In what way do the membranes of a eukaryotic cell vary?
a. phospholipids are found only in certain membranes.
b. certain proteins are unique to each membrane.
c. only certain membranes of the cell are selectively permeable.
d. only certain membranes are constructed from amphipathic molecules

b. Certain proteins are unique to each membrane.

Explanation:

Cell membranes of the eukaryotes are composed of proteins and lipids. The membranes of the eukaryotic cells are composed of lipid bilayers associated with the proteins. The proteins may differ in composition depending upon the type of cell. The membrane proteins act like a signal sequences to target other proteins to respective destinations to perform desired functions. Therefore, option B is correct.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."