Lesson 3.3.4.2.1

3.3.4.2.1 Mass transport in plant tissues Quiz: AQA Biology, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

In partnership with Revision Ninja

Lesson 3.3.4.2.1, Mass transport in plant tissues: 20 multiple choice questions for the AQA Biology (7402), Unit 3: Organisms exchange substances with their environment, written with Revision Ninja.

Host it live on the board and students join with a game code on their own devices, or revise alone with Free Play. The answers are revealed in the game.

Host this setFree Play

The 20 questions

  1. What is the function of xylem in a plant?

    • It transports water and mineral ions upwards from the roots through the stem and leaves.
    • It transports oxygen from the leaves to the roots for aerobic respiration.
    • It transports organic sugars from the leaves to the roots and storage organs.
    • It transports carbon dioxide from the roots to the leaves for photosynthesis.

  2. What is the function of phloem in a plant?

    • It transports oxygen from the stomata to the roots for respiration in the tissues.
    • It transports water and mineral ions upwards from the roots to the leaves.
    • It transports organic substances such as sucrose from the leaves to other parts of the plant.
    • It transports carbon dioxide from the mesophyll to the atmosphere through the stomata.

  3. What is the cohesion-tension theory of water transport in xylem?

    • Water is pushed up the xylem by root pressure, and cohesion stops the column of water from breaking.
    • Water evaporates from leaves, creating tension that pulls a continuous column of water up the xylem, held together by cohesion.
    • Water moves up the xylem by osmosis alone, because the xylem is filled with a concentrated sugar solution.
    • Water is pumped up the xylem by active transport in the root cells, which uses ATP to raise it.

  4. Why is the cohesion of water molecules important in the cohesion-tension theory?

    • Cohesion causes the xylem vessels to expand so that more water can enter from the roots.
    • Cohesion keeps the column of water intact so that tension at the top pulls the whole column upwards.
    • Cohesion allows water to be pumped out of the leaves by the phloem against the gradient.
    • Cohesion makes water molecules repel each other so that they move down the xylem against tension.

  5. Which feature of xylem vessels allows them to withstand the tension created in the cohesion-tension theory?

    • Their walls are strengthened by lignin, which resists collapse under negative pressure.
    • Their walls contain sieve plates that allow water to pass through the vessels by mass flow.
    • Their walls are thin and flexible and allow the vessel to stretch when water is pushed upwards.
    • Their walls are made of living cells that contract to pump water upwards continuously.

  6. What is the mass flow hypothesis for translocation in phloem?

    • Sugars diffuse slowly through sieve plates, with no pressure difference between source and sink.
    • Sugars are loaded into sieve tubes at the source, and water enters by osmosis, creating pressure that moves the sap to sinks.
    • Sugars are moved by the transpiration pull in the xylem and then exchanged with the phloem.
    • Sugars are carried upwards by xylem vessels, which pump the sap by active transport.

  7. What is a tracer experiment used to investigate in plant transport?

    • Measuring the rate at which water is absorbed by the roots through the root hair cells.
    • Measuring the mass of a plant to determine the amount of photosynthesis taking place.
    • Tracing the movement of labelled substances, such as radioactive isotopes, through the xylem or phloem.
    • Measuring the number of stomata on the surface of a leaf to estimate transpiration rate.

  8. What does a ringing experiment show about the phloem?

    • When the phloem is removed in a ring, water accumulates below the ring, showing that the phloem carries water.
    • When the xylem is removed in a ring, sugars accumulate above the ring, showing that the xylem carries them.
    • When the phloem is removed in a ring, the plant absorbs more water through the roots at a faster rate.
    • When the phloem is removed in a ring, sugars accumulate above the ring, showing that the phloem carries them downwards.

  9. A potometer is used to investigate the rate of transpiration. Which factor would increase the rate of water uptake measured?

    • A lower temperature that reduces the rate of evaporation from the leaf surface.
    • A higher air movement that increases the rate of water loss from the leaves.
    • A higher humidity that reduces water loss from the leaves through the stomata.
    • A lower light intensity that closes the stomata and reduces the rate of water loss.

