GCSE BiologyAQA, Edexcel and OCR
40 biology questions on ecosystems. Pick your answer, then tap to see if you were right and why. Every answer comes from the Show Working science bank, checked against the GCSE content every board in England teaches.
01 / Quiz yourselfTry it, then tap to check
Choose your answer before you open it. Then read why, so it sticks.
01 / EcosystemsBoth tiers
The right order:
One organism belongs to a population of its species. All the populations in a habitat form a community, and the community together with its non-living surroundings is an ecosystem.
Checked against OpenStax Biology 2e, 44.1 The Scope of Ecology
02 / EcosystemsBoth tiers
Answer: B all the organisms of one species in a habitat
A population is all the organisms of one species living in a habitat. A community is all the populations of the different species living there together.
Checked against OpenStax Biology 2e, 44.1 The Scope of Ecology
03 / EcosystemsBoth tiers
Answer: A a community plus its non-living surroundings
An ecosystem is a community of living (biotic) things interacting with the non-living (abiotic) parts of their environment, such as water, soil and light. A community alone is only the living part.
Checked against OpenStax Biology 2e, 46.1 Ecology of Ecosystems
04 / EcosystemsBoth tiers
Answer: D soil pH
Abiotic factors are non-living: light, temperature, moisture, soil pH and minerals, wind, carbon dioxide and oxygen. Biotic factors are living: food supply, predators, pathogens and competing species.
Checked against OpenStax Biology 2e, 44.1 The Scope of Ecology
05 / EcosystemsBoth tiers
Answer: B Too little light reaches the ground
A change in one factor changes the whole community. Shade cuts the light plants need for photosynthesis, and a new predator eats more prey, so prey numbers fall.
Checked against OpenStax Biology 2e, 45.6 Community Ecology
06 / EcosystemsBoth tiers
Answer: D light, space, water and mineral ions
Plants compete for light and space, and for water and mineral ions from the soil. Animals compete for food, mates and territory. The best competitors are more likely to survive and breed.
Checked against OpenStax Biology 2e, 45.6 Community Ecology
07 / EcosystemsBoth tiers
Answer: A species depending on each other to survive
Species depend on each other for food, shelter, pollination and seed dispersal. Removing one species can therefore affect the whole community. This is called interdependence.
Checked against OpenStax Biology 2e, 45.6 Community Ecology
08 / EcosystemsBoth tiers
Answer: A the transfer of biomass up the chain
A food chain starts with a producer and shows who is eaten by whom. Each arrow points from the food to the eater, showing the transfer of biomass (and energy) along the chain.
Checked against OpenStax Biology 2e, 46.2 Energy Flow through Ecosystems
09 / EcosystemsBoth tiers
Answer: C They rise and fall in cycles
When prey are plentiful, predators have more food and their numbers rise. More predators eat more prey, so prey numbers fall, and then predator numbers fall too. The pattern repeats in cycles.
Checked against OpenStax Biology 2e, 45.1 Population Demography
10 / EcosystemsBoth tiers
Answer: D carbon
Materials such as carbon, water and nitrogen are used again and again: they pass between living things and the air, soil and water. Energy is different: it flows through an ecosystem and is not recycled.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
11 / EcosystemsBoth tiers
Answer: C photosynthesis
Photosynthesis takes carbon dioxide out of the air. Respiration by plants, animals and microorganisms, and burning fuels, put it back. Feeding passes carbon along food chains.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
12 / EcosystemsBoth tiers
Answer: C It returns carbon dioxide for photosynthesis
Carbon is in all the big molecules of life. The carbon cycle returns it to the air as carbon dioxide, so plants can keep using it to build biomass. Plants respire all the time, not only at night.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
13 / EcosystemsBoth tiers
Answer: B It supplies them with fresh water
Water evaporates, condenses into clouds and falls as rain or snow, then drains back to the sea. On the way it brings fresh water to plants and animals on land.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
14 / EcosystemsBoth tiers
Answer: A transpiration
Plants take water from the soil and lose it as water vapour from their leaves. This transpiration is part of the water cycle, along with evaporation from seas and lakes.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
15 / EcosystemsBoth tiers
Answer: A bacteria and fungi
Bacteria and fungi break down dead organisms and waste. As they respire they release carbon dioxide into the air, and the breakdown releases mineral ions into the soil.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
16 / EcosystemsBoth tiers
Answer: D They release mineral ions from dead material
When microorganisms break down dead organisms, the mineral ions locked inside them go back into the soil. Plant roots take them up again, so materials keep cycling.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
17 / EcosystemsBoth tiers
Answer: D at coordinates picked using random numbers
Choose coordinates with random numbers so you do not pick spots by eye and bias the sample. Throwing a quadrat is not truly random, because you still decide where to throw it.
