Question

What are tropic movements? Briefly explain various types of tropic movements in plants.

Answer 1

The directional movement of plant parts towards or away from a stimulus is known as tropic movement or tropism.

Different types of tropic movements in plants:

Tropic Movement	Description
Phototropism	Movement of plant parts towards or away from light is termed phototropism. Because shoots of most plants grow towards the source of light, it is termed positive phototropism. Roots grow away from light and hence are negatively phototropic.
Geotropism	Movement of plant organs in response to gravity is termed geotropism. Roots are positively geotropic because they grow in the direction of gravity. The shoot grows upwards, i.e. against gravity, and hence is negatively geotropic.
Chemotropism	Movement of plant organs in response to a chemical stimulus is called chemotropism. When plant organs grow away from the chemical response, it is called negative chemotropism. When plant parts grow towards the chemical response, it is called positive chemotropism. The pollen tube grows towards the sugary substance secreted by the stigma of the flower.
Hydrotropism	Movement of plant organs in response to water is termed hydrotropism. Roots grow towards the source of moisture and hence are positively hydrotropic.
Thigmotropism	Movement of plant organs in response to stimuli caused by physical contact with solid objects is termed thigmotropism. Weak-stemmed plants use twining stems and tendrils to climb on other plants/objects which provide them support. Hence, twining stems and tendrils are positively thigmotropic.