Chapter 37, Problem 1TYK

Summary Introduction

Introduction:

The chemical substances that are responsible for accelerating, inhibiting, or affecting the growth of plants in any manner are called plant hormones. These are also termed as plant growth factors. These are involved in pathogen defense, regulation of organ size, embryogenesis, reproductive development, and stress tolerance.

Answer to Problem 1TYK

Correct answer:

The plant hormones like auxins, cytokinin, ethylene, and gibberellins are all involved in the stimulation of cell division.

Explanation of Solution

Justification/explanation for the correct answer:

Option (e) is given as: all stimulate cell division. The auxins are involved in stimulating the division of the cell and its further elongation. It is present in the apical buds’ meristem, young leaves, and seed embryo. The cytokinins are involved in the stimulation of the growth of lateral buds, cell division, and apical dominance. These hormones are transported to the different parts of plants from its synthesis center. The gibberellins are involved in stimulating the growth of fruits, seeds, and stems by stimulating the cell division in these areas. They also stimulate the elongation of cells. Ethylene is responsible for stimulating cambial cell division and forms xylem. Abscisic acid (ABA) does not stimulate cell division. Hence, option (e) is correct.

Justification/explanation for the incorrect answers:

Option (a) is given as auxins. Auxins are needed for the division of cells and for its elongation. They alone do not help in the cell division as cell division also requires cytokinins, ethylene, and gibberellins. So, it is an incorrect option.

Option (c) is given as cytokinins. The growth of lateral buds and the apical dominance is done by cytokinins. The cytokinins stimulate cell division along with ethylene, gibberellins, and auxins. So, it is an incorrect option.

Option (d) is given as ethylene. The cell division required for the formation of xylem is done by ethylene. The division of cells is also done by the auxins, gibberellins, and cytokinins. So, it is an incorrect option.

Option (e) is given as gibberellins. The cell division in the areas of fruits, seeds, and stems is done by the gibberellins. The gibberellins alone do not stimulate cell division as cytokinins, auxins and ethylene also contribute to it. So, it is an incorrect option.

Hence, options (a), (b), (c), and (d) are incorrect.

Conclusion

Therefore, it can be concluded that the chemicals that are involved in stimulating and regulating the growth of plants are plant hormones. The hormones that stimulate plant growth are auxins, gibberellins, ethylene, and cytokinins. The plant hormone that does not stimulate cell division is abscisic acid.