SAT Subject Biology Practice Question 423: Answer and Explanation
13. 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.
What proves that auxin is necessary for plant growth?
A. Plant 1 grew faster than Plants 2 or 3.
B. Plant 4 grew faster than Plants 2 or 3.
C. Plant 5 grew faster than Plant 1.
D. Plant 3 grew faster than Plant 2.
E. Plant 4 grew faster than Plant 5.
Correct Answer: B
B First go through the answer choices and eliminate obviously wrong ones, such as choices C and D. The data table given shows that Plant 5 grew more slowly than Plant 1, and that the growth of Plants 2 and 3 are about the same. To prove that auxin is necessary for plant growth, we have to show that when it is present plant growth occurs, and when it is absent, growth does not occur, or is much slower. Choice A is true, but it doesn't show the necessity for auxin, you can eliminate it. Choice E is true, but again, doesn't show the necessity for auxin, because auxin is present on both plants.