USA Biology Olympiad (USABO) Practice Exam

After a consumption experiment, which group is expected to produce the most urine?

1. Those who drank water

2. Those who drank coffee

3. Those who drank concentrated salt solution

4. Those who did not consume any liquid

The correct answer is: Those who drank coffee

The group that is expected to produce the most urine is the one that drank coffee. This is primarily due to the diuretic effect of caffeine, a major component of coffee. Caffeine stimulates the kidneys to increase urine production by inhibiting the reabsorption of sodium in the renal tubules and increasing renal blood flow, which leads to increased glomerular filtration rate. As a result, the body produces more urine when caffeine is consumed. In contrast, those who drank water would also produce urine, but the volume is likely to be less compared to those who consumed coffee due to the body's ability to efficiently retain water when needed. Those who drank concentrated salt solution would retain water to counterbalance the high salt intake, thus producing less urine. The group that did not consume any liquid would produce minimal urine since there would be little fluid intake, leading to minimal production as the body would conserve water. Therefore, the consumption of coffee leads to the highest expected urine production due to its diuretic properties.