Communities — AQA GCSE Combined Science
Test yourself on Communities with AQA GCSE practice questions.
7 days Premium · Then free forever · No card, no charge
Communities explained
In this subsection, students learn the levels of organisation in an ecosystem, from individual organisms to populations, communities, and the whole ecosystem.
Read the full explanation
An ecosystem is the interaction of a community of living organisms with the non-living parts of their environment. Students must describe how plants compete for light, space, water, and mineral ions, while animals compete for food, mates, and territory. They should explain interdependence, where species depend on each other for food, shelter, pollination, and seed dispersal. Removing one species can affect the whole community. A stable community is one where all species and environmental factors are in balance, keeping population sizes fairly constant.
different levels of organisation in an ecosystem from individual organisms to the whole ecosystem
Ecology studies life at several nested levels. An individual organism is one member of a species, such as a single oak tree. A population is all the individuals of that species in a habitat. A community is all the populations of different species living together, for example the oaks, insects, fungi and birds in a wood. The community plus the non-living conditions, such as light, water, temperature and soil, forms the ecosystem. The whole ecosystem is therefore the largest level, including living organisms and their physical surroundings interacting together. Moving up each level adds something: more individuals, then more species, then the abiotic environment. Being able to place examples at the correct level is the key skill, and questions often ask you to identify or order these levels.
the importance of interdependence and competition in a community.
In a community, every population depends on others. Interdependence means that organisms rely on each other for food, shelter, pollination, seed dispersal and other needs. For example, bees depend on flowers for nectar while flowers depend on bees for pollination; if the bees disappear, the plants may not reproduce. Competition happens when organisms need the same limited resource. Plants compete for light, water, space and mineral ions; animals compete for food, mates and territory. Competition can be between members of the same species or between different species. Both interdependence and competition affect which organisms survive and reproduce, so they help determine the size and distribution of populations in a community. Removing or adding one species can therefore affect many others.
Students should be able to, when provided with appropriate information:
This statement is a stem that introduces the practical skills assessed in the Communities topic. It tells you that exam questions will supply data, such as a table of population counts, a graph of predator and prey numbers, or a written description of a habitat, and you must work with that information rather than recall facts alone. The phrase 'when provided with appropriate information' means the answer is extractable from the resource: you read values, spot trends, compare sets of numbers and apply ecological ideas such as interdependence, competition and cycling of resources. For example, given counts of two plant species across a shaded-to-sunlit transect, you might describe how one declines as light increases. Always quote figures with units and link each point to the ecology you have learned.
suggest the factors for which organisms are competing in a given habitat
Organisms in a community share a habitat, so when a resource is in short supply they compete for it. Plants compete for light, water, mineral ions and space; animals compete for food, water, mates and territory. In a given habitat you should identify which of these is likely to be limiting by reading the description: a dense woodland suggests light is scarce for ground plants, while a dry desert suggests water is the key factor. The command word 'suggest' means you apply your knowledge to the context rather than recall a list. Name the factor, then justify it from the habitat details, for example 'the shrubs compete for light because the tall trees cast shade'. Competition between members of the same species is intraspecific; between different species it is interspecific.
suggest how organisms are adapted to the conditions in which they live.
Adaptation means a feature that helps an organism survive and reproduce in its habitat. To suggest adaptations, first identify the challenge of the conditions, then link a feature to how it meets that challenge. For example, a camel lives in hot, dry desert with little water: a hump stores fat, which releases water when respired, and thick fur reduces heat gain, while concentrated urine limits water loss. Adaptations are behavioural (migration, basking), physiological (water retention, antifreeze proteins) or structural (thick fur, streamlined shape, waxy cuticle). In cold regions, small ears and thick insulation reduce heat loss; in dry regions, deep roots and reduced leaves limit water loss. Always connect each feature to survival and reproduction in that specific environment.
An ecosystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.
An ecosystem is not just the organisms present; it is the whole system in which a community of living organisms interacts with the non-living parts of the environment. The biotic parts are all the living organisms, including plants, animals, fungi and microorganisms, and their interactions such as feeding, competition and disease. The abiotic parts are the non-living conditions, including light intensity, temperature, moisture, soil pH, mineral content, wind and oxygen availability. These parts interact: plants compete for light and water, animals compete for food and territory, and abiotic factors affect which species can survive. For example, in a pond, fish, plants and microorganisms interact with water temperature, oxygen concentration and light.
To survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there.
