Fig. 1 shows a simplified section through a human alveolus and a nearby blood capillary. The person has been exercising at a high altitude training camp. Ai...
Question 1 Report
Fig. 1 shows a simplified section through a human alveolus and a nearby blood capillary. The person has been exercising at a high altitude training camp. Air in the alveolus has a higher oxygen concentration than the blood arriving at the capillary. Red blood cells pass through the capillary one at a time.
The capillary walls and alveolar walls are each one cell thick. The athlete's doctor also measured the number of red blood cells in a blood sample. It was 5.8 million cells per mm3, compared with 5.1 million cells per mm3 before the training period.
(a) Describe the movement of oxygen shown by the arrow in Fig. 1. [2]
(b) Suggest two features of an alveolus that allow rapid gas exchange. [3]
(c) Use the blood data to calculate the increase in red blood cells per mm3. [2]
(d) Suggest how the increase in red blood cells could help the athlete during exercise. [2]
Answer Details
(a) Oxygen diffuses from the alveolar air into the blood. It moves down its concentration gradient, from higher oxygen concentration in the alveolus to lower oxygen concentration in the arriving blood. [2]
(b) Three features allowing rapid gas exchange are:
- a large surface area;
- walls one cell thick, giving a short diffusion distance;
- a good blood supply, which maintains a concentration gradient.
A moist surface, allowing gases to dissolve, is also acceptable. [3]
(c) \[5.8\text{ million cells mm}^{-3}-5.1\text{ million cells mm}^{-3}=0.7\text{ million cells mm}^{-3}\] The increase was 0.7 million red blood cells per mm3. [2]
(d) More red blood cells contain more haemoglobin, so more oxygen can be carried in the blood. Muscles can then carry out more aerobic respiration and release more energy during exercise. [2]
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