GCSE Biology Topic 7: Ecology MCQs – 30 Practice Questions with Answers (AQA 8461)
Free practice for AQA GCSE Biology 8461 on ecology, covering ecosystems, food chains and trophic levels, material cycles, sampling, human impact and food production, with a short explanation after every question.
Ecosystems, Communities and Adaptations
Q1. How is an ecosystem defined?
- (A) A single species living alone, without other organisms or non-living surroundings
- (B) A community plus the non-living parts of its environment, interacting together
- (C) A food chain with only producers
- (D) A habitat with no living organisms
Show Answer
Answer: B – An ecosystem is a community of organisms plus the non-living parts of their environment, such as soil, water and climate, interacting together.
Q2. Which of these is an abiotic factor?
- (A) Competition between plants
- (B) Predation by foxes
- (C) Disease spreading through a herd
- (D) Light intensity in a woodland
Show Answer
Answer: D – Abiotic factors are non-living influences such as light, temperature, water availability and pH, while biotic factors are living influences.
Q3. Which of these is a biotic factor affecting a population?
- (A) Competition for food with another species
- (B) Soil pH, a non-living chemical property of the environment
- (C) Rainfall
- (D) Temperature
Show Answer
Answer: A – Biotic factors are living influences such as competition, predation and disease.
Q4. What is a community in ecology?
- (A) All the members of one species in an area, which is a population not a community
- (B) All the non-living parts of a habitat
- (C) All the populations of different species living together in a habitat
- (D) A single food chain
Show Answer
Answer: C – A community is made up of all the populations of different species that live together in a habitat.
Q5. What is meant by an organism being adapted to its environment?
- (A) It can live anywhere on Earth, in any habitat at all, without special features
- (B) It never changes over time
- (C) It has no predators
- (D) It has features that help it survive and reproduce in its habitat
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Answer: D – Adaptations are features that help an organism survive and reproduce in its particular habitat.
Q6. Which is an example of a structural adaptation of a desert plant?
- (A) Flowering only at night for one week each year in the desert heat
- (B) A thick waxy cuticle and small leaves that reduce water loss
- (C) Growing taller every year
- (D) Producing seeds that float on water
Show Answer
Answer: B – A thick waxy cuticle and reduced leaves limit water loss, which suits a dry desert habitat.
Q7. Organisms in the same habitat compete for what?
- (A) The same limited resources, such as light, water, food or territory
- (B) The same predators, which hunt several different species in the area
- (C) The same non-living habitat only
- (D) The same scientific name
Show Answer
Answer: A – Competition happens when organisms need the same limited resources, such as light, water, food or territory, and animals may also compete for mates.
Q8. What is interdependence in an ecosystem?
- (A) One species living without any other species around it, entirely on its own in the habitat
- (B) A species that eats only producers
- (C) Species depending on each other for food, shelter, pollination or other needs
- (D) A population that never changes in size
Show Answer
Answer: C – Species in a community are interdependent: they rely on each other for food, shelter, pollination, seed dispersal and other needs.
Food Chains, Food Webs and Trophic Levels
Q9. In a food chain, what do the arrows show?
- (A) The direction in which animals move through the habitat each day when feeding and hunting
- (B) The direction of energy flow, from the organism eaten to the organism eating it
- (C) The direction of water flow in the soil
- (D) The order in which species evolved
Show Answer
Answer: B – Arrows in a food chain show the direction of energy flow, from the organism being eaten to the organism eating it.
Q10. Which organism is a producer?
- (A) A rabbit eating grass
- (B) A fox eating rabbits
- (C) A fungus breaking down dead wood and returning nutrients to the soil
- (D) A green plant making its own food by photosynthesis
Show Answer
Answer: D – Producers, usually green plants and algae, make their own food by photosynthesis.
Q11. What is a trophic level?
- (A) A feeding stage in a food chain
- (B) A measure of soil acidity, given as a pH value
- (C) The top predator in a habitat
- (D) A type of decomposer
Show Answer
Answer: A – A trophic level is a feeding stage in a food chain, such as producer, primary consumer or secondary consumer.
