3.5 -Population Size And Ecosystems Flashcards
Define population
An interbreeding group of organisms of the same species occupying a particular habitat
Define birth rate
The reproductive capacity of a population; the number of new individuals derived from reproduction per unit time
Define immigration
The movement of individuals into a population of the same species
Define equilibrium species
Species that control their population by competition rather than by reproduction and dispersal
Name factors in an ecosystem that affect all organisms living in it, these factors are constantly changing, so ecosystems are dynamic:
1) intensity if energy flowing through the ecosystem varies
2) biological cycles such as the nitrogen cycle vary mineral availability
3) habitats change over time as succession occurs
4) new species arrive and done speacies are no longer present
How can the size of a population at a particular time be determined?
1- birth rate (increase pop)
2- death rate/ mortality (decrease pop)
3- immigration (increase pop)
4- emigration (decrease pop)
When does a population size increase
When the combined effects of birth and immigration exceed those of death and emigration the population size increases
What are fugitive species?
Species that are poor at competition, instead they rely on a large capacity for reproduction and dispersal to increase numbers.
They invade a new environment rapidly e.g algae colonising bare rock
What are equilibrium species
A species which control their population by competition within a stable habitat. Their usual pattern of growth is a sigmoid (s-shaped) curve called the one step growth curve.
Example: when bacteria are put into fresh nutrient solution
What are the 4 stages of the one step growth curve?
- Lag phase
- Exponential log phase
- Stationary phase
- Death phase
Define the term environmental resistance
Environmental factors that slow down population growth
Define biotic
A part of the environment of an organism that is living e.g pathogens or predators
Define abiotic
A part of the environment of an organism that is non living e.g air temperature or oxygen availability
Define carrying capacity
The maximum number around which a population fluctuates in a given environment
Describe the lag phase
It is a period of adaptation or preparation for growth with intense metabolic activity where there’s slow growth in population.
Describe the exponential phase (log phase)
As numbers increase (as long as there’s no factor limiting growth) more individuals become available for reproduction. E.g bacterial cells divide at a constant rate per unit time (cell number increases logarithmically) :: also called log phase
Why can’t the exponential phase be maintained?
Environmental resistance sets in:
- less food available
- concentration of waste products becomes increasingly toxic
- not enough space or nesting sites
(The population still increases but more slowing so the gradient of the graph decreases)
Name environmental resistance factors affecting the growth of bacteria in a flask:
1- available nutrients
2- overcrowding
3- competition
4- accumulation of waste
Name some biotic factors that affect non artificial environments e.g rabbits on an island
1- all environmental resistance stated previously
2- predation
3- parasitism and disease (increased population density allows disease to spread more rapidly)
4- competition from other species for nesting/food sites
Name some abiotic factors affecting non artificial population size
1- light intensity
2-temperature
Describe the stationary phase
- Occurs when the birth rate = death rate.
- the population has reached its carrying capacity for that particular environment
- actual number depends on resources available e.g more food = higher carrying capacity
- the population is not absolutely constant and fluctuates around the carrying capacity based on environmental changes e.g number of predators
Describe the death phase
The factors that slow population growth at the end of the lag phase become more significant and population size decreases until the death rate is greater than the birth rate and the graph has a negative gradient
Describe the effect a predator-prey relationship has on a population
1- causes both populations to oscillate which are regulated by negative feedback
2- predators are normally larger than prey
3- the abundance of prey limits the numbers of predators and the number of predators controls the numbers of prey
Describe the predator prey relationship between lynx and hares
1- a large number of lynx predate hares, so the hare population decreases
2- there is not enough food for the lynx so lynx numbers decrease
3- there is less predation on the hares so hate numbers increase again
4- there is more prey for lynx so lynx numbers increase
What is a density dependent factor? Give examples
Environmental factors thay have more effect if the population in a given area is larger.
These biotic factors include disease, parasitism and depletion of food supply
E.g If a population is denser parasites are transmitted more efficiently
What are density independent factors?
They are abiotic f acc tor’s which do not depend on the population density. The effect is the same regardless of the size of the population, and is usually a sudden abiotic change e.g fire or flood.
Describe how population size is regulated by negative feedback
If the population rises above the carrying capacity a density dependent factor increases mortality or reduces breeding to an extent where the population declines
If the population falls below the carrying capacity environmental resistance is temporarily relieved so the population rises again
Define biogeography and explain its founder
The study of species abundance and distribution, coined by Alfred R Wallace who modelled 6 biogeographic regions and saw different animals in similar habitats which contributed to his understanding of natural selection.
