Chapter 22, Problem 33A

Summary Introduction

Introduction :

In plants, the roots growing down, stems growing upward, trees are dropping their leaves, and leaves of some plants trapping an insect are due to responses of plants to their environment. A tropism is the response to an external stimulus by growth of a plant. If the resulting plant growth is in the direction of stimulation it is called a positive tropism. If the resulting growth of plants is away from the stimulus, this is called a negative tropism.

Answer to Problem 33A

Correct answer :

The correct answer is option (C) C

Explanation of Solution

Explanation/justification for the correct answer :

Option(C) C. Gravitropism is a response to gravity on plant growth.The growth of the plants away from the gravity is assumed to be negative gravitropism.So, the correct answer is option (C).

Explanation for incorrect answer :

Option (A)A.Phototropism is the exposure of plants to light caused by uneven auxin distribution. When the growth of the plant happens towards the light. Then it is said the phototropism is positive.So, this is an incorrect answer.

Option (B) B.When the growth of the plant happens away from light. Then, the phototropism is assumed to be negative.So, this is an incorrect answer.

Option (D)D. Thigmotropism is the response of growth to mechanical stimuli like contact with an object, another organism or even wind.So, this is an incorrect answer.