WHAT IS TROPISM?

What is tropism?

It is the turning of all or part of an organism in a particular direction in response to an external stimulus. The response is due to the differential growth of a part of the organism. Note that the whole organism is not displaced or moved from one spot to another. It is a positive or negative response to the external stimulus. A positive response means "towards the stimulus" and a negative response means "away from the stimulus". Tropisms are typically associated with plants but not necessarily restricted to them. Tropism occurs due to the effect of the plant growth hormone called auxin. Tropisms are usually named for the stimulus involved. Here are some examples:

1. • Chemotropism: It is the movement or growth in response to chemicals.
   • Geotropism (or gravitropism): It is the movement or growth in response to gravity. For example, the roots grow towards the ground.
   • Heliotropism: It is the movement or growth in response to sunlight. For example, the shoot grows towards the sunlight.
   • Sonotropism: It is the movement or growth in response to sound.
   • Hydrotropism: It is the movement or growth in response to water.
   • Phototropism: It is the movement or growth in response to light or colors of light.
   • Thermotropism: It is the movement or growth in response to temperature.
   • Electrotropism: It is the movement or growth in response to an electric field.
   • Thigmotropism: It is the movement or growth in response to touch or contact. For example, the climbing plants, such as vines, develop tendrils that coil around supporting objects. Touched cells produce auxin and transport it to untouched cells. Some untouched cells will then elongate faster so cell growth bends around the object.