MCQs / Biology / O Level Biology: Organisms and the Environment

O Level Biology: Organisms and the Environment MCQs — Biology

35 multiple-choice questions on O Level Biology: Organisms and the Environment from Biology, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. Which is a result of deforestation?

  1. Increased carbon dioxide in the atmosphere
  2. More biodiversity
  3. Reduced flooding
  4. Less soil erosion

Answer: A) Increased carbon dioxide in the atmosphere

Explanation: Fewer trees photosynthesise. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.4 Effects of humans on ecosystems

Discuss this question

2. Over-harvesting means

  1. planting trees
  2. removing a species faster than it can reproduce
  3. recycling plastics
  4. controlling pests

Answer: B) removing a species faster than it can reproduce

Explanation: Populations collapse when over-harvested. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.4 Effects of humans on ecosystems

Discuss this question

3. In eutrophication, fish die because

  1. algae poison them
  2. water becomes too cold
  3. nitrates kill them directly
  4. dissolved oxygen falls as decomposers respire

Answer: D) dissolved oxygen falls as decomposers respire

Explanation: Decomposers use up oxygen. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.4 Effects of humans on ecosystems

Discuss this question

4. Why do food chains rarely have more than five trophic levels?

  1. Animals cannot eat each other
  2. Decomposers eat the top consumers
  3. Too much energy is lost at each level
  4. Plants do not make enough oxygen

Answer: C) Too much energy is lost at each level

Explanation: Energy loss limits chain length. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

Discuss this question

5. One reason to conserve species is to

  1. maintain biodiversity
  2. increase pollution
  3. speed up extinction
  4. reduce food supply

Answer: A) maintain biodiversity

Explanation: Conservation keeps biodiversity. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.5 Conservation

Discuss this question

6. Methane is produced by

  1. combustion of hydrogen
  2. nitrogen fixation
  3. photosynthesis
  4. cattle and rice paddies

Answer: D) cattle and rice paddies

Explanation: Methane is a greenhouse gas from agriculture. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.4 Effects of humans on ecosystems

Discuss this question

7. Plants absorb nitrogen from the soil mainly as

  1. amino acids
  2. ammonia gas
  3. nitrogen gas
  4. nitrate ions

Answer: D) nitrate ions

Explanation: Roots take up nitrate ions. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.2 Nutrient cycles

Discuss this question

8. Which pyramid can be inverted?

  1. Pyramid of energy
  2. Pyramid of biomass in most land ecosystems
  3. None can be inverted
  4. Pyramid of numbers

Answer: D) Pyramid of numbers

Explanation: One tree can support many insects. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

Discuss this question

9. A sustainable resource is one that

  1. runs out quickly
  2. is made only by humans
  3. is never used
  4. is produced as rapidly as it is removed

Answer: D) is produced as rapidly as it is removed

Explanation: It does not run out. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.5 Conservation

Discuss this question

10. Which method conserves forests?

  1. Removing protected areas
  2. Clearing land for farming
  3. Replanting trees
  4. Burning trees

Answer: C) Replanting trees

Explanation: Replanting replaces trees cut down. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.5 Conservation

Discuss this question

11. The main source of energy for most food chains is

  1. the Sun
  2. the soil
  3. producers
  4. decomposers

Answer: A) the Sun

Explanation: Sunlight drives photosynthesis. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

Discuss this question

12. Energy is lost between trophic levels mainly through

  1. diffusion of oxygen
  2. osmosis
  3. respiration, as heat
  4. photosynthesis

Answer: C) respiration, as heat

Explanation: Respiration releases heat to the environment. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

Discuss this question

13. Nitrifying bacteria convert

  1. nitrates into nitrogen gas
  2. proteins into amino acids
  3. ammonium ions into nitrate ions
  4. nitrogen gas into ammonia

Answer: C) ammonium ions into nitrate ions

Explanation: Nitrification makes nitrates. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.2 Nutrient cycles

Discuss this question

14. Which process returns carbon to the air from fossil fuels?

  1. Fossilisation
  2. Photosynthesis
  3. Combustion
  4. Feeding

Answer: C) Combustion

Explanation: Burning releases CO₂. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.2 Nutrient cycles

Discuss this question

15. A food web is

  1. a nutrient cycle
  2. a single food chain
  3. a network of interconnected food chains
  4. a pyramid of numbers

Answer: C) a network of interconnected food chains

Explanation: Food webs link many chains. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

Discuss this question

16. Denitrifying bacteria convert

  1. ammonium into nitrates
  2. nitrogen gas into nitrates
  3. amino acids into protein
  4. nitrates into nitrogen gas

Answer: D) nitrates into nitrogen gas

Explanation: Denitrification returns N₂ to the air. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.2 Nutrient cycles

Discuss this question

17. It is more efficient for humans to eat crops than meat because

  1. animals do not respire
  2. meat has no energy
  3. there are fewer trophic levels, so less energy is lost
  4. crops contain more protein

Answer: C) there are fewer trophic levels, so less energy is lost

Explanation: Each extra level loses energy. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

Discuss this question

18. An ecosystem is

  1. all the plants in a field
  2. one species in an area
  3. a food chain
  4. a community and its environment interacting together

Answer: D) a community and its environment interacting together

Explanation: Definition of ecosystem. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.3 Ecosystems and biodiversity

Discuss this question

19. Which method helps conserve fish stocks?

  1. Fishing all year round
  2. Fishing in breeding grounds
  3. Removing quotas
  4. Using nets with a larger mesh size

Answer: D) Using nets with a larger mesh size

Explanation: Larger mesh lets young fish escape. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.5 Conservation

Discuss this question

20. A population is

  1. all the species in an area
  2. a community and its environment
  3. a group of one species living in the same area at the same time
  4. the number of species in an area

Answer: C) a group of one species living in the same area at the same time

Explanation: Definition of population. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.3 Ecosystems and biodiversity

Discuss this question

21. Decomposers break down proteins in dead organisms, releasing

  1. ammonium ions
  2. nitrate directly into the air
  3. nitrogen gas
  4. oxygen

Answer: A) ammonium ions

Explanation: Decomposition produces ammonium. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.2 Nutrient cycles

Discuss this question

22. Non-biodegradable plastics harm aquatic animals because they

  1. are decomposed quickly
  2. are fertilisers
  3. can trap animals or be eaten
  4. dissolve and add oxygen

Answer: C) can trap animals or be eaten

Explanation: Plastics persist and cause harm. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.4 Effects of humans on ecosystems

Discuss this question

23. All the populations of different species in an area make up a

  1. ecosystem
  2. population
  3. community
  4. trophic level

Answer: C) community

Explanation: Definition of community. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.3 Ecosystems and biodiversity

Discuss this question

24. Which factor limits the growth of a population?

  1. Food supply
  2. Plenty of space
  3. Absence of disease
  4. Absence of predators

Answer: A) Food supply

Explanation: Limited food restricts growth. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.3 Ecosystems and biodiversity

Discuss this question

25. A closed season in fishing means

  1. fishing only for large fish
  2. fishing only at night
  3. unlimited fishing
  4. no fishing during the breeding season

Answer: D) no fishing during the breeding season

Explanation: Fish can breed undisturbed. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.5 Conservation

Discuss this question

Page 1 of 2 Next

Practise O Level Biology: Organisms and the Environment MCQs

More Biology chapters