BRAINCAKEOpening and Closing the Stomata
Guard cells open and close the stomata by changing their turgidity. The process depends on the movement of ions and water.
Opening (in light)
• Light stimulates guard cells to use ATP to actively pump hydrogen ions (H+) out of the cell.
• This makes the inside more negative, so potassium ions (K+) move into the guard cells through channel proteins. Starch is also converted to malate ions.
• The build-up of K+ and malate lowers the water potential of the guard cells.
• Water enters by osmosis from neighbouring epidermal cells.
• The guard cells swell and become turgid. Because the thick inner wall stretches less than the thin outer wall, the cells bend outwards and the pore opens.
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Key terms in this lesson
- guard cell
- One of a pair of specialised epidermal cells that surround a stoma and control its opening and closing by changing shape.
More in Gas Exchange
- Very Active Insects
- Gas Exchange in Fish
- Fish Gills
- Ventilating the Gills
- The Countercurrent Exchange System
- Gas Exchange in Plants
- Stomata
- Lenticels
All 23 lessons in Gas Exchange · All Edexcel AS-level Biology topics