guard cell
noun [ C ] biology specialized uk/ˈɡɑːd ˌsel/ us/ˈɡɑːrd ˌsel/
植物的保卫细胞（保卫细胞组成环状，构成了叶子的气孔，能控制气流的进出，阻止水分流失。）
on a leaf, one of a pair of cells positioned around each stoma (= a small hole in the surface) that open it to release gases or close it to prevent water from being lost