disadvantages of rudurals?
The drawbacks of this strategy are that they can neither compete effectively with competitors, which outgrow them, nor can they tolerate the harsher environments colonised by stress tolerators. They persist either in environments that are regularly physically disturbed, or where the environmental conditions are unpredictable.
Physical disturbance, such as soil tillage for arable agriculture, removes all surface vegetation. Long-lived species, which wait to establish themselves before reproducing, are disadvantaged in this environment. Short-lived species, which can return seeds to the soil before the disturbance occurs, are better adapted to these conditions.
The majority of so-called ‘weeds’ in arable fields or domestic gardens are ruderals. A good example is the field poppy (Papaver rhoeas, Figure 4.2.29). This is a summer annual of arable fields, bearing large flowers throughout much of the summer. A single plant can produce up to half a million seeds before dying. The seeds can lie dormant in the soil for many years and rapidly germinate when they are brought to the surface by cultivations.
610
In which strategy would you place a long-lived chamaephyte?
The S (stress-tolerant) strategy because chamaephytes are low-growing woody plants, according to the Raunkiaer system. Therefore, they are not tall, which is required to be classed as C, and being long-lived discounts the R strategy.
An example of a long-lived chamaephyte is bilberry, which grows widely on moorland such as in the Teign Valley.
611
What would the height be like for a competitor, stress tolerater and a ruderal?
C - varied S- small R- varied
612
What would the growth rate be like for a competitor, stress tolerater and a ruderal?
C - high
S - low
R - high
613
What would the life span be like for a competitor, stress tolerater and a ruderal?
C- mod to long
S- long to v long
R-short
614
What would the flowering be like for a competitor, stress tolerater and a ruderal?
C- late
S - late
R - early
615
Which strategy opts for early reproduction and what is its analogue under the Raunkiaer system?
The R strategy of Grime, which is analogous to Raunkiaer’s therophyte life form.
616
Which strategy describes the characteristics of a tall forest tree species, such as lime (Tilia cordata), which once dominated much of Britain?
The C strategy because lime trees are competitors.
617
What is the major environmental variable considered in the woodward scheme and what are they?
The major environmental variable considered in Woodward’s scheme is temperature. He interprets the temperature requirements of plants on two key fronts:
tolerance of cold
temperature sensitivity.
618
What is meant by a plants tolerance to cold?
Tolerance of cold
There are several levels of cold tolerance. These are often determined by the composition of the plant’s cell membranes. Many tropical species are not adapted to cold and their membranes are damaged by exposure to temperatures below 10 °C, even for a few hours.
Subtropical species have more resilient membranes, which can function at temperatures as low as 0 °C. However, they are disrupted by ice crystal formation if the temperature falls lower. Species adapted to grow at higher latitudes can withstand freezing. They can survive even when the soil freezes, preventing water uptake, by becoming dormant. It is possible to categorise vegetation types on this basis.
619
What is meant by the temperature sensitivity of a plant?
Temperature sensitivity of leaf growth
Biological reactions controlling rates of leaf expansion proceed faster at higher temperatures. The precise response to temperature depends on the structure of the enzyme proteins involved. Some enzymes function at low temperatures but their activity rate does not increase greatly at higher temperatures. Other enzymes are capable of much higher maximum rates, but stop functioning at the lower temperatures (Figure 4.2.33). This is called a trade-off.
620
Where is Tundra usually found?
Tundra is the low-growing vegetation of the Arctic, persisting on soils that are frozen for much of the year
621
What is coniferous forest dominated by?
Boreal coniferous forest is dominated by gymnosperms (conifers) such as pine (Pinus), spruce (Picea) and fir (Abies) (Figure 4.2.34b).
622
What is temperate deciduous broadleaf woodland dominated by?
Temperate deciduous broadleaf woodland is dominated by species of genera such as oak (Quercus), maple (Acer), beech (Fagus) and lime (Tilia) (Figure 4.2.34c).
