Final answer:
The primary difference between aerobic and anaerobic cellular metabolism is the presence of oxygen, which enables aerobic respiration to produce a significant amount of ATP compared to anaerobic respiration.
Step-by-step explanation:
The fundamental difference that differentiates aerobic from anaerobic cellular metabolism is Option 1: The presence of oxygen. Aerobic respiration occurs in the presence of oxygen and takes place in the mitochondria. It makes use of glucose, fatty acids, or even proteins as fuel sources, with glucose being the primary one. Aerobic respiration is capable of producing a large amount of ATP, approximately 36-38 ATP molecules per glucose molecule. In contrast, anaerobic metabolism occurs in the absence of oxygen, typically in the cytosol, and utilizes only glucose as its fuel source. Anaerobic respiration results in the production of pyruvate and lactic acid while generating only a small amount of ATP, about 2 ATP molecules per glucose molecule.