Question 1 Which of the following best describes the electron transport chain? Electrons are pumped across a membrane by active transport. Acetyl CoA is fully oxidized to $$ \mathrm{CO}_{2} $$. Hydrogens are added to $$ \mathrm{CO}_{2} $$ to make an energy-rich compound. Electrons pass from one carrier to another, releasing a little energy at each step.

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The electron transport chain (ETC) is a crucial component of cellular respiration, primarily involved in the production of ATP through oxidative phosphorylation. Here's a breakdown of the provided options:

1. **Electrons are pumped across a membrane by active transport.**
   - *Clarification:* While the ETC does involve the movement of electrons, it's the **protons (hydrogen ions)** that are actively pumped across the membrane to create a proton gradient, not the electrons themselves.

2. **Acetyl CoA is fully oxidized to $$ \mathrm{CO}_{2} $$.**
   - *Clarification:* This process describes the citric acid cycle (also known as the Krebs cycle), not the ETC.

3. **Hydrogens are added to $$ \mathrm{CO}_{2} $$ to make an energy-rich compound.**
   - *Clarification:* This statement pertains to processes like carbon fixation in photosynthesis, not the ETC.

4. **Electrons pass from one carrier to another, releasing a little energy at each step.**
   - *Clarification:* This accurately describes the ETC. Electrons are transferred through a series of protein complexes and electron carriers within the mitochondrial membrane. With each transfer, a small amount of energy is released, which is then used to pump protons and ultimately produce ATP.

**Best Answer:**  
Electrons pass from one carrier to another, releasing a little energy at each step.
Electrons move through carriers, releasing energy at each step.

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