Which of the following is not a product of the Krebs cycle?
The correct answer and explanation is :
The correct answer is Oxygen (O₂).
Explanation (300 words):
The Krebs cycle, also known as the citric acid cycle (CAC) or tricarboxylic acid (TCA) cycle, is a key metabolic pathway that occurs in the mitochondrial matrix of eukaryotic cells. It is the second stage of aerobic respiration, following glycolysis and preceding the electron transport chain (ETC).
The primary function of the Krebs cycle is to oxidize acetyl-CoA (derived from carbohydrates, fats, and proteins) to generate high-energy electron carriers NADH and FADH₂, which are later used in oxidative phosphorylation to produce ATP.
Main Products of the Krebs Cycle:
Each turn of the cycle produces:
- 3 NADH – Carries electrons to the electron transport chain.
- 1 FADH₂ – Another electron carrier for the electron transport chain.
- 1 GTP (or ATP) – Directly usable energy.
- 2 CO₂ – Released as a waste product from the decarboxylation reactions.
Why is Oxygen (O₂) Not a Product?
Although oxygen is essential for cellular respiration, it is not produced in the Krebs cycle. Instead, it serves as the final electron acceptor in the electron transport chain, where it combines with electrons and protons to form water (H₂O).
The Krebs cycle itself does not produce oxygen; it only generates electron carriers (NADH and FADH₂), which then transfer electrons to the ETC, leading to ATP production in the presence of oxygen.
Thus, among the given choices, oxygen (O₂) is not a product of the Krebs cycle but rather a requirement for the final stage of aerobic respiration.