Plants Control the Diffusion of Water Vapor and Gases Across

Question

Plants control the diffusion of water vapor and gases across the epidermis by means of ____.  
A) xylem
B) phloem
C) periderm
D) companion cells
E) stomata

Accepted Answer

Stomata are small pores located on the leaves, stems, and other parts of the plants that allow for gas exchange and water vapor to transpire. The guard cells surrounding the stomata can open or close the pore depending on the plant's needs for water and gas exchange. Therefore, stomata control the diffusion of water vapor and gases across the epidermis. Xylem and phloem are the plant tissue responsible for the transport of water and nutrients, respectively. Periderm is the protective tissue that replaces the epidermis in woody stems and roots. Companion cells are specialized cells found in the phloem that contribute to the loading and unloading of sugars during photosynthesis. None of these tissues control the diffusion of water vapor and gases across the epidermis.