Movement in Sensitive Plant:
The movement in sensitive plant leaves takes place in response to touch (shock) stimulus. When terminal pinnacle is touched, the stimulus is conducted to its base and the pinnacles droop down.
This happens in change in osmotic pressure (decrease) causing shrinkage. When the stimulus time is over, osmotic pressure increases and the cells swell, the pennules become normal.
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Thus, movement happens at a point different from the point of touch (stimulus). So, the information that a touch has occurred communicated through electrical-chemical means from cell to cell, but not through specialized tissues.
Plant cells change in shape by changing amount of water in them, resulting in swelling or shrinking, during movement.
Movement in Human Legs:
Human legs are provided with nerves which have connection with muscles. To lift the leg, the brain passes information to nerves.
The information travels as an electrical impulse. On reaching leg muscles, impulse is converted into a chemical signal and the muscles contract to lift the leg.
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Movement of legs takes place due to muscle contraction and relaxation, which is under the control of our nervous system.
When nerve impulse reaches the muscle ceils the cells move by changing their shapes. Special proteins cause both changes in shape and their arrangement in the cell in response to nervous electrical impulses.