[Campbell Biology P.1047] Based on the provided data for average daily water gain and loss, w... | Practice Question

Based on the provided data for average daily water gain and loss, which routes of water balance make up a significantly larger share of the total for a kangaroo rat compared to a human?

  • A: Water gain derived from metabolism.
  • B: Water loss via urine.
  • C: Water loss via evaporation.
  • D: Water gain from ingested liquid.

Explanation

To determine the share, we compare the proportion of each route to the total gain/loss for both animals. For water gain, the kangaroo rat's metabolic water 1.8 mL/day makes up a very high percentage of its total gain 0.2+0+1.8 = 2.0 mL/day , around 90%. For humans, metabolic water 250 mL/day is a smaller percentage of their total gain 750+1500+250 = 2500 mL/day , around 10%. Thus, metabolic water gain is a much larger share for the kangaroo rat. For water loss, the kangaroo rat's evaporative loss 1.46 mL/day is about 73% of its total loss 0.45+0.09+1.46 = 2.0 mL/day . For humans, evaporative loss 900 mL/day is about 34.6% of their total loss 1500+100+900 = 2600 mL/day . Therefore, evaporative water loss also makes up a much larger share for the kangaroo rat.