Repost again: Plants and animals (and all other living things) are part of all the natural cycles through food chains and food webs. The four classes of macromolecules used by living things are carbohydrates, lipids, proteins, and nucleic acids. For each class of macromolecule, research what components are needed to make them, and relate the importance of the nitrogen and carbon cycle to the formation of these macromolecules.