The diagram shows a capillary network in the skin of a human runner. Blood enters the capillaries at A and leaves at B. At A, the pressure of the blood is h...
Question 1 Report
The diagram shows a capillary network in the skin of a human runner. Blood enters the capillaries at A and leaves at B. At A, the pressure of the blood is high. Some plasma is forced out of the capillary and forms tissue fluid around body cells. Most of this fluid returns to the blood near B.
(a) Describe how oxygen moves from blood at A into the body cells. [2]
(b) Explain why plasma proteins usually remain in the capillary rather than entering tissue fluid. [2]
(c) State two substances that may be present in tissue fluid but are used by body cells. [2]
(d) Explain one advantage of forming tissue fluid around cells. [2]
Answer Details
(a) Oxygen moves by diffusion from a higher oxygen concentration in the blood at A to a lower oxygen concentration in the body cells. [2]
(b) Plasma-protein molecules are too large to pass through the pores in the capillary wall, so they normally remain in the capillary rather than entering tissue fluid. [2]
(c) Any two suitable substances are oxygen, glucose, amino acids and fatty acids. They may be present in tissue fluid and are taken up for use by body cells. [2]
(d) Tissue fluid provides a medium for exchange between capillary blood and cells. It gives cells a short diffusion distance, helping maintain delivery of useful substances and removal of wastes. [2]
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