What structural role does the plasma membrane play in cells?

The plasma membrane serves a crucial structural role by providing a barrier that separates the interior of the cell from its external environment. This selective boundary is essential for maintaining the integrity of the cell, allowing it to regulate the internal conditions necessary for life processes. The plasma membrane is composed of a phospholipid bilayer with embedded proteins that contribute to its selective permeability, thereby ensuring that essential molecules can enter the cell while waste products and harmful substances are kept out. This barrier function is vital for homeostasis, allowing cells to maintain an optimal internal environment, which is critical for numerous cellular functions.