The `e^(-)` carrier molecules and cytochrome -

Options

A. Are reduced as they pass electrons on to the next molecule
B. Transfer electrons between the electron carrier complexes
C. Shuttle protons to ATP synthase
D. Are found in outer mitochondrial membrane

Answer

### Step-by-Step Solution:

1. **Understanding Electron Carrier Molecules**:
- Electron carrier molecules are integral components of the electron transport chain (ETC) in cellular respiration. They facilitate the transfer of electrons from one molecule to another.

2. **Role of Cytochromes**:
- Cytochromes are a specific type of electron carrier that contain heme groups. They play a crucial role in the electron transport chain by transferring electrons between different complexes.

3. **Behavior of Electron Carriers**:
- As electrons are transferred through the electron transport chain, the electron carriers do not undergo permanent oxidation or reduction. Instead, they temporarily hold and pass on the electrons to the next carrier in the chain.

4. **Options Analysis**:
- **Option 1**: "Reduced as they pass electron on the next molecule." - This is incorrect because while they may temporarily hold electrons, they do not change their oxidation state permanently.
- **Option 2**: "Transfer electrons between the electron carrier complexes." - This is correct as it accurately describes the function of electron carriers.
- **Option 3**: "Settle protons to ATP synthase." - This is misleading; while the proton gradient is important for ATP synthesis, the carriers themselves do not directly settle protons.
- **Option 4**: "Are found in the outer mitochondrial membrane." - This is incorrect; electron carriers are primarily located in the inner mitochondrial membrane.

5. **Conclusion**:
- The correct answer is **Option 2**: "Transfer electrons between the electron carrier complexes."