(a) Fig. 5.1 is a photograph of a section through a kidney. [Figure 5.1]

1. (a)On Fig 5.1, use label lines and letters to label the regions of the kidney where the following are located: L – loop of Henlé D - distal convoluted tubule P - podocyte cells.[3]
2. (b)In a cold environment, people urinate more frequently. This condition is called cold diuresis. In a cold environment, homeostatic mechanisms keep heat loss to a minimum. Blood is diverted away from the skin so that more blood circulates around the main body organs, including the kidney. Suggest and explain why cold diuresis occurs.[4]
3. (c)The water potential of the blood is maintained at a constant level by a mechanism called negative feedback. With reference to the maintenance of the water potential of the blood, explain what is meant by negative feedback.[5]
4. (d)ADH affects the number of water channel proteins, aquaporins, in the cell surface membranes of the cells of the distal convoluted tubule. State what happens to the water potential and volume of the urine if cells in the distal convoluted tubule have more aquaporins in their cell surface membranes. water potential volume of urine[1]

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