Temperate evergreen broadleaf woodland also has oaks but they are the evergreen species such as holm oak (Quercus ilex), and in the southern hemisphere, eucalypts (Eucalyptus spp.) (Figure 4.2.34d).
623
What are tropical rainforests dominated by?
Tropical rainforest is composed of evergreen, broadleaf species belonging to groups such as the dipterocarps or giant members of the legume family
624
What are the best known ecological rankings?
The best-known ecological rankings are Ellenberg’s, which were developed for continental Europe but are also applicable in the UK.
625
What are the two main methods for assigning species to groups?
There are several different methods for assigning species to groups. Two were considered in more detail: Grime’s C–S–R strategy and Woodward’s physiological tolerance scheme.
626
Which two problems can you envisage in attempting to count all the individuals in a population?
First, the population may exist over a very large area, so there is the practical problem of effort and time.
Second, the individuals may be mobile, very small or hidden. Not even plants sit above ground all year and wait to be counted. Even a population with very large, immobile individuals, such as the pedunculate oak (Quercus robur), has small inconspicuous individuals, such as viable acorns in the soil or newly emerged seedlings.
There is an additional problem with plants. Neighbouring plants may all be part of the same genetic individual that has spread by vegetative reproduction, such as rhizomes.
627
What are the three main sampling techniques for counting population?
Ecological research has provided conservation workers with numerous different sampling techniques. Three of them – sampling by direct counting of individuals, indirect methods and using traps – are discussed next along with examples of their application.
The solution to the first of these problems is to sample the population, counting individuals or measuring the population size in another way in a small area (or set of areas). This can then be extrapolated to the whole population. Sampling provides an estimate of the size of a population in the absence of an absolute count of all the individuals in the whole population.
628
An alternative to counting animals directly in a sample is collecting evidence of their activities.
What kind of evidence of animal activity might provide information on the abundance of such animals?
Faecal pellets, bark scraping or leaf chewing can all provide information on the presence of individuals. Through sampling, an indirect estimate of the abundance of the animals that caused them can be made.
629
Knowing:
the defecation rate per elephant per day (R)
the number of days over which droppings have accumulated (A) (taking into account decomposition rates, which vary throughout the year)
the number of (estimated) droppings in the whole area (D)
a formula can be derived to estimate the number of elephants (N) in the whole area:
N=D/(RxA)
In a study in the Kasungu National Park in Malawi, D was estimated as 8 267 000; R was measured as 17 droppings per elephant per day, and A was 188 days.
Using these values, calculate the value of N, the estimated number of elephants in the park.
The answer is 2587. Given that D, R and A may all vary considerably, an estimate of 2000–3000 is probably reasonable.
630
What is the best method for sampling population?
However, the best estimates of population size come from capturing animals, marking them, releasing them, and then recapturing a proportion of them at a later time.
Mark–release–recap
631
What are the basic steps for mark release recapture method for sampling population?
Mark–release–recapture methods provide data that allow the size of a population to be estimated. If each animal is given a unique mark, estimates can also be made of the distance it has covered (if it is caught in different traps) and its longevity.
The basic steps in any mark–release–recapture sampling are as follows.
Animals are caught in traps, or by another method, over a short period of time, e.g. one night.
All of these animals are marked in some way and then released. The number of caught and marked animals is recorded. It is important that neither the mark nor the trapping affects the behaviour or survival of the animal. Although this is an assumption of mark–release–recapture techniques, it is not always satisfied. (For example, individuals may actively seek out the bait in traps, resulting in overestimates of the population size.)
Traps are reset and some animals are recaptured, perhaps on the night after marking and release. Two pieces of information are recorded, the total number of captures and the number of recaptured animals (i.e. those marked on the first trapping occasion).
632
How do you estimate population numbers using the mark release recapture method?
Concept of mark–release–recapture illustrated by overlapping rectangles. The total number (T) is unknown: 20 animals (N1) are caught on the first occasion and marked; 30 animals are caught on the second occasion (N2), of which 10 have been marked (M2).
