Question 1

The Krebs cycle (citric acid cycle / TCA cycle) takes place in the:

Accepted Answer

Mitochondrial matrix. The TCA cycle operates in the mitochondrial matrix; the ETS is on the inner membrane.

Question 2

Before entering the Krebs cycle, pyruvate is converted to ______ by oxidative decarboxylation:

Accepted Answer

Acetyl CoA. Pyruvate dehydrogenase converts pyruvate to acetyl CoA, releasing CO₂ and forming NADH.

Question 3

The compound with which acetyl CoA combines to start the Krebs cycle, forming citrate, is:

Accepted Answer

Oxaloacetic acid (OAA). Acetyl CoA (2-C) condenses with OAA (4-C) to form citric acid (6-C), regenerating CoA.

Question 4

For each turn of the Krebs cycle, the number of CO₂ molecules released and NADH produced is:

Accepted Answer

2 CO₂ and 3 NADH. One TCA turn releases 2 CO₂ and yields 3 NADH, 1 FADH₂ and 1 GTP (ATP).

Question 5

Per glucose molecule, complete oxidation via glycolysis + Krebs cycle produces how many NADH in total (before ETS)?

Accepted Answer

10 NADH. Glycolysis (2) + pyruvate→acetyl CoA (2) + Krebs (6) = 10 NADH, plus 2 FADH₂, per glucose.

Question 6

The only ATP produced directly (substrate-level) within the Krebs cycle is at the step:

Accepted Answer

Succinyl CoA → Succinate (forming GTP/ATP). Succinyl CoA synthetase makes one GTP (≈ATP) by substrate-level phosphorylation.

Aerobic Respiration & Krebs Cycle — NEET Biology MCQs with Solutions

Questions with solutions