Plant hormones

Tropisms help plants survive.

What is geotropism?

Plan an investigation to find the effect of the direction of light on the growth of plant seedlings.

You may use the equipment shown in Figure 15 and any other laboratory equipment.

Plant responses are controlled by hormones.

Which hormone controls a plant’s response to the direction of light?

How does the hormone you named in Question 10.3 control the plant’s response to the direction of light?

Tick (✓) one box.

Explain how a plant’s response to light helps the plant survive.

Tropisms help plants survive.

What is geotropism?

Plan an investigation to find the effect of the direction of light on the growth of plant seedlings.

You may use the equipment shown in Figure 3 and any other laboratory equipment.

Plant responses are controlled by hormones.

Which hormone controls a plant’s response to the direction of light?

How does the hormone you named in Question 03.3 control the plant’s response to the direction of light?

Tick () one box.

Explain how a plant’s response to light helps the plant survive.

Plants grow in response to the direction of light and to gravity.

What name is given to a plant’s growth response?

Tick (✓) one box.

Which substance controls the response to light in plant shoots?

Tick (✓) one box.

A plant root grows downwards in response to gravity.

Which two substances can the root absorb in larger amounts when it grows downwards?

Tick (✓) two boxes.

Plan an investigation to show the effect of light from one direction on the growth of plant seedlings.

You should include:

• a control

• the measurements you would record

• any other observations you would make.

You may use the equipment shown in Figure 7 and any other laboratory apparatus.

Gardeners can grow plants from:

• seeds

• cuttings taken from adult plants.

A gardener investigated the growth of roots on cuttings from a geranium plant.

This is the method used.

1. Take 6 cuttings from the stems of the same plant.

2. Prepare 6 test tubes, each containing a different concentration of a solution of chemical Q.

3. Place 1 cutting in each test tube with the cut end of each stem in the solution.

4. Leave the test tubes at room temperature for 10 days.

Figure 8 shows the results.

Tube 1 contains no chemical Q.

Tube 1 is a control.

Why did the gardener include tube 1 in the investigation?

How many times more concentrated is chemical Q in tube 6 than in tube 2 ?

What was the best concentration of chemical Q for stimulating root growth?

Tick (✓) one box.

Give evidence from Figure 8 that a high concentration of chemical Q may be toxic to geranium plants.

The gardener has four types of geranium plant: A, B, C and D.

Plant A produces larger, more brightly-coloured flowers than any of the other plants.

The gardener wants to grow more plants of type A.

Explain why the gardener chooses to take cuttings from plant A instead of growing seeds from plant A.

A student investigated the effect of gravity on the growth of bean seedlings.

The student put ink marks on the root of each bean seedling.

Figure 5 shows a bean seedling with ink marks.

The student set up apparatus A and apparatus B.

Figure 6 shows both sets of apparatus.

The student left both sets of apparatus in a dark cupboard for 24 hours.

Give the reason why the student placed both sets of apparatus in the dark.

What are two reasons for surrounding the seedlings with damp blotting paper?

Tick () two boxes.

Apparatus B is a control.

Explain why apparatus B is needed.

Figure 7 shows one seedling from apparatus A at the start of the investigation and after 24 hours.

The drawing of the seedling after 24 hours is not complete.

Complete Figure 7 to show:

• the appearance of the root after 24 hours

• the ink marks on the root after 24 hours.

Figure 6 is repeated below.

The student left both sets of apparatus in a dark cupboard for 24 hours.

Describe how a root from apparatus B would look different from the root you drew in Question 04.4.

Auxin is a plant hormone.

Explain how auxin causes the results in apparatus A.

Farmers can use plant hormones to control the growth of plants.

Give two uses of auxin.

A farmer sprayed an apple tree with gibberellin.

Suggest two reasons why the farmer sprayed the apple tree with gibberellin.

A plant shoot responds to the stimulus of light shining on it from one side.

