CAIE A Level Biology 9700 · Transport in mammals
In a capillary network, the arteriole end has a blood hydrostatic pressure of approximately 4.3 kPa and a plasma colloid osmotic (oncotic) pressure of approximately 3.6 kPa. At the venule end, the blood hydrostatic pressure falls to about 1.6 kPa, while the colloid osmotic pressure remains at 3.6 kPa.
Explain how these pressure differences result in the formation and reabsorption of tissue fluid, and state what happens to any fluid that is not reabsorbed.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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