These revision notes provide an in depth summary of this specific chapter of AQA Biology in the A Level Specification -
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Biology revision – Populations in ecosystems (Unit 19)
Populations and ecosystems
- Ecology – is the study of the inter-relationships between organisms and their
environment
o The environment includes both non-living (abiotic) factors such as temp and
rainfall as well as living (biotic) factors such as competition and predation
Ecosystems
- Dynamic systems made up of a community and all the non-living factors of its
environment
- Ecosystems can range from being small to being very large
- Within an ecosystem there are two key processes:
o The flow of energy through the system
o The cycling of elements within the system
- An example of an ecosystem is a freshwater pond or lake
o It has its own community of plants to collect the necessary sunlight energy to
supply the organisms within it
- Nutrients such as nitrate ions and phosphate ions are recycled within the pond or lake
- There is little or no loss or gain between it and other ecosystems
- Within each ecosystem there are a number of species
- Each species is made up of a group of individuals that make up a population
Populations
- Population – a group of individuals of one spcies that occupy the same habitat at the
same time and are potentially able to interbreed
- An ecosystem supports a certain size of population of a species called the carrying
capacity
- The size of a population can vary as a result of:
o The effects of abiotic factors
o Interactions between organisms, for example, intraspecific and interspecific
competition and predation
- The boundaries of a population are often difficult to define
- Populations of different species form a community
Community
- Community – all the populations of different species living and interacting in a
particular place at the same time
Habitat
- Habitat – the place where an organism usually lives and is characterised by physical
conditions and the other types of organisms present
- Within an ecosystem there are many habitats
- Within each habitat there are smaller units, each with their own microclimate
o These are called microhabitats
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