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Exam questions · Biology · Transport in Plants

Transpiration and the Xylem

  • 7 exam questions
  • 19 marks
  • 8 quick checks
  1. 1 State [1 mark]

    Name the process by which water vapour is lost from the leaves of a plant.

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    Model answer

    Transpiration.

    Mark scheme

    • Transpiration — 1 mark
  2. 2 Name [3 marks]

    Figure 1 shows a plant. Name the parts labelled A, B and C.

    A plant with three parts marked A, B and C.
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    Model answer

    A is a root hair cell. B is the xylem. C is a stoma.

    Mark scheme

    • A: root hair cell — 1 mark
    • B: xylem — 1 mark
    • C: stoma — 1 mark
  3. 3 Explain [3 marks]

    Explain how a root hair cell is adapted to take up water and mineral ions.

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    Model answer

    It has a long, thin extension that gives a large surface area. Water enters by osmosis. Mineral ions are taken up by active transport, using energy released by the many mitochondria in the cell.

    Mark scheme

    • Large surface area from the extension — 1 mark
    • Water by osmosis — 1 mark
    • Ions by active transport using energy from mitochondria — 1 mark
  4. 4 Explain [3 marks]

    Explain how the structure of xylem is related to its function.

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    Model answer

    Xylem is made of dead cells with no cross-walls, which form hollow tubes so that water can flow through easily. The walls are strengthened with lignin, which stops the tubes collapsing. The tubes carry water and mineral ions from the roots to the leaves.

    Mark scheme

    • Hollow tubes, no cross-walls — 1 mark
    • Lignin strengthens the walls — 1 mark
    • Carries water and minerals up the plant — 1 mark
  5. 5 Describe [3 marks]

    Describe how water is lost from a leaf by transpiration.

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    Model answer

    Water evaporates from the surface of cells inside the leaf. The water vapour diffuses through the air spaces and out through the stomata. This pulls more water up the xylem to replace it.

    Mark scheme

    • Evaporation from the cells in the leaf — 1 mark
    • Diffusion out through the stomata — 1 mark
    • Pulls more water up the xylem — 1 mark
  6. 6 Explain [4 marks]

    Explain why the rate of transpiration is faster on a hot, dry, windy day.

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    Model answer

    The higher temperature gives the water molecules more energy, so they evaporate and diffuse faster. The dry air has a low concentration of water vapour, so the concentration gradient from the leaf to the air is steeper. The wind blows the water vapour away from the leaf, which keeps the gradient steep.

    Mark scheme

    • Higher temperature speeds evaporation and diffusion — 1 mark
    • Dry air gives a steeper gradient — 1 mark
    • Wind removes the water vapour — 1 mark
    • Gradient kept steep so a faster rate — 1 mark
  7. 7 Explain [2 marks]

    A plant in a very dry soil closes its stomata. Explain how this helps the plant to survive.

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    Model answer

    Closing the stomata reduces water loss by transpiration. The plant keeps more of the water that it has, so it does not wilt as quickly.

    Mark scheme

    • Reduces water loss — 1 mark
    • Prevents wilting / saves water — 1 mark

Quick check

  1. 1

    How do mineral ions enter root hair cells?

    1. ABy osmosis
    2. BBy diffusion only
    3. CBy active transport
    4. DBy transpiration
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    C: By active transport

    The ions are at a lower concentration in the soil, so they are taken up by active transport, using energy.

  2. 2

    Which tissue carries water up a plant?

    1. AXylem
    2. BPhloem
    3. CEpidermis
    4. DPalisade mesophyll
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    A: Xylem

    Xylem carries water and mineral ions from the roots to the leaves.

  3. 3

    What strengthens the walls of the xylem?

    1. ACellulose only
    2. BLignin
    3. CStarch
    4. DChlorophyll
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    B: Lignin

    Lignin strengthens the xylem walls so that they do not collapse.

  4. 4

    Which condition would decrease the rate of transpiration?

    1. AA higher temperature
    2. BA strong wind
    3. CBright light
    4. DHigh humidity
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    D: High humidity

    High humidity means less difference in water vapour concentration, so transpiration is slower.

  5. 5

    Where does most water vapour leave a leaf?

    1. AThrough the waxy cuticle
    2. BThrough the xylem
    3. CThrough the stomata
    4. DThrough the roots
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    C: Through the stomata

    Most water vapour diffuses out through the stomata.

  6. 6

    Why do root hair cells contain many mitochondria?

    1. ATo release energy for active transport
    2. BTo absorb light
    3. CTo store water
    4. DTo make lignin
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    A: To release energy for active transport

    Mitochondria release energy from respiration, which is needed for active transport of ions.

  7. 7

    What is the movement of water up the xylem called?

    1. AThe phloem stream
    2. BOsmosis
    3. CTranslocation
    4. DThe transpiration stream
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    D: The transpiration stream

    The movement of water from the roots to the leaves is the transpiration stream.

  8. 8

    Why does a bright light increase the rate of transpiration?

    1. AIt cools the leaf
    2. BIt opens the stomata wider
    3. CIt closes the stomata
    4. DIt makes the soil wetter
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    B: It opens the stomata wider

    In bright light the guard cells open the stomata wider, so more water vapour can escape.