Control of Phototropism: The figure shows some of the treatments and results of

Question

Control of Phototropism: The figure shows some of the treatments and results of the Darwins' studies of phototropism in grass seedlings. Which of the following is not a conclusion that resulted from these studies?

Light is sensed in the tip of the coleoptile.
A signal travels from the tip downward.
Light did not directly affect the growing region where bending occurred.
Light caused movement of a growth-promoting substance from the tip to the growing region.
Bending occurred in a region below the tip.

Pls help with explanation :)

Explanation / Answer

Plants respond to light by growing or bending towards light. The first person to study about this phenomenon was Charles Darwin. He did most of his studies on a canary grass. From his experiments he concluded that "Heliotropism prevails so extensively among the higher plants, that there are extrememly few, of which some part, either the stem, flower peduncle, petiole, or leaf does not bend towards the lateral light.

The question was which part of the plant is sensing the light? or Where is eye of the plant? He made a hypothesis that it is the tip of the plant that senses the light. The first thing he did is, he chopped off the tip of the plant and he observed that the plant lost the ability to bend towards the light.

Conclusion: the tip senses the light. He also did a control exeriment where he covered the tip of the plant with a cap which is impermeable to light, and he observed that the plant didnot bend towards the light, thus concluding that i) eye of the plant is present at tip of the plant which senses light or ii) the weight of the cap inhibited bending.
For the second conclusion he did another control experiment where he placed a glass cap at the tip of the plant. He observed that the plant did bend towards the light.
Thus tip of the plant senses light and somehow signals the light energy down to the bottom of the plant, i.e. signal moves from the tip to the base which is causing it to bend. In his words " when seedlings are freely exposed to lateral light, some influence is transmitted from the upper to the lower part causing the latter to bend".

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