Guard cell
/ˈɡɑrd ˌsɛl/
Definition
Guard cell refers to one of the two specialized plant epidermal cells that surround a stoma, the tiny pore on a leaf or stem surface. By swelling or shrinking as their water content changes, guard cells open or close the pore. This regulates gas exchange, including carbon dioxide uptake for photosynthesis, and controls water loss through transpiration. Their paired shape and movement distinguish them from other surface cells.
Function in Plants
- Stomatal opening control: A guard cell changes shape to open or close the pore, regulating how much carbon dioxide enters for photosynthesis and how much water vapor leaves the leaf.
- Water balance under stress: During drought, heat, or dry air, signals such as the plant hormone abscisic acid promote closure. This helps limit water loss, though it can also reduce photosynthesis.
- Response to light and environment: Blue light, internal carbon dioxide levels, humidity, and temperature can influence guard cell activity. That rapid adjustment helps match gas exchange to changing conditions.
- Relevance to plant performance: Because stomatal behavior affects cooling, water use, and sugar production, guard cell function is closely tied to growth, wilting risk, and tolerance of environmental stress.
Related Terms
Stoma
Stoma refers to a microscopic pore in the epidermis, the outer cell layer of leaves and young stems. Each stoma is…
Transpiration
Transpiration is the plant process of losing water vapor to the air, mainly through tiny leaf pores called stomata, and…
Osmosis
Osmosis is a biological process in which water moves across a selectively permeable membrane, such as a plant cell…
Plasmolysis
Plasmolysis is a biological process in plant cells in which the cell membrane pulls away from the cell wall after the…
Vacuole
Vacuole refers to a membrane-bound compartment inside a plant cell, best known as the large central vacuole found in…
Photosynthesis
Photosynthesis is the biological process in which plants, algae, and some bacteria use light energy to convert carbon…