Why are physical features e.g soil type and temperature first described when a new habitat is assessed?
Because they determine the number and types of organisms that live there e.g a very cold habitat may support only lichens but a warmer habitat may support a vast number of animals
Define the term abundance
The number of individuals in a species in a given area/volume
How can animal abundance be assessed?
1) capture mark recapture experiments using the Lincoln index calculation
2) kick sampling in a stream and counting aquatic invertebrates
How can plant species abundance be assessed
1) using a quadratic to calculate the mean number of individuals in several quadrants of a known area, to find the density (number/m squared)
2) estimating % cover of a plant in which individuals are hard to recognise
3) estimating % frequency
Define the term distribution
The area or volume in which the organisms of a species are found
How do you measure the distribution of a species if the habitat is uniform?
What does a small area indicate?
Why is this technique used?
- Mark the position of the outermost plants on a map and the area they surround can be measured.
- A small area indicates the species may under threat of extinction
- botanists use this technique to assess the distribution of threatened plant species so they can protect specific sites against mining companies/road building mitigating species loss.
What does a line transect show?
Shows the organisms that lie on a line at measured intervals (pg 70 for example)
What does a belt transect show?
The abundance data for a given area at measured distances along the transect. A quadratic is placed at each co-ordinate along the transect and readings are taken for:
- the density of chosen species
- % frequency of chosen species
- % area cover for all species
What diagram can be drawn to show the % cover of a species along a belt transect?
A kite diagram
If a transect is positioned horizontally along a footpath what can the species distribution in the kite diagrams/ line/belt transect show?
Can show which species are more resistant to tramping because they still grow in the middle of the path/ most sensitive to trampling as they grow on the outer edges of the path.
Why are belt transects represented in kite diagrams better than line transect?
They are better because they are two dimensional which provides more information about species distribution and abundance than the one dimensional line transect.
However numbers are rounded when kite diagrams are drawn so accuracy is lost in comparison with a table of data.
What are transects suitable for measuring?
What are transects not suitable for measuring?!
Suitable: plants, sessile animals
Not suitable: motile anomalies because they move.
Name ways of measuring animal distribution
1- direct observation of individuals or their nests
2- faecal deposits
3- markings
4- vegetation
Define the term ecosystem
A characteristic community of interdependent species interacting with the abiotic components of their habitat
Give an example of a small ecosystem, large ecosystem, long lasting ecosystem and temporary ecosystem
Small= humans large intestine and it’s community of micro-organisms
Large= seas cover about 70% of the earths surface and the Pacific basin is the largest marine ecosystem
Temporary= puddle left after the rain
Long lasting= Lake Baikal in Siberia has existed for 25 million years
Give an example of a marine ecosystem, it’s abiotic and biotic feature
Example: Pacific Ocean
Abiotic features: high mineral salt concentration
Biotic features: algae, starfish
Give an example of a arctic tundra ecosystem, it’s abiotic and biotic feature
Example: Siberia
Abiotic: temperatures between -50 and 12 degrees Celsius
Biotic: moss, arctic hare
Give an example of a desert ecosystem, it’s abiotic and biotic feature
Example: Sahara
Abiotic: less than 25cm rainfall annually, high temperatures & light intensity
Biotic: cactus, camel
Define the term energy
The ability to do work, no change happens unless energy changes occur.
What is the law of thermodynamics?
The functioning of an ecosystem can be thought of as a sequence of energy changes in which energy flows through the components of the ecosystem subject to rules.
Name some examples of energy source on earth
1) Geothermal energy
2) Electrical energy
3) Chemical energy (early organisms used energy released in chemical reactions to make carbohydrates via chemiosmosis)
4) Light energy (significant as it radiates from the sun providing energy for photosynthesis)
Define the term habitat
The place in which an organism lives
Define the term community
Interacting populations of two or more species in the same habitat at the same tine
Define the term trophic level
Feeding level, the number of times that energy has been transferred between the sun and successive organisms alone a food chain
Define the term biomass
The mass of biological material in living or recently living organisms
Define microhabitat
A very small area that differs from its surroundings and has the features that make it suitable for a particular species
E.g the cabbage looper feed on the lower surface of leaves of cabbages
What does a habitat provide for an organism?
A means of survival such as food, water, soil, appropriate temperature and pH.
What does community ecology study?
Studies the interactions of species related to their:
- distribution and abundance
- genotype and phenotypic differences
- considered food web structured and predator-prey relationships
What is ecological energetics?
