Identify the biomolecules A, B, and C based on the given characteristics: A: An amino acid where the R group is a hydroxymethyl group. B: A simple lipid which is chemically trihydroxy propane. C: A fatty acid with 20 carbon atoms including the carboxyl carbon.

Step-by-step solution

A is Serine because its variable R group is a hydroxymethyl group. Alanine has a methyl group and glycine has a hydrogen atom as their respective R groups. B is Glycerol, which is a simple lipid chemically known as trihydroxy propane. Lecithin is a complex lipid (phospholipid) and cholesterol is a derived lipid with a complex ring structure. C is Arachidonic acid, which is a fatty acid containing 20 carbon atoms (including the carboxyl carbon). Palmitic acid contains 16 carbon atoms. Answer: A - Serine, B - Glycero