Chapter 24, Problem 79A

Interpretation Introduction

Interpretation: The hydrophilic heads located outside the cell membranes are to be explained.

Concept introduction: The fundamental constituents of the plasma membrane are phospholipids, which are organized in the form of a bilayer. Phospholipid bilayers in cell membranes serve as permeability barriers between the different aqueous compartments.

Answer to Problem 79A

The hydrophilic head is located on the outside of the cell membrane because the cytoplasm is composed of water, and the head is attracted to water.

Explanation of Solution

The phospholipid bilayer is composed of two layers of phospholipid. One is a hydrophilic, polar head composed of glycerol and phosphate molecules. The other is a hydrophobic, nonpolar tail made up of chains of fatty acids. Since the cytoplasm is made up of water and the head is hydrophilic, it is located outside of the cell membrane. This is because the head is attracted to water.

Conclusion

The hydrophilic head is located on the outside of the cell membrane because the cytoplasm is composed of water, and the head is attracted to water.