Two examples of lipids include fat and which other substance?

Lipids are a broad category of hydrophobic organic molecules that are essential for various biological functions. Fats, which are a type of lipid, serve as a major energy source and play a key role in cellular structure, while cholesterol is another significant lipid. Cholesterol is primarily known for its role in cellular membranes and as a precursor for steroid hormones and bile acids.

In the context of this question, cholesterol aligns with the definition of lipids as it is a steroid alcohol and is insoluble in water, categorizing it alongside fats as a lipid. The other substances listed, such as sugar, fiber, and amino acids, do not fall under the lipid classification; sugars are carbohydrates, fiber is a type of carbohydrate as well, and amino acids are the building blocks of proteins. Thus, cholesterol is the correct choice for another substance that exemplifies the lipid category.