Checked against OpenStax Biology 2e, 45.1 Population Demography
18 / EcosystemsBoth tiers
Answer: C quadrats along a transect
A transect is a line across a habitat where conditions change. Quadrats placed at intervals along it show how the distribution of organisms changes, for example with light or water.
Checked against OpenStax Biology 2e, 45.1 Population Demography
19 / EcosystemsBoth tiers
Answer: C 300
Find the mean number per quadrat, then scale up to the whole area. Here 30 ÷ 10 = 3 snails per m², and 3 × 100 = 300. Multiplying the total count by the area is a common mistake.
Checked against OpenStax Biology 2e, 45.1 Population Demography
20 / EcosystemsBoth tiers
Answer: C clearing rainforest for cattle farming
Building, farming, quarrying, dumping waste and pollution destroy habitats and reduce biodiversity. Breeding programmes, protecting habitats, replanting hedgerows and recycling help protect it.
Checked against OpenStax Biology 2e, 47.4 Preserving Biodiversity
21 / EcosystemsBoth tiers
Answer: B Less photosynthesis and more burning
Cutting down and burning forest means less carbon dioxide is taken in by photosynthesis, and more is released by burning and decay. It also destroys the habitats of many species.
Checked against OpenStax Biology 2e, 47.3 Threats to Biodiversity
22 / EcosystemsBoth tiers
Answer: C fertiliser running off farmland
Sewage, fertiliser and toxic chemicals pollute water, and smoke and acidic gases pollute air. Rising carbon dioxide and methane add to global warming. Pollution kills plants and animals and reduces biodiversity.
Checked against OpenStax Biology 2e, 47.3 Threats to Biodiversity
23 / EcosystemsBoth tiers
Answer: B Species rely less on any single other species
With many species, each depends less on any single one for food or shelter, so one loss does less harm. Biodiversity also gives us food, medicines and materials, and many species are still unstudied.
Checked against OpenStax Biology 2e, 47.2 The Importance of Biodiversity to Human Life
24 / EcosystemsBoth tiers
Answer: D Local people may need the land to earn a living
Conservation costs money and land, and can clash with people needing farmland, housing and jobs. Species and habitats cross borders, so countries must agree, then keep checking that schemes work.
Checked against OpenStax Biology 2e, 47.4 Preserving Biodiversity
25 / EcosystemsBoth tiers
Answer: B It cuts down water loss
Abiotic conditions decide which organisms can live in a place. Organisms have features, called adaptations, that suit them to their conditions: a cactus loses little water through its small spines, and an Arctic fox loses little heat through small ears and thick fur.
Checked against AQA GCSE Biology 8461 specification, 4.7.1.4 Adaptations
26 / EcosystemsBoth tiers · separate only
Answer: D warm, moist and with oxygen
Decomposers' enzymes work faster when warm, they need water, and most need oxygen to respire. If it gets too hot their enzymes are denatured, so decay slows again. Light does not affect decay.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
27 / EcosystemsBoth tiers · separate only
Answer: A The cold slows the decomposers' enzymes
Cold slows the enzymes of bacteria and fungi but rarely kills them, so food still rots once it warms up. Drying removes the water that decomposers need to grow.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
28 / EcosystemsBoth tiers · separate only
Answer: D It is slower and can make methane
Without oxygen, decay is anaerobic: it is slower and can produce methane. In waterlogged bogs little oxygen reaches dead plants, so they decay very slowly and build up as peat.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
29 / EcosystemsHigher only · separate only
Answer: A Another factor may have changed as well
Changes in temperature, water and gases in the air shift where species live, and many UK species have moved north as it warmed. But a link in data is not proof: other changes, such as habitat loss, must be ruled out.
Checked against OpenStax Biology 2e, 47.3 Threats to Biodiversity
30 / EcosystemsHigher only · separate only
Answer: A Species that need wet soil are lost
How much water is available decides which species can live in a place. When an area dries out, species that need wet conditions die out or move away, and species that cope with drought may move in.
Checked against OpenStax Biology 2e, 47.3 Threats to Biodiversity
31 / EcosystemsBoth tiers · separate only
Answer: B level 2
Level 1 is the producers (plants and algae), level 2 herbivores (primary consumers), level 3 carnivores that eat herbivores, level 4 carnivores that eat carnivores. Apex predators have no predators of their own.
Checked against OpenStax Biology 2e, 46.2 Energy Flow through Ecosystems
32 / EcosystemsBoth tiers · separate only
Answer: A They release enzymes onto it and absorb the products
Decomposers such as bacteria and fungi secrete enzymes onto dead plant and animal matter. The enzymes break it into small soluble molecules, which then diffuse into the decomposer.
Checked against OpenStax Biology 2e, 46.3 Biogeochemical Cycles
33 / EcosystemsBoth tiers · separate only
Answer: C the mass of living material at that level
Each bar shows the biomass at one trophic level, with producers at the bottom. Biomass is lost between levels, so each bar is usually narrower than the one below it.
