The correct option is A is false but R is true
Explanation
Aerobic cellular respiration consists of distinct stages: Glycolysis, the Krebs cycle (Citric Acid Cycle), and the Electron Transport System (ETS). Understanding where oxygen is specifically utilized is central to distinguishing these phases.
Statement-wise Analysis:
- Assertion (A): Incorrect. Oxygen does not play a direct role in the Krebs cycle, nor is it used in the early stages of this pathway. The Krebs cycle involves the enzymatic breakdown of Acetyl-CoA into carbon dioxide within the mitochondrial matrix. While the cycle is aerobic (meaning it stops in the absence of oxygen because electron carriers cannot be recycled), oxygen itself is not a reactant in any of the chemical reactions constituting the cycle.
- Reason (R): Correct. Oxygen acts as the final hydrogen (electron) acceptor in the Electron Transport System (ETS). Located in the inner mitochondrial membrane, the ETS transfers electrons through a series of carriers. At the very end of this chain (Complex IV), molecular oxygen accepts electrons and combines with protons (H+) to form metabolic water.
Key Takeaway:
Oxygen is the terminal electron acceptor in aerobic respiration and is directly consumed only at the very end of the Electron Transport System; it does not participate in the reactions of the Krebs cycle.