Campbell Biology Concepts & Connections Practice Test

Stomata are openings on the leaf surface that primarily regulate gas exchange and water loss. Their main job is to control the movement of carbon dioxide into the leaf for photosynthesis and the release of oxygen, while also allowing water vapor to exit in a process called transpiration. Guard cells surrounding each stoma change shape to open or close the pore in response to light, CO2 levels, humidity, and signals like drought stress, which helps balance photosynthetic needs with water conservation. When stomata are open, CO2 diffuses into the leaf for fixation, and O2 exits as a byproduct; transpiration helps pull water up from the roots through the xylem, aiding nutrient transport and temperature regulation. Absorbing sunlight happens in chloroplasts inside leaf cells, not through stomata; water transport from roots is done by the xylem; and chlorophyll is produced in chloroplasts, not in the stomata.