Chapter 22, Problem 36A

Summary Introduction

To write: The tropic responses are permanent while nastic responses are reversible.

Introduction: The roots heading down in plants, the branches rising upward, the trees lowering their leaves and the leaves of certain plants catching an insect are due to the responses of plants to their environment.

Explanation of Solution

A tropism is the reaction to an external stimulation by growth of a plant. Whether the resulting plant development is in the direction of stimulus it is considered a positive tropism. If the subsequent development of plants is away from the stimulus, this is considered a negative tropism.

A plant response which causes motion independent of stimulus direction is a nastic response. It is not a response to growth is reversible and can be repeated several times. Solar tracking that certain plants show, such as a sunflower, is a nastic reaction.

Conclusion

Thus, nastic response provides maximum light exposure while the tropic response plant growth towards the external stimulus.