Question

Name the cells that surround a stomatal pore.

• A. Pallisade parenchyma
• B. Spongy parenchyma
• C. Guard cells
• D. Mesophyll

Answer 1

Answer: (C)

Guard cells

• Guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata.
• Guard cells are specialized cells in the epidermis of leaves, stems and other organs that are used to control gas exchange.
• The guard cells are produced in pairs with a gap between them that forms a stomatal pore. The stomatal pores are largest when water is freely available and the guard cells are turgid and closed when water availability is critically low and the guard cells become flaccid.
• Plants must balance the amount of CO${}_2$absorbed from the air with the water loss through the stomatal pores, and this is achieved by both active and passive control of guard cell turgor and stomatal pore size.
• Opening and closure of the stomatal pore is mediated by changes in the turgor pressure of the two guard cells. The turgor pressure of guard cells is controlled by movements of large quantities of ions and sugars into and out of the guard cells.