What is the primary function of a cell membrane?

The primary function of a cell membrane is to regulate what enters and leaves the cell while also providing structural support. The cell membrane is composed of a phospholipid bilayer that creates a semi-permeable barrier between the interior of the cell and the external environment, allowing selective transport of substances. This selective permeability is crucial for maintaining the cell's internal conditions, known as homeostasis, by controlling the flow of ions, nutrients, and waste products. Additionally, the fluid mosaic model describes how the membrane's components—lipids, proteins, and carbohydrates—interact dynamically, contributing to various functions such as signaling, communication, and structural integrity.