Which of the following compounds is classified under lipids?

Lipids are a diverse group of hydrophobic organic compounds that include fats, oils, waxes, and sterols. Cholesterol and phospholipids are both significant lipid types. Cholesterol is a sterol that plays a vital role in cell membrane structure and function, while phospholipids are essential components of cell membranes, forming bilayers that create barriers to separate the interior of cells from their external environment.

In contrast, the other options consist of compounds that belong to different classifications. Proteins and amino acids are building blocks of proteins, forming a separate macromolecule group essential for structure and function in living organisms. Glucose and starch are carbohydrates, which primarily serve as energy sources and structural components. Lastly, cellulose and hemicellulose, also carbohydrates, primarily contribute to plant cell wall structure and integrity. Therefore, cholesterol and phospholipids are correctly identified as lipids, highlighting their crucial roles in biological systems.