Presence of oxygen is vital in aerobic respiration because

Options

A. It derives the whole process by removing hydrogen from ETS
B. Oxygen causes phosphorylation which is light stimulated
C. Oxygen directly stimulates complex V to generate ATP
D. Oxygen is initial electron acceptor

Answer

### Step-by-Step Solution:

1. **Understanding Aerobic Respiration**:
- Aerobic respiration is a biological process that requires oxygen to produce energy (ATP) from glucose. It occurs in the mitochondria of cells.

**Hint**: Remember that aerobic respiration is dependent on the presence of oxygen.

2. **Role of Oxygen**:
- Oxygen serves as the final electron acceptor in the electron transport chain (ETS). This is crucial because it allows the chain to continue functioning, facilitating the transfer of electrons.

**Hint**: Think of oxygen as the end-point that completes the electron transport process.

3. **Electron Transport Chain (ETS)**:
- The ETS consists of a series of protein complexes (Complex I, II, III, IV, and V) that transfer electrons derived from NADH and FADH2. As electrons move through these complexes, energy is released and used to pump protons across the mitochondrial membrane.

**Hint**: Visualize the ETS as a conveyor belt where electrons are passed along, releasing energy at each step.

4. **Formation of Water**:
- When oxygen accepts electrons at the end of the ETS, it combines with protons (H+) to form water (H2O). This reaction is essential for maintaining the flow of electrons through the chain.

**Hint**: Remember that the formation of water is a key step that prevents a backup in the electron transport chain.

5. **ATP Generation**:
- The energy released during the electron transfer is used to generate ATP through a process called oxidative phosphorylation, primarily occurring at Complex V (ATP synthase). The presence of oxygen allows for a greater yield of ATP compared to anaerobic respiration.

**Hint**: Consider ATP as the energy currency of the cell, and oxygen’s role is to maximize its production.

6. **Comparison with Anaerobic Respiration**:
- In the absence of oxygen, cells switch to anaerobic respiration, which yields significantly less ATP and produces byproducts like lactic acid or ethanol.

**Hint**: Contrast the efficiency of aerobic respiration with anaerobic respiration to understand the importance of oxygen.

### Conclusion:
The presence of oxygen is vital in aerobic respiration because it acts as the final electron acceptor in the electron transport chain, enabling the production of a large amount of ATP and the formation of water, which is essential for the continuation of the process.