| either of two specialized epidermal cells that flank the pore of a stoma and usually cause it to open and close. |
| guard cell n. One of the paired epidermal cells that control the opening and closing of a stoma in plant tissue. |
guard cell  (gärd) Pronunciation Key
One of the paired cells in the epidermis of a plant that control the opening and closing of a stoma of a leaf. When swollen with water, guard cells pull apart from each other, opening the stoma to allow the escape of water vapor and the exchange of gases. When drier, guard cells become more flaccid and move closer together, allowing the plant to conserve water. Unlike the other cells in the epidermis, guard cells have chloroplasts and conduct photosynthesis. See more at stoma. |