Which microscopic pores on the epidermis of leaves and stems facilitate gas exchange and regulate water loss?

• A. Guard cells
• B. Stomata
• C. Mesophyll
• D. Lenticels

Answer: (B)

Stomata are the microscopic pores in the epidermis of leaves and stems that enable gas exchange and regulate water loss. Each pore is surrounded by two guard cells that change shape to open or close the pore in response to light, CO2 levels, humidity, and the plant’s water status. When open, CO2 can enter for photosynthesis and water vapor exits as transpiration; when closed, water loss is reduced during drought or heat. Guard cells control the opening, but the pores themselves are the stomata. Mesophyll is the internal photosynthetic tissue, and lenticels are openings on woody stems for gas exchange through the periderm, not the leaf epidermis.