OCR A2 Biology F215 Ecosystems and Sustainability topic revision notes

Covers the ecosystems and sustainability topic of F215 A2 OCR Biology. Some fill in gaps bits ie. nitrogen cycle

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  • Created on: 06-06-12 09:45
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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
ECOSYSTEMS AND SUSTAINABILITY REVISION NOTES
2.3.1 What is an ecosystem?
Ecosystem=group of living organisms and non-living things occurring together, and the
interrelationships between them.
Components of an ecosystem:
Habitat-place where an organism lives
Population-all of the organisms of one species, who live in the same place, and the same
time and can breed together
Community-all populations of different species who live in the same place at the same time,
and can interact with each other
Niche-role that each species plays in an ecosystem, each organism interacts with living and
non living things, so almost impossible to define its niche entirely. Description of a niche
could include things like how it feeds and what it feeds on, and how it reproduces. It is
impossible for 2 species to occupy the exact same niche in the same ecosystem.
Biotic factors=food supply, predation & disease
Abiotic factors=pH, temp, soil type-effects of all non-living components of an ecosystem
Dynamic ecosystems- in most ecosystems, population sizes rise & fall, this = because community
of living things in an ecosystem interact with each other and with their physical environment-any
small change in one can affect the other. Eg:
If predators population goes up, the population of their prey-goes down.
Nitrogen levels in soil can affect population sizes growing there-nitrogen fixing plants would
grow successfully in nitrogen-deficient soil, but they would affect their environment by
increasing the soil nitrogen levels-this change would help other plants grow there too.
Matter=constantly recycled within an ecosystem:
All living organisms need energy; they release energy from organic molecules eg. Glucose, in their
food, this energy originally came from sunlight-at start of almost all food chains = a plant, which
captures light energy through photosynthesis, and converts it to chemical energy stored in
molecules like glucose
Producers=supply chemical energy to all other organisms. Eg. plants, algae and some bacteria

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
Primary consumers=feed on plants & are eaten by carnivorous secondary consumers
Secondary consumers=feed on primary consumers & eaten by tertiary consumers
Tertiary consumers=feed on secondary consumers
Decomposers=feed on waste material/dead organisms
2.3.…read more

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
Net productivity =amount of energy that is available to the next tropic level.
Productivity
Even pyramids of energy have limitations:
Only take a snapshot of an ecosystem at one moment in time-because population sizes can
fluctuate over time, this may provide a distorted idea of the efficiency of energy transfer.…read more

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
Secondary succession-happens on land that's been cleared of all plants, but where soil remains eg.…read more

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
Succession on sand dunes
Sand dunes show all stages of succession in the same place at the same time:
Pioneer plants, like sea rocket and prickly sandwort colonise the sand just above the high
water mark, these can tolerate salt water spray, lack of fresh water and unstable sand
Wind-blown sand builds up around the base of these plants, forming a `mini' sand dune.…read more

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
support them-the climax community would be the grassy field-this isn't a natural seral
stage-there should be things like small flowering plants-so succession has been deflected.
Climax communities
Climax community = an ecological community in which populations of plants or animals remain
stable and exist in balance with each other and their environment. A climax community is the final
stage of succession, remaining relatively unchanged until destroyed by an event such as fire or
human interference.…read more

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
1. Nitrogen fixation-Nitrogen gas makes up 79% of the earth's atmosphere but = very unreactive.
This means it is impossible for plants to use it directly despite its abundance. Instead, they need a
supply of `fixed' nitrogen eg ammonium ions or nitrate ions, nitrogen fixation can occur when
lightning strikes or through the Haber process, but these only account for about 10% of nitrogen
fixation. Nitrogen fixing bacteria accounts for most of the nitrogen fixation.…read more

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
Parts of the nitrogen cycle can be carried out artificially on an industrial scale-the Haber process
produces ammonia from atmospheric nitrogen-used to make fertilisers.
2.3.7 What affects population size?
In some circumstances a species' population size may stay fairly stable over time; however,
population size may also rise or fall quite suddenly, or oscillate up and down with a regular pattern.
The size of the population depends on the balance between the death rate and the rate of
reproduction.…read more

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
colonise a disturbed habitat before k-strategists, dispersing into other habitats once limiting factors
start to have an effect.
R-strategists = good at colonising disturbed habitats because they usually have a very fast rate of
reproduction-much faster than k-strategists
K-strategists=more likely to be members of a climax community because their population size is
determined by the carrying capacity, climax community=stable population.
Predator=animals that hunts other animals (prey) for food.…read more

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ECOSYSTEMS AND SUSTAINABILITY Kirsty Stephen
INTERSPECIFIC ­ happens between individuals of different species and can affect both the
population size of a species and the distribution of species in an ecosystem.…read more

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