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Exam questions · Biology · The Endocrine System

Plant Hormones

  • 7 exam questions
  • 21 marks
  • 8 quick checks
  1. 1 State [2 marks]

    State two effects of plant hormones on the growth of a plant.

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    Model answer

    Any two of: shoots grow towards light, roots grow down, seeds germinate, fruit ripens, stems grow, leaves are shed.

    Mark scheme

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

    Figure 1 shows a shoot and a seedling. Name the parts shown at A, B and C.

    A shoot bending towards light and a seedling on its side with three parts marked A, B and C.
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    Model answer

    A is the shoot tip. B is auxin. C is the root.

    Mark scheme

    • A: shoot tip — 1 mark
    • B: auxin — 1 mark
    • C: root — 1 mark
  3. 3 Explain [4 marks]

    Explain how auxin causes a shoot to grow towards the light.

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    Model answer

    Light comes from one side of the shoot. Auxin moves to the shaded side of the shoot. The auxin makes the cells on the shaded side elongate more than the cells on the lit side. The shoot therefore bends towards the light.

    Mark scheme

    • Light from one side — 1 mark
    • Auxin moves to the shaded side — 1 mark
    • Cells on the shaded side elongate more — 1 mark
    • Shoot bends towards the light — 1 mark
  4. 4 Explain [3 marks]

    A seedling is laid on its side. Explain why its root bends downwards.

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    Model answer

    Auxin collects on the lower side of the root. In the root, a high concentration of auxin stops the cells elongating. The cells on the upper side elongate more, so the root bends downwards.

    Mark scheme

    • Auxin collects on the lower side — 1 mark
    • Auxin stops elongation in roots — 1 mark
    • Upper side grows faster so the root bends down — 1 mark
  5. 5 Describe [3 marks]

    Describe three ways in which people use plant hormones.

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    Model answer

    Any three of: selective weedkillers using synthetic auxin, rooting powder for cuttings, spraying flowers to make seedless fruit, ripening fruit with ethene, ending seed dormancy with gibberellins.

    Mark scheme

    • Any three uses — 3 marks
  6. 6 Explain [3 marks]

    Explain why fruit is often picked unripe and then treated with ethene.

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    Model answer

    Unripe fruit is firmer, so it is less easily damaged during transport. The fruit can then be ripened when it reaches the shops. Ethene is the plant hormone that makes fruit ripen.

    Mark scheme

    • Unripe fruit less easily damaged — 1 mark
    • Ripened when needed — 1 mark
    • Ethene makes fruit ripen — 1 mark
  7. 7 Explain [3 marks]

    Explain how a selective weedkiller can kill weeds without killing the crop.

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    Model answer

    The weedkiller contains a synthetic auxin. Broad-leaved weeds take it in and grow too fast, so they die. The crop, such as wheat, has narrow leaves and is not affected in the same way.

    Mark scheme

    • Contains synthetic auxin — 1 mark
    • Weeds grow too fast and die — 1 mark
    • The crop is not affected — 1 mark

Quick check

  1. 1

    Which hormone makes shoot cells elongate?

    1. AEthene
    2. BAuxin
    3. CGibberellin
    4. DInsulin
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    B: Auxin

    Auxin makes the cells of shoots elongate.

  2. 2

    Which hormone is a gas that makes fruit ripen?

    1. AAuxin
    2. BGibberellin
    3. CThyroxine
    4. DEthene
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    D: Ethene

    Ethene makes fruit ripen.

  3. 3

    What is phototropism?

    1. AA growth response to light
    2. BA growth response to gravity
    3. CFruit ripening
    4. DSeed germination
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    A: A growth response to light

    Phototropism is a growth response to light.

  4. 4

    Where does auxin collect in a shoot with light from one side?

    1. AOn the lit side
    2. BAt the root
    3. COn the shaded side
    4. DIn the leaves
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    C: On the shaded side

    Auxin moves to the shaded side.

  5. 5

    What do gibberellins do?

    1. AMake fruit ripen
    2. BEnd the dormancy of seeds
    3. CMake leaves fall
    4. DClose the stomata
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    B: End the dormancy of seeds

    Gibberellins end seed dormancy so that seeds germinate.

  6. 6

    Which of these is a use of auxin?

    1. ARipening bananas
    2. BMaking plants flower
    3. CKilling bacteria
    4. DRooting powder for cuttings
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    D: Rooting powder for cuttings

    Rooting powder contains auxin to make cuttings grow roots.

  7. 7

    What is gravitropism?

    1. AA growth response to gravity
    2. BA growth response to light
    3. CA response to water
    4. DA response to touch
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    A: A growth response to gravity

    Gravitropism is a growth response to gravity.

  8. 8

    In which direction does a root grow in response to gravity?

    1. AUpwards
    2. BSideways
    3. CDownwards
    4. DTowards the light
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    C: Downwards

    Roots grow downwards, in the direction of gravity.