Concept:Stomata open and close due to changes in the turgor pressure of guard cells, which are specialized epidermal cells.Explanation:Each stoma is surrounded by a pair of guard cells. When guard cells take in water, they become turgid and the pore opens. When they lose water, they become flaccid and the pore closes. This movement is driven by potassium ion (K+) concentration. Higher K+ inside guard cells lowers water potential, drawing in water by osmosis. External factors like light, humidity, and the hormone abscisic acid also influence this process.Answer:B. Guard cell