The study of the flow or energy through the ecosystem
What do photosynthetic organisms do?
Convert sunlight energy into chemical energy which passes from one organism to the next along a food chain.
How are food chains and biomass related?
The energy available to a trophic level contributed to its biomass and hence food chains can be thought of as a means of transferring biomass.
What are producers (give examples) and describe their role in the food chain
Green plants, Cyanobacteria and some protoctista are producers because they incorporate the suns energy into their carbohydrates which are the food and energy source for successive organisms in the food chain.
They trap solar energy and synthesise sugars from inorganic compounds by photosynthesis
What should I note about the proportion of light energy that is stored in producers
Only a small proportion of the total light energy that reaches the plant is incorporated into the plants tissue as some is reflected/used to evaporate water.
What are primary consumer?
Herbivores. They are animals that feed in plants
Describe the consumer role of carnivores
They are secondary, tertiary and higher consumers, they are animals that feed on other animals.
What’s important to know about energy transfer between trophic levels?
Energy in the food consumed is incorporated into the molecules of the consumer
As energy is passed along the food chain from one trophic level to the next there is a loss of energy, and the energy flowing through the ecosystem reduces and ultimately the energy leaves the system as respiratory heat.
Define the term saprobiont
A micro-organism that obtains it’s good from the dead or decaying remains of other organisms
What happens to the energy when producers or consumers die?
The energy remains in the organic compounds of which they are made
Detrivores and decomposers feed as saprobionts (derive their energy from dead and decaying organisms) and contribute to the recycling of nutrients.
What are detritivores?
Organisms (such as earthworms woodlice and millipedes) which feed on small fragments of organic debris (detritus; the remains of dead organisms and fallen leaves)
What are decomposers?
Microbes (such as bacteria and fungi) that obtain nutrients from dead organisms and animal waste. They complete the process of decomposition started by detritivores.
Sum up a detritus food chain:
Detritus—> detritivore —> decomposer
Define the term food chain. Give an example
A linear sequence of organism in a food web.
Grazing food chain example:
Producer —> primary consumer —> secondary consumer —> tertiary consumer
Note that there is 4 trophic levels present
What does a food web show?
Shows how the organisms in a community interact with each other through the food they eat
Why is the number of links in a food chain normally limited to 4/5?
Energy is lost at each link along the food chain and :: after link 4/5 there is not enough energy to support one another.
What are factors that can limit the length of a food chain?:
1- the more energy that enters a food chain in the first trophic level the longer the chain can be :: food chains which have high light all year tend to be longer than arctic food chains
2- the more efficient the transfer of energy between trophic levels the longer the food chain
3- predators and prey populations fluctuate and their relative abundance can affect the food chain length
4- larger ecosystems can support longer food chains
What factors can increase the leaf efficiency in absorbing energy per unit area?
If it is thicker, has a thinner cuticle, more chloroplasts, more chlorophyll and more grana.
About 60% of light energy that falls on a plant may not be absorbed by photosynthetic pigments due to:
- light being the wrong wavelength
- light being reflected
- light being transmitted straight through the leaf
What is the photosynthetic efficiency (PE) equation?
PE= Quantity of light energy incorporated into products/ Quantity of energy falling on the plant
X100
Define the term gross primary productivity
The rate of production of chemical energy in organic molecules by photosynthesis in a given area in a given time, measured in kj m-2 y-1
Define net primary productivity
Energy in the plants biomass which is available to primary consumers measured in kJ m-2 y-1
What is the equation linking GPP and NPP?
Why is this?
GPP - respiration = NPP
This is because a substantial proportion of gross production is released by the respiration of the plant to fuel e.g protein synthesis
What are standard values for GPP and NPPin most plants (not genetically modified crop plants)
GPP= around 1% NPP= around 0.5%
Define primary productivity
The rate at which energy is converted by producers into biomass
Define secondary productivity
The rate at which consumers convert the chemical energy of their food into biomass. This occurs in heterotrophs such as animals, fungi, some bacteria and some protoctista.
What is the general efficiency for primary and secondary productivity
Primary productivity= 10%
Secondary productivity= 20%
Define the term succession
The change in structure and species composition of a community over time
Define climax community
A stable, self-perpetuating community that has reached equilibrium with its environment, and no further change occurs
Define primary succession
The change in structure and species composition of a community over time in an area that has not previously been colonised
Define pioneer species
The first species to colonise a new area in an ecological succession e.g algae and misses in a xerosere
Define the term sere
The sequence of communities, with different species and structures
Define the term xerosere
A sere that exists in a very dry environment
Define the term seral stages
The stages of a series, each seral stage changes the environment and makes it more suitable for other species
Give an example of succession that has previously occurred in Britain (step by step ice age)
1) first organisms to colonise bare rock were algae and lichens (pioneer species) and form a (pioneer community)
2) weathering rock, erosion by lichens and mass of decomposing organic material creates primitive soil.
