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Coordination in Plants

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Coordination in Plants - Lesson Summary

All living things respond to environmental stimuli.  Plants also respond to stimuli with the help of chemical compounds secreted by the cells. Plants being living organisms, exhibit some movements.

Types of movements
The movement of a plant during its growth can be directional or non-directional.

Directional movements: These are also called as tropic movements. Tropic movements are the movements which occur in the direction of the stimulus.

       • Positive phototropism is seen in shoots which respond by bending towards light.  Negative geotropism is seen in shoots by growing away from the ground.
       • Roots bend away from light exhibiting negative phototropism. They grow towards the ground exhibiting positive geotropism.
       • Thigmotropism is the directional growth of a plant part in response to the touch stimulus of an object.  
       • Hydrotropism is a growth response in which the direction is determined by the stimuli of water.
       • Chemotropism is a growth movement of a plant part in response to chemical stimulus. e.g. Growth of pollen tubes towards ovules.

Non- directional movements:  These are also called as nastic responses.  These are exactly the movement of plant parts.
       • These movements are independent of growth.  
       • Plant cells must change their shape for this movement to happen. 
       • The movement in plants occurs in the direction opposite to the stimulus.

Plant hormones
Plants have various hormones, which help to coordinate growth, development and response to the environment.  Hormones are the chemical compounds released by stimulated cells. Hormones diffuse all around the cell.  Different hormones secreted by the plant are auxins, gibberellins, cytokinins, abscisic acid.

       • Auxins are the hormones synthesised at the tip of the stem.  These help the plant in  growth by cell elongation.
       • Gibberellins are hormones that help in the growth of the stem, seed germination, bolting, and flowering.
       • Cytokinins are hormones present in the areas of rapid cell division, such as fruits and seeds. They also promote the opening of the stomata.
       • Abscisic acid is a hormone that inhibits the growth in various parts.  It is also responsible for the closure of stomata.

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