Final answer:
Animals primarily use carbohydrates, especially glucose, for energy, with proteins and lipids serving as additional energy sources. Lipids provide the most energy per gram.
Step-by-step explanation:
The groups of molecules that commonly serve as sources of energy for animals are carbohydrates, proteins, and lipids. Among them, carbohydrates like glucose, are the primary source of the body's energy. Proteins are used for their amino acids to build the body's own proteins and can be used for energy if necessary. Lipids, including fats and oils, are used to build new cells, store energy, and for proper digestion. They also serve as a significant energy reserve, providing more energy per gram than carbohydrates or proteins. While nucleic acids are essential biological macromolecules, they are not typically used as a direct energy source.