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In case of plants, growth and development is in a coordinated manner. The higher plants do not show locomotion. However, locomotion is seen in structures like sperm cells of ferns and mosses that swim towards the egg. The other movements shown by the plants are associated with the growth of the plants. For example, the shoot system moves towards sunlight and the root system towards earth. Thus, the plants also respond to their environment.
The movement of plants in the direction of stimulus is known as 'tropism'. There are mainly three types of tropism. They are:
Phototropism - Bending towards light
 Geotropism - Downward movement in response to gravity
 Chemotropism - Movement in response to chemical activity
Apart from these, nastic movement may also be observed in some plants. This is the movement of plant parts caused by an external stimulus but unaffected in direction by it.
Example: The leaves of the 'touch -me - not' plant droop on touching.
The growth of the plants, their development and their responses to the environment are controlled or coordinated with the help of chemicals. These chemicals are called the growth regulators as they either promote or inhibit the growth of the plants.
Flowering and seed germination are regulated by the duration of light. This is known as photoperiodism. Plants respond to photoperiodism by a specialised pigment called phytochrome present in very small quantity.
Growth in plants has three stages - cell division, cell enlargement and cell differentiation. These stages are controlled by different growth regulators.
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