Fatty acids is a central energy source in animals(especially the liver, heart, and resting skeletal muscle), many protists and some bacteria; the only energy source for hibernating animals and migrating birds; not a major energy source in plants Sources for cells to obtain fatty acids: diet: stored lipid droplets; synthesized from the excess carbohydrates and amino acids by some special organs(e.g, liver)• Fatty acids is a central energy source in animals (especially the liver, heart, and resting skeletal muscle), many protists, and some bacteria; the only energy source for hibernating animals and migrating birds; not a major energy source in plants. • Sources for cells to obtain fatty acids: diet; stored lipid droplets; synthesized from the excess carbohydrates and amino acids by some special organs (e.g., liver)