What are guard cells responsible for regulating?

Guard cells are specialized cells that flank the stomata, which are small openings on the surface of leaves and stems that facilitate gas exchange in plants. The primary role of guard cells is to regulate the opening and closing of these stomatal pores. When water is abundant, guard cells take up water and swell, causing the stomata to open. This opening allows carbon dioxide to enter the leaf for photosynthesis and facilitates the release of oxygen. Conversely, when the plant is in need of conserving water, the guard cells lose water, become flaccid, and close the stomata, thereby reducing water loss through transpiration.

This regulation is essential for maintaining the plant's water balance, ensuring optimal gas exchange, and ultimately supporting healthy growth and photosynthesis. The other choices encompass processes that are either indirect effects of guard cell function or unrelated roles in plant physiology.