Final answer:
The carboxyl group (-COOH) is the functional group involving both fatty acids and amino acids; it releases H+ and contributes to the hydrophilic nature of these molecules.
Step-by-step explanation:
The functional group that involves both fatty acids and amino acids is the carboxyl group. This group has the formula -COOH and is known to release a hydrogen ion (H+) when ionized, leaving behind a negatively charged carboxylate ion (COO-). This release of H+ makes its parent molecule hydrophilic due to the attraction between the negatively charged ion and water molecules.
The carboxyl group is an important functional group in biological molecules such as fatty acids, which are the building blocks of triglycerides and phospholipids, and amino acids, which are the building blocks of proteins.