Final answer:
The lipid bilayer is primarily composed of phospholipids, which are the major components of the plasma membrane of cells. Cholesterol and various proteins also contribute to the structure and function of the membrane.
Step-by-step explanation:
The lipid bilayer is predominantly composed of phospholipids. These molecules are critical in forming the plasma membrane of cells. The structure of a phospholipid includes a glycerol backbone, two fatty acid tails, and a phosphate group linked to a head group. This configuration allows phospholipids to orient themselves in a bilayer, with the hydrophilic (water-attracting) head groups facing the aqueous environment on both sides of the membrane, and the hydrophobic (water-repelling) tails facing each other, creating a barrier that separates the interior of the cell from the external environment.
Other components such as cholesterol and proteins are also present in the membrane. Cholesterol plays a role by providing flexibility to the membrane, while integral and peripheral proteins are involved in functions such as transport and cell recognition. Although carbohydrates are a smaller component, they're crucial on the cell surface, often attached to proteins (glycoproteins) or lipids (glycolipids) to form recognition sites.