Exam questions · Biology
Plant Adaptations and Hormones
- 24 exam questions
- 71 marks
- 36 quick checks
Plants in Extreme Environments
Just this lesson-
1 State [1 mark]
State what is meant by an adaptation.
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Model answer
A feature of an organism that helps it to survive in its environment.
Mark scheme
- A feature that helps survival — 1 mark
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2 State [2 marks]
State two ways in which the leaves of a plant from a desert reduce the loss of water.
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Model answer
Any two from: small leaves, or spines, which have a small surface area; a thick waxy cuticle; few stomata, or stomata sunk in pits; stomata open only at night.
Mark scheme
- First — 1 mark
- Second — 1 mark
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3 Explain [3 marks]
Explain how rolled leaves help marram grass to survive on a windy sand dune.
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Model answer
The stomata are on the inside of the roll, where moist air is trapped. This reduces the concentration gradient of water vapour between the leaf and the air, so less water diffuses out of the leaf, and the wind does not blow away the humid air.
Mark scheme
- Stomata are inside the roll — 1 mark
- Humid air trapped — 1 mark
- Smaller gradient, so less water lost — 1 mark
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4 Explain [3 marks]
The stomata of a water lily are on the upper surface of its leaves, but the stomata of a bean plant are mostly on the lower surface. Explain why.
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Model answer
The lower surface of the water lily leaf is in contact with the water, so gases cannot enter there, and the upper surface is in the air. In the bean plant, having the stomata on the lower surface in the shade reduces water loss.
Mark scheme
- Lower surface of the water lily is in water — 1 mark
- Upper surface in contact with air for gas exchange — 1 mark
- Bean stomata on the lower surface lose less water — 1 mark
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5 Calculate [3 marks]
A flat leaf is modelled as a block 5 cm by 5 cm by 0.2 cm. Calculate its surface area to volume ratio. Give your answer to the nearest whole number.
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Model answer
Surface area = 2 × 25 + 4 × (5 × 0.2) = 50 + 4 = 54 cm squared. Volume = 5 × 5 × 0.2 = 5 cm cubed. Ratio = 54 ÷ 5 = 10.8, which is 11 : 1.
Mark scheme
- Surface area 54 — 1 mark
- Volume 5 — 1 mark
- Ratio 11 : 1 — 1 mark
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6 Evaluate [6 marks]
A student suggests that a plant with very large leaves and many stomata would survive well in a desert. Evaluate this idea, using ideas about leaf size and shape, the cuticle and the stomata.
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Model answer
Large leaves have a large surface area, so they would lose a lot of water by transpiration, and in a desert there is very little water to replace it. Many stomata would also let more water vapour escape, especially in the heat of the day. The plant would probably wilt and die. A large surface area does catch a lot of light for photosynthesis, which would be a benefit, and many stomata would let in a lot of carbon dioxide. However, desert plants have small leaves or spines, a thick cuticle, and few stomata, which may be open at night, because the loss of water is a much greater problem than a shortage of light. The idea is therefore a poor one.
Mark scheme
- Large leaves lose a lot of water — 1 mark
- Water is scarce in a desert — 1 mark
- Many stomata let more water vapour escape — 1 mark
- Large surface area gives more light for photosynthesis — 1 mark
- Desert plants have small leaves, a thick cuticle and few stomata — 1 mark
- A reasoned conclusion — 1 mark
Quick check
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1
What are the leaves of a cactus adapted into?
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C: Spines
They are reduced to spines, which have a very small surface area.
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2
Why do many desert plants have a thick waxy cuticle?
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A: To reduce the loss of water
It reduces the loss of water through the surface.
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3
Where are the stomata of a water lily leaf found?
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D: On the upper surface
They are on the upper surface, which is in contact with the air.
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4
Why are sunken stomata useful in a dry environment?
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B: They trap humid air
The pit traps humid air, which slows the diffusion of water vapour out of the leaf.
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5
Which statement about a water lily leaf is correct?
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C: It has a thin cuticle
It has a thin cuticle, because water is not short.
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6
A cube has a surface area of 24 cm squared and a volume of 8 cm cubed. What is the surface area to volume ratio?
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A: 3 : 1
\(24 \div 8 = 3\), so the ratio is 3 : 1.
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7
Why do some cacti open their stomata only at night?
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D: Less water is lost in the cooler air
It is cooler at night, so less water is lost.
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8
Why is a low, rounded cushion shape useful for a plant on a cold, windy mountain?
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B: It reduces the wind and the surface area
It gives shelter from the wind, and has a small surface area for its volume.
