Charles Darwin and his son Francis did a series of experiments to test their hypothesis that the tips of grass coleoptiles sense the direction of light. In the first experiment, coleoptiles with their tips cut off did not bend toward light, but intact coleoptiles did. Why was it necessary to follow this experiment with another experiment where only the tips of treated coleoptiles were covered with opaque foil?
A) More than one repetition of an experiment is needed to test a hypothesis.
B) Only correct hypotheses can be proven by experiments.
C) An alternative explanation for the first experiment could be that cutting off the tips injured the plants, so they could not respond.
D) Coleoptiles actually bend below the tip, so the tip is needed to know where the bending begins.

Question

Quizplus · Accepted Answer

The follow-up experiment with the tips covered was necessary to rule out the possibility that the lack of bending in the first experiment was due to injury from cutting the tips, rather than the absence of light perception at the tips.

Charles Darwin and His Son Francis Did a Series of Experiments