What name is given to the type of response shown by the plant shoot? Tick (✓) one box.

A student investigated the effect of one-sided light on the growth of plant seedlings. Figure 5 shows how the student set up the investigation.

Why did the student set up experiment 2 in this investigation?

The student wanted to make the investigation of the effect of one-sided light more valid. The student decided to set up a third experiment. How should the student set up the third experiment? Tick (✓) one box.

What is a suitable control variable for the investigation? Tick (✓) one box.

Give one stimulus a plant root responds to. Do not refer to light in your answer.

Scientists often repeat investigations several times. Give two reasons why.

Students investigated the response of plant shoots to one-sided light. Figure 13 shows how the students set up three experiments.

Suggest two control variables the students should have used in their investigation.

Describe how experiment B and experiment C acted as controls for the investigation.

Give two conclusions that the students could make from the ink marks on the shoot in experiment A.

Name the type of response shown by the seedling in experiment A.

Auxin is a plant hormone. Auxin is made in the shoot tip. Scientists investigated the role of auxin in the response of shoot tips to light. This is the method used.

1. Grow four seedlings in the dark for a few days.

2. Cut the tip off the shoot of each seedling.

3. Place each shoot tip on a small block of agar jelly.

4. Place the shoot tips and agar in different conditions as shown in Figure 14.

5. After 24 hours, measure the mass of auxin in the agar blocks.

The numbers under each block show the mass of auxin that diffused into the blocks from the shoot tips. The mass of auxin is given in arbitrary units.

A scientist made a hypothesis: ‘Light causes auxin to move from the side of the shoot nearest to the light to the side furthest from the light.’ Describe the evidence from Figure 14 which supports the hypothesis.

Another scientist made a different hypothesis: ‘Light causes the breakdown of auxin.’ Give the evidence from Figure 14 that shows that auxin is not broken down by light.

A student investigated the effect of light intensity on the growth of seedlings.

Figure 2 shows the equipment.

Which two improvements should the student make to the investigation?

Tick (✓) two boxes.

What is the dependent variable in the investigation?

Tick (✓) one box.

In each dish the seedlings compete with each other.

Give two factors the seedlings compete for.

Figure 3 shows a seedling growing towards a lamp.

What happened to the growth of the seedling on side P compared with the growth on side Q ?

Tick (✓) one box.

Plant responses are called tropisms.

Which tropism causes the seedling to grow towards light?

Tick (✓) one box.

Which hormone causes the seedling to grow towards the light?

Tick (✓) one box.

This question is about plant hormones.

Farmers can spray seeds with gibberellins to start germination. What are two other uses of gibberellins? Tick (✓) two boxes.

Students investigated the effect of light intensity on the height of seedlings.

Figure 3 shows the equipment.

Describe two improvements the students should make to their investigation.

Figure 4 shows a seedling growing towards a lamp.

Suggest how the students measured the length of the curved seedling in Figure 4.

Explain what happened to the growth of the seedling on side Q compared with the growth on side P.

Bananas are often stored separately from other fruits because bananas release a plant hormone. Why does storing bananas with other fruits cause the other fruits to ripen faster?

Phototropism is a growth response by part of a plant to light.

Name one other tropism.

Give the stimulus the plant responds to in the tropism you have named.

Plan an investigation to show the effect of light from one direction on the growth of plant seedlings.

Include details of any controls needed.

You may use some of the equipment shown in Figure 17 and any other laboratory apparatus.

Explain how phototropism in a plant shoot helps the plant to survive.

Phototropism is a growth response by part of a plant to light.

Name one other tropism.

Give the stimulus the plant responds to in the tropism you have named.

Plan an investigation to show the effect of light from one direction on the growth of plant seedlings.

Include details of any controls needed.

You may use some of the equipment shown in Figure 4 and any other laboratory apparatus.

Explain how phototropism in a plant shoot helps the plant to survive.

Table 2 gives the classification of four plant species.

Species 1 and 3 are the most closely related.

