Edexcel International A Level Biology

Topic Questions

Plant Hormones

16 marks

Exposure to light controls the germination of seeds and the direction of growth of plants.

In an investigation the seeds of plantains (a type of banana) were exposed to light.

The seeds were first exposed to red light and then to far-red light.

The percentage of seeds that germinated when exposed to different periods of red and far-red light was recorded.

The results are shown in the table.

Exposure to red light / min Percentage germination (%)
Exposure to far-red light / seconds
1 5 10 15 30 60 960
32 100 20 14 6 4 6 10
16 92 30 40 28 30 33 20
8 100 62 50 57 44 47 56
4 100 67 60 57 40 37 92

Comment on the effect of red and far-red light on the germination of these seeds and the processes that occur in their cells.

Use the information in the table to support your answer.

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2
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6 marks

The drawing shows the results of some experiments investigating phototropisms.

The diagram shows a coleoptile of a seedling.

q5b-unit-5-january-2022-edexcel-ial-biology

Scientists concluded that these results suggest a plant growth substance is involved in regulating the phototropic response.

Discuss how the results of these experiments support the role of a plant growth substance in the phototropic response of plants.

Use the information for these experiments and your own knowledge to support your answer.

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