Final answer:
Water exits a plant through pores called stomata, which are regulated by guard cells. These cells change shape to open or close the stomata, balancing photosynthesis with water conservation.
Step-by-step explanation:
Water exits a plant through pores called stomata (singular: stoma). Surrounding each pore is a pair of cells called guard cells that regulate the opening and closing of the pore. Stomata are essential for plants as they control the transpiration of water vapor and the exchange of carbon dioxide and oxygen, which are critical for the process of photosynthesis. Leaves typically have a waxy cuticle to prevent water loss; however, the stomata must open to allow gas exchange. The guard cells, which are specialized cells found in pairs, change shape by taking in or losing water through osmosis, thus opening or closing the stomata. The turgor pressure in the guard cells is influenced by environmental factors such as light intensity, leaf water status, and carbon dioxide concentrations which impact the stomatal movement.