Question

1. which step(s) cannot occur without the presence of oxygen?

☐ glycolysis
☐ krebs cycle
☐ electron transport chain

Explanation:

• Glycolysis: Occurs in the cytoplasm. It can happen in both aerobic and anaerobic conditions. It does not require oxygen.
• Kreb's Cycle: Occurs in the mitochondrial matrix. It is part of aerobic respiration. But it does not directly use oxygen. However, it depends on the availability of electron acceptors (like \(NAD^{+}\) and \(FAD\)) which are regenerated in the electron - transport chain (which requires oxygen).
• Electron Transport Chain: Occurs in the inner mitochondrial membrane. Oxygen acts as the final electron acceptor (\(O_{2}+4e^{-}+4H^{+}\to 2H_{2}O\)). Without oxygen, the electron - transport chain cannot function as there is no molecule to accept the electrons at the end of the chain.

Answer:

Electron Transport Chain