3) wind blown spores allow missed to grow, and as soil develops herbaceous plants outcompete misses and become established. Dispersed species that can germinate seed in daylight are favoured
4) animals include ants spiders and mice
5) as plants & animals die and decay soil become thicker with more minerals, this (humus) can hold water more efficiently allowing deeper rooted plants and small trees to outcompete herbaceous plants.
6) over a long time large trees e.g oak trees outcompete shrubs and small trees to become established, growing to form a self perpetuating climax community.
Name 3 features of a stable self perpetuating climax community
- great species diversity
- complex food web
- dominated by long-lived plants
Why is the climax community sometimes called the climatic climax community?
Because the species in the climax community largely depend on the climate
At what stage in a sere is animal diversity the greatest?
In the climax community as there’s invertebrates e.g slugs/snails and vertebrae e.g foxes and birds
At what stage in a sere is the plant biodiversity greatest
In the pre climax stage because the tree canopy limits the intensity of light reaching the woodland floor and so plant diversity slightly decreases
Summarise the general xerosere sequence
Pioneers—> herbs and grasses
Herbs and grasses —> shrubs and small trees
Shrubs and small trees—> large trees
What is balanced in a climax community?
1) GPP and total respiration
2) Energy used from sunlight and released by decomposition
3) uptake of nutrients from the soil and their return by decayed plant and animal remains
4) new growth and decomposition, so the quantity of humus is constant
Give a generic example (short) of succession (6)
1) bare rock colonised by algae
2) pioneer community of heather and misses
3) herbs and low growing shrubs
4) taller shrubs
5) birch and pine saplings
6) oak/beech forest
What is increased as a xerosere progresses?
1) soil thickness and availability of water, humid and minerals
2) biomass
3) biodiversity
4) resistance to invasion by new species
5) stability to disruption by environmental challenges e.g abnormal weather
Define the term secondary succession
The changes in a community following the disturbance of damage to a colonised habitat
Which is quicker, primary or secondary succession and why?
Secondary succession is quicker because the soil is still fertile and organisms still present :: the overall sequence is still the same as primary succession but more rapid.
Which succession is more commonly observed, primary or secondary succession?
Secondary succession (e.g after a tree has fallen) is a lot more commonly observed that primary succession.
List some commons species that rapidly colonise during secondary succession
Grasses, other herbaceous plants, heathers, brambles and birch trees.
What is a disclimax
It’s where human interference can affect succession and may prevent the development of the climax community
Give 3 examples of a disclimax
1) grazing by sheep and cattle maintains grassland and prevents the shrubs and trees of a normal succession from growing
2) farming of land removes all except deliberately introduced species and great efforts is expended in excluding all others
3) deforestation removes a conmunity of large trees and smaller trees may be replanted
Describe the disclimax of heather Moors and explain why it’s necessary to the grouse population.
There are 4 stages of heather growth: pioneer, building, mature and degenerate.
-Adult grouse feed on young succulent heather shoots (the pioneer stage)
-The building phase provides the best shelter for grouse nesting
without management (in the form of burning every 12 years) the heather would pass through the mature to the degenerate stage and conditions would be unsuitable for breeding of grouse.
What are the 3 factors affecting succession
1) migration
2) competition
3) facilitation
How does migration affect succession?
The arrival of spores, seed and animals is vital for succession to progress as non-native seeds may spread themselves widely altering the community of the soil
Define the term niche
The role and position a species has in its environment, including all interactions with the biotic and abiotic factors of its environment
In a community what do animals compete for? What do plants compete for?
Animals compete for:
- food
- shelter
- space
- reproductive partners
Plants compete for:
- light
- space
- water
- nutrients
What are the 2 main forms of competition, define them.
1) Intraspecific competition -competition between individuals of the same species
2) Interspecific competition -competition between individuals of different species.
Describe how an increase in population of one species can affect intraspecific competition.
Intraspecific competition is a density dependent factor :: as the population increases, competition increases and therefore a greater proportion fail to survive as organisms produce more offspring than the habitat can support, so numbers are regulated.
