A2 OCR Biology: Ecosystems

A2 OCR Biology: Ecosystems

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  • Created by: Hamed
  • Created on: 25-05-11 00:07
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Ecosystems
An ecosystem is a place that consists of a community of organisms, the physical
(abiotic) factors that influence it and all interactions between organisms.
Ecosystems are dynamic with energy flowing from the sun through autotrophs to
heterotrophs and decomposers. Elements such as carbon, nitrogen, sulphur and
phosphorous are continually cycled within ecosystems between the living organisms and
the abiotic environment. Energy flow is influenced by human activities such as livestock
farms.
Food Chains and Food Webs
A trophic level is a feeding level in a food chain. Producers are organisms that trap
sunlight and make use of the energy in photosynthesis. The energy is used to convert the
simple inorganic compounds, carbon dioxide and water, into complex organic
molecules, such as sugars and amino acids. This pattern of energy flow is the grazing food
chain;
Key Terms
Habitat ­ A place where an individual, population or community lives
Niche ­ The role of an organism in a community ­ where it is, what it does, how it
feeds, how it behaves.
Population ­ A group of individuals of the same species in the same area at the same
time.
Community ­ All population of plants, animals and microorganisms in a well defined
area at the same time.
Ecosystem ­ A community and abiotic factors that influence it; interactions between
the organisms.
Abiotic Factors ­ Physical and chemical factors that influence populations in a
community.
Biotic Factors ­ Biological factors that influence populations in a community.
Detritus is dead organic matter that is a food source of detritivores, such as earthworms.
Decomposers, such as bacteria, use dead organic matter from plants and animals as an
energy source. This pattern of energy flow is the decomposer food chain. Energy is

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Much of the energy that enters the organisms at one trophic level is used by those
organisms and is, therefore, not available to the next trophic level; energy is lost during
respiration and in heat loss.
Energy is not recycled ­ it leaves the ecosystem as infrared radiation. The flow of energy
between trophic levels is not very efficient:
Energy flow from Plants to Primary Consumers
Little of the light energy that strikes plants is used in photosynthesis.…read more

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Energy consumed by tertiary consumers
Ecological Efficiency =
Energy consumed by secondary consumers ×100%
Arable farmers and growers attempt to make net primary productivity as high as possible.
Livestock farmers do the same for secondary productivity.
Method Crop Plants Livestock
(Producers) (Primary Consumers)
Maximise Energy Input Optimum planting distances Provide good quality feed
between crop plants;
Provide light for greenhouse
crops on overcast days
Maximise Growth Provide water, fertilisers; Provide food supplements,
Selective breeding for fast e.g.…read more

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When ground becomes available for colonisation for the first time a process of primary
succession begins in which the community changes over time. The sequence of
communities that develops is known as a sere. Plants and animals in different seral
communities show adaptations to survive. Earlier stages in succession are very productive.
Decomposition and Nutrient Cycling
Detritivores are organisms that ingest dead matter (detritus). Examples of detritivores
are earthworms and woodlice.…read more

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Digest proteins in detritus into amino Oxidises ammonium ions to nitrite ions to
acids provide energy
Deaminate amino acids to form Oxidises nitrite ions to nitrate ions to
ammonium ions provide energy
Nitrate ions released are available for
plants to absorb
There is a large quantity of nitrogen in the atmosphere in the form of the gas,
dinitrogen which has a triple bond between two nitrogen atoms.…read more

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After reaching a certain size, the trunks of some mature trees are cut down to a stump.
Fresh shoots then grow out of these stumps and can be harvested. Rotational coppicing
allows wood to be harvested without loss of biodiversity and also helps young shoots as
light is then allowed more onto the woodland floor.…read more

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