Explanation:
**Answer:**
Oxygen is used in the two-stage process of cellular respiration to break down sugar and produce energy.
**Explanation:**
In the first stage, glycolysis occurs in the cytoplasm, breaking down glucose into pyruvate and generating a small amount of energy. The second stage, aerobic respiration, takes place in the mitochondria and requires oxygen. Here, pyruvate undergoes further breakdown in the Krebs cycle and electron transport chain, releasing a significant amount of energy. Oxygen is crucial in this stage as the final electron acceptor in the electron transport chain, enabling the efficient extraction of energy from sugar molecules. The overall process produces energy for the cell and results in the formation of water and carbon dioxide as byproducts.
