Which of the following is NOT classified as a lipid?

Chylomicrons are actually classified as lipoproteins rather than lipids themselves. While they are associated with lipid transport in the body, they serve as carriers for triglycerides, cholesterol, and other lipids in the bloodstream. Chylomicrons consist of a core of triglycerides surrounded by a layer of phospholipids and proteins, which allow them to move through the water-based environment of the blood.

In contrast, triglycerides, cholesterol, and phospholipids are all types of lipids. Triglycerides are the main form of stored energy in animals, cholesterol is a sterol that is important for cell membrane structure and hormone production, while phospholipids are essential components of all cell membranes. Thus, while chylomicrons play a crucial role in lipid metabolism, they are not classified as lipids themselves.