CBSE Class 10 Answered

The closing of the leaves of the touch me not plant is not a tropic movement, but a nastic one. It is not dependent on the direction of the stimulus. When touched or shaken, the compound leaves fold inward and droop.

The movement occurs when specific regions of cells lose turgor pressure. When the plant is disturbed, specific regions on the stems are stimulated to release chemicals including potassium ions which force water out of the cell vacuoles and the water diffuses out of the cells, producing a loss of cell pressure and cell collapse; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole.