Question

Most of the energy in the cells is liberated by oxidation of carbohydrates when-

• A. A and B only
• B. B and C only
• C. A and D only
• D. E only

Hint:

Aerobic Respiration = Max Energy (\(\approx\)32 ATP).
Anaerobic Respiration/Fermentation = Min Energy (2 ATP).
Complete oxidation always ends in CO\(_2\) and H\(_2\)O.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks at which stage of cellular respiration is the maximum amount of energy (ATP) released from glucose molecules.

Step 2: Detailed Explanation:

• Stages of Respiration:
- Glycolysis: Sugar to Pyruvic acid (Net 2 ATP).
- Link Reaction: Pyruvic acid to Acetyl-CoA.
- Kreb's Cycle and ETC: Complete oxidation of Acetyl-CoA to CO\(_2\) and H\(_2\)O.

• Analysis of Options (from screenshot):
- (A) Pyruvic acid to Sugar (Reverse/Gluconeogenesis).
- (B) Pyruvic acid to Acetyl-CoA (Small yield).
- (C) Sugar to Pyruvic acid (Glycolysis, low yield).
- (D) Glucose to Alcohol and CO\(_2\) (Fermentation, very low yield - 2 ATP).
- (E) Pyruvic acid to CO\(_2\) and H\(_2\)O (Complete aerobic oxidation).

• Energy Yield: Complete aerobic respiration through the Kreb's cycle and the Electron Transport Chain (ETC) yields 30-32 ATP per glucose molecule. This represents the full "liberation of energy" compared to partial oxidation in glycolysis or fermentation.
Final Answer:
The complete breakdown (Stage E) results in the highest energy liberation.