-the offspring with alleles that make them best suited to the environment reproduce more successfully by natural selection
Describe some common needs as part of interspecific competition and some individual needs
Common need= all fish species compete for dissolved oxygen in water
Different= each species has its own niche (occupies a particular place with a particular role in a community and :: a niche is the total description of an organisms way of life)
In which seral stages does competition operate? Who can occupy a niche?
All seral stages
Two species can’t occupy the same niche in a specific habitat and :: whoever has the competitive advantage will survive
What theory did Russian scientist Gause come up with
Studied two species of Paramecium and came up with ‘competitive exclusion principle’ which stated that when two species occur in the same habitat, one will outcompete the other, the two species can’t occupy the same niche.
What are the two types of facilitation that can affect succession? Define both.
1) Mutualism -an interaction between organisms of two species from which both derive benefit
2) Commensalism -an interaction between organisms of two species from which one benefits but the other is not affected
Define the term symbiosis
The association between individuals of two different species.
Sometimes the association is long term and organisms are highly inter-dependent and others association is loose.
What is the benefit to organisms of facilitation in a xerosere
Facilitation in an ecological community provides better resource availability, and refuge from physical stress, predation and competition.
Give 2 examples of mutualism
1) the highly inter-dependent interaction between a fungus and an alga
2) the relationship between flowing plants and their pollinators in a climax community e.g bumblebees pollinating horse chestnut trees
3) a bird eats insects off a deer so itself is feeding and the deer becomes insect free, this is loose association.
Give an example of commensalism
1) a squirrel in a climax oak woodland is protected from predators and sheltered by an oak tree (which is not affected)
Describe how facilitation interactions can change over time giving an example
However note that overtime as the species in an interaction evolve their relationship may change e.g bacteria in the mammalian gut provide their host with vitamin k which may also be obtained from died (commensalism) but if the hosts deficient in vitamin k the relationship becomes mutualistic
What’s important to note about the difference in transfer of energy and minerals in an environment
Energy is transferred in a linear fashion whereas minerals cycle between biotic and abiotic components of the environment e.g carbon/nitrogen cycle
What are the two human activities that have been a main cause for in increase in concentration of carbon dioxide in the atmosphere?
1- burning fossil fuels releases carbon dioxide that was previously locked up in them, into the atmosphere
2- deforestation has removed large quantities of photosynthesising biomass and so less carbon dioxide is being removed from the atmosphere
What are the 3 main biological processes involved in the carbon cycle?
1) respiration (carbon dioxide is added to the air by the respiration of animals, plants, microorganisms and combustion of fuels
2) photosynthesis takes place on a great scale re-using almost as much carbon dioxide as is released to the atmosphere by respiration on a daily basis.
3) decomposition- the dead remains of plants and animals (containing c+p+f) are acres upon by detritivores and saprobionts in the soil which release carbon dioxide back into the atmosphere.
What happens if decay of biological remains is prevented by anaerobic or acidic condition?
Organisms may become fossilised into coal, oil, natural gas or peat.
In aquatic systems what form is carbon dioxide in?
What extra process occurs in the aquatic carbon cycle?
HCO3- ions, which undergo the same processes as describe for terrestrial organisms as well as incorporating magnesium and calcium carbonate in mollusc shells and exoskeletons.
They become components of chalk limestone and marble after sinking.
If geological processes expose them to the atmosphere they are eroded again releasing carbon dioxide.
LEARN DIAGRAM OF CARBON CYCLE ON PG 84 🌍 ⛽️
LEARN DIAGRAM OF CARBON CYCLE ON PG 84 🌍 ⛽️
How do humans impact on the carbon cycle (list 4)
1- deforestation
2- climate change
3- greenhouse effect
4- global warming
In what two ways does deforestation increase the carbon dioxide levels in the atmosphere
1- when trees are cut down they may be burned or left where they’re cut to decay. Both of these processes release CO2.
2- the rate at which CO2 is removed from the atmosphere by the process of photosynthesis is reduced by cutting down forests.
Define the term global warming
The increase of average global temperature in excess of the greenhouse effect caused by the atmospheres historical concentration of carbon dioxide.
Name 3 ways climate has changed
Changes in average:
- temperature
- wind patterns
- rainfall
What are the two major reasons for carbon dioxide levels increasing from 300ppm to 400ppm in the last 100 years?
Why is the increase important?
