Question

This question consists of two statements, Assertion and Reason. While answering this question you are required to choose any one of the following five responses.

Assertion: A correct concentration of auxin and cytokinin is required for the development of root and shoot in a callus.

Reason: When the ratio of kinetin to auxin is high, then only shoots develop. But when the ratio is low then only roots develop.

Answer 1

Assertion-Reason relation
Auxin and cytokinin are the plant growth promoting regulators which are involved in cell division and cell proliferation in plants. Auxin is primarily responsible for root growth while cytokinin is responsible for shoot growth. Hence, appropriate concentration of both phytohormones can induce growth of callus from explant.

Hence, the given assertion- “A correct concentration of auxin and cytokinin is required for the development of root and shoot in a callus” is correct.

Varying concentration of auxin and cytokinin decides if growth of root, shoot or proper development of callus is induced from an explant. Kinetin is a type of cytokinin which promotes plant growth along with auxin.

Being responsible for root growth initiation, higher concentration of auxin and lower concentration of kinetin induces growth of root while the lower concentration of auxin and higher concentration of cytokinin induces growth of shoot.

Hence, the given reason- “When the ratio of kinetin to auxin is high, then only shoots develop. But when the ratio is low then only roots develop” is correct and the correct explanation of the given assertion.