Advanced Placement (AP) Biology Practice Exam

Which component of the phospholipid bilayer is hydrophobic?

1. Phosphate head

2. Fatty acid tail

3. Glycerol backbone

4. Protein channels

The correct answer is: Fatty acid tail

The component of the phospholipid bilayer that is hydrophobic is the fatty acid tail. In the structure of a phospholipid, there are two hydrophobic fatty acid tails that can repel water. These tails consist of long hydrocarbon chains that do not interact well with water due to their nonpolar nature. In contrast, the phosphate head is hydrophilic, meaning it interacts well with water and is oriented towards the aqueous environment both inside and outside the cell. The glycerol backbone serves as a linking structure between the hydrophilic head and the hydrophobic tails, but it is not inherently hydrophobic or hydrophilic on its own. Protein channels, found within or on the surface of the phospholipid bilayer, play roles in transport and communication but are not part of the phospholipid structure itself.