Example of compound that is phospholipids include:

Phospholipids are amphipathic lipid molecules comprising a glycerol backbone, two fatty acid tails, and a phosphate group linked to a polar head group. Lecithin, chemically known as phosphatidylcholine, is a major class of phospholipids found in biological membranes and cellular components. It plays essential roles in maintaining structural membrane integrity, facilitating signal transduction, and acting as an emulsifying agent in both physiological systems and pharmaceutical formulations. In contrast, other options represent entirely distinct biological macromolecules or monomeric building blocks, such as carbohydrates, amino acids, or glycosaminoglycans. Consequently, lecithin is the only correct answer representing a compound classified as a phospholipid among the provided choices.

A. Glycogen is a branched polysaccharide of glucose that serves as the primary form of carbohydrate energy storage in animals.

B. Leucine is an essential branched-chain amino acid used in protein synthesis, not a lipid or phospholipid structure.

D. Hyaluronic acid is a high molecular weight non-sulfated glycosaminoglycan polysaccharide found in connective tissues, not a lipid.

E. Phenylalanine is an essential aromatic amino acid involved in protein synthesis and neurotransmitter precursor pathways, not a lipid.

- Nelson, D. L., & Cox, M. M. (2021). Lehninger Principles of Biochemistry (8th ed.). W. H. Freeman. Chapter 10: Lipids, Section 10.1: Storage Lipids and Structural Lipids in Membranes, pp. 343–348.

- Berg, J. M., Tymoczko, J. L., Gatto, G. J., & Stryer, L. (2019). Biochemistry (9th ed.). W. H. Freeman. Chapter 12: Lipids and Cell Membranes, Section 12.1, pp. 353–358. DOI: https://doi.org/10.1016/C2018-0-02223-X