Question 1
Triple only (what this means)
Triple only: only in Triple Biology. Combined Science students can skip it. What the labels meanWhich change would decrease the rate of diffusion across an exchange surface?
- Increasing the surface area
- Increasing the concentration difference
- Increasing the thickness of the membrane
- Increasing the surface area and the concentration difference
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Answer: C (increasing the thickness of the membrane)
Question 2
Triple only (what this means)
Triple only: only in Triple Biology. Combined Science students can skip it. What the labels meanIn some lung diseases the walls of the alveoli become thicker. Explain how this affects the rate of diffusion of oxygen into the blood.
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- diffusion distance increases (1)
- so the rate of diffusion decreases / less oxygen enters the blood (1)
Question 3
Triple only (what this means)
Triple only: only in Triple Biology. Combined Science students can skip it. What the labels meanA membrane has a surface area of 50 units and a thickness of 4 units. The concentration difference across it is 8 units. Use Fick’s law to calculate the rate of diffusion in arbitrary units.
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- surface area × concentration difference = 50 × 8 = 400 (1)
- ÷ thickness = 400 ÷ 4 (1)
- 100 (arbitrary units) (1)
Question 4
Triple only (what this means)
Triple only: only in Triple Biology. Combined Science students can skip it. What the labels meanA student says that the rate of diffusion across a membrane will double if both the surface area and the thickness of the membrane are doubled. Use Fick’s law to evaluate the student’s idea.
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- rate of diffusion is proportional to surface area (1)
- and inversely proportional to thickness, so doubling both cancels out (1)
- rate stays the same, so the student is not correct (1)