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Module 3: Exchange and transport
Quick questions on Blood vessels and tissue fluid: artery, vein, capillary structure and fluid exchange - OCR A-Level Biology A
5short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is formation of tissue fluid?Show answer
Tissue fluid bathes the body cells and is formed from blood plasma. Two opposing pressures decide the direction of fluid movement across the capillary wall:
What is return of tissue fluid?Show answer
As blood flows along the capillary, hydrostatic pressure falls (fluid has been lost and there is frictional resistance). Meanwhile the plasma proteins are now more concentrated, so the oncotic pressure stays high. At the venous end, oncotic pressure exceeds hydrostatic pressure, so most of the water is reabsorbed into the capillary by osmosis, carrying dissolved waste (such as carbon dioxide and urea) back into the blood.
What is q1?Show answer
Describe one structural difference between a capillary and an artery, and explain its functional importance. [2 marks]
What is q2?Show answer
State the two pressures that determine the movement of fluid across a capillary wall. [2 marks]
What is q3?Show answer
Explain why plasma proteins remain in the capillary while glucose leaves to form tissue fluid. [1 mark]
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