Communities and Interdependence
Practise Communities and Interdependence for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Organisms depend on each other for food, shelter and reproduction, and a stable community keeps its population sizes roughly constant.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
An ecosystem is the interaction of a community of living organisms with the non-living parts of their environment.
Organisms need materials from their surroundings and from other living organisms in order to survive and reproduce. Plants compete for light, space, water and mineral ions from the soil. Animals compete for food, mates and territory.
Within a community, species depend on one another for food, shelter, pollination and seed dispersal. This is called interdependence. If one species is removed it affects the whole community, and a stable community is one where all the species and environmental factors are in balance so population sizes remain roughly constant.
Revision notes
Competition
Plants compete for light and space, and for water and mineral ions from the soil.
Animals compete for food, mates and territory. Organisms that compete most successfully are more likely to survive and reproduce.
Interdependence
Within a community, each species depends on others for food, shelter, pollination and seed dispersal.
If one species is removed it can affect the whole community, which is why removing a single predator or pollinator can have far-reaching consequences.
Stable communities
In a stable community, all the species and environmental factors are in balance so that population sizes remain roughly constant.
Examples include tropical rainforests, ancient oak woodlands and mature coral reefs.
Key points
- An ecosystem includes living and non-living components.
- Plants compete for light, space, water and mineral ions.
- Animals compete for food, mates and territory.
- Interdependence means species rely on one another.
- Removing one species can affect the whole community.
- In a stable community population sizes stay roughly constant.
Worked examples
Example 1
State three things plants compete for. [3 marks]
Model answer
Light (1 mark), space (1 mark), and water or mineral ions from the soil (1 mark).
Example 2
Explain what is meant by interdependence. [2 marks]
Model answer
Interdependence means that species within a community depend on one another for things such as food, shelter, pollination and seed dispersal (1 mark), so if one species is removed it can affect the whole community (1 mark).
Example 3
Explain what is meant by a stable community. [2 marks]
Model answer
A stable community is one in which all the species and environmental factors are in balance (1 mark), so that population sizes remain roughly constant over time (1 mark).
Common mistakes
Giving the same competition factors for plants and animals.
Plants compete for light and mineral ions; animals compete for mates and territory.
Saying an ecosystem is only the living organisms.
It includes the non-living parts of the environment too.
Saying a stable community never changes.
Population sizes fluctuate but remain roughly constant overall.
Confusing a community with a population.
A population is one species; a community is all the populations in an area.
Exam tips
- Learn separate lists for plant and animal competition.
- Define interdependence in terms of species relying on each other.
- Say roughly constant when describing a stable community.
- Keep population, community and ecosystem clearly distinct.
Key terms
- Ecosystem
- The interaction of a community with the non-living environment.
- Community
- All the populations of different species in an area.
- Interdependence
- The reliance of species on one another within a community.
- Stable community
- A community where population sizes remain roughly constant.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.