Fig. 1 shows two simplified nephrons. One is from a desert rodent that obtains very little water from its food. The other is from a human. The length of the...
Question 1 Report
Fig. 1 shows two simplified nephrons. One is from a desert rodent that obtains very little water from its food. The other is from a human. The length of the loop is shown to the same scale.
(a) Name the parts labelled X and Y. [2]
(b) Describe the difference in the structure of the two nephrons shown. [2]
(c) Explain how the longer loop helps the desert rodent conserve water. [4]
(d) State two waste products, other than excess water, that may be removed from a mammal's blood by the kidneys. [2]
(e) Explain why the concentration of urine can change during one day even when the concentration of urea produced is constant. [3]
(f) Suggest one advantage of producing a small volume of concentrated urine in a dry habitat. [3]
Answer Details
(a) Both X and Y are the loop of Henle. [2]
(b) The desert rodent nephron has a longer loop of Henle, extending further into the kidney. The human nephron has a shorter loop. [2]
(c) A longer loop creates a more concentrated, lower-water-potential region in the kidney. More water then moves by osmosis out of the nephron. This water is reabsorbed into the blood, leaving less water in the urine. [4]
(d) Two waste substances other than excess water are urea, excess mineral ions or salts, and drugs or toxins. [2]
(e) Water intake changes during a day, as does water loss through sweating. The kidneys vary how much water is reabsorbed, so urine concentration changes even if the amount of urea produced is constant. [3]
(f) Producing a small volume of concentrated urine reduces water loss. This lowers the risk of dehydration and helps maintain blood water concentration for normal cell function. [3]
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