Final answer:
The lipid portion of the cell membrane acts as a selective barrier, while the protein portion determines various specific functions such as transport and cell recognition. Correct answer: b. lipid, protein.
Step-by-step explanation:
The lipid portion of the cell membrane functions as a barrier while the protein portion determines specific functions, which include pumps, receptors, adhesion, and more. Hence, the correct answer is b. lipid, protein. Components such as phospholipids form the bilayer and provide the main structural barrier of the cell membrane. Their hydrophobic tails face inward, shielded from water, while the hydrophilic heads face outward. This arrangement creates a semi-permeable membrane that governs what enters and exits the cell. Proteins embedded in the membrane have various functions, such as forming transport channels (integral proteins), serving as receptors, facilitating cell adhesion, and participating in the cell's recognition sites along with carbohydrates, specifically in functions like cell-cell recognition, acting as peripheral proteins. Carbohydrates are found on the external surface of the plasma membrane and are typically bound to proteins (as glycoproteins) or to lipids (as glycolipids), contributing to the cell's interactive capabilities.