Final answer:
Cell membranes are primarily composed of lipids and proteins, with carbohydrates attached to the exterior. Protein makes up about 50% of a typical human cell membrane's mass, while lipids make up about 40%, and carbohydrates 10%.
Step-by-step explanation:
Cell membranes are mainly made up of lipids and proteins. These include phospholipids, cholesterol, and a variety of proteins that serve different functions within the cell membrane. Carbohydrates are also present, attached to lipids and proteins on the outward-facing surface of the membrane.
The majority of a typical human cell membrane's mass is approximately 50% protein, 40% lipids, and 10% carbohydrates. It is important to note that the proportions of these macromolecules can vary significantly in different types of cell membranes. For instance, in myelin, the lipid content is much higher than in other cell membranes.