Admission Test for Dental Hygiene (ATDH) Practice Exam Prep & Study Guide

The role of the cell membrane is central to the structure and function of the cell. It acts as a selective barrier, defining what is inside and outside the cell and regulating the movement of substances in and out. This function is pivotal for maintaining homeostasis, allowing essential nutrients to enter while keeping harmful substances out. The cell membrane is composed of a phospholipid bilayer that provides not only a physical boundary but also facilitates communication and interaction with the external environment through various proteins embedded within it.

While the other options describe important cellular functions—like nutrient storage, cellular respiration, and protein synthesis—they do not directly address the primary role of the cell membrane. Therefore, defining the inside and outside of the cell is the most accurate choice, as it encompasses the fundamental protective and regulatory functions of the membrane.