What is the waste product of the electron transport chain in cellular respiration?

• A. $C_{\mathrm{O}}2$
• B. $O_2$
• C. $\mathrm{ATP}$
• D. $H_{2}O$

Answer: (D)

Verified step by step guidance

1. Understand that the electron transport chain (ETC) is the final stage of cellular respiration, occurring in the inner mitochondrial membrane.
2. Recognize that the primary function of the ETC is to transfer electrons from electron donors like NADH and FADH2 to electron acceptors such as oxygen, through a series of protein complexes.
3. Recall that as electrons move through the ETC, protons (H⁺ ions) are pumped across the mitochondrial membrane, creating a proton gradient that drives ATP synthesis.
4. Identify that oxygen acts as the final electron acceptor in the chain, combining with electrons and protons to form water (H₂O) as a byproduct.
5. Conclude that the waste product of the electron transport chain is water, formed when oxygen accepts electrons and protons at the end of the chain.