SAT Subject Biology Practice Question 326: Answer and Explanation

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Question: 326

16. A volunteer was injected intravenously with several test substances to determine the effect of each substance on normal body variables. The results are shown in Table 1. Assume that enough time was allowed between injections so that the substances do not interfere with one another.

Table 1

Under what conditions might substance D be released normally?

A. Soon after a meal
B. When blood pressure is low
C. Between meals
D. When there has been limited intake of dietary calcium
E. When dietary calcium is in excess

Correct Answer: B


B Substance D causes an increase in serum sodium, which is the effect aldosterone has on the body. Aldosterone is released when blood pressure is low, because excess sodium will have the effect of causing water retention, which will increase blood volume, which will increase blood pressure. (Note: Even if you did not know this, you should have been able to eliminate the other choices.)

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