Communities and interdependence — Edexcel GCSE Combined Science
Levels of organisation in an ecosystem, abiotic and biotic factors, interdependence, parasitism and mutualism.
Revision notes
4 short notes, in the order of the specification. Each one in short:
The levels of organisation in ecology go from organism to population, community and ecosystem, and each level contains the one before. A population is all the organisms of one species in an area, a community is all the populations of different species there, and an ecosystem is a community together with the non-living (abiotic) parts of its environment.
Abiotic factors are the non-living factors that affect a community, such as temperature, light, water and pollutants. Biotic factors are the living factors, such as competition and predation. Changes in either can change which species live in a community and how many there are. On a predator-prey graph, the predator peak comes after the prey peak.
Interdependence is the way species in a community depend on one another for food, shelter, pollination and seed dispersal. Because of this, a change to one population can affect many others. A community with many different species is more stable, because the loss of one species is less likely to cause the whole community to fail.
Parasitism is a relationship in which a parasite lives on or in a host and takes food from it, so the parasite benefits and the host is harmed, as with a tapeworm or a flea. Mutualism is a close relationship between two species in which both benefit, such as nitrogen-fixing bacteria in the root nodules of legumes.
Exam questions
5 exam-style questions (12 marks), each with its mark scheme.
Answer the questionsFlashcards
12 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of ecosystems and material cycles on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
Put in order from smallest to largest: ecosystem, population, organism, community.
Show answer
Organism, population, community, ecosystem.
Name two abiotic factors that affect communities.
Show answer
Any two of: temperature, light, water, pollutants.
What is meant by competition?
Show answer
Organisms needing the same limited resource, such as food, light or water.
What is the difference between parasitism and mutualism?
Show answer
In parasitism the parasite benefits and the host is harmed. In mutualism both organisms benefit.
Frequently asked questions
What is the difference between a population and a community?
A population is all the organisms of one species living in the same area, such as all the badgers in a wood. A community is all the populations of different species living in the same area. An ecosystem is a community together with the non-living, abiotic parts of its environment, such as soil, water and light.
What are abiotic and biotic factors?
Abiotic factors are non-living factors that affect a community, such as temperature, light, water and pollutants. Biotic factors are living factors, such as competition for food, water, light and space, and predation. A change in either type can change which species live in a community and how many of each there are.
Why does the predator peak come after the prey peak?
The predator peak comes after the prey peak because predator numbers rise only once there is more food. When prey numbers rise, predators have more to eat, so their numbers increase. More predators eat more prey, so prey numbers fall. With less food, predator numbers then fall, and the prey population can recover.
Why is interdependence important in a community?
Interdependence matters because species depend on one another for food, shelter, pollination and seed dispersal, so a change to one population can affect many others. If a species declines, those that feed on it may starve and those it feeds on may increase. A community with many different species is more stable.
Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026