SAT Subject Biology Practice Question 422: Answer and Explanation

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Question: 422

12. The following experiment was performed to test the effect of an auxin on plant growth. The auxin was dissolved in a gelatin block; gelatin does not affect the biological activity of the auxin. Several plant seedlings were prepared as described below and growth was measured every five days.

Which of the following plants in the experiment acted as a control?

I. Plant 1

II. Plants 2 and 3

III. Plant 5

A. I only
B. II only
C. III only
D. I and II only
E. I, II, and III

Correct Answer: D

Explanation:

D First, this is a I, II, III-style question, so you will be eliminating answer choices as you work through the options. Second, you should always be able to identify the control or controls in an experiment; this comes up very frequently on the SAT Biology E/M Subject Test. Option I is true. Plant 1 was left in its natural state. You can eliminate choices B and C. Option II is also true. Neither Plant 2 nor Plant 3 is treated with the test substance (auxin), but they are subjected to the other conditions the test plants are subjected to. You can eliminate choice A. Option III is false. Plant 5 is testing the effects of auxin when it is applied at a location other than the tip of the plant. You can eliminate choice D. NOTE: Don't get careless and mix up your option numbers with your plant numbers! It's an easy mistake to make.

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