Stomatal Guard Cells

Definition - What does Stomatal Guard Cells mean?

Stomatal guard cells, located on a plant's stomata on its leaves, are responsible for controlling small openings (the stomata) on a plant’s leaves through which the plant can “sweat”. These cells help to encourage gas exchange during photosynthesis, and while the process does result in water loss, it is a necessary trade-off for growth.

On the underside of a plant’s leaves are pore-like openings called stomata. Guard cells surround these pores, and help to regulate their opening and closing.

MaximumYield explains Stomatal Guard Cells

Plants rely on photosynthesis for the food they consume and the energy they need for growth. However, during this process, gases must be exchanged – oxygen must be expelled, and carbon dioxide must be taken in. This cannot happen if a plant keeps itself sealed off – stomatal guard cells help ensure that gas exchange can occur, and ensure that not too much water is lost during the process.

On the underside of a plant’s leaves are pore-like openings called stomata. Guard cells surround these pores, and help to regulate their opening and closing. When open, moisture can escape from the plant, and gas exchange occurs. Ultimately, more than 95 per cent of water loss in a plant is due directly to water vapor lost through stomatal activity.

When the pores close, gas exchange stops, but so does moisture loss. By regulating the number of open and closed pores at any given time, stomatal guard cells are able to maintain a balance between moisture levels within the plant, and the needed gas exchange to ensure healthy growth.

Guard cells function based on the influx of water and light. When light shines on the cells, the outer walls bow, while the inner walls remain rigid. This pulls the stomata open, allowing gases to exchange. When darkness falls, water is lost, and the moisture levels inside the walls drops. This allows the pores to close.

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