Question

The stomata in angiosperms open and close due to______________

• A. The presence of gases inside the leaves.
• B. Their genetic constitution.
• C. Turgour pressure of guard cells.
• D. Turgour pressure of subsidiary cells.

Answer 1

The correct option is C Turgour pressure of guard cells.

• 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.
• Photosynthesis depends on the diffusion of carbon dioxide (CO${}_2$) from the air through the stomata into the mesophyll tissues. Oxygen (O${}_2$), produced as a byproduct of photosynthesis, exits the plant via the stomata.
• When the stomata are open water is lost by evaporation and must be replaced via the transpiration stream with water taken up by the roots. 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.

Therefore, the correct answer is option C.