OCR Biology F215: Ecosystems

Following OCR specification

  • Created by: Kitkat
  • Created on: 24-04-11 13:40

(a) Define the term ECOSYSTEM

All living organisms & non living components in a specific habitat, & their interactions / the interrelationship between all the organisms (living) & the environment (non-living)

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(b) State that

Ecosystems are dynamic systems

(always changing, never a constant state, any change in one factor is going to change another)

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(c) Define the terms biotic factor and abiotic factor, using named examples

Biotic factor --> living organisms, how they affect each other e.g. food supply, predation, disease, consumers, decomposers, producers

Abiotic factor --> non-living, the effect on the ecosystem e.g. pH, temperature, soil type, light intensity/availability, O2 availability

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(d) Define the terms producer, consumer, decomposer and trophic level

Producer --> an organism that converts simple inorganic compounds into complex organic compounds

Consumer --> an organism that gains energy from complex organic matter

Decomposer --> an organism that feeds on waste from other or dead organisms/ breaks down dead tissues & uses the organic molecules as a source of energy

Trophic level --> a stage in the food chain

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(e) Describe how energy is transferred through ecosystems

Energy is transferred by organisms consuming each other. This is shown in a food web/ chain with arrows representing the flow of energy between organisms.
The transfer of energy is a one-way process. Energy can't be recylcled & much of the energy escapes from the ecosystem as heat.
Energy is always lose between one trophic level & the next, this means that there is relatively little energy available for the final consumer in a food chain, usually they're large carnivors so the numbers of these animals is quite low.
The loss of energy at each trophic level limits the number of levels in a chain.

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(f) Outline how energy transfers between trophic levels can be measured

Energy content from each trophic level can be measured:
--> each sample is dried in an oven
-->the samples are weighed
-->the samples are burned in a bomb calorimeter
--> the energy produced passes through a known mass of water & the temperature rise of the water is measured

--> how much energy is released per gram is calculated

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(g) Discuss the efficiency of energy transfers between trophic levels

Energy is lost between trophic levels because animals:
--> can never eat all the available food
--> can't digest all of the food they eat
--> use energy to respire
--> lose heat energy to the surroundings
--> lose energy in urine & faeces

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(h) Explain how human activities can manipulate the flow of energy through ecosystems

--> replacing natural vegetation& fauna with crops & livestock
--> deflecting natural succession to maintain grassland
--> increasing productivity of producers through
     --> soil improvement
     --> irrigation
     --> fertilisers
     --> removal of: competing weeds & damaging pathogens & pests
--> increasing productivity of producers & consumers through selective breeding or genetic engineering
--> sheltering organisms from damaging environmental factors

--> restricting movement of primary consumer = more energy for producing wanted products & reduces energy needed for homeostasis
--> harvest primary consumer before they reach adulthood
--> use steriods to increase the growing rate
--> select animals with a faster growing rate

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(i) Describe one example of primary succession resulting in a climax community

Sand dunes
--> pioneer species e.d. sea rocket, colonises the sand just above the high water mark. These can tolerate the salt water spray, lack of fresh water & unstable sand
--> wind-blown sands build up around the base of these plants, forming a 'mini' sand dune. As the plants die, decomposers will break them down & nutrients accumulate in the 'mini' dune. As the dune gets bigger, plants e.g. sea couch grass, colanise it, whish have underground stems which help stabalise the sand
--> with more stability & accumulation of more nutrients, plants like marram grass start to grow. Marram grass shoots trap wind-blown sand &, as the sand accumulates, the shoots grow taller, trapping more sane
--> as the sand dune & nutrients build up, other plants colonise the sand. Many are legumes which have nodules in their roots which contain bacteria which convert nitrogen to nitrates. With nitrates available, more species colonise the dune, stabilising them further

the pioneer species leed to a change in the abiotic conditions which causes the pioneer species to die & nutrients build up so other plant species can move in & then animals leading to a climax community

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(i) alternative..

--> bare rock
--> various spores or seeds will land on the rock by the wind. Vast majority will have no effect, but some will attach & develop - very simple organisms, lichen
--> lichens will trap dust & in time die
--> decomposers will break down the lichens to form a very simple soil
--> simple soil will remain in the cracks of the rock. This provides a habitat for slightly more complex plants e.g mosses
--> mosses further change the environmental conditions
--> grasses may appear < community has changed
--> eventually animals move in as habitats form. This is the climax community (final stable community)

Secondary succession is where succession occurs of previously colonised land where the habitat has been disturbed or damaged e.g. after a forest fire. Secondary succession is likely to be quicker as it doesn't have to go through all the seres (stage in succession)

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(j) Describe how the distribution & abundance of the organisms can be measured, using line transects, belt transects, quadrats and point quadrats

Line transects --> lines across a habitat & record how many species are found touching the line or place a quadrat at intervals along the transect 

Belt transect --> place a line transect and the place a quadrat next to it all the way along the transect

Quadrat --> frame subdivided into smaller squares. Random numbers are used for the coordinates of where to place the quadrat. Each species present is identified & recorded, along with the number of times it is touched

Point quadrats --> frames with long pins lowered vertically. Each species which touches a pin is recorded along with the number of times it is touched

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(k) Describe the role of decomposers in the decomposition of organic material

Decomposers feed sapotrophically on waste from other organisms (release enzymes into material which hydrolyse organic molecules whithin material into smaller soluble ones, which are taken up into cells of bacteria/fungi to be used as respiratory substrates). They recycle materials such as carbon & nitrogen. If they didn't break down dead organisms, energy & valuble nutrients would remain in the dead organism

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(l) Describe how microorganism =s recycle nitrogen within ecosystems (only nitrosomonas, nitrobacter and rhizobium need to be identified by name)

N2 --> NH4+ (nitrogen --> ammonium)
Nitrogen is fixed by bacteria such as rhizobium that live in root nodules. They have a mutualistic relationship with the plant - they fix nitrogen for the plant & the plant provides the bacteria with carbon compounds (glucose). There are proteins which absorb oxygen, keeping conditions anaerobic so that nitrogen reductase can reduce nitrogen gas to ammonium ions

NH4+ --> NO2- (ammonium --> nitrites)
Ammonium ions are released by bacteria in the putrefaction of proteins found in dead or waste organic matter. Nitrosomonas bacteria obtain their energy by oxidising ammonium ions to nitrites under aerobic conditions

NO2- --> NO3- (nitrites --> nitrates)
Nitrobacter obtain their energy by oxidising nitrites to nitrates in aerobic conditions

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(l) cont..

NO3- --> N2+N2O
Either plants absorb the nitrates from the soil to make nucleotide bases or, dentrifying bacteria under anaerobic conditions use nitrates as a source of oxygen for respiration, producing nigrogen gas & nitrous oxide

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