Question

The area of response in phototropism and geotropism is
A. Apical meristem
B. Subapical meristem
C. Region of elongation
D. Area of differentiation

Answer 1

Hint: Auxin changes the rate of elongation in plant cells, controlling their length. They are mostly made in the tips of the growing stems and roots, which are the meristems.

Complete answer:
Movement in pants can take place either naturally or due to the response to an external stimulus. There are different kinds of movements that are based either on spontaneous or induced movement.

In general, tropism is an organism's movement in response to stimuli. It involves the growth rather than body movement. Phototropism occurs when light is provided to plants in a single direction. The plants tend to move or to bend towards the light source. Auxins are plant hormones with growth-regulatory properties. In general, they are formed by the growing tips of the stems and roots, where they move to the other regions. Auxins are responsible for promoting cell elongation, a process that is needed prior to cell differentiation. The stem on the shaded region produces more auxin and grows longer, making the stem bend towards the sun. Geotropism is related to phototropism, where the plant experiences directional growth, but as a response to gravity. In a horizontally positioned stem, the bottom side produces more auxin and expands more, thus allowing the stem to curve upwards against gravity.

Hence, the correct answer is option (C)

Note: Growth in plants is regulated by chemical substances called PGR (plant growth regulators). Various groups of PGRs are found in plants, mostly belonging to five categories: auxins, gibberellins, abscisic acid, cytokinins, and ethylene. They are produced in different sections of the plant and they regulate differentiation and development.