OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
(a) ecosystems, which range in size, are dynamic and are influenced by…
Full specification wording
Ecosystems: (a) ecosystems, which range in size, are dynamic and are influenced by both biotic and abiotic factors
An ecosystem is a community of organisms interacting with each other and with their non-living environment.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 1 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
An ecosystem is a community of organisms interacting with each other and with their non-living environment. Ecosystems range in size from a drop of pond water or a rotting log to a whole forest or ocean, so there is no fixed minimum or maximum scale. They are dynamic: populations, species composition and physical conditions change over time, for example through succession or seasonal change. Both biotic factors, such as predation, competition and disease, and abiotic factors, such as light intensity, temperature, water availability and soil pH, influence which organisms survive and how the community is structured. A change in one factor can shift the balance of the whole system.
What earns the marks
- Defines an ecosystem as a community of organisms interacting with their abiotic environment.
- States that ecosystems range in size, giving an example of a very small and a very large ecosystem.
- Explains that ecosystems are dynamic, with populations and conditions changing over time.
- Identifies biotic factors such as competition, predation or disease that influence the community.
- Identifies abiotic factors such as light, temperature, water or soil pH that influence the community.
- Explains how a change in a biotic or abiotic factor can affect the organisms present.
Common mistakes and how to put them right
Treating an ecosystem as only the living organisms.
Put it right: It includes the abiotic environment and the interactions between them.
Assuming ecosystems must be large.
Put it right: They range in size from tiny to vast.
Describing an ecosystem as static.
Put it right: It is dynamic, with populations and conditions changing over time.
Exam tips
- Distinguish biotic from abiotic factors clearly when the question asks for both.
- Give a named example of a small and a large ecosystem to show the range in size.
- When explaining dynamism, refer to a specific change such as succession or seasonal variation.
Try the lesson
The start of the Ecosystems: (a) ecosystems, which range in size, are dynamic and are influenced by both biotic and abiotic factors lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following is an abiotic factor that could affect the organisms in a freshwater pond?
Listen
An ecosystem is a community of organisms interacting with each other and with their non-living environment. Ecosystems range in size from a drop of pond water or a rotting log to a whole forest or ocean, so there is no fixed minimum or maximum scale. They are dynamic: populations, species composition and physical conditions change over time, for example through succession or seasonal change. Both biotic factors, such as predation, competition and disease, and abiotic factors, such as light intensity, temperature, water availability and soil pH, influence which organisms survive and how the community is structured. A change in one factor can shift the balance of the whole system. A strong answer earns marks for these points. Defines an ecosystem as a community of organisms interacting with their abiotic environment. States that ecosystems range in size, giving an example of a very small and a very large ecosystem. Explains that ecosystems are dynamic, with populations and conditions changing over time. Identifies biotic factors such as competition, predation or disease that influence the community. A common slip: Treating an ecosystem as only the living organisms. Instead, it includes the abiotic environment and the interactions between them. Exam tip: Distinguish biotic from abiotic factors clearly when the question asks for both.
Key words
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Ecosystem
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Biotic factors
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Abiotic factors
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Dynamic
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See every definition
- Ecosystem
- A community of organisms interacting with each other and with their non-living environment.
- Biotic factors
- Living influences such as predation, competition and disease that affect which organisms survive and how the community is structured.
- Abiotic factors
- Non-living influences such as light intensity, temperature, water availability and soil pH that affect which organisms survive and how the community is structured.
- Dynamic
- Populations, species composition and physical conditions change over time, for example through succession or seasonal change.
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