23- ecosystems Flashcards

nitrogen cycle not included

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1
Q

What is an ecosystem?

A

An ecosystem is made up of all the living organisms that interact with one another in a defined area. Also the physical factors present in that region.

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2
Q

what factors affect an ecosystem?

A

All ecosystems are dynamic- they’re constantly changing. Biotic factors - living factors e.g the size of a population of a species. Abiotic factors- the non-living/ physical factors e.g amount of rainfall.

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3
Q

What are biotic factors, give examples

A

Often refer to the interactions between organisms that are in the ecosystem. These interactions include competition, either within a population or between populations. Also includes mutualism and parasitism.

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4
Q

Give 5 abiotic factors that effect an ecosystem

A

Light
Temperature
Water availability
Oxygen availability
Edaphic (soil) factors

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5
Q

Why does light affect an ecosystem?

A

light is required for photosynthesis, so in general, the greater the availability of light the greater the success of a plant species.
Plants can develop strategies to cope with different light intensities e.g areas of low light may have larger leaves, and may develop photosynthetic pigments that require less light or reproductive systems that only operate when light availability is at an optimum.

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6
Q

How does temperature affect an ecosystem?

A

Biggest effect is on enzymes controlling metabolic reactions. Plants will develop more rapidly in warmer temps, as will ectothermic animals.
Changes in temp of the ecosystem e.g due to changing seasons can tigger migration in some animal species, and hibernation in others. In some plant species it can trigger leaf fall, dormancy and flowering.`

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7
Q

How does water availability affect an ecosystem?

A

In most plant and animal populations, lack of water leads to stress, which if severe can lead to death.
Plants- lack of water causes wilt, as keeps cells turgid and therefore upright, photosynthesis needs water as well.

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8
Q

How does oxygen availability affect ecosystems?

A

in aquatic ecosystems, it is beneficial to have fast- flowing cold water as it contains high concs of oxygen. If water becomes too warm, or the flow rate is too slow, the dip in oxygen conc can lead to suffocation of the organisms.
In waterlogged soil, the air spaces between the soil particles are filled with water. This reduces the oxygen available for plants.

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9
Q

How do edaphic (soil) factors affect an ecosystem?

A

Clay- This has fine particles, easily waterlogged, and forms clumps when wet.
loam- has different sized particles, it retains water but doesn’t become waterlogged.
sandy- has coarse, well separated particles that allow free draining- sandy soil doesn’t retain water and is easily eroded.

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10
Q

What is biomass?

A

It is the mass of living material present in a particular place or in particular organisms. Can be equated to energy content.

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11
Q

How do you calculate the biomass at each trophic level?

A

Multiply the biomass present in each organism by the total number of organisms in that trophic level. This can then be represented as a pyramid of biomass. This pyramid represents the biomass present at a particular moment in time- it doesn’t take into account seasonal changes.

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12
Q

Why is the dry mass used to calculate biomass?

A

Using the mass of the fresh material present is the easiest way, however, water contents must be discounted and the presence of varying amounts of water in different organisms makes this technique very unreliable unless large samples are used.

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13
Q

What are the problems with using dry mass to calculate biomass?

A

organisms have to be killed in order to be dried. The organisms are placed in an oven at 80 degrees until all water is evaporated- identified by atleast 2 identical mass readings.
To minimise destruction of organisms, only a small sample is taken, however this sample might not be representative of the population as a whole.

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14
Q

What is ecological efficiency?

A

the efficiency with which biomass or energy is transferred from one trophic level to the next.

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15
Q

Why do producers only convert 1-3% of light energy into chemical energy, and hence, biomass?

A
  1. Not all solar energy available is used for photosynthesis - approximately 90% is reflected, some is transmitted through the leaf and some is of unstable wavelength.
  2. other factors my limit photosynthesis e.g water availability.
  3. a proportion of energy is lost as it is used for photosynthetic reactions.
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16
Q

What is the equation for net (biomass) production?

A

Net production = gross production - respiratory losses

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17
Q

Why do consumers only convert 10% of biomass into their own organic tissue?

A
  1. Not all of the biomass of an organism is eaten, e.g plant roots or animal bones aren’t consumed.
  2. Some energy is transferred to the environment as metabolic heat, as a result of movement and respiration.
  3. Some parts of an organism are eaten but are indigestible- these are egested as faeces.
  4. some energy is lost from the animal excretory materials e.g as urine
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18
Q

what is the equation for ecological efficiency?

A

([energy of biomass available after the transfer] / [ energy of biomass available before transfer]) X100

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19
Q

How can humans manipulate biomass through ecosystems?

