Question

Net gain of ATP molecules per hexose during aerobic respiration is

• A. 12
• B. 18
• C. 36
• D. 30

Answer 1

The Correct Option is C

 To determine the net gain of ATP molecules per hexose (glucose) during aerobic respiration, we need to understand the process and stages involved in glucose metabolism.

Aerobic respiration occurs in several stages:

1. Glycolysis: This occurs in the cytoplasm and converts one molecule of glucose (hexose) into two molecules of pyruvate, yielding a net gain of 2 ATP and 2 NADH. Each NADH can potentially produce 2.5 ATP, resulting in additional ATP from NADH:
   • Net ATP from glycolysis: 2 ATP
   • ATP from 2 NADH: \(2 \times 2.5 = 5\) ATP
2. Pyruvate to Acetyl-CoA (Link Reaction): Each pyruvate molecule is converted into Acetyl-CoA, generating 1 NADH per pyruvate. Thus, from 2 pyruvate, we have:
   • ATP from 2 NADH: \(2 \times 2.5 = 5\) ATP
3. Krebs Cycle (Citric Acid Cycle): Each Acetyl-CoA produces 3 NADH, 1 FADH₂, and 1 ATP (GTP), so from 2 Acetyl-CoA:
   • ATP directly produced: 2 ATP
   • ATP from 6 NADH: \(6 \times 2.5 = 15\) ATP
   • ATP from 2 FADH₂: \(2 \times 1.5 = 3\) ATP

Total ATP Calculation:

Stage	Net ATP
Glycolysis	2 ATP + 5 ATP (from NADH)
Pyruvate to Acetyl-CoA	5 ATP (from NADH)
Krebs Cycle	2 ATP + 15 ATP (from NADH) + 3 ATP (from FADH2)
Total	36 ATP

Thus, the net gain of ATP from the complete oxidation of one glucose molecule during aerobic respiration is 36 ATP.

This explains why the correct answer is: 36.