Adaptations, interdependence and competition — AQA GCSE Combined Science: Trilogy
Levels of organisation, competition, interdependence, abiotic and biotic factors, and how organisms are adapted to their environment.
Revision notes
4 short notes, in the order of the specification. Each one in short:
An ecosystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment. A population is all the organisms of one species in an area, and a community is all the populations of different species there. Plants compete for light, space, water and mineral ions; animals compete for food, mates and territory.
Abiotic factors are the non-living factors that can affect a community. They include light intensity, temperature, moisture levels, soil pH and mineral content, wind intensity and direction, carbon dioxide levels for plants and oxygen levels for aquatic animals. A change affects the organisms that depend on that factor, and then the species that feed on or depend on those organisms.
Biotic factors are the living factors that can change a community. The four you need to know are the availability of food, new predators arriving, new pathogens, and one species outcompeting another so that its numbers are no longer sufficient to breed. A change in one population affects others, for example when a new predator reduces the number of prey.
Adaptations are features that enable organisms to survive in the conditions in which they normally live. They may be structural, such as a polar bear's thick fat; behavioural, such as migrating for winter; or functional, such as a camel producing very little, concentrated urine. Extremophiles, such as bacteria in deep sea vents, live in very extreme environments.
Exam questions
5 exam-style questions (13 marks), each with its mark scheme.
Answer the questionsFlashcards
14 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of ecology on one page, so you can see where this subtopic fits.
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Quick check questions
Put in order, smallest to largest: community, organism, ecosystem, population.
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Organism, population, community, ecosystem.
What do plants often compete for?
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Light, space, water and mineral ions from the soil.
What do animals often compete for?
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Food, mates and territory.
What is a stable community?
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One where all the species and environmental factors are in balance so population sizes remain fairly constant.
What is an extremophile?
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An organism that lives in very extreme conditions, such as high temperature, pressure or salt concentration.
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 frogs in a pond. A community is all the populations of the different species living in that area, including the plants, animals and microorganisms. A community together with the non-living parts of its environment makes an ecosystem.
What is interdependence in ecology?
Interdependence means that within a community each species depends on other species for food, shelter, pollination, seed dispersal and so on. If one species is removed it can affect the whole community. For example, if a plant pollinated by one insect is removed, that insect loses its food, and so do the animals that eat it.
What is the difference between abiotic and biotic factors?
Abiotic factors are non-living parts of the environment, such as light intensity, temperature, moisture levels, soil pH and mineral content, wind, carbon dioxide and oxygen levels. Biotic factors are living, such as the availability of food, new predators, new pathogens and one species outcompeting another. A change in either kind can affect a whole community.
What are the three types of adaptation?
The three types of adaptation are structural, behavioural and functional. Structural adaptations are features of the body, such as a polar bear's thick fat and white coat. Behavioural adaptations are the way an organism acts, such as migrating for winter. Functional adaptations are how body processes work, such as a camel producing very little, concentrated urine.
Written and checked against the AQA GCSE Combined Science (8464) specification · Updated October 2026