Answer:
Plasma membranes are lipid bilayers that control entry and exit of substances into and out of cells.
Explanation:
Plasma membranes are lipid bilayers and are made of two layers of amphipathic phospholipids. Proteins are embedded in the lipid bilayer while carbohydrates are attached to the surface of the bilayer. Phospholipids have polar heads and non-polar tails. The non-polar tails are two layers of phospholipids that make the core of the membranes.
This non-polar core does not allow the polar, charged and large substances to pass through it. Therefore, plasma membranes are selectively permeable membranes and allow only certain non-polar, uncharged and small molecules to pass through them. In this way, they control the entry and exit of substances into and out of cells.
