sondenso wrote:
When a caterpillar emerges from the egg on a tree branch, it immediately climbs upward until it finds a leaf bud to eat. Biologists thought that this behavior displayed an innate tendency to move in the direction opposite to the pull of gravity. In a recent experiment, a strong light source was placed at the bottom of a tree, and caterpillars, after hatching, climbed downward.
Which of the following hypotheses is best supported by the statements given?
A. Caterpillars have an innate tendency to move in the direction of gravity.
B. Newly hatched caterpillars are unable to see in the dark.
C. Newly hatched caterpillars move towards the strongest light source in the environment.
D. Newly hatched caterpillars move toward the leaf bud nearest to them.
E. The eyes of newly hatched caterpillars become less sensitive to light over time.
When a caterpillar emerges from the egg on a tree branch, it immediately climbs
upward until it finds a leaf bud to eat. Old hypothesis: They have a tendency to move in the direction opposite to the pull of gravity.
(Pull of gravity is downward and they move upward so the hypothesis was that they move against gravity)
In a recent experiment, a strong light source was placed at the bottom of a tree, and caterpillars, after hatching, climbed downward.
(This experiment showed that the gravity hypothesis was not correct. The caterpillars moved downward in case of a strong light source at the bottom)
So it seems that the caterpillars are driven by light. That they move in the direction of the brightest light available.
Normally, a tree would be lit by sunlight and since it is stronger at the top than at the bottom, the caterpillar moves upwards. A
strong light at the bottom of the tree would make the bottom more lit than the top. That would explain why the caterpillar moved downwards in that case.
Hence, (C) makes sense.
Certain words clarify the intention. The use of "strong light" in the argument implies that the bottom of the tree would be more brightly lit.
D. Newly hatched caterpillars move toward the leaf bud nearest to them.
This is not supported by the argument. They move in the direction that suits them till they reach a leaf bud. Normally they move upward. When there is a strong light at the bottom, they move downward.
Answer (C)