  10. Why is the mass flow hypothesis supported by experiments using tracers and ringing?

    • Tracers show that water moves through the phloem, and ringing shows that sugars are carried by the xylem.
    • Tracers show that the phloem is not involved in sugar movement, and ringing shows no effect on the plant.
    • Tracers show that sugars move through the xylem, and ringing shows that blocking the xylem stops water movement.
    • Tracers show that sugars move through the phloem, and ringing shows that blocking the phloem stops downward sugar movement.

  11. A student claims that the mass flow hypothesis proves that phloem sap moves at the same speed in all sieve tubes. Evaluate this claim.

    • The claim is supported, because the hypothesis states that sap moves only by diffusion at a constant rate.
    • The claim is supported, because mass flow always produces identical speeds in every sieve tube of a plant.
    • The claim is partly supported, because the xylem is used to measure the speed of sap in each sieve tube.
    • The claim is not supported, because the hypothesis describes a pressure-driven movement and does not state equal speeds.

  12. Which tissue is the main site of sugar loading into the phloem at the source?

    • Guard cells, which release sucrose into the phloem by simple diffusion.
    • Xylem vessels, which pump sucrose into the sieve tubes using ATP.
    • Root hair cells, which absorb sucrose from soil water by osmosis.
    • Companion cells, which actively load sucrose into the sieve tubes.

  13. Which feature of phloem sieve tubes is adapted to mass flow?

    • Dead cells with no cytoplasm, which resist the flow of sap through the tube.
    • Narrow tubes filled with air, which prevent sugars from diffusing back to the source.
    • Thick lignified walls, which resist the pressure of sap moving through the vessel.
    • Sieve plates between the cells, which allow sap to flow through with little resistance.

  14. Sucrose concentration is 0.5 mol/dm^3 in a source leaf and 0.1 mol/dm^3 in a root sink. Which direction does sap move by mass flow?

    • From the root towards the leaf, because sugars always move up the xylem to the photosynthetic cells.
    • Sap does not move, because both values are positive and sugars do not flow in either direction.
    • From the root, the sink, towards the leaf, against the concentration gradient.
    • From the leaf, the source, towards the root, the sink.

  15. A potometer capillary tube has a cross-sectional area of 0.5 mm^2, and an air bubble moves 10 mm along it in one hour. What volume of water has been taken up?

    • 50 mm^3
    • 20 mm^3
    • 5 mm^3
    • 0.05 mm^3

  16. What is transpiration?

    • The movement of sugars from the leaves to the roots through the phloem sieve tubes.
    • The absorption of water by root hair cells through osmosis across the membrane.
    • The conversion of water into oxygen by the light-dependent reactions of photosynthesis.
    • The loss of water vapour from the leaves through the stomata, driven by evaporation.

  17. A student claims that ringing proves that phloem transports water. Evaluate this claim.

    • The claim is wrong, because ringing shows sugar accumulating above the ring rather than water transport in the phloem.
    • The claim is right, because removing a ring of phloem stops water from rising in the xylem.
    • The claim is right, because phloem is the only tissue in the plant in which water is found.
    • The claim is partly right, because ringing shows both water and sugar accumulating below the ring.

  18. Why are radioactive tracers such as carbon-14 used in plant transport experiments?

    • Labelled molecules are absorbed faster than unlabelled ones, so they show the path quickly.
    • Labelled molecules are made of cellulose, so they stay in the xylem and cannot be traced.
    • Labelled molecules can be detected as they move, showing the path they take through the plant.
    • Unlabelled sugars cannot move through the plant, so tracers are needed to make them move.

  19. A plant closes its stomata so that transpiration stops. What is the predicted effect on the xylem water column?

    • The phloem takes over water transport, so the rate of water uptake is unchanged by the closure.
    • The tension falls, so the column is pulled up more slowly and the rate of water uptake drops.
    • The water column breaks at once, because cohesion between water molecules is unaffected by transpiration.
    • The tension increases, so the column rises faster and the rate of water uptake increases.

  20. A plant is grown in very high humidity so that it transpires less. Which statement follows?

    • The phloem carries more water to compensate for the reduced transpiration of the leaves.
    • More water is pulled up the xylem, because high humidity increases the tension in the column.
    • Less water is pulled up the xylem, so the rate of water uptake from the roots falls.
    • Water uptake is unchanged, because water moves up the xylem only by root pressure.

All AQA Biology quizzes