The primary component of cellular membranes is phospholipids. Phospholipids are amphipathic molecules, consisting of a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails. This unique structure allows them to form a bimolecular layer, creating a semi-permeable barrier that regulates the movement of substances in and out of cells. The arrangement of phospholipids, along with embedded proteins and carbohydrates, forms the fluid mosaic model of cellular membranes, essential for maintaining homeostasis and facilitating communication and transport.