Chapter 23, Problem 17A

Summary Introduction

Introduction :

Flower is the most beautiful part of a plant. Certain plants only flowered at certain times of the year. This response of flowering plant is known as photoperiodism. The beginning of flower development for each plant species was a response to a range in the number of darkness. This range of hours is called the critical period of plants. Depending upon the critical period, flowering plants can be classified into four different groups. They are short-day plants, intermediate-day plants, day-neutral plants, and long-day plants.

Answer to Problem 17A

Correct answer :

The correct answer is option (A) hours of darkness are greater than the hours of light.

Explanation of Solution

Explanation/justification for the correct answer :

Option (A) hours of darkness are greater than the hours of light. In short-day plants, the number of exposure of darkness is greater than its critical period. They flower during the winter and spring. In these plants, the hours of darkness are more than the hours of light. So, the correct answer is option (A).

Explanation for incorrect answer :

Option (B) hours of darkness are less than the hours of light. In long-day plants, the number of exposure of darkness is less than its critical period. These plants flower during the summer. In this period, the hours of darkness are less than the hours of light. So, this is an incorrect option.

Option (C) hours of darkness are equal to the hours of light. In day-neutral plants, the number of exposuresto darkness is equal to its critical period. Cotton, roses are those plants which number of exposureto the darkness is equal to its critical period. So, this is an incorrect answer.

Option (D) hours of darkness and light are not factors. In short-day plants the hours of darkness and light are the main factors. In these plants, the hours of darkness are more than the hours of light. So, this is an incorrect answer.