What information in Table 2 gives evidence for this?

Figure 6 shows the inheritance of flower colour in two species of plant.

• In pea plants and in snapdragon plants, flower colour is controlled by one pair of alleles.

• In Figure 6 the parental generation plants are homozygous for flower colour.

• In heterozygous pea plants, the allele for red flower colour is dominant.

• In heterozygous snapdragon plants, the alleles for flower colour are both expressed.

Use the following symbols for alleles in your answers to Questions 05.2 to 05.4:

Pea plants
Snapdragon plants

R = allele for red flowers C^R = allele for red flowers r = allele for white flowers
C^W = allele for white flowers

What is the genotype of the red-flowered pea plants in the F₁ generation?

What is the genotype of a white-flowered snapdragon plant?

A gardener crossed two pink-flowered snapdragon plants.

Draw a Punnett square diagram to show why only some of the next generation plants had pink flowers.

Identify the phenotypes of all the offspring plants.

What percentage of the offspring would you expect to have pink flowers?

Commercially, hundreds of pink-flowered snapdragon plants can be produced from one pink-flowered plant.

Figure 7 shows a tissue culture technique used for producing many plants from one plant.

Give a reason for each of the following steps shown in Figure 7.

Several groups of cells are scraped off the leaf:

Nutrients are added to the agar jelly:

Hormones are added to the agar jelly:

The plant cells are kept in sterile conditions:

The plant cells are kept at 20^oC:

Explain why the method shown in Figure 7 produces only pink-flowered plants.

Some students investigated phototropism in plant seedlings.

This is the method used.

1. Measure the lengths of the shoots of 20 seedlings.

2. Set up four groups of seedlings as follows:

• A – bottom of shoot covered in aluminium foil

• B – tip covered in aluminium foil

• C – tip removed

• D – no changes.

3. Put the seedlings in a cardboard box.

4. Use a lamp to shine a light into the box through a hole in one side.

5. After one day, re-measure the lengths of the shoots.

6. Make a drawing of the appearance of one seedling from each group.

Figure 10 shows the appearance of one seedling in each group at the start of the investigation.

Which two conditions should the students have kept constant for each group of seedlings?

Tick two boxes.

What is the purpose of the aluminium foil?

Tick one box.

Figure 11 shows the students’ results.

Suggest how the students measured the lengths of the curved shoots of seedlings A and D at the end of the investigation.

The students concluded that the tip of the shoot is needed for the plant to respond to light.

Give evidence for this conclusion from Figure 11.

A hormone stimulates growth in shoots.

Which distribution of the hormone would cause the results seen in shoot D ?

Tick one box.

Some students investigated geotropism in the roots of bean seedlings.

Figure 6 shows the apparatus used.

This is the method used.

1. Measure the length of the root of each of 10 bean seedlings.

2. Pin 5 seedlings to the cork mat in apparatus A.

3. Pin 5 seedlings to the cork mat in apparatus B.

4. Leave A and B in a dark cupboard for 2 days.

5. After the 2 days:

make a drawing to show the appearance of each seedling

measure the length of the root of each seedling.

Why did the students surround the seedlings with damp blotting paper?

Tick one box.

Apparatus B is a control.

Apparatus B rotates slowly.

How does apparatus B act as a control?

Table 4 shows the students’ results.

One student stated:

‘The mean length change for the seedlings in apparatus B is not valid.’

Suggest the reason for the student’s statement.

Suggest one improvement the students could make to obtain a more valid mean length change for the seedlings in apparatus B.

Figure 7 shows the students’ drawings of two seedlings at the end of the 2 days.

A plant hormone is made in the root tip.

The hormone diffuses from the tip into the tissues of the root.

Explain how the hormone causes the appearance of the seedlings in Figure 7 to be different.

You should refer to both seedlings in your answer.

In horticulture plant hormones are used for controlling plant growth.

Draw one line from each plant hormone to the correct use of that hormone.