Mitochondrial electron transport chain is

Options

A. Cyclic phosphorylation
B. Oxidative phosphorylation
C. Noncyclic phosphorylation
D. Photooxidation.

Answer

### Step-by-Step Solution:

1. **Understanding the Mitochondrial Electron Transport Chain (ETC)**:
- The mitochondrial electron transport chain is a series of protein complexes located in the inner mitochondrial membrane. It plays a crucial role in cellular respiration by transferring electrons derived from nutrients to oxygen.

2. **Identifying the Process**:
- The primary function of the ETC is to facilitate the transfer of electrons from electron donors like NADH (nicotinamide adenine dinucleotide) to oxygen, which is the final electron acceptor.

3. **Components of the ETC**:
- The electron transport chain consists of four multi-protein complexes (Complex I, II, III, and IV) and two mobile electron carriers (ubiquinone and cytochrome c).

4. **Coupling with ATP Synthesis**:
- As electrons move through the complexes, they release energy, which is used to pump protons (H+) from the mitochondrial matrix into the intermembrane space, creating a proton gradient.

5. **Oxidative Phosphorylation**:
- This proton gradient is then utilized by ATP synthase (another protein complex) to synthesize ATP from ADP (adenosine diphosphate) and inorganic phosphate (Pi). This process is known as oxidative phosphorylation because it involves the oxidation of electron carriers and the phosphorylation of ADP to form ATP.

6. **Conclusion**:
- Therefore, the mitochondrial electron transport chain is best described as oxidative phosphorylation, as it is the process that couples electron transport with ATP synthesis.

### Final Answer:
The mitochondrial electron transport chain is **oxidative phosphorylation**.

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