A

Manipulate the environment to favour plant species that we can eat, and rear animals for food or their produce. Plants and animals are provided with the abiotic conditions that they need to thrive e.g. adequate watering and warmth. Competition from other species is removed - pesticides and herbicides - as well as the threat of predators - by creating barriers e.g. fences to exclude wild herbivores.

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20
Q

Why are food chains in agriculture kept to a minimum length?

A

minimum energy is lost as there are fewer trophic levels present than in the natural ecosystem. This ensures that as much energy as possible is transferred into biomass that can be eaten by humans.

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21
Q

What is decomposition?

A

The chemical process in which a compound is broken down into smaller molecules, or its constituent elements. Processes organic material into inorganic elements and compounds which are a more useable form, and returned to the environment.

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22
Q

What is a decomposer?

A

Its an organism that feeds on and breaks down dead plant or animal matter, thus turning organic compounds into inorganic ones, available to photosynthetic producers in the ecosystem. They’re primarily microscopic fungi and bacteria, but also include larger fungi e.g. toadstools and bracket fungi.

23
Q
A
23
Q

Why are decomposers saprotrophs?

A

They obtain their energy from dead or waste organic material. They digest their food by secreting enzymes onto dead organisms or organic waste matter.

24
Q

How do decomposers create inorganic ions?

A

They digest their food by secreting enzymes onto dead organisms or organic waste matter. The enzymes break down the complex organic molecules into simpler soluble molecules. Through this process, decomposers release stored inorganic compounds and elements back into the environment.

25
Q

What are detritivores?

A

They’re another class of organism involved in decomposition. They help speed up the decay process by feeding on detritus- dead and decaying material. They break it down into smaller pieces of organic material, which increases the surface area for decomposers to work on. e.g. woodlice and earthworms.
They perform internal digestion.

26
Q

What is nitrogen fixation?

A

Nitrogen fixating bacteria contain the enzyme nitrogenase, which combines atmospheric nitrogen with hydrogen to produce ammonia- this forms nitrogen that can be absorbed by plants. This process is called nitrogen fixation.

27
Q

Why do the bacteria in the root nodules of leguminous plants - Rhizobium- and the plants themselves have a symbiotic mutualistic relationship?

A

The plant gains amino acids from rhizobium, which are produced by fixating nitrogen gas in the air into ammonia in the bacteria.
The bacteria gain carbohydrates produced by the plant during photosynthesis, which they use as an energy source.

28
Q

What is nitrification?

A

It is the process by which ammonium compounds in the soil are converted into nitrogen- containing molecules that can be used by plants. Free living bacteria in the soil called nitrifying bacteria are involved.

29
Q

What happens during nitrification?

A

Its an oxidation reaction that only takes place in well-aerated soil.
1. Nitrifying bacteria oxidise ammonium compounds into nitrates
2. Nitrobacter oxidise nitrites into nitrates.

Nitrate ions are extremely soluble, and are therefore the form in which most nitrogen enters the plant.

30
Q

what is denitrification?

A

In the absence of oxygen, e.g. in waterlogged soils, denitrifying bacteria convert nitrates in the soil back into nitrogen gas. It only happens under anaerobic conditions. The bacteria use the nitrates as a source of energy for respiration and nitrogen gas is released.

31
Q

Why do Co2 levels fluctuate during the day in the atmosphere?

A

Photosynthesis only takes place in the light, so during the day, CO2 is removed from the atmosphere. Respiration is carried out by all living organisms throughout the day and night, releasing CO2 at a relatively constant rate into the atmosphere. So, atmospheric CO2 levels are higher during the night than in the day.

32
Q

Why do localised CO2 levels fluctuate seasonally?

A

CO2 levels are higher on a summers day than a winters day as photosynthesis rates are higher.

33
Q

What is ammonification?

A

Its the name given to the process by which decomposers convert nitrogen- containing molecules in dead organisms, faeces, and urine into ammonium compounds.

34
Q

Why have CO2 levels increased significantly over the past 200 years?

A

Combustion of fossil fuels- released CO2 back into the atmosphere from carbon that had previously been trapped for millions of years.
Deforestation - removed significant quantities of photosynthesising biomass. Therefore, less CO2 is removed from the atmosphere. In many cases, the forest is burnt, producing more CO2.

35
Q

What are the 2 types of sucession?

A

Primary succession- this occurs on an area of land that has been newly formed or exposed such as bare rock. There is no soil or organic material present to begin with.
Secondary succession- this occurs on areas of land where soil is present but it contains no plant or animal species. e.g. the bare earth that remains after a forest fire.

36
Q

How does primary succession occur?

A
  • Volcanoes erupt, depositing lava- when lava cools and solidifies igneous rock is created.
    -sand is blown by the wind or deposited by the sea to create new sand dunes
  • silt and mud are deposited at river estuaries
  • glaciers retreat, depositing rubble and exposing rock.
37
Q

What are the stages of succession?

