Chapter 33, Problem 1CC

Test your knowledge of the five major classes of plant hormones (auxins, cytokinins, gibberellins, abscisic acid, ethylene) by matching one hormone to each lettered box. (Note that some hormones will match up to more than one box.)

Summary Introduction

To complete: The given map of the five major classes of plant hormones.

Concept introduction:

Plant hormones are chemical messengers that are produced in trace amounts, but profoundly affect the growth and development of a plant. These include auxins, cytokinins, gibberellins, abscisic acid and ethylene.

The plant hormones perform various functions such as promoting growth, breaking dormancy, mediating fruit ripening and providing tolerance to stress.

Explanation of Solution

Pictorial representation: Fig.1 shows the completed map representing the five major classes of plant hormones.

Fig.1: The five major classes of plant hormones.

(a)

Correct answer: Auxin.

Explanation: Auxins are a group of plant hormones that promotes cell elongation. They are produced by the apical meristems of shoot and root. They promote the growth of root and shoot of the plant. Hence the correct answer is auxin.

(b)

Correct answer: Gibberellins.

Explanation:  The gibberellins are a group of plant hormones that stimulate the elongation of stem by promoting cell elongation. Hence the correct answer is gibberellins.

(c)

Correct answer: Auxin.

Explanation: Auxin is produced by the apical bud of the shoot and functions to inhibit the growth of axillary buds, a phenomenon called apical dominance. Hence, the correct answer is auxin.

(d)

Correct answer: cytokinin.

Explanation: The cytokinins are a group of plant hormones that stimulate rapid cell division in roots and shoots of the plant. It also promotes the growth of lateral buds, thereby nullifying the effects of auxin. Hence, the correct answer is cytokinin.

(e)

Correct answer: Auxin.

Explanation: In addition to cell elongation, the auxins also function to retard the abscission of leaves. It also plays a crucial role in nullifying the effects of ethylene. Hence, the correct answer is auxin.

(f)

Correct answer: Ethylene.

Explanation: Ethylene is a gaseous hormone that promotes ripening of fruit and abscission of leaves from trees. Hence, the correct answer is ethylene.

(g)

Correct answer: Gibberellin.

Explanation: The gibberellin is a plant hormone that promotes the germination of seed. It inhibits seed dormancy by nullifying the effects of abscisic acid. Hence the correct answer is gibberellin.

(h)

Correct answer: Abscisic acid.

Explanation: The abscisic acid is a plant hormone that is involved in the stress responses. It inhibits growth, promotes seed dormancy during winter or periods of drought. Hence, the correct answer is abscisic acid.