Final answer:
The major component of cell membranes is a lipid bilayer, which includes phospholipids and cholesterol, while proteins and carbohydrates also play important roles but are not the main structural component. (option 4)
Step-by-step explanation:
The major component of cell membranes is a lipid bilayer. The lipid bilayer consists primarily of phospholipids, which contain two fatty acid tails that are hydrophobic and a phosphate-linked head that is hydrophilic. This dual nature of phospholipids allows the cell membrane to form a barrier that is selectively permeable to various substances. Cholesterol is another important lipid found in the bilayer, imparting flexibility to the membrane. While proteins and carbohydrates play significant roles in cell membrane function, including transport and cell recognition, they are not the primary structural components. The proteins float in or attach to the lipid bilayer, and carbohydrates are mostly found on the extracellular surface, where they are attached to proteins (forming glycoproteins) or lipids (forming glycolipids).