SAT Subject Biology Practice Question 421: Answer and Explanation

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Question: 421

11. 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.

Based on the results of the experiment, one can conclude that the tip of the plant contains

A. gelatin
B. water
C. auxin
D. paste
E. nothing significant

Correct Answer: C


C Plant 1, the intact plant, grows at a rate of about 3 mm per day. Removal of the tip, as in Plant 2, reduces that growth to only about 1 mm per day. However, returning the auxin to the cut plant (as in Plant 4) restores the growth to about 3 mm per day.

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