Guard Cell
Plant Epidermal Cell
About the Guard Cell
Plant Epidermal Cell
Leaf surface
Pairs of guard cells surround tiny pores in the leaf epidermis and open or close them.
Clinical and real-world context
Guard cells are plant-specific, but they are a clear model of how cells use water pressure to change shape and control gas exchange.
3 structures to explore
Stoma
The adjustable pore
The gap between the two guard cells is the stoma. CO2 enters through it for photosynthesis, and water vapour leaves.
Most water a plant loses leaves through its stomata.
Chloroplasts
Light and sugar sensors
Unlike most epidermal cells, guard cells contain chloroplasts, which help them respond to light and adjust the pore.
Most other epidermal cells of a leaf are colourless.
Unevenly Thick Wall
The built-in hinge
When guard cells take up water they swell, and the uneven wall makes them bow outward so the pore opens. When they lose water, the pore closes.
Guard cells can open stomata within minutes.