To test the effect of hormones on plant growth, six potted plant seedlings of the same species were measured and then sprayed with auxin, a growth hormone. After four weeks of growth under ideal conditions, the plants were measured again. What should the investigator do to set up a proper control for this experiment?

Question

A.Wash the auxin off three of the plants after two weeks.
B.Spray the same plants with different amounts of auxin.
C.Spray auxin on six plant seedlings of the same species and grow them in the dark for four weeks.
D.Grow another six plant seedlings of the same species under the same conditions, spraying them only with distilled water.

Answer 1

D.Grow another six plant seedlings of the same species under the same conditions, spraying them only with distilled water.

By growing another set of plant seedlings under the same conditions but only spraying them with distilled water, the investigator can compare the growth of the plants that were sprayed with auxin to those that were not. This will help determine the specific effects of the hormone on plant growth.