Question 1
Which statement describes active transport?
- Direction: down a concentration gradient; energy from respiration: needed
- Direction: against a concentration gradient; energy from respiration: needed
- Direction: against a concentration gradient; energy from respiration: not needed
- Direction: down a concentration gradient; energy from respiration: not needed
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Answer: B (1)
Question 2
Describe two differences between diffusion and active transport.
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- diffusion is down a concentration gradient but active transport is against a concentration gradient (1)
- active transport needs energy from respiration but diffusion does not (1)
Question 3
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanThe concentration of nitrate ions is lower in the soil than inside a root hair cell. Explain how the root hair cell takes in nitrate ions and why it has many mitochondria.
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- by active transport (1)
- movement is against the concentration gradient (1)
- mitochondria release energy (from respiration) needed for active transport (1)
Question 4
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean(a) State what moves molecules or ions across a cell membrane during active transport. [1] (b) Explain why active transport stops in a cell that cannot respire. [2]
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- protein carriers (1) allow carrier proteins; ignore 'proteins' alone
- respiration releases the energy needed for active transport (1) reject 'respiration makes / produces energy'
- without this energy, particles cannot be moved against their concentration gradient (1)
Question 5
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanBarley roots were placed in solutions with and without oxygen. The uptake of nitrate ions was measured. (a) Describe the effect of removing oxygen on nitrate uptake. [1] (b) Explain this effect. [3]
| Condition | Nitrate uptake / arbitrary units |
|---|---|
| Oxygen present | 45 |
| Oxygen absent | 6 |
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- uptake is much lower / falls from 45 to 6 without oxygen (1)
- no oxygen so less aerobic respiration (1)
- less energy released (1)
- less active transport of nitrate ions (against the concentration gradient) (1)