either of two specialized epidermal cells that flank the pore of a stoma and usually cause it to open and close.
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British Dictionary definitions for guard cell
botany one of a pair of crescent-shaped cells that surround a pore (stoma) in the epidermis. Changes in the turgidity of the cells cause the opening and closing of the stoma
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Scientific definitions for guard cell
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.
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