An experiment measured how quickly oxygen diffused across artificial membranes of different thickness, using the same concentration gradient each time. The ...
Question 1 Report
An experiment measured how quickly oxygen diffused across artificial membranes of different thickness, using the same concentration gradient each time. The diagram compares a thin and a thick membrane, and Table 1 shows the results.
| Membrane thickness / units | Oxygen diffusing per minute / arbitrary units |
|---|---|
| 1 | 40 |
| 2 | 20 |
| 4 | 10 |
(a) Describe the relationship between membrane thickness and the amount of oxygen that diffuses across it. [2]
(b) Calculate how many times faster oxygen diffused across the 1 unit membrane than across the 4 unit membrane. [2]
(c) Explain why a thinner membrane allows faster diffusion. [2]
(d) Explain how the structure of the wall of an alveolus is related to these results. [3]
Answer Details
The table shows oxygen diffusing per minute against membrane thickness (1 unit gives 40, 2 units give 20, 4 units give 10 arbitrary units), with the concentration gradient kept constant each time.
(a) As membrane thickness increases, the amount of oxygen diffusing across decreases (the thicker the membrane, the slower the rate). This is an inverse relationship. [2]
(b) Compare the 1-unit and 4-unit membranes: \[ \frac{40}{10} = 4 \] So oxygen diffuses 4 times faster across the 1-unit membrane. [2] (working \(40 \div 10\), answer 4)
(c) A thinner membrane allows faster diffusion because there is a shorter distance for the particles to travel [1], so they cross the membrane more quickly [1]. [2]
(d) Linking this to a real alveolus [3]: the wall of the alveolus is very thin / only one cell thick [1], giving a short diffusion distance [1], so gases (oxygen and carbon dioxide) diffuse across it rapidly [1], exactly as these results predict.
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