This set mixes the five skills in plant transport: the pathway, environmental effects, potometer data, xylem and phloem, and structure with function. The questions go from easier to harder. All data are invented for teaching.
Write each answer fully before opening the working. Use the mistake log and retest queue to record any slip you want to repeat later.
Questions
Q1 (easy). Name the tissue that carries water up a stem and the tissue that carries sucrose. State one other substance each carries.
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The xylem carries water, together with mineral ions. The phloem carries sucrose, together with amino acids.
Q2. Name the process by which water enters a root hair cell, and explain why the water moves in.
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Osmosis. The cell sap is more concentrated than the soil water, so there is a water potential gradient. Water moves down the gradient across the partially permeable membrane into the cell.
Q3. Put these stages in order. Water evaporates from mesophyll cell walls; water enters the xylem in the root; water vapour diffuses out through stomata; water moves up the stem; water enters a root hair cell.
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- Water enters a root hair cell.
- Water enters the xylem in the root.
- Water moves up the stem.
- Water evaporates from mesophyll cell walls.
- Water vapour diffuses out through stomata.
Q4. In a potometer, a bubble moves 45 mm in 5 minutes. Calculate its speed in mm per minute.
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Speed = distance ÷ time = 45 ÷ 5 = 9 mm per minute.
Check: 9 × 5 = 45.
Q5. A shoot was placed in air of different humidity for one hour each and the water lost was measured.
| Humidity | 40% | 60% | 80% |
|---|---|---|---|
| Water lost (g) | 9.0 | 6.0 | 3.0 |
Describe the trend, explain it, and say how many times greater the loss was at 40% than at 80%.
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Trend: as humidity increases, water loss decreases. Each 20% rise in humidity lowers the loss by 3.0 g.
Explanation: at higher humidity the air already holds more water vapour, so the concentration gradient between the leaf air spaces and the outside air is smaller. Vapour diffuses out more slowly through the stomata.
Multiple: 9.0 ÷ 3.0 = 3 times. Check: 3.0 × 3 = 9.0.
Q6. A shoot lost 8 g of water in an hour in still air and 20 g in an hour with a fan on. Calculate the percentage increase.
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Increase = 20 − 8 = 12 g. Percentage increase = 12 ÷ 8 × 100 = 150%.
Check: 150% of 8 is 12, and 8 + 12 = 20.
Q7. A potometer has a capillary tube of diameter 1.2 mm. The bubble moves 30 mm in 10 minutes. Calculate the volume of water taken up and the rate in mm³ per minute. Give 3 significant figures.
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Radius = 1.2 ÷ 2 = 0.6 mm. Area = π × 0.6² = π × 0.36 = 1.13 mm² (3 s.f., from 1.131).
Volume = area × distance = 1.131 × 30 = 33.9 mm³.
Rate = 33.9 ÷ 10 = 3.39 mm³ per minute.
Check: 3.39 × 10 = 33.9.
Q8. A ring of bark is removed from around the trunk of a young tree. The tree survives for some weeks, but the roots then begin to fail. Explain why.
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The bark contains the phloem. With a ring removed, sucrose made in the leaves cannot be translocated down past the ring to the roots. The roots have no sugar for respiration, so they eventually fail. The xylem deeper in the wood still carries water up, which is why the tree survives at first.
Q9. Phloem sieve tubes have few organelles but each sits beside a companion cell with many mitochondria. Explain how this arrangement supports the job of the phloem.
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Sieve tubes have few organelles, so there is less in the way of the flow of sucrose through the tube, and sieve plates let the contents pass. The companion cell’s mitochondria release energy in respiration, which is needed to load sucrose into the sieve tube. The feature (many mitochondria) gives the function (energy supply) and so the effect (sucrose is loaded and moved).
Q10 (harder). A student says a potometer proves how much water a shoot loses by transpiration. Give two reasons this is not exact and one improvement to the method.
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Reason 1: the potometer measures water uptake, and some of that water is used in photosynthesis or kept in the cells, so uptake is not the same as loss.
Reason 2: the shoot is cut, so its xylem may be damaged, and leaks or air in joints can move the bubble.
Improvement: repeat the readings and calculate a mean, and keep temperature, light and air movement constant, so the comparison is fairer.
If you got these wrong
| If the error was in | Go back to |
|---|---|
| Naming the pathway or osmosis (Q2, Q3) | Explain water movement from roots to leaves |
| Explaining humidity, wind or percentage change (Q5, Q6) | Relate transpiration to environmental conditions |
| Speed, volume or limitations (Q4, Q7, Q10) | Interpret a potometer-style dataset with limitations |
| Mixing up xylem and phloem or the ring-of-bark result (Q1, Q8) | Distinguish xylem and phloem transport |
| Naming a feature without its effect (Q9) | Connect a structural feature with a transport role |
For each error, decide whether it was a fact, an arithmetic slip or an incomplete explanation. Fix the cause, then redo the question a few days later from a blank page.
What if a pattern keeps repeating?
A repeated slip across different questions usually points to one habit, such as stopping at a feature or forgetting units. Online one-to-one Biology tuition gives you a teacher who can spot that habit in your own written answers and work on it directly.