How Does Carbon Dioxide Enter a Leaf

How does carbon dioxide enter a leaf?

A) CO2 passes through openings called stomata on the leaf surface.
B) CO2 diffuses through the epidermal cells into the mesophyll.
C) CO2 is moved by active transport into the leaf by special cells called guard cells.
D) Atmospheric pressure forces CO2 through pits on the leaf surface.
E) CO2 travels dissolved in the water in the xylem.