Coordination in plants

• Plants do not have nervous system or muscles to respond to the stimulus.
• Plants show two different types of movement in respond to the stimulus i) one dependent on growth ii) another independent of growth.

Movement dependent on growth

Plants respond to stimuli by growing in a particular direction and because of the directional growth it appears as if the plant is moving.

Tropic movement or tropism is the plant movement that is determined by the direction of an environmental stimulus.

Tropic movements can be towards the stimulus or away from it.

The tropic movements are of various types depending on the nature of stimulus-

• Phototropism – Here, the stimulus is light. Shoots respond by bending towards light while roots respond by bending away from it.

Fig. phototropism  

• Geotropism- Here, the stimulus is gravity. Roots of plants grow downward towards gravity whereas shoots grow upward against gravity.

Fig. Roots grow towards gravity  

• Hydrotropism- In hydrotropism, stimulus is water. Roots always grow towards water.

Fig. hydrotropism  

• Chemotropism- the movement in response to chemical stimulus is called as chemotropism. Growth of pollen tubes towards ovules, where ovules produce chemicals for the growth and passage of pollen tubes.

Fig. chemotropism 

Movement independent of growth

• As no growth is involved, so plants move by changing the shape of the cells.

For eg. i) In sensitive plants, the plants move its leaves in response to touch

ii) The movement takes place at a point different from the point of touch.

iii) Some cells change shape by changing the amount of water in them and as a result the cells either shrink or swell and therefore change shapes.

Fig. sensitive plant