Transpiration

Stomata are minute specialised pores generally present on leaf epidermis. Each stoma is bordered by two specialised epidermal cells called guard cells. Stomata normally open when the light strikes the leaf and close during night. When the light strikes the leaf causes a change in the turgor of the guard cells. The inner wall of each guard-cell flanking each stoma is thick and elastic. Due to turgor pressure, the thin outer walls buldge out and force the inner walls to attain crescent shape. This mediates opening of stomata. When the guard cells lose turgor, the elastic inner wall helps to regain their original shape and the stoma closes.