Exam questions · Biology
Plant Hormones
- 24 exam questions
- 73 marks
- 36 quick checks
Auxins, Phototropism and Gravitropism
Just this lesson-
1 State [1 mark]
State what is meant by gravitropism.
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Model answer
A growth response of a plant to gravity.
Mark scheme
- Growth response to gravity — 1 mark
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2 Name [2 marks]
Name the hormone that causes phototropism, and state where it is made in a shoot.
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Model answer
Auxin, made in the tip of the shoot.
Mark scheme
- Auxin — 1 mark
- Tip — 1 mark
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3 Explain [3 marks]
A seedling is lit from the left. Explain why the shoot bends towards the left.
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Model answer
Auxin moves to the shaded, right-hand side of the shoot. The cells on the shaded side elongate faster. The shoot bends towards the left, which is towards the light.
Mark scheme
- Auxin moves to the shaded side — 1 mark
- Cells on the shaded side elongate faster — 1 mark
- Shoot bends towards the light — 1 mark
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4 Explain [4 marks]
A seedling is placed on its side. Explain why the root grows downwards and the shoot grows upwards.
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Model answer
Auxin collects on the lower side of both. In the shoot, the extra auxin makes the lower side grow faster, so the shoot bends up. In the root, the extra auxin slows the growth on the lower side, so the upper side grows faster, so the root bends down.
Mark scheme
- Auxin collects on the lower side — 1 mark
- Lower side of the shoot grows faster — 1 mark
- Shoot bends up — 1 mark
- Lower side of the root grows slower, so it bends down — 1 mark
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5 Calculate [3 marks]
The mean cell length on the lit side of a shoot was 30 micrometres, and on the shaded side it was 42 micrometres. Calculate the percentage by which the cells on the shaded side were longer.
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Model answer
42 − 30 = 12. 12 ÷ 30 × 100 = 40%.
Mark scheme
- Difference of 12 — 1 mark
- Divided by 30 — 1 mark
- 40% — 1 mark
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6 Evaluate [6 marks]
Describe how the responses of a plant to light and to gravity help it to survive, and explain how they are caused.
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Model answer
A shoot shows positive phototropism, so it grows towards light. This puts its leaves in the best position to absorb light for photosynthesis, which makes the glucose that the plant needs. The shoot also shows negative gravitropism, so it grows upwards, away from the soil. A root shows positive gravitropism, so it grows downwards into the soil, where it can take up water and mineral ions and anchor the plant. All of these are caused by unequal distributions of auxin. In a shoot, auxin makes the cells on the shaded or lower side elongate faster. In a root, auxin on the lower side slows the growth, so the root bends downwards. Without these responses, the plant would not get enough light or water.
Mark scheme
- Shoot grows towards light for photosynthesis — 1 mark
- Shoot grows upwards, away from gravity — 1 mark
- Root grows down to take up water and minerals — 1 mark
- Root anchors the plant — 1 mark
- Unequal auxin distribution causes unequal growth — 1 mark
- Opposite effects of auxin on shoot and root — 1 mark
Quick check
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1
What is the response of a plant to the direction of light called?
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B: Phototropism
It is called phototropism.
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2
Where is auxin made?
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C: In the tips
In the tips of shoots and roots.
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3
In a shoot lit from one side, where does the auxin move to?
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A: The shaded side
It moves to the shaded side.
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4
What does auxin do to the cells on the shaded side of a shoot?
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D: Makes them elongate faster
It makes them elongate faster.
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5
What is the growth of a root in the direction of gravity called?
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B: Positive gravitropism
Positive gravitropism.
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6
What does extra auxin on the lower side of a root do?
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C: It slows the growth
It slows the growth there, so the root bends down.
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7
Why are shoots with their tips covered in foil unable to bend towards light?
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A: The tip cannot detect the light
The tip detects the light, so the shoot cannot respond if the tip is covered.
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8
Why is gravitropism useful in a root?
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D: It takes the root to water and anchors the plant
The root grows down to water and mineral ions and anchors the plant.
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9
The cells on the lit side of a shoot are 20 micrometres long, and those on the shaded side are 30 micrometres long. What is the percentage difference, based on the lit side?
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C: 50%
\((30 - 20) \div 20 \times 100 = 50\%\).
Investigating Plant Responses
Just this lesson-
1 State [1 mark]
State the independent variable in an investigation of the effect of light on the growth of seedlings.
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Model answer
The direction of the light.