Every organism must obtain materials to stay alive and to produce offspring. Plants take carbon dioxide from the air and water plus mineral ions from the soil, using light energy to make glucose by photosynthesis. Animals cannot photosynthesise, so they eat other organisms, gaining energy and the atoms needed to build proteins, fats, and DNA. Decomposers such as bacteria and fungi release enzymes onto dead material, absorbing nutrients. Crucially, they release carbon into the atmosphere as carbon dioxide during respiration, while returning mineral ions to the soil. A woodland food web shows this flow: oak leaves, caterpillars, blue tits, and sparrowhawks. If any supply fails, growth, repair, and reproduction are reduced.
Plants in a community or habitat often compete with each other for light and space, and for water and mineral ions from the soil. Animals often compete with each other for food, mates and territory.
Competition occurs when organisms need the same resource that is in limited supply. Plants compete for light, space, water and mineral ions. A tall oak shades smaller plants, while shallow-rooted grasses and deep-rooted shrubs draw water and ions from different soil depths. Animals compete for food, mates and territory. Red squirrels and grey squirrels compete for food and nesting sites; male deer compete for mates and territory. The better-adapted competitor survives and reproduces, so its alleles become more common. Competition can be intraspecific, between members of the same species, or interspecific, between different species. It is a major driver of natural selection and affects population sizes within a community.
Within a community each species depends on other species for food, shelter, pollination, seed dispersal etc. If one species is removed it can affect the whole community. This is called interdependence. A stable community is one where all the species and environmental factors are in balance so that population sizes remain fairly constant.
A community is all the populations of different species living together in a habitat. Interdependence means each species relies on others: for food through food webs, for shelter such as trees housing birds, for pollination as bees transfer pollen between flowers, and for seed dispersal as birds or mammals carry fruits away. Removing one species can ripple through the community. For example, if a bee population falls, insect-pollinated plants set fewer seeds, so seed-eating birds decline and predators of those birds may also fall. A stable community has all species and environmental factors in balance, so population sizes stay fairly constant over time. Stability does not mean nothing changes; numbers fluctuate slightly around a steady level because births, deaths, predation and resources balance out.
Students should be able to extract and interpret information from charts, graphs and tables relating to the interaction of organisms within a community.
This skill means reading data about organisms in a community and working out what the numbers show about their interactions. Charts, graphs and tables might show population sizes over time, predator and prey numbers, or the effect of removing a species. To extract information, read the axes, units, labels and key carefully, then quote specific values. To interpret, describe the trend and link it to an interaction: for example, if prey numbers rise, predator numbers may rise soon after because more food is available, and then prey numbers fall as more are eaten. Predator-prey graphs often show peaks and troughs with the predator peak lagging behind the prey peak. Always compare like with like, use the data rather than general knowledge alone, and suggest a reason for each pattern you describe.
Your focus
- Define levels of organisation from individual organisms to whole ecosystems.
- Describe what plants and animals compete for in a community.
- Explain interdependence and the concept of a stable community.
Show all 33 objectives
- State the ecological levels from individual organism to whole ecosystem in the correct order.
- Classify a given example, such as all the frogs in a pond or a woodland with its soil and climate, at the correct level.
- Explain how each level includes the previous level and what is added at the ecosystem stage.
- Define interdependence and competition using correct ecological terms.
- Give named examples of resources that plants and animals compete for.
- Explain how a change in one population can affect other populations through interdependence and competition.
- Extract relevant numerical or descriptive information from a table, graph or passage about a community.
- Describe patterns and trends in the supplied information using correct units and comparative language.
- Relate observations from the resource to ecological processes such as competition, predation or interdependence.
- Identify the resources that plants and animals compete for in a described habitat.
- Justify a suggested competitive factor using evidence from the habitat description.
- Distinguish between competition for different resources and explain why the resource is limiting.
- Identify the key conditions of a named habitat that affect organisms.
- Describe structural, behavioural and physiological adaptations and link each to a survival advantage.
- Explain how an adaptation increases an organism's chance of surviving and reproducing in its environment.
- Define an ecosystem and distinguish it from a community and a population.
- Classify factors as biotic or abiotic and give examples of each.
- Explain how interactions between biotic and abiotic components affect the organisms in an ecosystem.
- State the materials plants obtain from air and soil and the materials animals obtain from food.
- Explain how decomposers recycle mineral ions to the soil and carbon dioxide to the atmosphere.
- Link an insufficient supply of materials to reduced survival or reproduction in a named organism.
- List the resources plants and animals compete for in a named habitat.
- Distinguish between intraspecific and interspecific competition with an example of each.
- Explain how the outcome of competition affects which organisms survive and reproduce.
- Define community and interdependence, and give named examples of species depending on each other for food, shelter, pollination or seed dispersal.
- Predict and explain how removing one species can affect other populations in the community.
- Describe the features of a stable community and explain why population sizes remain fairly constant.
- Extract specific values and trends from charts, graphs and tables about organisms in a community.
- Interpret predator-prey and other interaction data to explain how one population affects another.
- Use data as evidence to support conclusions about interdependence within a community.
Communities exam tips
Marking Points
- Define the levels of organisation: individual organisms, populations (one species), communities (multiple species), and ecosystems (biotic and abiotic parts).
- Describe competition in plants for light, space, water, and mineral ions from the soil.
- Describe competition in animals for food, mates, and territory.
- Explain interdependence, giving examples such as plants providing food and shelter, insects pollinating flowers, and animals dispersing seeds.
- Define a stable community as one where species and environmental factors are in balance, so population sizes remain fairly constant.
- An individual organism is a single member of a species, for example one dandelion plant.
- A population is all the organisms of one species in a habitat, for example all the dandelions in a field.
- A community is all the populations of different species living and interacting in a habitat.
- An ecosystem is the community plus the non-living (abiotic) conditions, such as light intensity, temperature, water and soil.
- The levels form a sequence of increasing inclusiveness: individual → population → community → ecosystem.
- Correct use of the terms population, community and ecosystem when describing a named habitat.
- Interdependence is the reliance of organisms in a community on each other for resources and processes such as food, shelter, pollination and seed dispersal.
- Competition occurs when organisms require the same resource that is in limited supply.
- Plants compete for light, water, space and mineral ions; animals compete for food, mates and territory.
- Competition may be between individuals of the same species or between different species.
- Interdependence and competition influence survival and reproduction, and therefore affect population sizes and distribution.
- A change to one population, such as a fall in bee numbers, can affect other populations because of interdependence.
- Read the supplied resource carefully and identify the ecological quantities it contains, such as population size, percentage cover, light intensity or temperature.
- Quote numerical values with correct units when describing a pattern, for example 'the population rose from 40 to 120 between day 2 and day 6'.
- Describe trends using comparative language such as increase, decrease, plateau or fluctuate, rather than listing numbers without comment.
- Link each observation back to an ecological process, for example competition for light, predation, or interdependence between species.
- Where the resource shows more than one variable, compare the variables directly instead of describing each one in isolation.
- Use the command word in the question to decide the depth needed: describe requires the pattern, explain requires a mechanism or reason.
- Name a specific resource, such as light, water, mineral ions, space, food, mates or territory, rather than writing the vague phrase 'resources'.
- Match the named factor to the habitat described, for example water in a dry environment or light in a shaded woodland.
- Justify the choice by referring to a feature of the habitat, such as dense canopy, low rainfall or a crowded rock pool.
- Distinguish between intraspecific competition within one species and interspecific competition between different species where the question allows.
- Recognise that competition occurs when a resource is limited, and that the organism best adapted to obtain it is more likely to survive and reproduce.
- Give more than one factor where the habitat description supports it, since real habitats usually have several limiting resources.
- Identify the abiotic and biotic challenges of the stated habitat, such as temperature, water availability, light, predation or competition.
- Name a specific feature of the organism, for example thick fur, waxy cuticle, streamlined body, migration or water storage.
- Explain the mechanism linking the feature to survival, such as reducing heat loss, limiting water loss or avoiding predators.
- Classify the adaptation as structural, behavioural or physiological where the question asks for types.
- Link the adaptation to successful reproduction, so the advantageous alleles are passed to offspring.
- Use comparative language, such as more or less, to show how the feature improves fitness in that environment.
- Define the community as all the populations of different species living and interacting in a habitat.
- Identify biotic components as living organisms and their interactions, such as predation, competition and disease.
- Identify abiotic components as non-living conditions, such as light, temperature, water, soil pH and oxygen.
- Explain that an ecosystem includes both the community and the abiotic environment, and the interactions between them.
- Give a specific example of an interaction, such as plants competing for light or animals competing for water.
- Recognise that a change in one component, such as reduced rainfall, can affect the whole community.