1) burning fossil fuels
2) deforestation
Increase is important because CO2 is a greenhouse gas and :: it absorbs radiation from the earth and if it accumulates in excess it leads to global warming
List some common greenhouse gases
Carbon dioxide (H) Methane (H) Nitrous oxide CFCs Ozone Water vapour
Describe how greenhouse gases cause the earth to ‘warm up’
1- gases allow high energy short wavelength solar radiation to pass through the earths surface
2- energy is absorbed by the earth which warms up
3-earth re-radiates lower energy, longer wavelength under-red radiation
4- this is absorbed/trapped by greenhouse gases in the atmosphere
5- the greenhouse gases re-radiate the energy in all directions and the energy re-radiated back to the earths surface is absorbed
6- planetary surface and atmosphere warm up
What’s important to note about the greenhouse effect
It’s a natural process without which the average temperature on earth would be -20 degrees and :: is needed to sustain life.
List 2 global warming statistics
1) if we stopped greenhouse gas emissions stopped immediately the average global temperature would increase by 1.5 degree Celsius over the past 100 years
2) models predict that the average global temperate could increase up to 6.5 degree Celsius within the next 50 years
List some causes of global warming (8)
1- melting of polar ice resulting in flooding in costal areas
2-increased frequency of extreme weather e.g droughts and hurricanes
3-increased frequency of forest fires
4-may be increased crop yields with warmer temperature but pest populations may also increase
5-world food production may decrease
6-decreasing pH of oceans due to increasing CO2 threatens organisms e.g bleaching of coral reef/ limit fish gas exchange
7-fishing areas and crop belts may move with climate change
8-evolutionary adaption is to slow as climate changes :: plants can’t disperse :: driven to extinction/ animals dependent on plant driven to extinction and ecosystems collapse
How is agriculture vulnerable to global warming?
Affected through changes in temperature and quantity of rain. Extreme weather ruin crops.
Fluctuations in river flow increase and reduced water supply can halve crop yield
Research is ongoing to develop drought resistant crops.
Define the term carbon footprint
The equivalent amount of carbon dioxide generated by an individual a product or a service in a year
How does altered farming practices reduce their CO2 emissions
(Include source of CO2)
Source= decomposition of soil organic matter
Altered farming methods:
1)conservation tillage (leave crop residue and organic matter on the soil surface to reduce erosion, improve water use.
2)cover cropping (enhance soil structure by adding organic matter to top soil and clover to clover soil protects and improves soil between crops
3)crop rotation reduces pest numbers and mineral depletion
How does altered farming practices reduce their Nitric oxide and nitrous oxide emissions
(Include source of nitric/nitrous oxide)
Source= waterlogged and anaerobic soils
Altered farming practise:
1)improve drainage to remove water and aerate soil
How does altered farming practices reduce their Methane emissions When the source of methane is digestive activities of farm animals used in the meat and dairy industry
1) reduce dietary intake of meat and dairy products
2) high-sugar grasses, oats, rapeseed and Maine silage in cows diets reduce the methane they release
How does altered farming practices reduce their Methane emissions When the source of methane is the decomposition in wet soils e.g rice paddies
1) use rice varieties that grow in drier conditions
2) select varieties that have a higher crop yield
3) ammonium sulphate addition can favour non-methane producing micro-organisms in paddy fields in some conditions
How do farms alter their practises when there’s low, fluctuating water supply?
Name the source of the problem
Source= low rainfall; high temperature
Altered farming practise=
Use drought-tolerant crops, e.g in Kenya the use of drought-tolerant sorghum, cowpea and millet have increased yields significantly
How do farms alter their practises when there’s a raised sea level
Name the source of the problem
Source= cultivated land inundated by salt water
Altered farming practise:
1) salt tolerant crops e.g a salt-tolerant potato, a salt-tolerant durum wheat yielding 25% more grain than the parent variety
What is the relationship between the global warming potential of nitrous oxide and methane with CO2?
1 molecule NO= 298 molecules CO2
1 molecule CH4= 25 molecules CO2
These are expressed as carbon dioxide equivilants
In what forms do crops have a carbon footprint?
1- production of farming tools
2-production of insecticides, herbicides, fungicides and fertilisers
3-farm machinery powered by fossil fuels
4-transport of producers (most shipped hundreds of miles)
What are the 3 ‘Rs’
- Reduce
- Reuse
- Recycle
Suggest ways we can lower our carbon footprint
- recycle packing material
- drive less/share lifts
- use less air conditioning and heating
- choose a diet to reduce animal protein (especially red meat) rice (because of methane emitting paddies) and foods transported long distances.
Define the term nitrification
The addition of nitrogen to the soil, most commonly as nitrite (NO2-) and nitrate (NO3-) ions.