T= (N1 x N2)/M^2
where:
N1 is the number of individuals caught and marked on a first occasion
N2 is the total number of individuals caught on a second occasion
M2is the number of marked individuals captured on a second occasion.
633
It is very difficult to determine the probability of extinction in real populations.
How can a probability of population extinction be calculated in the field?
The only way is to monitor several populations over long periods of time. The proportion that becomes extinct in each time period is then recorded and used to estimate the probability of extinction. This requires long-term detailed population studies, repeated at different sites.
634
Imagine two populations with approximately equal mean size but very different standard deviations. Which population has the higher probability of extinction in any one year?
The population with the higher standard deviation will have a higher probability of extinction. This is because its fluctuations are larger, leading to low population sizes occasionally and therefore a greater risk of extinction.
635
Imagine two populations with approximately equal standard deviations but very different mean values. Which population has the higher probability of extinction?
The population with the lower mean value will have a higher probability of extinction. This is because the same fluctuations (equal standard deviation) will result in lower population values.
636
What are the 2 categories of extinction?
extinct – there is no reasonable doubt that the last individual has died (e.g. the passenger pigeon)
extinct in the wild – known to survive only in captivity, or as a naturalised population well outside its past range.
637
What are the three categories of threatened groups called?
There are three threatened categories:
critically endangered – facing an extremely high risk of extinction in the wild in the immediate future
endangered – not critically endangered, but facing a very high risk of extinction in the wild in the near future
vulnerable – not critically endangered or endangered, but facing a high risk of extinction in the wild in the medium-term future.
638
What is the conservation assessment of population size and dynamics called?
The conservation assessment of population size and dynamics is called population viability analysis. These data can be included in measures of species vulnerability, such as the IUCN red list.
639
What word defines a simple count of how many different species are present in a particular community or location?
Species richness is a simple count of how many different species are present in a particular community or locatio
640
What word defines account both the presence of different species and their relative abundance?
species diversity?
641
What are the two types of succession? Under what conditions do they occur?
Primary succession begins on a substrate with no soil, for example a newly formed volcanic island or a disused quarry.
Secondary succession begins on soil cleared of its original vegetation. The methods of clearance include physically removing vegetation (e.g. by logging or ploughing) and burning. These influence the rate and course of succession.
642
As annual plants are characteristic of the early stages of secondary succession, what is the effect of rabbits on secondary succession?
Rabbits, in creating conditions suitable for early successional plants, slow down or even reverse succession.
643
How can rabbit scause species diversity?
Deflected climax communities on chalk grassland affected by rabbits are typified by very short, clipped vegetation, scrape holes and few trees. Because no single plant species can dominate, the number of plant species per unit area may be very high, perhaps 30–40 species in 1 m2. Therefore, we might consider rabbits, or other grazers such as sheep, as potential management tools for maintaining chalk grassland. This will create conditions suitable for numerous plant species and favouring early successional plant species which otherwise might be quite rare.
644
What are examples of habitat management?
Habitat management often involves altering the course or rate of succession. Examples include the coppicing of woodland and the grazing of grasslands.
645
Explain briefly what is meant by the term ‘grassland’.
Grasslands are areas dominated by grassy vegetation and maintained by burning, grazing, drought or freezing temperatures. They include non-woody grasslands, savannahs, and scrublands in which trees or shrubs are scattered at low density within the herbaceous vegetation. They can also include croplands.
646
Roughly what proportion of the Earth’s surface is occupied by grassland? List the principal reasons why grasslands are seen as important.
Roughly half of the Earth’s land surface is occupied by grassland.
The principal reasons why grasslands are important are that they provide resources in the form of livestock (food, game, hides and fibre) and genetic resources. They also provide services in the form of employment, recreation, habitat, water purification and nutrient cycling.
647
What are tthe three types of systems?
isolated
closed
open
648
What is an isolated system?
The simplest kind of system to understand is an isolated system (Figure 5.1.1a). In this case, the boundary is such that it prevents the system from exchanging either matter or energy with its surroundings. The concept of an isolated system is easy to understand, but although it is possible to have boundaries that prevent the passage of matter, in the real world it is impossible for any boundary to be so perfectly insulating that energy can neither enter nor escape.
