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1. Glycolysis takes place in which cellular compartment?
A. Cytoplasm / Cytosol
B. Mitochondrial matrix
C. Inner mitochondrial membrane
D. Chloroplast stroma
Answer: A. Cytoplasm / Cytosol
Explanation: Glycolysis occurs in the cytoplasm of all living organisms, both aerobic and anaerobic.
2. Glycolysis is also commonly referred to as the EMP pathway after which three scientists?
A. Embden, Meyerhof, and Parnas
B. Engelmann, Melvin, and Priestley
C. Embden, Mitchell, and Pasteur
D. Edward, Miller, and Peter
Answer: A. Embden, Meyerhof, and Parnas
Explanation: The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof, and J. Parnas, hence it is often referred to as the EMP pathway.
3. What is the net gain of ATP molecules during glycolytic conversion of one molecule of glucose into two molecules of pyruvic acid?
A. 2 ATP
B. 4 ATP
C. 8 ATP
D. 36 ATP
Answer: A. 2 ATP
Explanation: 4 ATP molecules are directly synthesized by substrate-level phosphorylation, but 2 ATP are consumed in the initial priming steps, giving a net gain of 2 ATP.
4. Which enzyme catalyzes the conversion of glucose to glucose-6-phosphate in the first step of glycolysis?
A. Hexokinase
B. Phosphofructokinase
C. Aldolase
D. Pyruvate kinase
Answer: A. Hexokinase
Explanation: Glucose is phosphorylated to glucose-6-phosphate by the enzyme hexokinase utilizing 1 ATP molecule.
5. In anaerobic alcoholic fermentation, yeast converts pyruvic acid into ethanol and carbon dioxide using the enzymes:
A. Pyruvic acid decarboxylase and Alcohol dehydrogenase
B. Lactate dehydrogenase and Hexokinase
C. Pyruvate dehydrogenase and Citrate synthase
D. Aldolase and Enolase
Answer: A. Pyruvic acid decarboxylase and Alcohol dehydrogenase
Explanation: Pyruvic acid is first decarboxylated to acetaldehyde by pyruvic acid decarboxylase, which is then reduced to ethanol by alcohol dehydrogenase.
6. During strenuous exercise, oxygen becomes inadequate in muscle cells and pyruvic acid is reduced to lactic acid by the enzyme:
A. Lactate dehydrogenase
B. Pyruvate carboxylase
C. Succinate dehydrogenase
D. Malate dehydrogenase
Answer: A. Lactate dehydrogenase
Explanation: In animal muscle cells under anaerobic conditions, pyruvic acid is reduced to lactic acid by lactate dehydrogenase using $NADH + H^+$.
7. What concentration of alcohol naturally proves toxic and fatal to yeast cells?
A. 13%
B. 5%
C. 25%
D. 50%
Answer: A. 13%
Explanation: Yeasts poison themselves to death when the concentration of alcohol reaches about 13 percent.
8. The oxidative decarboxylation of pyruvate to Acetyl CoA (Link Reaction) occurs in the:
A. Mitochondrial matrix
B. Cytoplasm
C. Intermembrane space
D. F1 particles
Answer: A. Mitochondrial matrix
Explanation: Pyruvate enters the mitochondrial matrix where it undergoes oxidative decarboxylation catalyzed by pyruvate dehydrogenase complex.
9. Which mineral cofactor is required by the pyruvate dehydrogenase complex during the link reaction?
A. Magnesium ($Mg^{2+}$)
B. Calcium ($Ca^{2+}$)
C. Iron ($Fe^{2+}$)
D. Zinc ($Zn^{2+}$)
Answer: A. Magnesium ($Mg^{2+}$)
Explanation: Pyruvate dehydrogenase complex requires coenzyme A, NAD+, and $Mg^{2+}$ as a essential mineral cofactor.
10. The TCA cycle (Krebs Cycle) begins with the condensation of Acetyl CoA with which 4-carbon compound?
A. Oxaloacetic acid (OAA)
B. Citric acid
C. α-Ketoglutaric acid
D. Malic acid
Answer: A. Oxaloacetic acid (OAA)
Explanation: The Krebs cycle starts with the condensation of acetyl group with oxaloacetic acid (OAA) and water to form citric acid, catalyzed by citrate synthase.
