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O Level Biology: Organisms and the Environment MCQs — Biology (page 2)

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.

26. An animal that eats only plants is a

  1. carnivore
  2. decomposer
  3. producer
  4. herbivore

Answer: D) herbivore

Explanation: Herbivores eat plants. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

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27. Introducing a non-native species can harm an ecosystem because it

  1. always dies quickly
  2. removes pollution
  3. may compete with or eat native species
  4. increases rainfall

Answer: C) may compete with or eat native species

Explanation: Invasive species lack natural predators. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.4 Effects of humans on ecosystems

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28. In a food chain, the arrows show

  1. the order of extinction
  2. the size of organisms
  3. who eats the most
  4. the direction of energy flow

Answer: D) the direction of energy flow

Explanation: Arrows show energy transfer. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

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29. Nitrogen fixation can be carried out by

  1. decomposers releasing CO₂
  2. denitrifying bacteria
  3. lightning and nitrogen-fixing bacteria
  4. plants' leaves

Answer: C) lightning and nitrogen-fixing bacteria

Explanation: Lightning and bacteria fix nitrogen. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.2 Nutrient cycles

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30. Which pyramid is always pyramid-shaped?

  1. Pyramid of energy
  2. Pyramid of age
  3. Pyramid of numbers
  4. None

Answer: A) Pyramid of energy

Explanation: Energy always decreases up the levels. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

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31. Fungi and bacteria that feed on dead material are

  1. decomposers
  2. carnivores
  3. producers
  4. herbivores

Answer: A) decomposers

Explanation: Decomposers break down dead organic matter. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.1 Energy flow

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32. Global warming is caused mainly by increased

  1. carbon dioxide and methane in the atmosphere
  2. rainfall
  3. oxygen in the atmosphere
  4. nitrogen in the soil

Answer: A) carbon dioxide and methane in the atmosphere

Explanation: These greenhouse gases trap heat. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.4 Effects of humans on ecosystems

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33. Biodiversity is

  1. the mass of all plants
  2. the number of different species in an area
  3. the size of a habitat
  4. the number of individuals of one species

Answer: B) the number of different species in an area

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

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34. What is the first step of eutrophication?

  1. Increase in decomposers
  2. Decrease in oxygen
  3. Death of fish
  4. Increased nitrate ions in the water

Answer: D) Increased nitrate ions in the water

Explanation: Fertilisers or sewage add nitrates first. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.4 Effects of humans on ecosystems

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35. Which process removes carbon dioxide from the air?

  1. Respiration
  2. Decomposition
  3. Combustion
  4. Photosynthesis

Answer: D) Photosynthesis

Explanation: Plants absorb CO₂ in photosynthesis. O Level Biology · Topic 19 Relationships of Organisms with One Another and with the Environment · 19.2 Nutrient cycles

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