Biochemistry,  MCQ


1. Incomplete oxidation of glucose into pyruvic acid with several intermediate steps is known as

(A) TCA-pathway

(B) Glycolysis

(C) HMS-pathway

(D) Krebs cycle.

Answer and Explanation:

1. (B)

Glycolysis is the biochemical change in which one molecule of glucose is converted into 2 molecules of pyruvic acid with the involvement of ten enzymes. It is independent of oxygen and is common to both aerobic and anaerobic condition. It takes place in the cytoplasm and all the reactions are reversible.

All the intermediates of glycolysis are not converted into pyruvic acid. Some of them build back the carbohydrates and the phenomenon is called oxidative anabolism. TCA cycle and Krebs cycle are synonyms where the pyruvic acid of glycolysis is utilized to form CO2. HMS is a hexose monophosphate shunt or pentose phosphate pathway which is an alternative pathway of glycolysis.

2. NADP+ is reduced to NADPH is


(B) Calvin Cycle

(C) Glycolysis

(D) EMP(1988)

Answer and Explanation:

2. (A)

HMP pathway generates NADPH molecule which is used as reductants in the biosynthetic process under conditions when NADPH molecules are not generated by photosynthesis. It is, therefore, important in non- photosynthetic tissues such as in differentiating tissues, generating seeds and during periods of darkness. Production of NADPH is not linked to ATP generation in the pentose phosphate pathway.

3. R.Q. is

(a) C/N

(b) N/C

(c) CO2/O2

(d) O2/CO2


(c) CO2/O2

4. End product of glycolysis is

(A) Acetyl CoA

(B) Pyruvic acid

(C) Glucose I-phosphate

(D) Fructose I-phosphate.

Answer and Explanation:

4. (B): In the glycolytic cycle, each molecule of glucose (a hexose sugar) is broken down in stepwise biochemical reactions under enzymatic control into two molecules of pyruvic acids. It takes place is cytosol.

5. R.Q- is ratio of

(A) CO2 produced to substrate consumed

(B) CO2 produced to O2 consumed

(C) Oxygen consumed to water produced

(D) Oxygen consumed to CO2 produced.


(B) CO2 produced to O2 consumed

6. EMP can produce a total of

(A) 6 ATP

(B) 8 ATP

(C) 24 ATP

(D) 38 ATP.

Answer and Explanation:

6. (B): Glycolysis is also known as the EMP pathway after the names of its discoverers. Embden, Meyerhof and Paranas. In glycolysis, 8ATP are produced. 4ATP are formed from substrate-level phosphorylation, out of which 2ATP are used up and a net gain of 2 AT P. 6ATP are produced from oxidative phosphorylation. Hence, Total ATP produced in glycolysis is 8ATP.

7. Connecting link between glycolysis and Krebs cycle before pyruvate entering Krebs cycle is changed to

(A) Oxaloacetate


(C) Pyruvate

(D) Acetyl CoA.

Answer and Explanation:

7. (D): End product of glycolysis is pyruvic acid which is converted into acetyl coA before entering into the Krebs cycle, which is aerobic in nature.

8. Terminal cytochrome of respiratory chain which donates electrons to oxygen is

(A) Cyt. b

(B) Cyt. c

(C) Cyt. A1

(D) Cyt. a3.

Answer and Explanation:

8. (D): Cytochrome a3 helps in transfer of electron to oxygen. The oxygen has great affinity to accept the electrons and in presence of protons, a water molecule is formed.

9. Out of 36 ATP molecules produced per glucose molecule during respiration

(A) 2 are produced outside glycolysis and 34 during respiratory chain

(B) 2 are produced outside mitochondria and 34 inside mitochondria

(C) 2 during glycolysis and 34 during Krebs cycle

(D) All are formed inside mitochondria.

Answer and Explanation:

9. (B): During respiration, 36 ATP molecules are produced per glucose molecule. 2 molecules of ATP are produced outside mitochondria i.e. during glycolysis and other 34 molecules of ATP are produced inside mitochondria from Krebs cycle.

10. Link between glycolysis, Krebs cycle and P-oxidation of fatty acid or carbohydrate and fat metabolism is

(A) Oxaloacetic acid

(B) Succinic acid

(C) Citric acid

(D) Acetyl CoA.

Answer and Explanation:

10. (D): Krebs cycle is intimately related to fat metabolism. Dihydroxyacetone phosphate produced in glycolysis may be ‘converted into glycerol via glycerol – 3 – phosphate and vice-versa. Glycerol is an important constituents of fats. After P-oxidation, fatty acids give rise to active – 2 – C units, the acetyl-CoA which may enter the Krebs cycle. Thus, Acetyl-CoA is a link between glycolysis, Krebs cycle and P- oxidation of fatty acid or carbohydrate and fat metabolism.