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9
A desert plant has 60 stomata per square millimetre and a leaf from a bean plant has 240. What percentage fewer stomata does the desert plant have?
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C: 75%
\((240 - 60) \div 240 \times 100 = 75\%\).
Plant Hormones and Tropisms
Just this lesson-
1 State [1 mark]
State what is meant by phototropism.
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Model answer
The growth of a plant in response to the direction of light.
Mark scheme
- Growth in response to light direction — 1 mark
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2 State [2 marks]
State the name of the hormone that causes phototropism, and the part of a shoot where it is made.
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Model answer
Auxin, which is made in the tip of the shoot.
Mark scheme
- Auxin — 1 mark
- Tip of the shoot — 1 mark
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3 Explain [3 marks]
A shoot is lit from the right-hand side only. Explain why the shoot bends towards the light.
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Model answer
The auxin moves to the shaded, left-hand side of the shoot. This makes the cells on that side elongate more than those on the lit side. The shoot therefore bends towards the light.
Mark scheme
- Auxin moves to the shaded side — 1 mark
- Cells on that side elongate more — 1 mark
- Shoot bends towards the light — 1 mark
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4 Explain [3 marks]
Explain why a seedling placed on its side has a shoot that grows upwards and a root that grows downwards.
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Model answer
Auxin collects on the lower side of both. In the shoot, it makes the lower cells elongate, so that the shoot bends up. In the root, it slows the growth of the lower side, so that the root bends down.
Mark scheme
- Auxin collects on the lower side — 1 mark
- Shoot: lower side grows faster, bends up — 1 mark
- Root: lower side grows slower, bends down — 1 mark
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5 Explain [3 marks]
A scientist covered the tips of some shoots with foil, and found that they did not bend towards a lamp. Explain what this shows.
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Model answer
It shows that the tip is the part that detects the light. If the tip is covered, the auxin is not moved to the shaded side, so the shoot does not bend.
Mark scheme
- Tip detects the light — 1 mark
- Auxin not moved to the shaded side — 1 mark
- Therefore no bending — 1 mark
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6 Evaluate [6 marks]
Evaluate the importance of tropisms to the survival of a young plant.
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Model answer
A young shoot that grows towards the light is able to absorb more light for photosynthesis, which provides the glucose that the plant needs to grow. Gravitropism makes the shoot grow upwards, away from the soil, and out into the light. The root grows downwards in response to gravity, and so reaches water and mineral ions in the soil, and anchors the plant so that it is not blown over. Without these responses, the shoot might grow into the soil, and the roots into the air, and the plant would die. They are controlled by auxin, which is made in the tips, so they happen automatically, without the plant needing a nervous system. Because the responses are slow, they could not help a plant to avoid sudden danger, but they are very important for growth.
Mark scheme
- Shoot grows to the light for photosynthesis — 1 mark
- Gravitropism takes the shoot upwards — 1 mark
- Roots grow down to water and minerals — 1 mark
- Roots anchor the plant — 1 mark
- Controlled automatically by auxin — 1 mark
- A reasoned judgement — 1 mark
Quick check
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1
Where is auxin made in a shoot?
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B: In the tip
In the tip of the shoot.
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2
What does auxin do in a shoot?
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A: It makes the cells grow longer
It makes the cells elongate.
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3
In phototropism, where does auxin move to?
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C: The shaded side
It moves to the shaded side of the shoot.
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4
What is the growth of a root downwards called?
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D: Positive gravitropism
It is positive gravitropism, as the root grows towards gravity.
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5
What happens to the growth of root cells on the side with more auxin?
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B: They grow slower
Auxin slows the growth of cells in a root.
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6
A shoot is covered with foil at the tip, and lit from one side. What happens?
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A: The shoot does not bend
The tip cannot detect the light, so the shoot does not bend.
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7
Which scientist put the tips on agar blocks and showed that a chemical moved?
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C: Went
Frits Went in 1928.
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8
Why is negative gravitropism useful in a shoot?
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D: It brings the shoot to the light
The shoot grows up towards the light, away from the soil.
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9
A seedling is placed on its side in the dark. Which statement is correct?
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B: The shoot bends up and the root bends down
Gravity causes auxin to collect on the lower side, so the shoot bends up and the root bends down, even in the dark.
Investigating Tropic Responses
Just this lesson-
1 State [1 mark]
State the independent variable in an investigation of phototropism.
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Model answer
The direction of the light.
Mark scheme
- Direction of the light — 1 mark
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2 State [2 marks]
State two variables that should be kept the same in an investigation of the effect of light direction on seedlings.
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Model answer
Any two from: the type and age of seedlings, the temperature, the volume of water, the distance from the lamp, the size of the pot, and the time.