A

barren land-> pioneer community -> intermediate community (secondary and tertiary colonisers and scrublands) -> climax community( dominant species e.g. woodland) -> land altered e.g. due to fire or disease -> recolonisation -> climax community

38
Q

What is a pioneer community?

A

A pioneer species arrives as spores or seeds carried by the wind from nearby land masses or sometimes by the droppings of birds or animals passing through. examples include lichen and algae. This is the first seral stage.

39
Q

What adaptations do pioneer species have to enable them to colonise bare environments?

A
  • Ability to produce large quantities of seeds or spores, which are blown by the wind and deposited on ‘new land’
    -seeds that germinate rapidly
    -the ability to photosynthesise to produce their own energy - light, rainfall and air are often the only abiotic factors present.
  • tolerance to extreme environments
  • the ability to fix nitrogen from the atmosphere, so adding to the mineral content of the soil.
40
Q

What is humus and how does it help form an intermediate community?

A

When organisms of the pioneer species die and decomposed, small organic products are released into the soil. This organic component of soil is known as humus. This allows the soil to be able to support the growth of new secondary colonisers as it contains minerals including nitrates and has the ability to retain some water.

41
Q

Give an overall description of what happens as environmental conditions start to improve.

A

At each stage, the rock continues to be eroded and the mass of organic matter increases. When organisms decompose, they contribute to a deeper, more nutrient rich soil, which retains more water. This makes the abiotic conditions more favourable for small flowering plants such as grasses, shrubs and small trees.
At each stage, the plant and animal species are better adapted to the current conditions in the ecosystem. These organisms outcompete many of the species that were previously present and become the dominant species. These are the most abundant species present in the ecosystem at a given time.

42
Q

What is a climax ecosystem?

A

Final seral stage- when the community is in a stable state, will show very little change over time. Normally a few dominant plant and animal species. Not always the most biodiverse community, as biodiversity tends to reach a peak mid-succession. It then tends to decrease due to the dominant species out-competing pioneer and other species. The more successful a dominant species it, the less biodiversity in a given ecosystem.

43
Q

what is defected succession?

A

Human activities halt the natural flow of succession and prevent the ecosystem from reaching a climax community. When succession is stopped artificially, the final stage that is formed is known as a plagioclimax.

44
Q

How does agriculture lead to deflected succession?

A
  • Grazing and trampling of vegitation by domesticated animals- this results in large areas remaining grassland
    -removing existing vegitation such as shrub land to plant crops- the crop becomes the community
  • burning as a means of forest clearance- often leads to an increase in biodiversity as it provides a nutrients rich ash for other species to grow, e.g. shrubs
45
Q

How is distribution of organisms in an environment measured?

A

Line or belt transect is used.
Line- straight line across habitat, samples taken at regular intervals.
Belt- two parallel lines marked, samples taken of the areas between the lines.
Form of non- random sampling - systematic

46
Q

What are the advantages of using systematic sampling in an ecosystem?

A

Allows areas within an overall habitat to be identified, which can then be sampled separately.
Allows scientists to study how the differing abiotic factors in different areas of the habitat affect the distribution of a species.

47
Q

What is abundance of organisms?

A

refers to the number of individuals of a species present in an area at any given time.W

48
Q

Why might abundance of organisms fluctuate daily?

A

Immigration and births will increase the number of individuals
emigration and deaths will decrease the number of individuals.

49
Q

How can you calculate animal population size?

A

Can rarely be counted accurately- e.g. some animals can escape capture, it may be too time consuming to count all members of a pop. They’re therefore calculated using sampling techniques.
A sample is never entirely representative of the organisms present in that habitat. Use largest sample size possible - will lower the probability that chance will influence the result.

50
Q

How do you measure plant abundance in a habitat?

A

Place quadrats randomly, count number of individual plants present within the quadrat.

Estimated pop number = No of individuals in sample / Area of sample

51
Q

How do you measure animal abundance?

A

Capture-recapture:
1. Capture as many individuals as possible in a sample area
2. mark or tag each individual
3. release marked animals back and allow time for them to redistribute themselves.
4. recapture as many individuals as possible in the sample area
5. record the no. of marked and unmarked individuals present in the sample

no. individuals in sample 1 x no. individuals in sample 2 / no. of recaptured individuals

52
Q

What is simpson’s diversity index?

A

D= 1- the sum of (n/N)^2
D= diversity index
N= total no. of organisms in the ecosystem
n= number of individuals of each species

will always give an answer between 0 and 1, the higher the value, the more diverse the habitat.

53
Q
A