Immediate Response to Stimulus & Tropic Movement

We all know that plants cannot move as humans do. However, they move their leaves in response to some stimulus. Plants do not have a nervous system or a muscle system. Then, how do the plants respond to certain stimuli?

What is a Stimulus?

The changes in the environmental conditions to which the organisms respond are known as stimuli. Every living organism responds when an external stimulus acts on it. When various organs work together in a systematic manner to produce a response to the stimulus, it is called coordination. Plants do not move from their place but change their growth patterns. That is why plants of the same species have different body forms. This change in the growth pattern in response to a stimulus is known as tropism.

Unlike animals, the response of a plant is regulated by the interaction of two or more plant hormones. It takes a considerably longer time to observe the stimulus.

The plants use electrical-chemical means to convey the information, but they have no specific tissues. Plants change their shapes by changing the amount of water in their cells, resulting in shrinking and swelling. One such example of a plant that responds to a stimulus is Mimosa pudica. This response is growth independent.

Tropic Movement in Plants

Tropic movement is the biological phenomenon that indicates a movement of an organism, such as plants, towards an environmental stimulus. The various types of tropic movements are:

  • Geotropism– Response to gravity
  • Phototropism– Response to light
  • Thigmotropism– Response to mechanical stimulation
  • Chemotropism– Response to particular substances
  • Hydrotropism– Response to water
  • Traumatotropism– Response to wound lesion

These responses are growth dependent.

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