CAIE A Level Biology 9700 · Homeostasis
After prolonged exercise, a person becomes dehydrated, causing a decrease in blood water potential. Describe the sequence of events that leads to an increase in water reabsorption in the kidneys, including the roles of the hypothalamus, posterior pituitary, ADH, aquaporins, and the collecting ducts, and explain how this maintains blood water potential through negative feedback.
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.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
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