A student investigated exchange between blood and leg muscle tissue after cycling. Fig. 1 shows a capillary bed beside body cells. Table 1 gives concentrati...
Question 1 Report
A student investigated exchange between blood and leg muscle tissue after cycling. Fig. 1 shows a capillary bed beside body cells. Table 1 gives concentrations in blood entering and leaving the capillary bed.
| Substance | Blood entering capillary / arbitrary units | Blood leaving capillary / arbitrary units |
|---|---|---|
| Oxygen | 92 | 61 |
| Glucose | 5.0 | 3.8 |
| Carbon dioxide | 44 | 58 |
(a) Use Table 1 to calculate the decrease in oxygen concentration. [1]
(b) Complete the two arrows in Fig. 1 by stating one substance that moves from blood to tissue fluid and one substance that moves from tissue fluid to blood. [2]
(c) Explain how diffusion causes oxygen to move from a capillary into a muscle cell. [3]
(d) Describe how tissue fluid is formed and how excess tissue fluid returns to the blood. [4]
Answer Details
(a)
\[92-61=31\]
The oxygen concentration decreases by 31 arbitrary units. [1]
(b) A substance moving from blood to tissue fluid can be oxygen or glucose. A substance moving from tissue fluid to blood is carbon dioxide. [2]
(c) Oxygen concentration is higher in the blood than in the tissue fluid or muscle cells. Oxygen therefore moves down its concentration gradient. It diffuses through the thin capillary wall and cell membrane into the muscle cells. [3]
(d) At the arterial end of a capillary, high pressure forces fluid out through the capillary wall. This tissue fluid contains water and small dissolved substances. Most of it returns to capillaries at the venous end by osmosis or pressure effects. Excess tissue fluid enters lymph vessels and is eventually returned to the blood. [4]
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