Which statement about transpiration is true?

• A. Stomata are internal pores that only allow water vapor to exit
• B. Stomata are permanent openings that never close
• C. Transpiration reduces the plant's water loss
• D. Transpiration is the evaporation of water from leaves through stomata

Answer: (D)

Transpiration is the evaporation of water from leaf surfaces through the stomata. Stomata are openings in the leaf epidermis that regulate gas exchange—carbon dioxide in for photosynthesis and water vapor out with transpiration. Because water vapor exits when these openings are open, transpiration involves a loss of water from the plant, and is influenced by factors like temperature, humidity, airflow, and soil moisture. Stomata do not remain permanently open; they open and close in response to conditions to balance water loss with the plant’s need for CO2. They aren’t internal pores, and they don’t only allow water vapor to exit—they also control the entry of CO2.