Lesson 3.3.2.1

3.3.2.1 Gas exchange surfaces and their adaptations Quiz: AQA Biology, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.3.2.1, Gas exchange surfaces and their adaptations: 20 multiple choice questions for the AQA Biology (7402), Unit 3: Organisms exchange substances with their environment, written with Revision Ninja.

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The 20 questions

  1. Why can a single-celled organism exchange gases across its body surface without a specialised organ?

    • It has a circulatory system of arteries and veins that carries oxygen to every part of the body.
    • Its large size gives a small surface area to volume ratio, so it needs no transport system at all.
    • It has a thick cell wall of cellulose that actively pumps oxygen into the cytoplasm using ATP.
    • Its small size gives a large surface area to volume ratio and a short diffusion distance to every cell.

  2. In an insect, what is the role of the spiracles?

    • They are thin air sacs in the lungs where oxygen binds to haemoglobin.
    • They are gill filaments that exchange gases with water flowing across the body surface.
    • They are branched tubes that carry oxygenated blood to the muscles in the thorax.
    • They are openings on the body surface through which air enters the tracheal system.

  3. Which feature of fish gills increases the surface area available for gas exchange?

    • Branched tracheae that open to the air through many small spiracles.
    • A single thick gill membrane that surrounds the whole body of the fish.
    • Many gill filaments, each carrying numerous gill lamellae.
    • Sheets of cellulose cell walls that hold the gill filaments in place.

  4. What is the counter-current principle in fish gills?

    • Water flows in a circle around the body so that oxygen is recycled back into the mouth.
    • Blood flows through the gill filaments only once, and water flows past only at the surface.
    • Blood flows in the opposite direction to water over the gill lamellae, maintaining a diffusion gradient along their length.
    • Blood and water flow in the same direction, so the concentration gradient is removed along the gills.

  5. Which structures in a leaf are adaptations for gas exchange?

    • Mesophyll cells with air spaces and stomata that open to allow gas exchange.
    • Xylem vessels that transport water and dissolved minerals up from the roots.
    • Epidermis cells with thick cuticles that prevent any gas from entering or leaving.
    • Phloem sieve tubes that carry sugars to the roots and storage organs in the plant.

  6. Why is there a conflict between efficient gas exchange and water loss in terrestrial insects and xerophytic plants?

    • Large, moist gas exchange surfaces lose water, so these organisms must limit water loss while still exchanging gases.
    • Gas exchange depends on removing all water from the surface, which increases water loss by osmosis.
    • Gas exchange surfaces are always dry, so water can only be lost through the roots.
    • Water loss is needed to cool the gas exchange surface, so it must be encouraged in all cases.

  7. Which adaptation of a xerophytic plant reduces water loss while still allowing gas exchange?

    • Large, open stomata on the upper surface, which allow rapid water loss in dry air.
    • A thin cuticle and a flat, wide leaf, which increase the rate of diffusion of water vapour.
    • Stomata sunk in pits, with hairs on the epidermis, reducing air movement across the surface.
    • Stomata that stay open all day in dry conditions, which maximise photosynthesis at all times.

  8. Which of these statements about exchange surfaces is correct?

    • Exchange surfaces are thin, have a large surface area and maintain a steep concentration gradient.
    • Exchange surfaces are thick, have a small surface area and rely on a shallow concentration gradient.
    • Exchange surfaces are found only in plants, where they allow the uptake of water by osmosis.
    • Exchange surfaces are impermeable, so only active transport can take place across them.

  9. A student measures the rate of gas exchange in two fish of the same mass. Fish A has twice the number of gill filaments of fish B. What is the most likely result?

    • Fish A has a lower rate of gas exchange, because more filaments reduce the concentration gradient.
    • Fish A has a higher rate of gas exchange, because it has a greater surface area for exchange.
    • Fish B has a higher rate, because fewer filaments reduce the distance over which diffusion must occur.
    • Both fish have the same rate, because gill filaments do not affect the surface area for exchange.

  10. Why do insects with tracheae rely on diffusion of gases through tracheoles rather than a blood-based transport system?

    • The tracheoles reach close to the tissues, so the diffusion distance to the cells is very short.
    • Tracheoles are filled with haemoglobin that carries oxygen in the blood to every cell.
    • Tracheoles are made of cellulose, which allows gases to pass through them by osmosis.
    • Tracheoles are connected to the heart, which pumps gases around the insect body.

