Cell Membranes

 Cell membranes are the thin, flexible barriers that surround cells, separating the interior of the cell from the extracellular environment. They are composed of a lipid bilayer, which is made up of two layers of phospholipid molecules. These phospholipids have a hydrophobic (water-repelling) tail and a hydrophilic (water-attracting) head, which allows them to arrange themselves in a bilayer with the tails facing each other and the heads facing outward.

In addition to phospholipids, cell membranes also contain proteins, which perform various functions such as transporting molecules in and out of the cell, receiving signals from other cells, and anchoring the membrane to the cytoskeleton. Some cell membranes also contain cholesterol, which helps to maintain the fluidity and stability of the membrane.

Cell membranes are selectively permeable, meaning they only allow certain molecules to pass through while preventing others from crossing. This is achieved through various mechanisms, including passive diffusion, facilitated diffusion, active transport, and endocytosis/exocytosis.

Overall, cell membranes play a crucial role in maintaining the integrity and function of cells by regulating the flow of materials into and out of the cell.