SAT Subject Biology Practice Question 319: Answer and Explanation

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Question: 319

9. Diuretics are substances that help eliminate water from the body. The effects of various substances were tested on several volunteers. All volunteers had a mass of 70 kg. They drank nothing for eight hours before the test and urinated just prior to ingesting the test substance. The three substances (water, caffeine, and salt) were tested on three separate days. The results are shown in the tables below.

Table 1

Table 2

Table 3

The purpose of ingesting the plain water (Table 3) was to

A. rehydrate the volunteers
B. dissolve the substances
C. act as a control
D. flush out the kidneys
E. act as a positive test substance

Correct Answer: C


C Because the caffeine and the sodium chloride were dissolved in water, plain water was consumed as a control, to make sure the effects seen were due to the added substances and not the water. Questions about experimental controls come up fairly frequently on the SAT Biology E/M Subject Test; make sure you know the definition for a control and how to spot it in the experiment.

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