Mark scheme
- Direction of the light — 1 mark
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2 Name [2 marks]
Name two control variables in this investigation.
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Model answer
Any two from: type of seeds, age of the seedlings, number of seeds, temperature, volume of water, distance from the lamp, time.
Mark scheme
- First — 1 mark
- Second — 1 mark
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3 Explain [2 marks]
In an investigation of gravitropism, the seedlings were kept in the dark. Explain why.
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Model answer
Light would also cause the shoots to grow towards it. In the dark, gravity is the only stimulus, so the result is valid.
Mark scheme
- Light would affect the growth — 1 mark
- Gravity is then the only stimulus — 1 mark
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4 Calculate [3 marks]
The lengths of four shoots were 30, 34, 31 and 33 mm. Calculate the mean length.
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Model answer
30 + 34 + 31 + 33 = 128. 128 ÷ 4 = 32 mm.
Mark scheme
- Sum of 128 — 1 mark
- Division by 4 — 1 mark
- 32 mm — 1 mark
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5 Explain [3 marks]
Explain why a clinostat is used in an investigation of gravitropism.
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Model answer
A clinostat turns the seedlings, so gravity acts equally on all sides. If the seedlings on the clinostat do not bend, but those that are not turned do, it shows that gravity causes the bending.
Mark scheme
- Turns the seedlings so gravity acts equally — 1 mark
- It is a control — 1 mark
- Shows that gravity causes the bending — 1 mark
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6 Evaluate [6 marks]
A student measured the length of shoots with a ruler to the nearest millimetre, and drew them. The mean angle of bending of seedlings in light from one side was 40 degrees, but the seedlings in the dark also had a mean bend of 12 degrees. Evaluate the investigation.
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Model answer
The seedlings in light from one side bent much more than those in the dark, so the direction of light does cause the bending. However, the seedlings in the dark also bent by 12 degrees, so another factor, such as light getting into the box, was affecting them, which makes the investigation less valid. The student should make the box light-proof. The results could be made more repeatable by using more seedlings and finding a mean, and by repeating the investigation. A ruler with a resolution of 1 mm limits the accuracy of the lengths, and a protractor and photographs would give better measurements of the bending. The drawings are a useful record but cannot easily be used to compare results. With these improvements the conclusion could be trusted more.
Mark scheme
- Light from one side caused a much larger bend — 1 mark
- Dark seedlings bent, so another factor — 1 mark
- Suggest a cause and how to stop it — 1 mark
- More seedlings, a mean and repeats for repeatability — 1 mark
- Accuracy of the measuring — 1 mark
- A reasoned conclusion — 1 mark
Quick check
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1
What is required practical 8?
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C: Effect of light or gravity on seedlings
It investigates the effect of light or gravity on the growth of newly germinated seedlings.
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2
What must be recorded in this practical?
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B: Length measurements and labelled drawings
Length measurements and labelled biological drawings.
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3
What does a clinostat do?
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A: Cancels the effect of gravity by turning
It turns the seedlings so gravity acts on all sides equally.
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4
Which of these is a control variable?
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D: The temperature
The temperature must be the same for all the seedlings.
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5
Why are the dishes in the gravity investigation kept in the dark?
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C: So that light does not affect the growth
So that light does not change the direction of growth.
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6
What is meant by a resolution of 1 mm?
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B: The ruler detects changes of 1 mm
The ruler can detect a change of 1 mm.
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7
The shoot lengths were 20, 22 and 24 mm. What is the mean?
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A: 22 mm
\((20 + 22 + 24) \div 3 = 22\) mm.
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8
Which feature should a biological drawing have?
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D: Clear lines and labels
Clear single lines, with labels and no shading.
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9
Seedlings in the dark are long and pale. What does this suggest?
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B: They grow quickly to find light and have no chlorophyll
With no light they grow tall quickly to find light, and without light they cannot make chlorophyll.
Gibberellins and Ethene (Higher tier)
Just this lesson-
1 State [1 mark]
State the plant hormone that is important in initiating seed germination.
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Model answer
Gibberellin.
Mark scheme
- Gibberellin — 1 mark
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2 State [2 marks]
State two effects of ethene on a plant.
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Model answer
It controls cell division, and it controls the ripening of fruits.
Mark scheme
- Controls cell division — 1 mark
- Controls ripening of fruit — 1 mark
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3 Explain [3 marks]
A farmer puts a bag of ripe bananas next to some green mangoes. The mangoes ripen faster than mangoes in another room. Explain why.
