Biology · Cell Structure and Function

The cell membrane consists of a lipid bilayer where the hydrophilic heads of phospholipids face the aqueous internal and external environments, allowing the membrane to interact with water and maintain cellular integrity. The hydrophobic tails, however, face inward, away from water, creating a barrier to most water-soluble substances. This functional design is essential for the selective permeability of the membrane. The other options are incorrect as they either misrepresent the properties of the membrane or incorrectly suggest that both hydrophobic and hydrophilic characteristics are in contact with the environments.

The hydrophobic property refers to regions of molecules that repel water. In the context of the cell membrane, while the hydrophobic fatty acid tails of phospholipids play a crucial role in forming the lipid bilayer, they do not interact with the aqueous internal and external environments of the cell.

The hydrophilic property refers to regions of molecules that attract water. In the cell membrane, the hydrophilic heads of phospholipids face outward towards both the internal and external environments, allowing them to interact with the aqueous surroundings and facilitating the membrane's function.

The term 'neutral' does not accurately reflect the properties of the cell membrane. The membrane has distinct hydrophilic and hydrophobic regions that contribute to its selective permeability and structural integrity.

This option is misleading. While the cell membrane contains both hydrophobic and hydrophilic regions, only the hydrophilic heads are in direct contact with the internal and external environments. Thus, this option cannot be considered correct.