Specialized kidney-shaped cells that surround each stoma and control its opening and closing through changes in turgor pressure. Guard cells regulate gas exchange and water loss in plants.
The term combines 'guard' (from Old French 'garder,' to watch or protect) with 'cells,' reflecting their role as gatekeepers. This descriptive name was adopted in the 19th century as microscopy revealed their protective function.
Guard cells are like microscopic bouncers that decide who gets in and out of the plant's 'nightclub'! They can respond to over a dozen different environmental signals simultaneously, making split-second decisions about whether to open or close based on light, CO2 levels, humidity, and even the time of day.
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