Chapter 22, Problem 30A

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 30A

Correct answer :

The correct answer is option (A) Auxin

Explanation of Solution

Explanation/justification for the correct answer :

Option(A) Auxin. 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. An apical meristem produces auxin inhibiting the growth of side or lateral branches. However, removing apical meristem from a plant decreases the amount of auxin present. This favors side branch growth.So, the correct answer is option (A).

Explanation for incorrect answer :

Option (B)Gibberellins.The hormone group called gibberellins induces elongation of the cells, promotes cell division and affects seed production. Gibberellins are conveyed 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 (C) Ethylene. Ethylene is the primary known gaseous hormone. It is a simple compound which consists of two atoms of carbon and four of hydrogen. Ethylene can be found in plant tissues such as mature fruit, dying leaves and flowers. So, this is an incorrect answer.

Option (D)Cytokinins. Growth-inducing cytokinins are generated in cells which divide rapidly. They travel within xylem into other parts of the plant.So, this is an incorrect answer.