What is a nastic movement?

A nastic movement is a plant's response to a stimulus that is not directional, meaning it does not depend on the direction from which the stimulus comes. Nastic movements are caused by changes in the plant's turgor pressure, which is the pressure exerted by the cell contents against the cell wall. An example of a nastic movement is the opening and closing of stomata, small pores on the surface of plant leaves that regulate gas exchange. When the turgor pressure in the guard cells surrounding the stomata increases, the stomata open, allowing for gas exchange. When the turgor pressure decreases, the stomata close. This movement is independent of the direction of the stimulus, such as light, temperature, or humidity, and is not related to the plant's growth or reproductive processes.