- Plants absorb carbon dioxide from the air and water and mineral ions from the soil, using light for photosynthesis.
- Animals obtain energy and building materials by eating other organisms, so food chains begin with producers.
- Decomposers break down dead organisms and waste, returning mineral ions to the soil for reuse by plants.
- Decomposers release carbon into the atmosphere as carbon dioxide during respiration.
- Survival depends on a sufficient supply of materials; reproduction requires additional materials and energy for gametes, seeds, or eggs.
- Plants compete for light, space, water and mineral ions from the soil.
- Animals compete for food, mates and territory.
- Competition happens when resources are limited, so not all organisms obtain enough to survive and reproduce.
- Intraspecific competition occurs between members of the same species; interspecific competition occurs between different species.
- Successful competitors survive and reproduce, passing on advantageous alleles, which links competition to natural selection.
- Define a community as all the populations of different species living together in one habitat, and distinguish it from a population of a single species.
- Explain interdependence using named links: food (predator and prey in a food web), shelter (trees or burrows), pollination (insects transferring pollen) and seed dispersal (animals moving seeds away from the parent plant).
- Describe a consequence of removing one species, tracing the effect through at least two other species, such as loss of a pollinator reducing plant seeds and then reducing seed-eating bird numbers.
- State that a stable community has species and environmental factors in balance so population sizes remain fairly constant, and explain that small fluctuations still occur around that steady level.
- Use data or a food web to support a prediction about how removing or adding a species changes other populations.
- Read axes, units, labels and keys correctly, and quote specific values from the chart, graph or table.
- Describe trends over time, such as increases, decreases, peaks, troughs or cyclical patterns in population sizes.
- Interpret a predator-prey relationship by linking a rise in prey numbers to a later rise in predator numbers, and a fall in prey numbers to increased predation.
- Explain how data show interdependence, for example a fall in one species leading to a fall in a species that depends on it for food or pollination.
- Compare data for two or more species and use the comparison to support a conclusion about their interaction.
Examiner Tips
- 💡Learn precise definitions of population, community, habitat, and ecosystem, and use them in answers rather than informal wording.
- 💡When describing competition, explicitly state what plants compete for (e.g., light, space) versus what animals compete for (e.g., food, mates).
- 💡Learn the sequence individual → population → community → ecosystem and practise placing unfamiliar examples into it.
- 💡When a question gives a named habitat, name a real organism at each level to show the difference clearly.
- 💡Read the command word: 'describe' needs the levels in order, while 'explain' needs a reason why each level includes the one below.
- 💡Use the phrase 'limited resource' when defining competition, because competition only matters when supply is short.
- 💡Give named examples of what plants and animals compete for rather than writing 'resources' alone.
- 💡For interdependence questions, state the benefit each organism gains, such as food for the bee and pollination for the flower.
- 💡Underline the command word and the resource reference in the question before you start writing.
- 💡Plan two or three linked points, each pairing a figure with an ecological explanation, rather than writing one long unstructured paragraph.
- 💡If the resource is a graph, quote values at two clearly separated points to show the direction and size of the change.
- 💡Check that every claim you make can be traced to something visible in the supplied information.
- 💡Use the habitat words in the question as your evidence, quoting them briefly to justify each factor.
- 💡Aim for two or three different factors so you cover more of the available credit.
- 💡Write the factor first and the reason second, keeping each point to one clear sentence.
- 💡Check whether the question asks about plants, animals or both before choosing your factors.
- 💡Read the habitat description carefully and quote the condition, such as dry or cold, before suggesting a feature.
- 💡Use the structure feature, mechanism, benefit to keep each suggestion focused and complete.
- 💡If asked to suggest, offer plausible biological ideas rather than a single memorised example, and check each idea against the stated conditions.
- 💡Use the words biotic and abiotic accurately, and give at least one example of each when explaining an ecosystem.
- 💡When describing an interaction, name both the organisms or factors involved and state the effect on the community.
- 💡Check that your answer covers both the living community and the non-living environment, because the definition requires both.
- 💡Name the specific material and its source, for example, carbon dioxide from air or mineral ions from soil.
- 💡When describing decomposition, clearly distinguish between mineral ions going into the soil and carbon dioxide going into the air.
- 💡Match each resource to the correct group, for example light and space for plants, mates and territory for animals.
- 💡Use comparative language such as 'more likely to survive' or 'less likely to reproduce' when explaining the outcome.
- 💡Give a named example from a habitat you have studied to make your answer concrete.
