Help The diagram below shows a microscopic view of the lower epidermis of a maple leaf. The cell indicated by the letter B is a guard cell. Guard cells are found on each side of the stomata.

Which of the following statements correctly describes how guard cells affect the physiological processes in a leaf?

A. Guard cells shrink to let in pollen for plant reproduction and swell to keep in oxygen.

B. Guard cells shrink to let in carbon dioxide for photosynthesis and swell to limit transpiration.

C. Guard cells shorten to let in light for photosynthesis and elongate to keep water from entering the cell.

D. Guard cells become rounder to let in oxygen for cellular respiration and flatten out to block the release of carbon dioxide.