Which of the following is characterized by containing fatty acids?

Lipids are characterized by containing fatty acids, which are long hydrocarbon chains with a carboxyl group at one end. This structure allows fatty acids to be a significant component of various types of lipids, including triglycerides and phospholipids. Triglycerides consist of three fatty acid molecules bound to a glycerol molecule, making them a primary form of stored energy in animals and plants. Phospholipids, which are essential for forming cell membranes, also include two fatty acids attached to a phosphate group and glycerol.

The unique structure of fatty acids, including their hydrophobic (water-repelling) nature, contributes to the formation of lipid bilayers, which are vital for cell membrane integrity and function. In contrast, carbohydrates are primarily composed of sugar units, proteins are made up of amino acids, and nucleic acids consist of nucleotide monomers, none of which contain fatty acids in their structure. Thus, the defining characteristic of lipids being associated with fatty acids validates the selection of that option.