At a remote mountain rescue post, a medic takes blood samples from a cyclist before and after the blood passes through the cells of the thigh. The cyclist h...
Question 1 Report
At a remote mountain rescue post, a medic takes blood samples from a cyclist before and after the blood passes through the cells of the thigh. The cyclist has been pedalling a generator to charge a radio. Fig. 1 is a diagram showing a capillary beside human muscle cells. Oxygen and glucose are carried in the blood to provide energy for respiration.
Table 1 shows the oxygen concentration in equal volumes of blood collected at each end of this capillary network.
| Blood sample | Oxygen concentration / arbitrary units |
|---|---|
| Entering the muscle capillaries | 19.6 |
| Leaving the muscle capillaries | 13.9 |
(a) Name the type of blood vessel shown in Fig. 1. [1]
(b) Describe two structural features of this blood vessel that make exchange with body cells efficient. [2]
(c) Use Fig. 1 to explain how oxygen reaches the muscle cells and how carbon dioxide enters the blood. [4]
(d) Calculate the decrease in oxygen concentration between the two blood samples in Table 1. Show your working. [2]
(e) State one reason why the oxygen concentration falls as blood travels through these capillaries. [1]
Answer Details
(a) The vessel is a capillary. [1]
(b) Capillaries have walls one cell thick, giving a short diffusion distance. They also have a narrow lumen, keeping blood close to body cells. [2] A permeable wall or many capillaries providing large surface area are also acceptable.
(c) Oxygen moves from the blood to the muscle cells by diffusion, because oxygen concentration is higher in blood than in the cells. Carbon dioxide moves from muscle cells into blood by diffusion, because its concentration is higher in the cells than in the blood. [4]
(d)
\[19.6-13.9=5.7\text{ arbitrary units}\]
The oxygen concentration decreases by 5.7 arbitrary units. [2]
(e) Oxygen concentration falls because muscle cells use oxygen in aerobic respiration to release energy. [1]
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