stoma (redirected from Guard cells)

stoma

 or stomate

Any of the microscopic openings or pores in the epidermis of leaves and young stems. They are generally more numerous on the undersides of leaves. They provide for the exchange of gases between the outside air and the interconnecting air canals within the leaf. A stoma opens and closes in response to turgor pressure within its two surrounding guard cells. Because the inner wall of each of these sausage- or bean-shaped cells is thicker than the outer wall, when they fill with water and become turgid they balloon outward, enlarging the stoma. A drop in carbon-dioxide levels to lower than normal also causes the guard cells to become turgid. Guard cells control excessive water loss from the plant, closing on hot, dry, or windy days and opening when conditions are more favorable.

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stoma

1. Botany an epidermal pore, present in large numbers in plant leaves, that controls the passage of gases into and out of a plant

2. Zoology anatomy a mouth or mouthlike part

3. Surgery an artificial opening made in a tubular organ, esp the colon or ileum

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stoma [′stō·mə]

(biology)

A small opening or pore in a surface.

(botany)

One of the minute openings in the epidermis of higher plants which are regulated by guard cells and through which gases and water vapor are exchanged between internal spaces and the external atmosphere.