11. End products of aerobic respiration are

(A) Sugar and oxygen

(B) Water and energy

(C) Carbon dioxide, water and energy

(D) Carbon dioxide and energy.

Answer and Explanation:

11. (C): The food substances in living cells are oxidised in presence of oxygen, it is called aerobic respiration. Complete oxidation of food matter (1 .mole of glucose) occurs releasing 686 Kcal of energy. The ends of products formed are CO2 and H2O.

12. At a temperature above 35°C

(A) Rate of photosynthesis will decline earlier than that of respiration

(B) Rate of respiration will decline earlier than that of photosynthesis

(C) There is no fixed pattern

(D) Both decline simultaneously.

Answer and Explanation:

12. (A): The plants can perform photosynthesis on a range of temperature, while some cryophytes can do photosynthesis at 35°C. Usually, the plants can perform photosynthesis between 10°C – 40°C. The optimum temperature ranges between 25°C – 30°C. At high temperature, the enzymes are denatured and hence the photosynthetic rate declines.

13. Oxidative phosphorylation is production of

(A) ATP in photosynthesis

(B) NADPH in photosynthesis

(C) ATP in respiration

(D) NADH in respiration.

Answer and Explanation:

13. (C): In electron transport system the hydrogen donated by succinate is accepted by FAD which is reduced to FADH2. This hydrogen dissociates into electrons and protons and then passes through a series of carriers involving the phenomenon of oxidation and reduction. During this flow, ATP synthesis occurs at different steps and the phenomenon is called oxidative phosphorylation.

14. Apparatus to measure rate of respiration and R.Q. is

(A) Auxanometer

(B) Potometer

(C) Respirometer

(D) Manometer.

Answer and Explanation:

14. (C): Respirometer is an instrument used for measuring R.Q and rate of respiration. The apparatus consists of a graduated tube attached at right angles to a bulbous respiratory chamber in its upper end. Desired plant material who’s R.Q is to be determined is placed in the respiratory chamber.

15. End product of citric acid cycle/Krebs cycle is

(A) Citric acid

(B) Lactic acid

(C) Pyruvic acid

(D) CO2 + H2O.

Answer and Explanation:

15. (D): The end product of glycolysis is pyruvic acid whereas acetyl CoA is the connecting link between glycolysis and Krebs cycle. The TCA cycle was first described by Krebs, 1937 as a cyclic process in which acetyl coA is oxidised to C02 and water. Acetyl CoA combines with oxalo acetic acid to form citric acid. After a series of cyclic reactions, OAA is recycled back.

16. Out of 38 ATP molecules produced per glucose, 32 ATP molecules are formed from NADH/FADHin

(A) Respiratory chain

(B) Krebs cycle

(C) Oxidative decarboxylation

(D) EMP.

Answer and Explanation:

16. (A): During respiratory chain, complete degradation of one glucose molecule produced 38 ATP molecules. NAD and FAD is reduced to NADH/FADH2.

17. Life without air would be

(A) Reductional

(B) Free from oxidative damage

(C) Impossible

(D) Anaerobic.

Answer and Explanation:

17. (D): Anaerobic respiration (absence of oxygen) takes place in anaerobic bacteria and in plant seeds. Anaerobic respiration occurs in the organism which can live without oxygen. In this respiration, only glycolysis takes place due to the absence of oxygen.

18. The First phase in the breakdown of glucose, in animal cell, is

(A) Fermentation

(B) Krebs cycle

(C) Glycolysis

(D) E.T.S.


(C) Glycolysis

19. When yeast ferments glucose, the products obtained are

(A) Ethanol and CO2

(B) Methanol and CO2

(C) Ethanol and water

(D) Water and CO2.


(A) Ethanol and CO2

20. The ultimate respiratory substrate, yielding maximum number of ATP molecules, is

(A) Glycogen

(B) Ketogenic amino acid

(C) Glucose

(D) Amylose.

Answer and Explanation:

20. (c): Glucose is the chief respiratory substrate which fields maximum number of ATP molecules. Glucose is the most common substrate in glycolysis. Any other carbohydrate is first converted into glucose. During glycolysis it changes to pyruvic acid and net gain is of 2 ATP and 2 NADH2 molecules. And later on during Krebs cycle, 30 molecules of ATP are produced. So a total of 38 ATP molecules are produced from 1 mol of glucose during aerobic respiration.

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