CBSE Class 10 Answered

The leaves of Mimosa pudica plant close up under the inflence of various stimuli, such as touching, warming, blowing, or shaking. The stimulus can also be transmitted to neighbouring leaves. These types of movements have been termed seismonastic movements. The movement is caused when the leaves lose turgor pressure.

(Turgor pressure is the force that is applied onto the cell wall by water and other cell contents. This allows the plant to stay upright, but when it is disturbed by a stimuli, chemicals in the plant force the water to leave the cell. When this pressure is lost the result is a sagging plant. This characteristic is quite common within the Mimosaceae family.)

The seismonastic movement is caused by rapid shrinkage of motor cells of the main pulvinus in which dynamic changes in actin cytoskeleton occur. Before the movement, long and thick actin filaments are observed throughout the cytoplasm, whereas after the movement, only short and thin filaments are observed.