Define the term nitrogen cycle
The nitrogen cycle is the flow of nitrogen atoms between organic and inorganic nitrogen compounds and atmospheric nitrogen gas in an ecosystem.
Why do living organisms need nitrogen?
To make amino acids that polymerise for from proteins, chlorophyll and nucleic acids.
Briefly how is nitrogen transferred through the food chain?
1- plants absorb nitrates into their roots
2- organic nitrogen compounds produced by plants are eaten by primary consumers
3- the decomposition of plants and animals after death and their excreted waste produces release the minerals back into the soil.
What are the 4 main biological processes in the nitrogen cycle?
1) Ammonification
2) Nitrification
3) Denitrification
4) Nitrogen fixation
What is the role of ammonification in the nitrogen cycle?
Bacteria and fungi are decomposers which secrete enzymes that decay dead organisms and animal products, e.g:
- proteases digest proteins into amino acids
- deaminases remove (-NH2) groups from amino acids and reduce them to ammonium ion (NH4+)
What is the role of nitrification in the nitrogen cycle?
The ammonium (Nh4+) ions produced via ammonification are converted to nitrites (NO2-) by bacteria nitrosomonas and then nitrates (NO3-) by bacteria nitrobacter
Why are nitrification reactions considered to be oxidations?
What does this mean?
Because the ammonium ion progressively looses hydrogen atoms and gains oxygen atoms
This means that nitrosomonas and nitrobacter require aerobic conditions and will be inhibited in anaerobic conditions
What is the role of denitrification in the nitrogen cycle?
It is the loss of nitrate from the soil.
Anaerobic bacteria such as Pseudomonas convert nitrate ions to atmospheric nitrogen
NO3- —> N2 (g)
Why are denitrification reactions considered to be reduction?
What does this mean?
Where would this be a problem?
It’s a reduction because oxygen is lost and is hence favoured by anaerobic soil conditions and so it’s a particular problem in waterlogged soil.
Define the term nitrogen fixation
The reduction of nitrogen atoms in nitrogen molecules to ammonium ions by prokaryotic organisms
Why can’t organisms use the nitrogen that compares 79% of the air in the atmosphere?
Because very few organisms can use it as they don’t have the enzymes that break the triple bond between the atoms in nitrogen molecules.
Why does the biosphere rely on several prokaryotic species to use their enzymes reduce nitrogen molecules to ammonium ions?
Because geological processes releasing nitrates and ammonium ions are very very slow.
What is the name of the nitrogen fixing bacteria that lives in soil and accounts for most of biological nitrogen fixation?
Azotobacter
Give an example of symbiotic nitrogen fixing bacteria.
Where is this found?
Name: Rhizobium
Found: in the root modules of plants of the Fabaceae family (legumes i.e peas, beans and clover)
What are the labels on the diagram of the cross section of root and root modules of the legume
- Vascular tissue of root
- Vascular supply to the nodule
- N2(g) diffuses into the nodule
- Cells packed with Rhizobium
LEARN DIAGRAM OF THE CROSS SECTION OF ROOT AND ROOT NODULE OF LEGUME 🌱
LEARN DIAGRAM OF THE CROSS SECTION OF ROOT AND ROOT NODULE OF LEGUME 🌱
Sentence describing nitrogen getting in a legume
Nitrogen gas diffuses into the legume root nodule and nitrogenase catalysed it’s reduction for ammonium ions using energy from ATP.
Why are nitrogen fixing organisms often aerobic?
They require a lot of energy.
What type of reaction is nitrogen fixation?
How is this overcome by nitrogen fixing organisms?
It’s a reduction reaction and :: poisoned by oxidising conditions.
Root nodules contain leg-haemoglobin that binds to molecular oxygen in the nodules protecting them from oxidation reactions.
The root nodules turn pink
Show the whole process of nitrogen fixation
N2(g) —> NH4+ —> organic acids —> amino acids
Ammonium ions are converted to organic acids and then into amino acids for incorporation into bacterial proteins
N2(g) —> NH4+ carries out by nitrogenase
How do plants obtain nitrogen for their own metabolism?
Some amino acids and ammonium ions produced via nitrogen fixation are diverted into the vascular strand connecting the root nodule to the plant, obtaining the nitrogen.
How do plants without mutualistic nitrogen fixing bacteria take up nitrates and ammonium ions?
Via active transport and facilitated diffusion from the soil.
Describe how root nodules are formed from Newly germinated legumes and radical cells.
The radicals of newly germinated legumes don’t contain rhizobium.
