O Level / IGCSE Biology chapter 19: Relationships of organisms with one another and with the environment MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

52 exam-style questions on Relationships of organisms with one another and with the environment, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

52 questions · 5 topics · 10 per test

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What chapter 19 covers

Ten Relationships of organisms with one another and with the environment questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. What do the arrows in a food chain show?

  1. A
    the relative sizes of the organisms in the chain
  2. B
    which organism eats which, pointing from the predator to its prey
  3. C
    the direction of energy flow, from food to feeder
  4. D
    the direction in which the predator moves to catch its prey
Show answer

Answer: C. Arrows point from the organism that is eaten to the organism that eats it, showing the transfer of energy.

2. What is a community?

  1. A
    all the populations of different species in one area
  2. B
    the non-living physical environment in which organisms live
  3. C
    a group of one species living in one area at the same time
  4. D
    the total number of individuals of a single species in an area
Show answer

Answer: A. A community is all the populations living and interacting in an ecosystem.

3. How does using fishing nets with a larger mesh size help to conserve fish stocks?

  1. A
    the nets last much longer than small-mesh nets
  2. B
    more fish are caught each time the net is hauled in
  3. C
    young fish escape and can grow to breeding age
  4. D
    the fish are caught more quickly and more cheaply
Show answer

Answer: C. Letting young fish escape means they survive to reproduce and replace the fish that are caught.

4. How does deforestation increase the concentration of carbon dioxide in the atmosphere?

  1. A
    the soil absorbs less oxygen, so carbon dioxide builds up in the air
  2. B
    the cut trees absorb more carbon dioxide as they dry out
  3. C
    deforestation increases photosynthesis, which releases carbon dioxide
  4. D
    fewer trees photosynthesise, and burning them releases carbon dioxide
Show answer

Answer: D. Less carbon dioxide is removed by photosynthesis, while combustion and decay of the wood add more.

5. How does the growth of the human population affect global resources?

  1. A
    it increases the demand for food, water and land
  2. B
    it lowers the demand for food because more can be grown
  3. C
    it has no effect on resources, because they are replaced
  4. D
    it increases biodiversity, as more land is used by people
Show answer

Answer: A. More people need more food, water, land, fuel and materials, putting pressure on ecosystems.

6. Why does deforestation lead to loss of soil?

  1. A
    trees take all the nutrients from the soil, leaving dust
  2. B
    burning the trees destroys the soil by heating it
  3. C
    earthworms leave the area, so the soil disappears
  4. D
    without roots to bind it, soil is washed or blown away
Show answer

Answer: D. Tree roots bind the soil and the canopy breaks the force of rain; without them, soil erosion increases.

7. Why can deforestation increase flooding?

  1. A
    less water is taken up by trees, so more runs off into rivers
  2. B
    the soil left behind becomes more absorbent, so water drains away
  3. C
    trees release large amounts of water into the rivers through their roots
  4. D
    more rain falls on land that has been cleared of its trees
Show answer

Answer: A. Trees intercept rain and absorb water; without them water runs off quickly, carrying soil into rivers.

8. A pot plant in bright light is sealed in a transparent box. The concentration of carbon dioxide in the box falls. Which process is responsible?

  1. A
    photosynthesis
  2. B
    decomposition of dead leaves
  3. C
    respiration in the plant
  4. D
    combustion of a fuel
Show answer

Answer: A. Photosynthesis takes in carbon dioxide to make carbohydrates. Respiration, combustion and decomposition all release carbon dioxide.

9. What is produced when decomposers break down the proteins in dead plants and animals?

  1. A
    nitrogen gas
  2. B
    ammonium ions
  3. C
    nitrate ions directly
  4. D
    glucose
Show answer

Answer: B. Decomposition of protein releases ammonium ions; these are then nitrified to nitrate.

10. How do protected areas such as national parks help to conserve forests?

  1. A
    they allow logging companies to cut as many trees as they wish
  2. B
    they restrict logging and clearing, so habitats are protected
  3. C
    they allow non-native species to be introduced to increase variety
  4. D
    they increase the demand for timber from other forests
Show answer

Answer: B. Laws in protected areas prevent or limit damage to the forest and its species.

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Ways to practise this chapter

Relationships of organisms with one another and with the environment: questions students ask

How many Relationships of organisms with one another and with the environment MCQs are there?

52, each with the answer and a short explanation, across 5 topics: Energy flow, Nutrient cycles, Ecosystems and biodiversity, Effects of humans on ecosystems, Conservation. Every chapter test draws ten of them, so you can take it many times.

Is the O Level / IGCSE Biology chapter 19 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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