Stoma

What is Stoma?

A pore in the epidermis of a leaf, found mainly in the lower epidermis and bounded by two guard cells. Carbon dioxide diffuses into the leaf through the stoma and oxygen and water vapour diffuse out. The guard cells alter the size of the pore, and so control the rate of gas exchange and of water loss.

This definition is part of the Plant Nutrition chapter in Cambridge O Level Biology.

Concepts related to Stoma

• guard cell
• Diffusion
• air space
• water loss

Common mistakes with Stoma

• “Stomata absorb light for the plant.” Why it is wrong: a stoma is a hole. Light is absorbed by chlorophyll inside chloroplasts, and a pore contains neither. Say instead Stomata are pores that allow carbon dioxide to diffuse in and oxygen and water vapour to diffuse out. Light absorption is done by the chloroplasts in the mesophyll.