CAIE A Level Biology 9700 · Homeostasis
The nephron is the functional unit of the kidney. The proximal convoluted tubule (PCT), loop of Henle, and the action of antidiuretic hormone (ADH) on the collecting duct are all essential for the production of concentrated urine.
Explain how the structure of the PCT and loop of Henle, together with the action of ADH, enable the kidney to produce urine that is hypertonic compared to blood plasma.
6 marks, so the mark scheme is looking for about 6 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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