Here's why:
* Electron Transport Chain: This final stage of cellular respiration uses the energy stored in electrons from earlier stages to pump protons across a membrane, creating a concentration gradient. These protons then flow back across the membrane through a protein called ATP synthase, which uses the energy to produce ATP (the energy currency of cells).
* Water Formation: As electrons move down the electron transport chain, they ultimately combine with oxygen and protons (H+) to form water. This is the final step in the process, and it's why oxygen is essential for aerobic respiration.
So, the equation for this reaction is:
4H+ + 4e- + O2 → 2H2O
