CONTROL AND COORDINATION IN PLANTS

PLANT MOVEMENT TYPES Growth related:slow process Growth independent:fast process eg.folding-drooping of Mimosa pudica,this plant has pad like swellings called pulvini at the base of each leaf. The folding up of the leaves of a sensitive plant on touching is due to the sudden loss of water from the pulvini.

The leaves of Mimosa pudica are touch responsive using pulvini (pressure-based movement) ©1996 Norton Presentation Maker, W. W. Norton & Company This stimulus (touch) causes folding of leaves (response) !

Immediate Response to Stimuli Plants also use electrical-chemical pathways to convey information from cell to cell =>change in cell shape for movement =>this change is caused by changing the amount of water them(shrinking /swelling) =>change in shape

Tropism (Tropic Movement) A directional growth movement made by a part of a stationary plant in response to stimulus

Types of Tropism 1. The movement of a plant part in response to light is called phototropism. The stem of a growing plant bends towards the light (positive phototropism), while roots of a plant move away from light (negative phototropism). 2. The movement of a plant part in response to gravity is called geotropism. The roots of a plant move downwards in the direction of gravity. On the other hand the stem of a plant grow upwards and away from the earth. 3. The movement of a plant part in response to chemicals is called chemotropism e.g.. the growth of pollen tubes towards ovules during the process of fertilization. 4. The movement of a plant part in response to water is called hydrotropism. The roots of a plant always grow towards water. 5. The directional growth movement of a plant part in response to the touch of an object is called Thigmotropism.

Thigmotropism There are some plants called climbing plants(Creepers) which have weak stems, cannot stand erect on their own. They have climbing organs called tendrils. Tendrils are thin, thread like structures on the stem or leaves of climbing plants. Tendrils are sensitive to touch. When they come in contact with an object, wind around the object and cling to it. This is due to the growth of a tendril towards the object.

Types of Tropism stimulus tropism response water gravity unilateral light geotropism phototropism hydrotropism negative no response shoot positive root positive negative positive

Transmission modes Electrical impulses can reach only those cells that are connected by the nervous tissue. Once an electrical impulse is generated & transmitted in the cell the cell takes time to reset itself before it can generate and transmit a new impulse. Fast but less efficient. A Chemical impulse easily diffuses all around the original cell. Nearby cells detect this compound through special molecules (Receptors )on their surface ,leading to recognition and transmission of information. Slow but more efficient.