Question

Who discovered that phototropism is the result of the presence of more auxin on the shaded side than on the illuminated side?
A. Galston
B. Boysen – Jensen
C. Went
D. Kogh and Haagen – Smit

Answer 1

Phototropism is a phenomenon where plants make response against a light stimulus. Auxin is the responsible hormone for phototropism. The word photo means light and tropism means movement.

Complete answer: 1. Scientist F. W. Went discovered from his research work that when the tip of Avena coleoptile is cut, its elongation ceases.
2. Further, when he added auxin externally, the growth of coleoptile renewed.
From his experiment, went suggested that auxin is synthesized in the tip of coleoptile and then auxin is translocated downwards by the influence of the gravity.
3. Auxin moves from the illuminated side to the shaded side of a plant.
4. More auxin is present on the shaded side than on the illuminated side and influences the cell division. This is the reason for the plant to grow more on the shaded side and then bends towards the direction of the light source.
5. This phenomenon is known as positive phototropism where faster cell growth and elongation are seen on the shaded side and less cell growth is seen on the illuminated side.

Thus, the correct answer is option C. Went.

Note: Two types of phototropism are seen in plants – positive phototropism and negative phototropism. In positive phototropism different parts of plants respond towards the light stimulus. This is seen mainly in the case of plants.
In the case of negative phototropism, the parts of the plants respond against or away from the light stimulus.