Explain co-ordination in plants with the help of suitable examples.
Answers
Since plants do not have nervous and muscular system like animals,
coordination in plants occurs in response to particular stimuli.
Tropism/tropic movement is the term used for the movement or growth of
any plant part in response to an external stimulus.
These tropic movements can be of various types like:
Phototropism: The growth movement in plants in response to light stimulus
is known as phototropism. For example, the flower head of a sunflower is
positively phototropic as it moves from East to West, along with the
movement of the Sun.
Geotropism: The growth movement in plants in response to the force of
gravity is known as geotropism. In geotropism, the roots of the plant always
grow downwards, while the shoots always grow upwards, away from the
earth.
Chemotropism: The growth movement in plants in response to chemical
stimuli is known as chemotropism. For example, the growth of pollen tube
towards the ovule in the ovary (through the stigma and style) is an example
of positive chemotropism.
Hydrotropism: The growth movement in plants in response to water is
known as hydrotropism. For example, the roots of some plants grow towards
the water source, even when the water source is not present directly below it.
Thigmotropism: The growth movement in plants in response to a touch
stimulus or contact with a solid object is known as thigmotropism. For
example, in some plants, the coiling of tendrils occurs when they come in
contact with objects for support.