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Exam questions · Biology · Plant Hormones

Use of Plant Hormones (Higher tier)

  • 6 exam questions
  • 19 marks
  • 9 quick checks
  1. 1 State [1 mark]

    State what is meant by a selective weed killer.

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    Model answer

    A weed killer that kills some types of plant, such as broad-leaved weeds, but does not harm others, such as the crop.

    Mark scheme

    • Kills some plants only — 1 mark
  2. 2 State [3 marks]

    State three uses of auxins in agriculture and horticulture.

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    Model answer

    As weed killers, as rooting powders, and for promoting growth in tissue culture.

    Mark scheme

    • Weed killers — 1 mark
    • Rooting powders — 1 mark
    • Tissue culture — 1 mark
  3. 3 Explain [3 marks]

    Explain how gibberellins can help a grower of flowering plants.

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    Model answer

    Gibberellins can end the dormancy of seeds, so that they all germinate together. They can also promote flowering, so that the plants flower when they are to be sold. They can increase the size of the fruit.

    Mark scheme

    • End seed dormancy, so seeds germinate together — 1 mark
    • Promote flowering at the right time — 1 mark
    • Increase fruit size — 1 mark
  4. 4 Explain [3 marks]

    Explain how ethene is used by companies that import bananas.

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    Model answer

    The bananas are picked green and firm, so they are not damaged on the long journey. When they arrive, they are exposed to ethene, which controls the ripening of fruit, so that all the fruit ripens at the same time and is ready for sale.

    Mark scheme

    • Picked green, so not damaged — 1 mark
    • Ethene makes the fruit ripen — 1 mark
    • All ripen at the same time, ready for sale — 1 mark
  5. 5 Calculate [3 marks]

    Spraying with gibberellin raised the mean mass of a bunch of grapes from 400 g to 460 g. Calculate the percentage increase in mean mass.

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    Model answer

    460 − 400 = 60. 60 ÷ 400 × 100 = 15%.

    Mark scheme

    • Increase of 60 g — 1 mark
    • Divided by 400 — 1 mark
    • 15% — 1 mark
  6. 6 Evaluate [6 marks]

    Evaluate the use of auxin weed killers on a large cereal farm.

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    Model answer

    An auxin weed killer is selective, so it kills broad-leaved weeds, but not the narrow-leaved cereal crop. This reduces the competition for light, water and minerals, so the yield is higher, and the farmer can produce more food and make more money. The chemical is cheap and quick to use. However, killing the weeds takes away food and habitats from insects and the birds that feed on them, so there is less biodiversity. If the chemical is washed into streams by rain, it may harm water plants and animals. The farmer could reduce the harm by keeping field margins and hedgerows, and by spraying only where it is needed. Overall the benefits for food production are large, but the effects on the environment should be limited.

    Mark scheme

    • Selective, so the crop is not harmed — 1 mark
    • Less competition, so higher yield — 1 mark
    • Cost or convenience — 1 mark
    • Less biodiversity — 1 mark
    • Runoff may harm streams — 1 mark
    • Reasoned conclusion, or ways of limiting harm — 1 mark

Quick check

  1. 1

    Which hormone is used in rooting powder?

    1. AEthene
    2. BGibberellin
    3. CAuxin
    4. DInsulin
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    C: Auxin

    Auxin makes cuttings grow roots.

  2. 2

    Which hormone is used to control the ripening of fruit in storage?

    1. AEthene
    2. BAuxin
    3. CGibberellin
    4. DThyroxine
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    A: Ethene

    Ethene.

  3. 3

    Which is a use of gibberellins?

    1. ATo kill weeds
    2. BTo make roots grow on cuttings
    3. CTo ripen fruit
    4. DTo increase the size of fruit
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    D: To increase the size of fruit

    To end seed dormancy, to promote flowering and to increase fruit size.

  4. 4

    Why is an auxin weed killer selective?

    1. AIt kills all plants
    2. BIt kills broad-leaved plants but not narrow-leaved crops
    3. CIt only works in the dark
    4. DIt only kills roots
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    B: It kills broad-leaved plants but not narrow-leaved crops

    It kills broad-leaved weeds, and does not harm narrow-leaved crops.

  5. 5

    What is added to the jelly in tissue culture to promote growth?

    1. AEthene
    2. BSalt
    3. CAuxin
    4. DAlcohol
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    C: Auxin

    Auxin promotes the growth of the plant tissue.

  6. 6

    How can a weed killer reduce biodiversity?

    1. AIt kills plants that provide food and habitats
    2. BIt makes more species
    3. CIt makes the soil richer
    4. DIt stops the rain
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    A: It kills plants that provide food and habitats

    It kills plants that provide food and habitats for insects and birds.

  7. 7

    A bunch of grapes increased in mass from 200 g to 250 g. What is the percentage increase?

    1. A20%
    2. B25%
    3. C50%
    4. D125%
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    B: 25%

    \(50 \div 200 \times 100 = 25\%\).

  8. 8

    Why does tissue culture need sterile conditions?

    1. ATo make the plants grow bigger
    2. BTo keep the jelly cold
    3. CTo add colour
    4. DTo prevent bacteria and fungi growing
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    D: To prevent bacteria and fungi growing

    To prevent the growth of bacteria and fungi, which would compete with the plant tissue.

  9. 9

    A farmer sprays a field with an auxin weed killer and finds that fewer butterflies visit the field. Which explanation is most likely?

    1. AButterflies like the chemical
    2. BThe weeds that provided food were killed
    3. CThe crop grew taller
    4. DThe butterflies ate the crop
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    B: The weeds that provided food were killed

    The weed killer killed broad-leaved wild plants, which provided food for the butterflies and their caterpillars.