- 💡When asked about interdependence, name the species and state the exact benefit, such as 'the oak tree provides shelter for the owl', rather than writing 'they need each other'.
- 💡For removal questions, write a chain of at least two consequences using arrows or 'so' to show the direction of effect.
- 💡For stability questions, use the phrase 'population sizes remain fairly constant' and mention balance between species and environmental factors.
- 💡Quote numbers with units and refer to the correct species and time period in every data answer.
- 💡Use comparative language such as 'higher than', 'lower than' or 'increased by' rather than vague words like 'more' or 'less'.
- 💡When explaining a lag between predator and prey peaks, state that the predator response happens after the prey change because predators need time to reproduce.
Common Mistakes
- Using population and community interchangeably; correct this by stating that a population is one species in an area, while a community includes all the different species.
- Stating that animals compete for space; correct this by specifying that animals compete for territory, while plants compete for space.
- Treating interdependence as one-way; correct this by giving examples where species affect each other, such as pollinators and flowering plants.
- Calling a group of different species a population; the correction is that a population contains only one species, while a community contains many species.
- Describing an ecosystem as only the living organisms; the correction is that an ecosystem includes the abiotic conditions as well as the community.
- Confusing a habitat with an ecosystem; the correction is that a habitat is the place where organisms live, whereas an ecosystem includes the community and its physical environment.
- Treating interdependence as one-way, such as saying bees depend on flowers but ignoring that flowers depend on bees; the correction is that the relationship works in both directions.
- Assuming competition only happens between different species; the correction is that members of the same species also compete for the same resources.
- Saying competition always kills the weaker organism; the correction is that it reduces the resources available, affecting growth, survival and reproduction rather than always causing immediate death.
- Copying numbers from the resource without saying what they show. Correction: always add a comparative statement, such as 'species A increased while species B decreased'.
- Ignoring units or misreading the scale on a graph axis. Correction: check the axis label and scale before quoting any value, and carry the unit through.
- Writing generic ecology recall that is not supported by the resource. Correction: anchor every point to a specific figure or feature in the supplied information.
- Writing only 'food' for plants. Correction: plants make their own food by photosynthesis, so they compete for light, water, mineral ions and space.
- Naming a factor without linking it to the habitat. Correction: add a clause explaining why that resource is scarce, such as 'because the canopy blocks sunlight'.
- Confusing competition with predation. Correction: competition is a struggle for the same limited resource; predation is one organism eating another.
- Describing a feature without explaining its advantage; correct by adding a because clause that links the feature to survival.
- Confusing adaptation with acclimatisation; correct by stating that adaptations are inherited features of a population, not short-term changes by one individual.
- Giving a generic answer such as it is adapted to survive; correct by naming the habitat condition and the specific feature that meets it.
- Treating an ecosystem as only the living organisms; correct by including the abiotic conditions and their interactions.
- Confusing a community with a population; correct by stating that a community contains multiple species, while a population is one species.
- Listing abiotic factors without linking them to organisms; correct by explaining how a factor such as temperature affects survival or distribution.
- Saying plants take food from the soil: correct this by stating that soil supplies water and mineral ions, while food (glucose) is made by photosynthesis.
- Stating that decomposers return carbon to the soil: correct this by explaining that carbon is released into the atmosphere as carbon dioxide during respiration.
- Ignoring decomposers: correct this by naming bacteria and fungi that break down dead material and release mineral ions.
- Listing only food for animals: correct this by including mates and territory as well.
- Saying plants compete for food: correct this by stating that plants compete for light, space, water and mineral ions, because they make their own food.
- Treating competition as always between different species: correct this by distinguishing intraspecific from interspecific competition.
- Treating community and population as the same thing. Correction: a population is one species in a habitat, while a community is all the populations of all species there.
- Assuming removing a species only affects its direct predator or prey. Correction: effects can spread indirectly through the food web, for example to species two or more feeding links away.
- Believing a stable community never changes. Correction: population sizes fluctuate slightly; stability means they stay fairly constant because births, deaths and resources are balanced.
- Reading values from the wrong axis or ignoring the units. Correction: check the axis label and unit before quoting a number, and state the unit with the value.
- Describing a trend without using data. Correction: support every statement with a figure, such as 'the prey population rose from 200 to 600 between year 1 and year 3'.
- Confusing correlation with cause. Correction: use the data to suggest a possible interaction, then explain the biological reason, such as more prey providing more food for predators.