Question

Growth of both stem and root is mediated by auxin. However, stem grows into air while root grows into soil. The reason is

• A. Differential reaction of root and stem to auxin
• B. Only the stem tip produces auxin
• C. Only the root tip produces cytokinin
• D. Only the root cap can perceive gravity

Answer 1

The correct option is A Differential reaction of root and stem to auxin

Auxin is a plant hormone that plays important role in the growth of stem and roots to gravity. Root shows positive gravitropism and shoot shows negative gravitropism. This exactly opposite response of stem and root is due to changes in concentration of the auxin. Roots bend towards gravity due to regulated movement of the auxin known as polar auxin transport. Stem and root cells require differential optimum concentration for elongation. In roots, auxin accumulates towards the gravity that results in the inhibition of cell expansion on the lower side and the curvature of the roots towards gravity. In stems, auxin accumulates towards the gravity. However, it results in increase in cell expansion and results in the shoot curving up.

Thus, the correct answer is option A.