Q12. Why are food chains rarely more than four or five stages long?
- (A) Predators stop hunting after four stages and leave the remaining prey alone
- (B) Producers run out of sunlight
- (C) Energy is lost at each stage, so only part passes on to the next level
- (D) Decomposers remove the top predators
Show Answer
Answer: C – Biomass and energy fall at each stage because energy is lost through respiration, movement, excretion and egestion, so little remains for further levels.
Q13. Why are pyramids of biomass usually pyramid-shaped?
- (A) Producers are always the largest organisms in the habitat, outweighing all consumers combined in the whole habitat
- (B) So much is lost between levels that each level supports less living material than the one below
- (C) Consumers reproduce more slowly than producers
- (D) Decomposers add mass to the top level
Show Answer
Answer: B – Pyramids of biomass show the mass of living material at each level, and they are usually pyramid-shaped because so much energy is lost between levels.
Q14. What is the role of decomposers in an ecosystem?
- (A) They eat only living producers, like herbivores do, and never touch dead material
- (B) They photosynthesise to make food
- (C) They hunt top predators
- (D) They break down dead material and waste, returning nutrients to the soil
Show Answer
Answer: D – Decomposers break down dead plants and animals and waste, releasing carbon dioxide by respiration and returning mineral ions to the soil for plants to reuse.
Q15. What is a food web?
- (A) Many linked food chains in one habitat
- (B) A single chain from producer to top predator
- (C) A diagram of the water cycle
- (D) A pyramid showing biomass at each level
Show Answer
Answer: A – A food web shows many linked food chains in one habitat, reflecting that most organisms eat more than one type of food.
Material Cycles and Sampling
Q16. In the carbon cycle, which process removes carbon dioxide from the air?
- (A) Combustion of fossil fuels, which releases carbon dioxide
- (B) Respiration by animals
- (C) Photosynthesis by plants and algae
- (D) Decomposition of dead material
Show Answer
Answer: C – In the carbon cycle, carbon dioxide is taken in by photosynthesis and released by respiration, decomposition and combustion.
Q17. In the water cycle, what happens after water evaporates from seas and land?
- (A) It is permanently lost from the Earth and never returns to land, lakes, rivers or seas
- (B) It condenses and falls as precipitation, then returns to rivers, lakes and seas
- (C) It turns directly into soil minerals
- (D) It is absorbed only by decomposers
Show Answer
Answer: B – In the water cycle, water evaporates, condenses and falls as precipitation, then returns to rivers, lakes and seas.
Q18. Why are quadrats used in ecological sampling?
- (A) To count every single individual in a habitat exactly, with no estimation at all
- (B) To remove all the plants from an area
- (C) To measure the temperature of the soil
- (D) To estimate population sizes and distribution without counting every individual
Show Answer
Answer: D – Sampling with quadrats and transects lets biologists estimate population sizes and distribution without counting every individual.
Q19. What is a transect used for?
- (A) Studying how organisms are distributed across a habitat, along a line from one area to another
- (B) Trapping flying insects at night using light to attract them to a collector placed in the habitat overnight
- (C) Measuring the pH of a pond
- (D) Weighing the biomass of a tree
Show Answer
Answer: A – A transect is a line across a habitat along which samples are taken, showing how distribution changes from one place to another.
Q20. Which sampling method is suitable for small ground-living animals that move across the soil surface?
- (A) A quadrat for counting plants in a measured area
- (B) A sweep net for pond water
- (C) A pitfall trap sunk into the ground
- (D) A light trap in a tree canopy
Show Answer
Answer: C – Pitfall traps catch small animals moving across the ground surface, and are one of the counting techniques used to estimate populations.
Q21. Why should quadrat samples be placed randomly rather than only where plants look plentiful?
