Oxygen is very important for aerobic respiration, but oxygen never participates as a reactant in any reaction. What is the role of oxygen in cellular respiration?

Options

A. It is terminal electron acceptor for aerobic respiration.
B. It is a nucleotide source for ATP synthesis
C. It functions as an electron carrier
D. It is the final electron acceptor for anaerobic respiration

Answer

### Step-by-Step Solution:

1. **Understanding Cellular Respiration**:
- Cellular respiration is a biochemical process where organisms convert food (primarily glucose) into usable energy in the presence of oxygen.
- The overall equation for aerobic respiration can be simplified as:
\[ \text{Glucose (C}_6\text{H}_{12}\text{O}_6) + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{Energy (ATP)} \]

2. **Role of Oxygen**:
- Oxygen is crucial for aerobic respiration as it facilitates the complete oxidation of glucose.
- It does not directly participate as a reactant in the initial breakdown of glucose but is essential for the final steps of the process.

3. **Final Electron Acceptor**:
- The primary role of oxygen in cellular respiration is to act as the final electron acceptor in the electron transport chain (ETC).
- During the ETC, electrons are transferred through a series of proteins, and at the end of the chain, oxygen accepts these electrons along with hydrogen ions (protons) to form water:
\[ \text{4 e}^- + \text{4 H}^+ + \text{O}_2 \rightarrow 2 \text{H}_2\text{O} \]

4. **Energy Production**:
- The energy released during the transfer of electrons through the ETC is used to pump protons across the mitochondrial membrane, creating a proton gradient.
- This gradient drives ATP synthesis through ATP synthase, producing ATP, which is the energy currency of the cell.

5. **Waste Products**:
- The by-products of this process are carbon dioxide (CO2) and water (H2O), which are expelled from the organism.

6. **Conclusion**:
- Therefore, the role of oxygen in cellular respiration is primarily as the terminal electron acceptor, which is essential for the efficient production of ATP in aerobic conditions.