Final answer:
Biomembranes consist of phosphoglycerides, sphingolipids, and steroids. Phosphoglycerides and sphingolipids form the structural framework, while cholesterol, a steroid, contributes to membrane fluidity and serves as a precursor for hormones.
Step-by-step explanation:
The classes of lipids present in biomembranes include phosphoglycerides, sphingolipids, and steroids. Phosphoglycerides and sphingolipids are major constituents of the membrane, composing much of its framework. Steroids, particularly cholesterol, are also present in the membrane and are crucial for maintaining its fluid nature and permeability. Phospholipids, which are constructed from a glycerol or sphingosine backbone, fatty acids, and a phosphate-containing group, form a bilayer that is essential for membrane structure and function. Cholesterol, a type of steroid, not only plays a role in membrane fluidity but also serves as a precursor for steroid hormones.