- (A) Random placement is quicker than choosing spots
- (B) Random placement avoids bias and gives a fair estimate of the whole area
- (C) Random placement counts every plant
- (D) Random placement removes the need to repeat samples at all in the whole survey, giving a perfect result
Show Answer
Answer: B – Random sampling avoids choosing only rich-looking spots, so the estimate fairly represents the whole area.
Q22. What does decay do in an ecosystem?
- (A) It locks nutrients away forever in dead material, so living plants can never reuse them again
- (B) It turns dead material into fossil fuels at once
- (C) It stops the carbon cycle
- (D) It breaks down dead material, releasing nutrients and carbon dioxide back into the ecosystem
Show Answer
Answer: D – Decay by decomposers breaks down dead material, releasing carbon dioxide by respiration and returning mineral ions to the soil.
Human Impact, Biodiversity and Food Production
Q23. What is biodiversity?
- (A) The variety of living organisms in an area
- (B) The total mass of one single species in a habitat
- (C) The number of habitats in a country
- (D) The rate of photosynthesis in a forest
Show Answer
Answer: A – Biodiversity is the variety of living organisms in an area.
Q24. How does deforestation harm ecosystems?
- (A) It increases the number of habitats
- (B) It reduces rainfall everywhere at once, drying out all habitats completely
- (C) It removes habitats and releases carbon dioxide, reducing biodiversity
- (D) It increases the biomass at every trophic level
Show Answer
Answer: C – Deforestation removes habitats and releases carbon dioxide, and rising carbon dioxide and methane levels are linked to global warming.
Q25. Which of these helps to maintain biodiversity?
- (A) Clearing forests for farmland
- (B) Protecting habitats, reducing deforestation and breeding programmes for endangered species
- (C) Draining wetlands for building
- (D) Introducing a predator with no natural enemies into a habitat, where it can spread unchecked
Show Answer
Answer: B – Protecting habitats, reducing deforestation, breeding programmes for endangered species and protecting rare habitats all help maintain biodiversity.
Q26. How does pollution of water affect an ecosystem?
- (A) It has no effect on living organisms
- (B) It only affects decomposers, leaving all other organisms completely safe
- (C) It improves water quality for fish
- (D) It can kill organisms and disrupt food webs that depend on clean water
Show Answer
Answer: D – Pollution of land, water and air harms organisms, and damage at one trophic level can spread through the food web.
Q27. Why is food production under pressure as the human population grows?
- (A) More people need more food, while farmland and resources are limited
- (B) Plants stop photosynthesizing when human populations grow larger each year
- (C) Food chains become longer every year
- (D) Decomposers consume all the crops
Show Answer
Answer: A – A growing population increases demand for food, while land, water and other resources for farming remain limited.
Q28. Which farming practice can increase food yield but may reduce biodiversity if overused?
- (A) Leaving field margins wild
- (B) Rotating crops between seasons to rest the soil and reduce pests
- (C) Heavy use of pesticides that also kill non-target organisms
- (D) Planting hedgerows around fields
Show Answer
Answer: C – Pesticides raise yields by controlling pests, but heavy use can also kill non-target organisms and reduce biodiversity.
Q29. How can sustainable fishing help fish populations?
- (A) By catching as many fish as possible each season
- (B) By setting catch limits and protected areas so stocks can recover and reproduce
- (C) By fishing only the largest breeding fish in the stock, leaving juveniles to grow and breed later
- (D) By removing all predators from the sea
Show Answer
Answer: B – Catch limits and protected areas let fish stocks recover and reproduce, keeping the fishery productive over time.
Q30. Which statement best explains why protecting rare habitats matters?
- (A) Rare habitats hold species found nowhere else, so losing them can mean losing those species
- (B) Rare habitats are the only places on Earth where photosynthesis happens at all, unlike other habitats
- (C) Rare habitats have no food webs
- (D) Rare habitats never change over time
Show Answer
Answer: A – Rare habitats hold species found nowhere else, so losing such a habitat can mean losing those species entirely, which is why protecting rare habitats helps maintain biodiversity.
Work through any questions you missed again, then revise those areas before moving on to the next topic.