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Model answer
The ripe bananas produce ethene, which is a gas. The ethene spreads through the air to the mangoes. Ethene controls the ripening of fruits, so it makes the mangoes ripen faster.
Mark scheme
- Bananas make ethene — 1 mark
- It is a gas that spreads to the mangoes — 1 mark
- Ethene makes fruit ripen — 1 mark
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4 Calculate [3 marks]
In an experiment, 60 of 200 seeds in water, and 150 of 200 seeds in gibberellin solution, germinated. Calculate the percentage of each group that germinated.
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Model answer
Water: 60 ÷ 200 × 100 = 30%. Gibberellin: 150 ÷ 200 × 100 = 75%.
Mark scheme
- 30% — 1 mark
- 75% — 1 mark
- Correct method — 1 mark
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5 Explain [3 marks]
Explain why a control is needed in an experiment on the effect of gibberellin on seeds.
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Model answer
The control, in which seeds are given water only, shows how many seeds would germinate without gibberellin. If more seeds germinate with the gibberellin than in the control, the difference is likely to be caused by the gibberellin.
Mark scheme
- Control has no gibberellin — 1 mark
- Shows germination without the hormone — 1 mark
- Any difference is due to the gibberellin — 1 mark
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6 Evaluate [6 marks]
A store manager wants to keep a large amount of apples fresh for six months. Use your knowledge of ethene to suggest how this could be done, and explain how it works.
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Model answer
Ripe fruit makes ethene, which controls the ripening of fruits and makes other fruits ripen. If the ethene builds up in the store, all the apples will ripen quickly and then go bad. The manager should remove the ethene from the air, for example by using good ventilation or a chemical that absorbs it. Ripening is also slower in cold conditions, so the apples should be kept cool. Any apples that are overripe or damaged should be removed, because they make more ethene and will make the rest of the apples ripen faster. The apples should be picked before they are fully ripe, so they last longer.
Mark scheme
- Ripe fruit makes ethene — 1 mark
- Ethene makes other fruit ripen — 1 mark
- Remove the ethene from the store — 1 mark
- Keep the apples cool — 1 mark
- Remove damaged or overripe apples — 1 mark
- Pick before fully ripe — 1 mark
Quick check
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1
Which hormone is important in initiating seed germination?
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B: Gibberellin
Gibberellin.
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2
Which hormone controls the ripening of fruits?
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A: Ethene
Ethene.
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3
What state is ethene at room temperature?
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C: Gas
It is a gas.
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4
What does ethene also control, apart from ripening?
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D: Cell division
Cell division.
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5
What is seed dormancy?
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B: A resting state
A resting state in which the seed does not germinate.
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6
40 of 50 seeds germinated with a hormone. What percentage is this?
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A: 80%
\(40 \div 50 \times 100 = 80\%\).
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7
Why can a ripe fruit make other fruits ripen?
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C: It gives off ethene gas
It makes ethene gas, which spreads to the other fruits.
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8
Do students need to know the mechanism of how gibberellins work?
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D: No
No, the specification says that the mechanisms are not required.
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9
Fruit in a sealed bag with ethene ripened in 3 days, and fruit in a sealed bag without it took 9 days. What does this show?
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B: Ethene speeds up ripening
Ethene speeds up ripening, because the bag without ethene is the control.
Use of Plant Hormones (Higher tier)
Just this lesson-
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
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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
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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
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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
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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
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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
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1
Which hormone is used in rooting powder?
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C: Auxin
Auxin makes cuttings grow roots.
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2
Which hormone is used to control the ripening of fruit in storage?
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A: Ethene
Ethene.
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3
Which is a use of gibberellins?
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D: To increase the size of fruit
To end seed dormancy, to promote flowering and to increase fruit size.
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4
Why is an auxin weed killer selective?
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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.
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5
What is added to the jelly in tissue culture to promote growth?
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C: Auxin
Auxin promotes the growth of the plant tissue.
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6
How can a weed killer reduce biodiversity?
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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.
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7
A bunch of grapes increased in mass from 200 g to 250 g. What is the percentage increase?
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B: 25%
\(50 \div 200 \times 100 = 25\%\).
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8
Why does tissue culture need sterile conditions?
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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.
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9
A farmer sprays a field with an auxin weed killer and finds that fewer butterflies visit the field. Which explanation is most likely?
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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.