Mark scheme
- First — 1 mark
- Second — 1 mark
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3 Explain [2 marks]
In an investigation of gravitropism, the dishes were kept in the dark. Explain why.
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Model answer
Light would also affect the direction of growth, because shoots show phototropism. Keeping the dishes in the dark means that gravity is the only stimulus.
Mark scheme
- Light would also affect the direction of growth — 1 mark
- So that gravity is the only stimulus — 1 mark
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4 Calculate [3 marks]
The angles of bending of five seedlings were 20, 25, 30, 25 and 35 degrees. Calculate the mean angle.
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Model answer
20 + 25 + 30 + 25 + 35 = 135. 135 ÷ 5 = 27 degrees.
Mark scheme
- Sum of 135 — 1 mark
- Division by 5 — 1 mark
- 27 degrees — 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
It turns the seedlings slowly, so that gravity acts equally on all sides. If the seedlings then grow straight, and those which are not turned bend, it shows that gravity is the stimulus which causes the bending.
Mark scheme
- Turns seedlings so gravity acts equally on all sides — 1 mark
- Acts as a control — 1 mark
- Shows that gravity is the stimulus — 1 mark
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6 Evaluate [6 marks]
A student found that the shoots in the pot with light from one side bent towards it by 38 degrees, but that the shoots in the dark also bent by 10 degrees. Evaluate the investigation and suggest improvements.
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Model answer
The shoots with light from one side bent far more than those in the dark, so the light direction does seem to cause the bending. However, the shoots in the dark also bent, which suggests that something else, such as light leaking into the box, a difference in temperature, or the seedlings being uneven, affected them. This reduces the validity of the results. The student should make the dark box properly light-proof, use more seedlings, use seedlings of the same age and height, and repeat the investigation to find a mean. A protractor and photographs would make the measurement more accurate. With these improvements the investigation would be more reliable, and the conclusion could be accepted with more confidence.
Mark scheme
- Light-side bending much larger than dark — 1 mark
- Dark pot bent, so another factor — 1 mark
- Possible cause such as light leak or temperature — 1 mark
- Make the dark box light-proof — 1 mark
- More seedlings, repeats and a mean — 1 mark
- Better measurement, and a reasoned conclusion — 1 mark
Quick check
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1
What is the dependent variable when investigating phototropism?
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C: The angle of bending
The angle of bending of the shoots is what is measured.
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2
What does a clinostat do?
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A: Turns seedlings slowly
It turns the seedlings so gravity acts on all sides equally.
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3
Why is a pot with light from above included?
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D: As a control
As a control, to show that shoots grow straight when there is no difference between the sides.
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4
In a dish on its side, what happens to the roots?
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B: They curve downwards
They curve downwards, towards gravity.
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5
Which instrument is used to measure the angle of bending?
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C: A protractor
A protractor.
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6
The angles of bending were 10, 20 and 30 degrees. What is the mean?
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A: 20 degrees
\((10 + 20 + 30) \div 3 = 20\) degrees.
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7
Why should the gravity dishes be kept in the dark?
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D: So that light does not affect the growth direction
So that light does not affect the direction of growth.
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8
Why can the heat from a lamp be a problem?
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B: It may warm one side of the seedlings
It can warm one side, which may change the growth.
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9
Seedlings on a clinostat grow straight in all directions. What does this show?
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C: Gravity causes the bending in the stationary dish
Turning cancels the effect of gravity, so the bending seen in the other dish is caused by gravity.
Commercial Uses of Plant Hormones (Higher tier)
Just this lesson-
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
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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
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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
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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
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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
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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
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1
Which hormone is used in rooting powder?
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B: Auxin
Auxin makes cuttings grow roots.
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2
Why are auxin weedkillers selective?
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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.
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3
Which hormone makes fruit ripen?
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A: Ethene
Ethene is a gas that makes fruit ripen.
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4
What is the use of gibberellins on seeds?
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C: To end dormancy
They end dormancy, so the seeds germinate.
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5
Why are bananas picked green?
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B: They are less easily damaged
They are firm, so they are not damaged during transport.
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6
Which hormone can make grapes seedless and larger?
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D: Gibberellin
Gibberellin.
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7
40 of 50 cuttings rooted with powder. What percentage is this?
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A: 80%
\(40 \div 50 \times 100 = 80\%\).
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8
Which is an environmental risk of weedkillers?
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C: They can run into streams and harm wildlife
They can wash into streams and harm wildlife.
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9
A store is full of ripe fruit that makes ethene. How could the ripening of other fruit there be delayed?
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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.