Answer:
Explanation:
A cell membrane is composed of two phospholipid layers in which each molecule contains a single phosphate head and two lipid, or fatty acid, tails. The heads align along the inner and outer boundaries of the cell membrane, while the tails occupy the space in between. Only small, nonpolar molecules can pass through the membrane through simple diffusion. The lipid tails reject polar, or partially charged, molecules, which include many water-soluble substances such as glucose. However, the cell membrane is peppered with transmembrane proteins that provide passage to molecules that the tails would otherwise block.
