American Academy of Professional Coders (AAPC) Practice Exam 2025 - Free AAPC Practice Questions and Exam Prep Guide

The cell membrane serves as the boundary of the cell, which is crucial for maintaining the integrity and functionality of the cell. This semi-permeable barrier ensures that the internal environment of the cell is distinct from the external surroundings. It regulates what enters and exits the cell, allowing essential nutrients to pass while keeping out harmful substances. The lipid bilayer structure composed of phospholipids and proteins enables the cell membrane to be flexible yet strong, playing a vital role in protecting and organizing cellular components.

While the other options mention important cellular functions, they do not specifically describe the primary role of the cell membrane. Storing energy is primarily the function of organelles like mitochondria or chloroplasts, cellular division is largely governed by the processes involving the nucleus and microtubules, and the transport of nutrients is a function that is facilitated by the cell membrane but does not encompass its overall role as the defining boundary of the cell.