Nonpolar molecules, including water, oxygen, carbon dioxide, and fatty substrates, move through a cell membrane with the greatest ease. This mechanism of transporting molecules across cell membranes is known as simple diffusion.
The plasma membrane of the cell is a selectively permeable layer that enables just some particles to flow through while preventing the entry of other substances. Its major purpose is to preserve cellular integrity and shield the cell from the external environment.
Phospholipids and integral proteins are the fundamental elements of the cell membrane. The components of phospholipids are two fatty acids, glycerol, and a phosphate group. In the fluid-mosaic model, the two nonpolar fatty acids form the tails, while the polar phosphate group forms the head. This configuration is frequently referred to as a “lipid bilayer,” which facilitates the entry of hydrophobic molecules that quickly react with the nonpolar end of the lipid bilayer.
Several processes transport various compounds through cellular membranes. There are two types of membrane transports: passive and active. Passive transport is exemplified by molecules that flow through the membrane through simple diffusion. Facilitated diffusion is another type of passive transport in which polar molecules and ions are moved across a membrane by integral proteins.