  11. Why do the mesophyll cells in a leaf have a large surface area for gas exchange?

    • Mesophyll cells are arranged in a single layer that sits beneath the waxy cuticle only.
    • Mesophyll cells are tightly packed with no air spaces, so their outer surface is minimised.
    • Mesophyll cells are loosely packed with air spaces between them, exposing much of their surface to air.
    • Mesophyll cells are covered in a thick waxy cuticle, which increases their surface area.

  12. A researcher studying a single-celled organism finds that its gas exchange rate is higher when it is smaller. Which explanation is best supported?

    • A smaller organism has a higher surface area to volume ratio, which increases the rate of exchange per unit volume.
    • A smaller organism has more mitochondria per cell, which removes the need for exchange with the environment.
    • A smaller organism has a lower surface area to volume ratio, which reduces the rate of exchange per unit volume.
    • A smaller organism has no cell membrane, so its gas exchange rate is controlled by its cell wall.

  13. Which statement describes the tracheal system of an insect?

    • Blood enters through spiracles and passes along arteries to capillaries near the tissues.
    • Air enters through spiracles and passes along tracheae to tracheoles that reach the tissues.
    • Water enters through gill filaments and passes along tracheae to the lamellae near the tissues.
    • Air enters through the stomata of the leaf and passes along xylem vessels to the roots.

  14. A plant has many stomata on the lower surface of its leaves. Which statement describes an advantage of this arrangement for a terrestrial plant?

    • It prevents any gas exchange because the lower surface is shaded from the air.
    • It increases water loss because the stomata are exposed to the sun and wind on the lower surface.
    • It increases the rate of photosynthesis because the lower surface receives more direct sunlight.
    • It reduces water loss in hot, sunny conditions because the stomata are shaded from direct sun on the upper surface.

  15. Which feature is most important for the efficient exchange of gases across the lamellae of a fish gill?

    • A small number of thick lamellae with few blood vessels that reduce the rate of diffusion.
    • A large number of thin lamellae with a rich blood supply that maintains a steep gradient.
    • A continuous sheet of cellulose that separates the blood from the water completely.
    • A single large lamella with a thick cuticle that prevents water from reaching the blood.

  16. A student compares the gas exchange surface of an insect with that of a fish. Which statement is correct?

    • Both organisms use the same type of gill filament, which is supported by cellulose in the body wall.
    • The insect extracts dissolved oxygen from water, whereas the fish delivers air directly to tissues.
    • The insect delivers air directly to tissues, whereas the fish extracts dissolved oxygen from water at the gills.
    • Both organisms use spiracles to take in air, which is then delivered to the tissues by blood.

  17. Why is the structure of the gill lamellae well suited to gas exchange?

    • They contain xylem vessels that transport oxygen from the gills to all tissues in the body.
    • They are thin, with a large surface area and close contact with blood vessels, giving short diffusion distances.
    • They are covered in a waxy cuticle that blocks the passage of oxygen and carbon dioxide.
    • They are thick, with a small surface area and no contact with blood vessels, so diffusion is slow.

  18. A leaf is exposed to dry, windy conditions and its stomata close. Which effect is most likely?

    • Both carbon dioxide uptake and water loss are unaffected, because stomata do not control gas exchange.
    • Oxygen is absorbed through the cuticle at a faster rate, so photosynthesis is maintained.
    • Carbon dioxide uptake increases, and water loss through the stomata is also increased.
    • Carbon dioxide uptake for photosynthesis decreases, but water loss through the stomata is also reduced.

  19. Why does a ventilation mechanism that keeps water flowing over fish gills matter for gas exchange?

    • It removes the need for a blood supply to the lamellae, because water carries oxygen directly to the tissues.
    • It maintains a supply of oxygen-rich water over the gills, so the concentration gradient stays high.
    • It warms the water so that oxygen diffuses faster into the lamellae at all times of the day.
    • It prevents carbon dioxide from leaving the blood, so the blood remains at a stable acidity.

  20. Which feature of a dicotyledonous leaf most directly increases the rate of carbon dioxide diffusion into the mesophyll?

    • Densely packed palisade cells with no air spaces, which hold carbon dioxide in the leaf.
    • A thick waxy cuticle that concentrates carbon dioxide on the upper surface of the leaf.
    • Large xylem vessels that carry carbon dioxide from the roots up to the leaf for uptake.
    • Air spaces within the spongy mesophyll connected to open stomata.

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