649
What is a closed system?
The nearest thing to an isolated system in the real world is a closed system (Figure 5.1.1b). Such a system has a boundary that permits the exchange of energy with its surroundings, but not matter. Closed systems are very rare but, to a close approximation, the Earth is an example of one. Energy enters and leaves, but except for a few meteorites arriving from space and a tiny amount of gas leaking away from the atmosphere, the Earth has a nearly constant mass.
650
What is an open system?
The third kind of system, an open system (Figure 5.1.1c), is the most common of all, and exists when both energy and matter can be exchanged across the boundary. The hydrological cycle of an island on which the rain is falling provides a simple example of the model. Some of the water runs off via rivers or seeps downwards to become groundwater, while other water is used by plants or evaporates back into the atmosphere. Rainfall is derived from water outside of the island (i.e. outside the physical boundary of the system) and fluvial losses and evaporated water may also leave its shores.
651
What type of system is the biosphere, geosphere, hydrosphere and atmosphere?
The atmosphere, geosphere, hydrosphere and biosphere are all open systems, as matter and energy can move between them.
652
Thinking back to Block 3, why should the rock cycle be described as an open system?
Because the rock cycle has processes that involve the other main systems on the Earth and the exchange of matter between them (for example, the formation of carbonate sediments by life processes). It allows both matter and energy to cross its boundaries.
653
What are the two other main systems that this biogeochemical cycle system could interact with?
Space (outside the Earth’s atmosphere) and the interior of the Earth.
654
What is the main implication for life on Earth of an unvarying amount of the biologically important elements?
If life is to continue, these elements must recycle.
655
What is the main component of living tissue and also regulates the earths temperature?
Carbon is the main component of living tissue; all known life is based on carbon. Certain carbon compounds are important greenhouse gases, which regulate the Earth’s temperature.
656
Why is nitrogen an important element to life?
Nitrogen is an essential element for life, notably because it forms an integral part of amino acids, the basic building blocks of proteins, and is present in nucleic acids, which are also found in all living organisms.
657
Where can sulfur be found in the body?
Sulfur is generally present in very small amounts in living organisms, but is an essential nutrient and is found in certain amino acids, vitamins and hormones.
658
Why is phosphorus essential for the biosphere?
Phosphorus is one of the nutrients needed for the healthy growth of organisms in the biosphere. For example, plants cannot grow without phosphorus and animals cannot produce their skeletons without this element. Phosphorus is also an essential constituent of the energy-transferring molecules of living cells and is required for nucleic acid synthesis.
659
What does the term ‘biogeochemical’ tell you about the various reservoirs of the Earth’s biogenic elements?
The term ‘biogeochemical’ tells you that both the biosphere and the geosphere are involved.
660
What does the global carbon cycle involve?
the global carbon cycle involves movement of carbon between the land, the ocean and the atmosphere
661
Explain the steps in a terrestrial carbon cycle?
The terrestrial carbon cycle operates on short timescales.
Carbon dioxide is removed from the atmosphere and photosynthesis transforms it into organic compounds.
Some carbon is returned to the atmosphere quickly via respiration, while the rest becomes organic matter.
When a plant dies, the carbon is incorporated into the soil and microbial degradation releases it as CO2.
A small amount of carbon escapes respiration and decomposition and is buried on land or transported by runoff to the oceans.
662
Is the terrestrial carbon cycle a completely closed system
No. Some carbon does ‘escape’ through preservation and runoff.
663
In what ways can the terrestrial carbon subcycle be broken?
First, a small amount of material may never be fully decomposed back to CO2 and may be preserved as fossil organic matter
Second, a ‘leak’ in the terrestrial carbon cycle occurs when, before degradation of the organic matter is complete, carbon is released from the soil by erosion and is transported away by runoff.
664
Which organisms begin the process of breaking down dead plant material for recycling?
fungi
665
What process enables plants to get at the recycled nutrients from dead organic materials?
