Q4. How many ATP does the Krebs’ cycle contribute per glucose in NCERT’s balance sheet, and how?
24 ATP: 2 ATP made directly (from GTP), 6 NADH × 3 = 18 and 2 FADH × 2 = 4 (NCERT pages 159–160).
Q5. Assertion: the net gain of 38 ATP per glucose is only a theoretical figure. Reason: in a living system, intermediates are withdrawn from the pathways for other uses. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: the count assumes that no intermediate is used to make any other compound, which does not hold in a living system (NCERT page 161).
Q6. Which assumption of the balance sheet concerns the NADH made in glycolysis?
That it is transferred into the mitochondria and undergoes oxidative phosphorylation (NCERT page 161).
Q7. By NCERT’s count, how many of the 38 ATP are credited to the stages after glycolysis?
30: 6 for the conversion of pyruvate to acetyl CoA and 24 for the Krebs’ cycle (NCERT pages 158–160). The other 8 are credited to glycolysis, including the 6 from its 2 NADH, which are oxidised in the mitochondria by assumption (page 161).
Q8. By NCERT’s count, how many ATP does one turn of the Krebs’ cycle give, and how many does one pyruvic acid give from its conversion to acetyl CoA onwards?
One turn: 3 NADH × 3 = 9, 1 FADH × 2 = 2 and 1 ATP from GTP, 12 ATP. One pyruvic acid adds the NADH of its conversion to acetyl CoA (3 ATP): 15 ATP. Two pyruvic acid give 30, and glycolysis’s 8 make 38 (NCERT pages 158–160).
Q9. Of NCERT’s 38 ATP per glucose, how many are made by oxidative phosphorylation in the ETS?
34: 10 NADH × 3 = 30 and 2 FADH × 2 = 4. The other 4 are made directly: a net 2 in glycolysis and 2 (from GTP) in the Krebs’ cycle (NCERT pages 156–160).