Checked against OpenStax Biology 2e, 46.2 Energy Flow through Ecosystems
34 / EcosystemsBoth tiers · separate only
Answer: A Some food is egested as faeces
Not everything is eaten, such as bones and fur. Not all eaten food is absorbed: some is egested as faeces. Some is lost as waste, like urea in urine, and a lot is used in respiration, leaving as carbon dioxide and water.
Checked against OpenStax Biology 2e, 46.2 Energy Flow through Ecosystems
35 / EcosystemsBoth tiers · separate only
Answer: B 10%
Efficiency = biomass at the higher level ÷ biomass at the lower level × 100. Often only about a tenth is passed on, so there is too little to support many animals, or many levels, at the top.
Checked against OpenStax Biology 2e, 46.2 Energy Flow through Ecosystems
36 / EcosystemsBoth tiers · separate only
Answer: B having enough food to feed a population
Food security means having enough food to feed a population. It is threatened by a growing population, new pests and pathogens, environmental change such as failed rains, farming that cannot be sustained, such as overfishing, and the cost of farming inputs.
Checked against gov.uk, United Kingdom Food Security Report 2024
37 / EcosystemsBoth tiers · separate only
Answer: B Feeding livestock uses a lot of crops
Biomass is lost at each trophic level, so feeding crops to animals feeds fewer people than eating the crops. Richer diets with more meat need more land, and costly inputs can mean less food is grown.
Checked against gov.uk, United Kingdom Food Security Report 2024
38 / EcosystemsBoth tiers · separate only
Answer: A Failed rains can ruin harvests
Crops depend on the right temperature and rainfall. Droughts, floods and shifting climate can ruin harvests, and in some countries failed rains lead to famine.
Checked against gov.uk, United Kingdom Food Security Report 2024
39 / EcosystemsBoth tiers · separate only
Answer: A Crops resistant to pests or drought
Genetic modification can give crops genes for pest resistance, drought tolerance or better nutrition, raising yields. Pest-resistant crops usually need less pesticide, not more.
Checked against OpenStax Biology 2e, 17.1 Biotechnology
40 / EcosystemsHigher only · separate only
Answer: C Animals that need a lot of oxygen disappear from it
The gases dissolved in water, like the gases in the air, decide which species can live in a place. Where oxygen falls, animals that need a lot of it die or move away, and only species that cope with low oxygen remain.
Checked against OpenStax Biology 2e, 47.3 Threats to Biodiversity
02 / Longer answersMarked by levels
Write your answer first, on paper. Then open it and tick off the points you made. How 6-mark questions are marked.
6 marks / Carbon moving through the carbon cycleBoth tiers
Plants and algae take carbon dioxide from the air and use it in photosynthesis to make glucose. They then use the glucose to make other carbon compounds, such as starch, cellulose, fats and proteins, so the carbon becomes part of their biomass. When animals eat the plants, these carbon compounds are digested and become part of the animals' bodies, so carbon passes along the food chain. All living things respire, and respiration releases carbon dioxide back into the air. When plants and animals die, or when animals produce waste such as faeces, decomposers like bacteria and fungi feed on the dead material and break it down. As the decomposers respire, they release the carbon in it as carbon dioxide into the air, so it can be used by plants again. Decomposers are therefore essential, because without them carbon would stay locked up in dead bodies. If dead organisms do not decay, for example in waterlogged soil, their carbon can end up in fossil fuels such as coal over millions of years. Combustion of fossil fuels and wood releases this carbon into the air as carbon dioxide.
Writing “carbon” when you mean carbon dioxide, for example “plants take in carbon”. Plants take in carbon dioxide, and respiration and combustion release carbon dioxide; name the process at each step.
6 marks / Why food chains are shortBoth tiers · separate only
In a food chain, grass is eaten by rabbits and rabbits are eaten by foxes. A pyramid of biomass for this chain has a wide bar for the grass, a narrower bar for the rabbits and a very narrow bar for the foxes.
Only about 10% of the biomass at each trophic level becomes biomass in the level above, for several reasons. Firstly, not all of an organism is eaten. Rabbits eat the leaves of the grass but not the roots, and a fox does not eat a rabbit’s bones or fur. Secondly, not all the food that is eaten is absorbed, because some cannot be digested and is egested as faeces. Thirdly, much of the glucose that is absorbed is used in respiration to release energy for movement and, in mammals like rabbits and foxes, for keeping warm. The carbon dioxide and water made in respiration are lost from the body. Some absorbed material is also lost as waste, such as urea in urine. Only the small part that is built into new body tissue, through growth, is available to the next trophic level. This is why each bar of the pyramid is narrower than the one below. Because so much is lost at each step, after four or five levels there is too little biomass left to support another population of animals, so food chains are short.
Saying biomass or energy is “used up” without explaining where it goes. Give the actual losses: parts not eaten, faeces, waste such as urea, and glucose used in respiration.
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