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Feversham College

AQA Biology Unit 5

Frihah Parvaiz

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Populations and ecosystems
A population is all the organisms of one species in a habitat.
Populations of different species form a community.

An ecosystem is a system of organisms interacting with each other and their physical environment.
Ecosystems vary in size; a garden pond could be considered an ecosystem as…

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A critical appreciation of some of the ways in which the
numbers and distribution of organisms may be investigated.


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Random sampling with quadrats and counting along transects to obtain quantitative data.

A suitable number of quadrats are placed on the ground at
different points across the area that you are investigating.

The species frequency is recorded in each quadrat.

The sample needs to be random so the results are…

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· consider ethical issues arising when carrying out fieldwork, particularly
those relating to the organisms involved and their environment

All fieldwork affects the environment
eg people walking around may cause
soil erosion.
Some people don't think its right to
damage the environment so
investigations should be planned to
restrict the…

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· analyse and interpret data relating to the distribution of
organisms, recognizing correlations and causal relationships

· appreciate the tentative nature of
conclusions that may be drawn from such data.

Variation in population size
Population size may vary as a result of
· the effect of abiotic factors
· interactions…

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The prey population doesn't always increase; it just stops
decreasing so quickly. It only increases after
reproduction. This explains for both prey and predators
why there is a time lag between population decline and


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Human populations
Population size and structure, population growth rate, age-population pyramids
survival rates and life expectancy.



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