Decomposition is the breakdown of dead organic matter into simpler constituent materials.
666
Which group of organisms was given the distinctive title of ‘ecosystem engineer’?
earthworms’, which not only continue the work of the fungi, but also move huge volumes of material from higher up in the soil to lower down.
667
Which group of organisms finish the job of breaking down the plant materials in the soil?
Your answer is correct. Bacteria fulfil this function particularly within the guts of earthworms, but also within the soil itself.
668
What is the name for a group of decomposer organisms that break down their food externally and absorb the nutrients?
The correct answer is 'saprophytes', which are are organisms (such as fungi) that obtain their nutrients from dead organic material.
669
How do fungal hyphae (known collectively as mycelia) break down organic matter?
The fungal hyphae secrete digestive enzymes outside into the surrounding environment (such as the soil) and absorb the nutrients once the organic matter has been broken down into smaller components.
670
Where does the global carbon cycle take place?
The global carbon cycle involves processes in the atmosphere, on the land and in the sea. Both biological and non-biological reactions take place.
671
What three subcycles can the global carbon cycle be broken down into?
The global carbon cycle can be divided into three subcycles, each of which operates on a different timescale.
The terrestrial carbon cycle operates on a timescale of months to decades.
The marine carbon cycle operates over hundreds of thousands of years.
The geological carbon cycle operates over millions of years.
672
Which is the most important carbon sink: the atmosphere or the ocean?
The ocean (and the ocean floor in particular) is more important in this sense, because it stores about 50 times more carbon than the atmosphere.
673
Do the oceans regulate climate?
Yes – the oceans can regulate climate by absorbing carbon dioxide.
674
Will the ability of the ocean to regulate climate change with global warming?
Yes – the ability of the ocean to hold carbon dioxide decreases as ocean temperatures rise – leading to positive feedback.
675
What are the different step of the marine carbon cycle?
The marine carbon cycle operates on intermediate timescales.
Marine phytoplankton utilise dissolved CO2 in surface waters to generate organic matter, which eventually sinks down through the water column.
The CO2 in surface waters is replenished from the atmosphere and this transport of carbon to the deep ocean constitutes the biological pump.
As with the terrestrial carbon cycle, small amounts of organic matter escape degradation and are buried in sediments.
The small but steady leak of carbon from the terrestrial and marine carbon cycles due to burial allows carbon to enter the geological carbon cycle.
This cycle operates on long timescales and the rock reservoirs contain most of the carbon in the carbon cycle.
The carbon is returned to the atmosphere and ocean when tectonic processes expose buried carbon to be weathered or directly oxidised to CO2.
676
If the transport of photosynthetically produced organic matter to the deep ocean were to continue in isolation, what would be the consequence?
The surface waters would eventually be stripped of dissolved CO2.
677
What term defines The overall effect of the drawdown of CO2 from the atmosphere, the photosynthetic fixation of CO2 in surface waters, and the subsequent transport of the organic matter to deeper water
biological pump
678
CO2 is more soluble in water at lower temperatures and higher pressures. How will this property affect the concentration of dissolved CO2 in deep ocean waters?
The lower temperatures and higher pressures in deep ocean waters will allow them to hold more dissolved CO2 than surface waters.
679
Explain what the carbonate compensation depth is and how it balances itself?
Deeper parts of the ocean are more acidic due to the sinking of dissolved Co2 as lower temperatures and higher pressures hold more co2. The CCD is the level at which CaCO3 (that many shells of animals are made from) dissolve therefore reducing the CCd depth as this increases the CaCO3 balancing it out
680
The carbonate compensation depth (or ‘dissolving depth’) is always the same. (True or false?)
False. The CCD varies according to the calcium carbonate already present in the sea water – this is linked to the amount of shells present as well as the acidity of the water. As acidity rises, the CCD depth can move closer to the surface.
681
Sulfur dioxide is the main anthropogenic gas responsible for ocean acidification. (True or false?)
