Chapter 22, Problem 29A

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.

Answer to Problem 29A

Correct answer :

The correct answer is option (A) Apical dominance

Explanation of Solution

Explanation/justification for the correct answer :

Option(A) Apical dominance. The presence of auxin generates a phenomenon called apical dominance, which is when the growth of plants with few or no side branches is mostly upward. The auxin produced by an apical meristem inhibits side- or lateral branch growth. However, removing apical meristem from a plant decreases the amount of auxin present. gThis supports the growth of side branches.So, the correct answer is option (A).

Explanation for incorrect answer :

Option (B) Leaf drop.In some trees and shrubs the decreased amount of auxin causes ripened fruits to fall down and leaves to fall before winter.So, this is an incorrect answer.

Option (C)Dwarfism.The hormone group called gibberellins induces elongation of the cells, promotes cell division and affects seed production. Gibberellins are transmitted to vascular tissue. Dwarf plants often lack either genes for the development of gibberellins, or genes for protein receptors of gibberellins.So, this is an incorrect answer.

Option (D)Nastic movement. A plant response which causes movement independent of stimulus direction.So, this is an incorrect answer.