Commercial Uses of Plant Hormones (Higher tier)

1. 1 State [1 mark]

   State what is meant by a selective weedkiller.

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   Model answer

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

   Mark scheme

   • Kills some plants but not others — 1 mark
2. 2 State [2 marks]

   State two uses of gibberellins in agriculture.

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   Model answer

   Any two from: ending seed dormancy so they germinate; bringing on flower formation; increasing the size of fruit; making seedless fruit.

   Mark scheme

   • First — 1 mark
   • Second — 1 mark
3. 3 Explain [3 marks]

   Explain how a rooting powder helps a gardener to grow new plants from cuttings.

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   Model answer

   The powder contains a synthetic auxin. When the cut stem is dipped into it, the auxin makes the stem grow roots. More of the cuttings root, and they do so more quickly, so many identical plants can be grown from one parent plant.

   Mark scheme

   • Contains auxin — 1 mark
   • Auxin makes roots grow — 1 mark
   • More cuttings root, giving identical plants — 1 mark
4. 4 Explain [3 marks]

   Explain why bananas are picked while they are still green, and treated with ethene before they are sold.

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   Model answer

   Green bananas are firm, so they are not damaged or spoiled while they are transported. Ethene makes the fruit ripen, so that all of the fruit ripens at the same time, just before it is sold.

   Mark scheme

   • Green fruit is firm and survives transport — 1 mark
   • Ethene makes fruit ripen — 1 mark
   • Ripen together, when needed for sale — 1 mark
5. 5 Calculate [3 marks]

   A grower sprayed 150 grape vines with gibberellin, and 120 of them produced seedless grapes. Of 150 vines that were not sprayed, 15 produced seedless grapes. Calculate the percentage of each group that produced seedless grapes.

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   Model answer

   Sprayed: 120 ÷ 150 × 100 = 80%. Not sprayed: 15 ÷ 150 × 100 = 10%.

   Mark scheme

   • 80% — 1 mark
   • 10% — 1 mark
   • Correct method for both — 1 mark
6. 6 Evaluate [6 marks]

   Evaluate the use of plant hormones by farmers and growers.

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   Model answer

   Plant hormones make crops more uniform and predictable. Auxin weedkillers are selective, so they kill weeds without harming the crop, which increases the yield, and rooting powder lets growers produce many plants quickly. Gibberellins give seedless fruit, and bring on germination and flowering when needed, and ethene lets fruit be picked green, transported safely and ripened just before sale, so there is less waste. These benefits can increase profits, and the cost of the chemicals is small. However, weedkillers can run into streams and harm wildlife, which reduces biodiversity. Residues on food may be a concern, and some people feel that artificially ripened fruit is less tasty. Overall the benefits are large, if the chemicals are used carefully and within the limits that are set by law.

   Mark scheme

   • Selective weedkillers raise yield — 1 mark
   • Rooting powder and gibberellins give control — 1 mark
   • Ethene reduces waste in transport — 1 mark
   • Low cost compared with benefits — 1 mark
   • Environmental harm from weedkillers — 1 mark
   • A reasoned judgement — 1 mark

Quick check

1. 1

   Which hormone is used in rooting powder?

   1. AEthene
   2. BAuxin
   3. CInsulin
   4. DAdrenalin
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   B: Auxin

   Auxin makes cuttings grow roots.

2. 2

   Why are auxin weedkillers selective?

   1. AThey kill all plants
   2. BThey only kill grass
   3. CThey only work at night
   4. DThey kill broad-leaved weeds but not narrow-leaved crops
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   D: They kill broad-leaved weeds but not narrow-leaved crops

   Broad-leaved weeds take them up and die, but narrow-leaved crops are not harmed.

3. 3

   Which hormone makes fruit ripen?

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

   Ethene is a gas that makes fruit ripen.

4. 4

   What is the use of gibberellins on seeds?

   1. ATo stop germination
   2. BTo kill them
   3. CTo end dormancy
   4. DTo make them bigger
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   C: To end dormancy

   They end dormancy, so the seeds germinate.

5. 5

   Why are bananas picked green?

   1. AThey are sweeter
   2. BThey are less easily damaged
   3. CThey contain more vitamins
   4. DThey grow faster
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   B: They are less easily damaged

   They are firm, so they are not damaged during transport.

6. 6

   Which hormone can make grapes seedless and larger?

   1. AEthene
   2. BAuxin
   3. CInsulin
   4. DGibberellin
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   D: Gibberellin

   Gibberellin.

7. 7

   40 of 50 cuttings rooted with powder. What percentage is this?

   1. A80%
   2. B40%
   3. C50%
   4. D20%
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   A: 80%

   \(40 \div 50 \times 100 = 80\%\).

8. 8

   Which is an environmental risk of weedkillers?

   1. AThey increase biodiversity
   2. BThey make the soil richer
   3. CThey can run into streams and harm wildlife
   4. DThey stop photosynthesis in crops
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   C: They can run into streams and harm wildlife

   They can wash into streams and harm wildlife.

9. 9

   A store is full of ripe fruit that makes ethene. How could the ripening of other fruit there be delayed?

   1. AAdd more ethene
   2. BRemove the ethene and keep it cool
   3. CKeep it warm
   4. DAdd auxin
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   B: Remove the ethene and keep it cool

   Remove the ethene and keep the fruit cool, so it ripens more slowly.