A Level Biology Practice Exam

What are triglycerides composed of?

1. One glycerol and two fatty acids

2. One glycerol and three fatty acids

3. Three glycerol molecules

4. Two fatty acids and one phosphate group

The correct answer is: One glycerol and three fatty acids

Triglycerides are composed of one glycerol molecule and three fatty acids. The structure consists of the glycerol backbone to which three fatty acid chains are esterified. This arrangement allows triglycerides to serve as a major form of energy storage in organisms. They are significant in biology because they provide more than twice the energy per gram compared to carbohydrates and play critical roles in insulation and protection of organs. The other options do not accurately represent the structure of triglycerides. One option mentions only two fatty acids, which is insufficient for a complete triglyceride molecule. Another suggests three glycerol molecules, which does not align with the chemical composition of triglycerides. Lastly, a combination of two fatty acids and a phosphate group resembles the structure of phospholipids, not triglycerides. Thus, the correct choice is indeed the one that states triglycerides are made up of one glycerol and three fatty acids.