The primary function of the plasma membrane is to protect the cell from its surroundings. Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells.

How does oxygen pass through the Plasmalemma?

Oxygen and carbon dioxide move across cell membranes via simple diffusion, a process that requires no energy input and is driven by differences in concentration on either side of the cell membrane.

How does the phospholipid bilayer work?

In water, phospholipids spontaneously form a double layer called a lipid bilayer in which the hydrophobic tails of phospholipid molecules are sandwiched between two layers of hydrophilic heads (see figure below). ... The lipid bilayer acts as a barrier to the passage of molecules and ions into and out of the cell.