Question 1
Unit 1 style
Which change would cause the greatest decrease in the rate of diffusion of oxygen across the wall of an alveolus?
- Doubling the surface area of the alveolus
- Doubling the thickness of the alveolar wall
- Doubling the oxygen concentration in the alveolus
- Halving the thickness of the capillary wall
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Question 2
Unit 1 style
A gas exchange surface has an area of 80 mm², a thickness of 0.4 µm and a difference in oxygen concentration across it of 15 arbitrary units. A second surface has an area of 40 mm², a thickness of 0.4 µm and a concentration difference of 15 arbitrary units. Use Fick's law to calculate the relative rate of diffusion across each surface, and state the ratio of the first to the second.
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Question 3
Unit 1 style
Explain how the structure of the mammalian lung is adapted for rapid gaseous exchange.
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Question 4
Unit 1 style
Which statement about cholesterol in an animal cell-surface membrane is correct?
- It forms channels through which ions pass
- It lies between the phospholipid tails and helps to regulate the fluidity of the membrane
- It forms the outer carbohydrate layer used in cell recognition
- It is a protein that carries glucose across the membrane
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Question 5
Unit 1 style
In an investigation of membrane fluidity, a human cell and a mouse cell were fused. The surface proteins of the human cell were labelled with a green fluorescent marker and those of the mouse cell with a red fluorescent marker. The fused cells were kept at different temperatures. The table shows the percentage of the fused cells in which the two markers had completely mixed after 40 minutes. Use the data to explain how the experiment supports the fluid mosaic model of membrane structure.
| Temperature / °C | Cells with markers completely mixed / % |
|---|---|
| 4 | 5 |
| 15 | 20 |
| 25 | 55 |
| 37 | 95 |
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Question 6
Unit 3 style
A student wants to investigate the effect of temperature on the permeability of the membranes of beetroot cells. Describe how the student could carry out this investigation, including how to control variables, how the results would be measured and one safety precaution.
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Question 7
Unit 1 style
Cylinders of potato were left in sucrose solutions of different concentrations for 24 hours. The percentage change in mass of the cylinders was calculated. Determine the sucrose concentration at which there would be no net movement of water into or out of the potato cells, and explain what happens to the cells at 0.8 mol dm⁻³.
| Sucrose concentration / mol dm⁻³ | Percentage change in mass |
|---|---|
| 0.0 | +14 |
| 0.2 | +8 |
| 0.4 | +1 |
| 0.6 | −6 |
| 0.8 | −12 |
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Question 8
Unit 1 style
Compare and contrast facilitated diffusion and active transport.