Aquaporins: a. play an active role in the regulation of water movement in the xylem during mild drought b. are proteins embedded in the cell walls that transport water c. play an active role in the regulation of water movement outside the xylem during mild drought d. are proteins embedded in the mesophyll and bundle sheath apoplast that transport water

Option B, are proteins embedded in the cell walls that transport water

Explanation:

Aquaporins are water channels that are present in the membrane of root cell and belong to the group of major intrinsic protein (MIP) family. It not only assists in rapid Trans membrane water transport but also regulate the flux of water between cells and within the cell

They are small, hydrophobic, intrinsic membrane proteins that create water channels for movement of water into and between cells across all organ systems and hence they are known as plumbing system for cells and

Thus, option B is correct