False. Carbon dioxide is the main driver of ocean acidification.
682
If oceans become more acidic then shells and corals dissolve. (True or false?)
True. Calcium carbonate – which makes up shells and coral skeletons – dissolves in mild acids.
683
A small decrease in pH is not a serious problem for the oceans. (True or false?)
False. The pH of the ocean has decreased from approximately 8.18 to 8.08 over the last few hundred years. As pH is on a logarithmic scale, this 0.1 difference equates to about a 25% increase in H+ ion concentration.
684
As the ocean temperature rises, less carbon dioxide dissolves. (True or false?)
True. The ability of the ocean to absorb carbon dioxide decreases as the temperature of the oceans increase. This increases carbon dioxide in the atmosphere, exacerbating climate change.
685
What is the largest reservoir in the combined terrestrial and marine carbon cycle?
The deep ocean is by far the largest reservoir with 38 000 × 1012 kg C at any one time.
The remaining reservoirs in the marine carbon cycle are the surface waters (1000 × 1012 kg C) and the seabed sediments (3000 × 1012 kg C).
686
How can geological carbon that has been stored for a very long time end up back in the atmosphere?
the geological carbon cycle is a cycle and, eventually, this carbon returns to the Earth’s atmosphere.
One of the ways in which this happens is via the exposure and weathering of rock. Mountain-building pushes deeply buried carbon-containing rocks up to, or close to, the surface and exposes them to oxidation by atmospheric oxygen or oxygen dissolved in groundwaters. The inevitable consequence of this process is that the carbon is transformed back to CO2 and the cycle can begin again.
687
What are the two different types of carbon rich accumulations in sediments?
There are two different types of carbon-rich accumulations in sediments:
those containing carbonate (carbon in inorganic form)
those containing organic remains.
688
Describe what the carbon rich accumulation is that contains carbonate?
The first of these types of sediment is described as calcareous (Figure 5.1.12). These sediments are generally marine deposits containing accumulations of CaCO3 shells and skeletons, which have been made by organisms using dissolved inorganic carbon. Over millions of years, chemical and structural changes occur in the sediments and they become rocks such as chalk and limestone.
689
Describe what the carbon rich accumulation is that contain organic remains?
The second kind of carbon-rich accumulation, containing organic material, is often described as carbonaceous (Figure 5.1.13). As organic-rich material is covered with more organic matter and sediment, the weight of the overlying deposits causes compaction, squeezing out water and residual air from the pore spaces. In the resulting oxygen-poor environment, a dense residue enriched in carbon is formed.
Under continued deposition of organic matter and sediments, the original material may be buried to depths of several kilometres. As in the case of calcareous remains, high temperatures and pressures eventually cause the sediments to become lithified. Large accumulations of land plants may become coal, and marine sediments containing very high concentrations of phytoplankton debris can produce petroleum-source rocks.
690
What is the net result to the atmosphere of organic matter burial?
For every carbon atom that enters the rock reservoir, one oxygen molecule is left behind.
691
What is the implication for the atmosphere of organic carbon burial and silicate weathering on land?
Carbon ‘leaks’ out of the atmospheric reservoir and into the rock reservoir.
692
What will be the effect on the CCD and the distribution of ocean-floor carbonate sediments (as shown in Figure 5.1.8) if, due to fossil fuel use, atmospheric CO2 levels continue to rise? (Remember from study session 5.3 that atmospheric CO2 dissolves in seawater.)
Increased CO2 concentrations in the atmosphere would lead to a corresponding increase of dissolved CO2 in the ocean. Because dissolved CO2 forms an acidic solution, the average acidity of the ocean would increase and the CCD would shift to a shallower level. The area of carbonate sediments in Figure 5.1.8 would decrease.
693
Why will the carbon atoms contained in CH4 continue to take part in greenhouse warming after the CH4 has been destroyed by oxidation?
Because the oxidation product of CH4 is CO2, which is another greenhouse gas, the carbon atoms continue to play a role in greenhouse warming after CH4 is destroyed.
