Lesson T2.1.2

T2.1.2 Photosynthesis and life on Earth Quiz: KS3 Biology, Unit 2

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson T2.1.2, Photosynthesis and life on Earth: 20 multiple choice questions for the KS3 Biology (National Curriculum), Unit 2: Material cycles and energy, written with Revision Ninja.

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The 20 questions

  1. Which organisms carry out most of the photosynthesis in the sea?

    • Algae and phytoplankton
    • Jellyfish and starfish that drift and crawl on the seabed
    • Crabs and sea urchins that graze on rocks at the shore
    • Sharks and whales that hunt for fish in deep water

  2. What do all food chains start with?

    • Decomposers such as fungi that break down dead leaves
    • Top predators such as foxes that hunt in the countryside
    • Primary consumers such as rabbits that eat grass in fields
    • Producers such as plants and algae

  3. Why are plants called producers?

    • They produce more offspring than other organisms in habitats
    • They produce carbon dioxide that other species can use to breathe
    • They produce soil from dead rock and minerals in the ground
    • They make their own organic food using light energy

  4. Which gas is kept at a steady level in the atmosphere largely through photosynthesis?

    • Oxygen
    • Nitrogen
    • Hydrogen
    • Argon

  5. A forest is cut down. What is the most likely effect on atmospheric carbon dioxide?

    • Carbon dioxide levels stay the same, as trees do not respire at all
    • Oxygen rises immediately because the cut trees stop respiring at once
    • Carbon dioxide may rise, as fewer plants use it in photosynthesis
    • Carbon dioxide levels fall, because cut trees absorb it when burned

  6. Coal, oil and gas are formed from remains of ancient organisms. Which energy origin is stored in them?

    • Heat from volcanic rocks cooling underground
    • Energy from dead bacteria that stopped photosynthesis
    • Energy captured by photosynthesis
    • Energy left by mineral deposits in sea water

  7. Why does the amount of energy decrease at each step of a food chain?

    • Energy turns into light that is given off to the next organism
    • Energy is converted into oxygen at each step of the chain
    • Energy is absorbed into the soil by each organism in turn
    • Energy is lost as heat through respiration and in waste

  8. Why do almost all energy sources for living things trace back to the Sun?

    • The Sun makes oxygen directly from water in the upper air
    • The Sun heats rocks, which then release glucose into the soil
    • Photosynthetic organisms capture sunlight and store it as food
    • Animals absorb sunlight through their skin to make their own food

  9. What are organic molecules made by photosynthesis used for by other organisms?

    • A source of oxygen
    • A type of gas
    • A form of sunlight
    • An energy store

  10. Why might a fish tank with water plants have more oxygen in the water during the day?

    • Plants release water vapour that dissolves into the water for fish
    • Plants photosynthesise and release oxygen into the water
    • Fish produce oxygen by digesting their food in the gut
    • Plants absorb carbon dioxide and release nitrogen into the tank

  11. What would happen to oxygen levels if photosynthesis stopped but respiration carried on?

    • Oxygen would rise steadily as animals breathe out
    • Oxygen would increase, because carbon dioxide turns into oxygen
    • Oxygen would stay the same, because respiration makes oxygen
    • Oxygen would gradually be used up and fall

  12. Which process returns carbon dioxide to the atmosphere?

    • Dispersal of seeds by wind over long distances
    • Photosynthesis in the leaves of green plants during daylight
    • Pollination by insects visiting the flowers of many plants
    • Respiration by plants and animals

  13. Why are food chains usually said to start with the Sun?

    • Sunlight heats the water to form clouds that animals drink from later
    • The Sun provides carbon dioxide directly to consumers in the food web
    • Sunlight kills the decomposers living in the soil before they can act
    • Producers capture light energy from the Sun in photosynthesis

  14. A student says photosynthesis makes glucose from oxygen. What is the correct statement?

    • Glucose is made from water only, and carbon dioxide is released
    • Glucose is made from nitrogen gas and oxygen, with no water used
    • Glucose is made from carbon dioxide and water, releasing oxygen
    • Glucose is made from light and soil minerals, and oxygen is absorbed

  15. Why do most animals depend on plants?

    • Plants are the only source of protein that animals can eat safely
    • Plants are the producers at the bottom of most food chains
    • Plants produce nearly all of the water that exists in the atmosphere
    • Plants are the only organisms that release heat energy into the air

  16. Why is deforestation linked to climate change?

    • Trees cool the air by producing nitrogen gas during the hot summer days
    • Fewer trees means less carbon dioxide is removed from the air
    • Fewer trees means more oxygen is used up by animals in the wild
    • Trees release most of the world's methane gas into the atmosphere each year

  17. Why are phytoplankton in the oceans important to life on Earth?

    • They are the main source of nitrogen in the air that we breathe every day
    • They break down nearly all of the plastic waste that enters the sea each year
    • They produce a large share of Earth's oxygen through photosynthesis
    • They make salt from sea water to provide food for the marine life there

  18. When an animal eats a plant, what happens to the energy captured by photosynthesis?

    • It becomes chemical energy in the animal's body
    • It is stored in the animal's skin as a coloured pigment
    • It is stored as oxygen in the animal's blood and red cells
    • It is released immediately as light energy from its skin

  19. In a typical food web, which group usually has the largest population?

    • Top predators
    • Producers
    • Carnivores that hunt large prey
    • Secondary consumers

  20. Which human activity reduces the amount of photosynthesis happening on Earth?

    • Clearing rainforest for farmland
    • Growing crops in greenhouses
    • Using solar panels to make electricity
    • Planting trees in urban parks

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