Question

How does control and coordination takes place in plants?

Answer 1

1. No nervous system: Plants have no nervous system, no sense organs and no muscle tissue. So all control and coordination is carried out by chemical substances called plant hormones (phytohormones).
2. Mode of action: A hormone is made in one part of the plant, diffuses slowly to the region where it is needed, and controls growth there. The response is therefore slow and needs no nerve impulse.
3. Main plant hormones:
   • Auxin: This hormone promotes cell elongation. It also controls directional tropic growth.
   • Gibberellin: This hormone specifically promotes the growth of the stem.
   • Cytokinin: This chemical compound actively stimulates rapid cell division.
   • Abscisic acid (ABA): This substance acts as a growth inhibitor. It causes the wilting of leaves. It also triggers the closing of stomata.
4. Types of movement:
   • Growth-independent (nastic) movement: This is an immediate plant response. It does not depend on physical growth. For example, leaves of the touch-me-not plant fold when touched. This happens because water moves out of cells at the leaflet base.
   • Growth-dependent (tropic) movement: This is a slow growth movement. It occurs towards or away from a stimulus. Examples include phototropism, geotropism, hydrotropism, and chemotropism.