Final answer:
Biological macromolecules are relatively stable and require an input of energy to reach lower energy states.
Step-by-step explanation:
Biological macromolecules contain a large number of carbon and hydrogen atoms but they do not spontaneously convert into CO₂ and H₂O. This is because biological molecules are relatively stable and require an input of energy to reach lower energy states. Stability allows macromolecules to maintain their structure and function within cells.