Final answer:
Steroids are the lipids with four fused carbon rings found in cell membranes, notable examples including cholesterol, which helps maintain membrane fluidity and serves as a precursor for hormone synthesis.
Step-by-step explanation:
The lipids described as consisting of four fused carbon rings attached to various side chains and functional groups, and found in cell membranes, are known as steroids.
Steroids are a class of lipids that possess a unique structure comprising four interconnected carbon rings. One well-known example of a steroid that plays a critical role in cell membranes is cholesterol. Cholesterol functions to maintain the fluidity of the membrane and is also a precursor to steroid hormones such as testosterone and estrogen.
Unlike other lipids that are composed of fatty acid chains, steroids have this ring structure that makes them stand out and contributes to their diverse functions within eukaryotic cells, including membrane stabilization and hormone synthesis.