Book 29, Question 45
How do leaves breathe?
Leaves have thousands of tiny pores called stomata, mostly on the underside.
Each pore is guarded by two cells that open or close it. When open, carbon dioxide enters for making food, and water vapor and oxygen escape. On hot, dry days, plants close their pores to save water. A single leaf can have many thousands of stomata, too small to see without a microscope.