In the soil both rhizobium and newly emerged radical cells (NERC) secrete Chen-attractants and the NERC grows towards rhizobium cells and the rhizobium uses flagella to move towards the radical.
Rhizobium cells invade the vortex of the radicle and the large number produced when they replicate makes the swelling which is the root nodule.
Wha enables leguminous plants to grow successfully?
The root nodules and the bacteria they contain enable leguminous plants to grow successfully even when soil nitrates are scarce.
What happens when leguminous plants die?
Both the plant and the Rhizobium that the nodules contain are decomposed into ammonium compounds which are released into the soil.
The ammonium ions are nitrified to nitrites and nitrates, improving the soil quality further
Name 3 non biological processes that have an impact in the nitrogen cycle
1) the application of agricultural fertilisers adds nitrogen to the soil
2) lightning adds a small amount of nitrogen to the soil
3) leaching of minerals removes nitrogen from the soil
In what ways are humans attempting to make increasing amounts of food.
1) plant breeding
2) genetic modification
3) use of pesticides
4) treating soil and maintaining its structure
One human activity that improves circulation of nitrogen in agricultural soils is ploughing fields which improves soil aeration, what does this favour?
Favours:
- aerobic organisms e.g free living nitrogen fixers enhancing formation of ammonium ions in soil
- intriguing bacteria enhancing conversion of ammonium into nitrites and nitrates
- plant roots respire aerobically and generate ATP which fuels their active uptake of minerals
Another human activity that improves circulation of nitrogen in agricultural soils is draining land.
Describe this.
Allows air to enter the soil and so reduced anaerobic conditions which favour denitrifying bacteria :: loss of nitrates is reduced
Another human activity that improves circulation of nitrogen in agricultural soils is artificial nitrogen fixation.
Describe this.
The harbour process converts nitrogen (N2) to fertilisers (largely containing ammonium nitrate ions) essential in producing large quantities of food.
Another human activity that improves circulation of nitrogen in agricultural soils is the use of animal waste.
Describe this.
Examples include manure and cow dung
It is put on crops to improve the soil structure do that the soil holds more nutrients and water :: more fertile.
It releases nitrogen compounds to the soil gradually over a long period of time and encourages microbial activity which promotes the soils mineral supply, improving plant nutrition.
One human activity that improves circulation of nitrogen in agricultural soils is the use of treated sewage.
Describe this.
It’s a sustainable alternative to inorganic fertilisers, improves volume and quality of food.
One human activity that improves circulation of nitrogen in agricultural soils is planting fields of legumes.
Describe this
Examples include clover and alfalfa which enhance nitrogen fixation, as when a crop dies its ploughed back unto the soil as ‘green manure’ which is high in nitrogen content increasing quality and structure of the soils.
Define the term eutrophication
The artificial enrichment of aquatic habitats by excess nutrient often cause by run-off fertilisers.
Define the term oligotrophic
It has very few minerals dissolved in them e.g upland streams.
When is water described as dystrophic?
When the mineral concentration is so Hugh that organisms die
List some problems caused by excess nitrate in soils
1) the use of fertiliser has reduced species diversity on grassland
2) fertilisers increase the growth of grasses and plants such as nettles which shade smaller plants 🌱
List some problems caused by excess nitrates leaching into rivers
-eutrophication
Describe the process of eutrophication
1) nitrate is highly soluble and so will dissolve into a stagnant/slow moving body of water
2) as nitrate is a fertiliser the algae respond by forming an algal bloom causing the surface of the water to become green
3) light can’t penetrate the water
4) the plants in the deeper regions of the lake can’t photosynthesise and die
5) there is a general decrease in animal biodiversity as they rely on plants for food/shelter
6) the short lived algae die and are decomposed by saprobiontic fungi. These are aerobic organisms and use a lot of oxygen creating a biochemical oxygen demand
7) water in all but upper layer becomes deoxygenated so that fish and other oxygen requiring species die
8) anaerobic bacteria in the water reduce nitrate to nitrite, which flourish and release gases with a characteristic smell e.g hydrogen sulphide (egg)
What must farmers do to comply with the strict legislation to reduce the nitrate concentrations in waterways?
1- restrict the amount of fertiliser applied to the soil
2-only apply fertiliser at a time when the crops are actively growing so that it is readily used and not leached away
3- leave a strip at least 10m wife next to watercourses. This means nitrate can’t directly enter water and when they do so it’s over a prolonged period of time
4- dig drainage ditches so that the minerals concentrate in the drainage ditches which undergo eutrophication, protecting natural watercourses.
