Sample 1Medium
A figure shows a cycle in the mitochondrial matrix. An acetyl group from acetyl CoA joins a four-carbon compound A, with water, to form a six-carbon compound B. B then goes through a series of steps, releasing two molecules of CO2, until A is formed again. Which option names A and B and gives the yield of one turn?
- A
A – pyruvic acid, B – citric acid; 3 NADH + H+, 1 FADH2 and 1 GTP per turn
- B
A – oxaloacetic acid, B – citric acid; 3 NADH + H+, 1 FADH2 and 1 GTP per turn
- C
A – oxaloacetic acid, B – citric acid; 2 NADH + H+, 2 FADH2 and 2 GTP per turn
- D
A – succinic acid, B – α-ketoglutaric acid; 3 NADH + H+ and 1 FADH2 per turn
Show the answer
The answer is B.The Krebs cycle begins when acetyl CoA condenses with oxaloacetic acid and water to form citric acid. Each turn releases two CO2, reduces three NAD+ and one FAD, and forms one GTP by substrate-level phosphorylation.
- A.
Pyruvic acid has three carbons and is converted to acetyl CoA before the cycle begins. The four-carbon acceptor is oxaloacetic acid.
- C.
Each turn reduces NAD+ at three points and FAD at one point, and forms one GTP.
- D.
The acetyl group condenses with oxaloacetic acid to form citric acid. α-Ketoglutaric acid has five carbons and comes later in the cycle.
NCERT: Class 11 Biology, Chapter 12
Sample 2NEET level
Assertion (A): Glycolysis takes place inside the mitochondria in all living organisms. Reason (R): In anaerobic organisms, glycolysis is the only process in respiration. Choose the correct answer from the options given below.
- A
Both A and R are true and R is the correct explanation of A
- B
Both A and R are true but R is not the correct explanation of A
- C
A is true but R is false
- D
A is false but R is true
Show the answer
The answer is D.Glycolysis takes place in the cytoplasm of the cell and is present in all living organisms, so A is false. In anaerobic organisms it is the only process in respiration, so R is true.
- A.
A is false: glycolysis takes place in the cytoplasm.
- B.
A is false, so this cannot be the answer.
- C.
A is false and R is true, not the other way round.
NCERT: Class 11 Biology, Chapter 12 (Respiration in Plants), Glycolysis