Plant Hormones (Edexcel GCSE Biology)

Gravitropism is a plant growth response that causes roots to grow down towards the pull of gravity. Figure 1 shows two images of the same plant root, before and after it was left in the dark for three days. 

Figure 1

Explain how this change in root growth has occurred. 

(3)

(ii)

Suggest the advantages of this response for the plant. 

(2)

The same germinating seed produced a shoot. Complete the "after" diagram below showing how the shoot would respond to the stimulus of gravity if placed in the same position. 

Explain your answer. 

Plants can respond to the stimulus of light and produce a growth response called phototropism. 

Explain how phototropism is controlled in plant shoots.

Two students wanted to investigate the mechanism of phototropism in plants. They set up their investigation as shown in Figure 1. 

Figure 1

State why it was necessary for the students to set up a control experiment.

(1)

(ii)

Explain the results of experiments 2-4 shown in Figure 1.

(4)

Explain why this growth response is beneficial to plants. 

Higher Tier Only

Ethene is a plant hormone that stimulates the ripening of fruit. Figure 1 shows the effect of ethene concentration on the ripening of bananas after three days.

Figure 1

Describe the effect of ethene on the ripening of bananas. 

(1)

(ii)

A supermarket purchases 1420 bananas.

Calculate how many of these bananas are likely to be ripe upon arrival, before treating with ethene.

(2) 

Identify and explain which concentration of ethene would be most cost-effective for a supermarket to use when ripening bananas. 

Higher Tier Only

A gardener wanted to investigate the effect of a plant hormone weed killer on the growth of nettles in his field. He set up a trial to see which concentration of hormone would kill the most nettles. He counted the number of nettle plants in six 1 m² areas of the field. He made five different concentrations of hormone weed killer solution and kept one area as a control with no hormone. He applied the solutions to the six different areas. After two weeks he counted the number of nettles in each area.

The results are shown in Figure 1.

Figure 1

Give one variable the gardener should control when completing this trial. 

(1)

(ii)

Calculate the percentage decrease in the number of nettles when the concentration of weed killer hormone solution was 60 %. 

(2)

State and explain the conclusion that the gardener can make, based on his trial. 

In this experiment, the gardener observed that the nettles died but the grass surrounding them did not. 

Explain how plant hormones can act as selective weed killers.

Higher Tier Only

A scientist investigated the role of gibberellins in seed germination. They placed 20 cress seeds on agar jelly containing gibberellins and counted the number of seeds that had germinated after 5 days. Figure 1 shows the results.

Figure 1

Explain how the scientist could use a control to improve this investigation.

Suggest how the scientist could vary their experiment in order to investigate how the concentration of gibberellin solution affects the number of seeds germinated. 

State two other commercial uses of gibberellins, not including their role in germination.

Figure 1 shows an investigation into the growth of plant shoots.

Experiment 1:

The tip of a shoot was removed from the plant.

There was no growth in the shoot after 3 days.

Experiment 2:

The tip of a shoot was cut off and then placed back onto the shoot.

The shoot had grown 6 mm after 3 days.

Figure 1

Give one variable that must have been controlled for the plant shoot to grow vertically, as shown in experiment 2.

(1)

(ii)

State one conclusion that could be made based on these two experiments.

(1)

(iii)

Which plant hormone causes growth in the plant shoot?

(1)

Explain one way that this investigation could be improved.

(2)

Higher Tier Only

Commercial growers can use plant hormones to artificially ripen fruit and produce seedless fruit.

(i)

What is the name of the plant hormone used in fruit ripening?

(1)

Which plant hormone can commercial growers spray fruit with to produce seedless fruit?

(1)

Higher Tier Only

The effect of applying weed killer containing plant hormones to fields of wheat was investigated.

In field A, the weed killer was applied each year for five years.

In field B, no weed killer was applied for five years.

Each field was 1000 m² and all other conditions remained the same.

The results are shown in Figure 1.

Figure 1

Comment on the effect of using weed killer containing plant hormones in this investigation.

Figure 2 shows a pot plant before it fell over and the same pot plant two weeks after it fell over.

Figure 2

Explain how hormones in the roots and shoots of plants caused this directional growth.

Explain the effect that auxins have on the cells in shoot tips.

Explain why hormonal effects on the cells in shoot tips is beneficial for the plant.

A young seedling, growing in a forest was knocked over by animal activity.

Figure 1 shows how the plant grew after being knocked over.

Figure 1

Identify the stimulus and the response in Figure 1 (including its direction).

Describe the effect phototropism has on the growth of plant roots.

In the late 1800s, Charles Darwin performed an experiment where he grew maize seedlings in the dark, in a horizontal orientation.
Half of the seedlings had the root tip removed (A), the other half of the seedlings were left intact (B).
The results of his investigation are shown in Figure 2.

Figure 2

Explain what these results demonstrate for each experiment.

Figure 3 represents a plant shoot growing, it is illuminated from the side.

Figure 3

Draw an annotated diagram showing accumulation of auxins in response to light and how the shoot tip will grow.

Higher Tier Only

In UK supermarkets, bananas are usually in perfect condition even though they have been imported via ships from countries with tropical climates.

Describe how plant hormones can be used to ensure bananas arrive in perfect condition.

Higher Tier Only

Read the following two statements:

.

Evaluate the use of artificial auxins.

Which method of transport most likely explains how auxins travel to parts of the plant root or shoot?

There are a number of groups of plant hormones that control many aspects of plant growth. One such plant hormone is abscisic acid. When plant roots sense a water shortage in the soil, the hormone abscisic acid is released and binds to receptor proteins in guard cells, activating it. 

Suggest how abscisic acid may help plants in drought conditions. 

A student wanted to investigate the mechanism of phototropism in plants. They set up their investigation as shown in Figure 4.

Figure 4

In experiment A - the shoot tip was left untreated (as a control).

In experiment B - 2mm was removed from the growing end of the shoot tip.

In experiment C - The shoot tips were covered with caps of aluminium foil.

The shoot tips were initially measured and left for 48 hours next to a unidirectional light source.

Predict what differences in growth occurred in each experiment after 48 hours.

Explain why the plant shoots grow differently in experiments B and C.