11. Who elucidated the Tricarboxylic Acid Cycle (TCA cycle) in 1937?
A. Hans Krebs
B. Melvin Calvin
C. Peter Mitchell
D. Otto Warburg
Answer: A. Hans Krebs
Explanation: The TCA cycle was elucidated by Sir Hans Krebs, which is why it is widely known as the Krebs cycle.
12. How many molecules of $NADH + H^+$ and $FADH_2$ are generated per turn of the Krebs cycle (starting from 1 molecule of Acetyl CoA)?
A. 3 $NADH$ and 1 $FADH_2$
B. 2 $NADH$ and 2 $FADH_2$
C. 4 $NADH$ and 2 $FADH_2$
D. 1 $NADH$ and 3 $FADH_2$
Answer: A. 3 $NADH$ and 1 $FADH_2$
Explanation: During one turn of the TCA cycle, 3 molecules of $NADH$, 1 molecule of $FADH_2$, and 1 molecule of $GTP$ (substrate-level) are synthesized.
13. The only enzyme of the Krebs cycle that is bound to the inner mitochondrial membrane rather than the matrix is:
A. Succinate dehydrogenase
B. Citrate synthase
C. Isocitrate dehydrogenase
D. Malate dehydrogenase
Answer: A. Succinate dehydrogenase
Explanation: Succinate dehydrogenase (which forms Complex II of ETS) is located in the inner mitochondrial membrane, while all other TCA enzymes are in the matrix.
14. Electron Transport System (ETS) in plant mitochondria is located on the:
A. Inner mitochondrial membrane
B. Outer mitochondrial membrane
C. Mitochondrial matrix
D. Intermembrane space
Answer: A. Inner mitochondrial membrane
Explanation: The respiratory electron transport system consists of multi-protein complexes embedded in the inner mitochondrial membrane.
15. The terminal electron acceptor in the mitochondrial electron transport chain is:
A. Oxygen
B. Cytochrome c
C. Ubiquinone
D. Water
Answer: A. Oxygen
Explanation: Oxygen acts as the final hydrogen and electron acceptor in aerobic respiration, producing water.
16. Oxidation of one molecule of $NADH$ yields how many ATP molecules via oxidative phosphorylation?
A. 3 ATP
B. 2 ATP
C. 1 ATP
D. 4 ATP
Answer: A. 3 ATP
Explanation: Oxidation of 1 $NADH$ drives sufficient proton pumping to produce 3 ATP, whereas oxidation of 1 $FADH_2$ yields 2 ATP molecules.
17. Complex IV of the mitochondrial ETS is also known as:
A. Cytochrome c oxidase
B. NADH dehydrogenase
C. Succinate dehydrogenase
D. Cytochrome bc1 complex
Answer: A. Cytochrome c oxidase
Explanation: Complex IV is cytochrome c oxidase complex containing cytochromes a and a3, along with two copper centers.
18. A mobile electron carrier that transfers electrons between Complex III and Complex IV on the outer surface of the inner mitochondrial membrane is:
A. Cytochrome c
B. Ubiquinone
C. Plastocyanin
D. Ferredoxin
Answer: A. Cytochrome c
Explanation: Cytochrome c is a small mobile protein attached to the outer surface of the inner membrane, transferring electrons from Complex III to Complex IV.
19. How many protons ($H^+$) pass through ATP synthase ($F_0-F_1$ complex) from intermembrane space to matrix for each ATP produced?
A. 2 $H^+$
B. 4 $H^+$
C. 1 $H^+$
D. 6 $H^+$
Answer: A. 2 $H^+$
Explanation: According to standard NCERT biological calculations, for each ATP produced, 2 $H^+$ pass through $F_0$ from the intermembrane space back into the matrix down the electrochemical gradient.
20. The theoretical net energy yield from complete aerobic oxidation of one glucose molecule is:
A. 38 ATP
B. 30 ATP
C. 2 ATP
D. 12 ATP
Answer: A. 38 ATP
Explanation: Complete aerobic oxidation of glucose theoretically yields 38 ATP molecules (or 36 ATP depending on the shuttle system used for cytosolic NADH).
21. Respiratory quotient (RQ) is defined as the ratio of:
A. Volume of $CO_2$ evolved / Volume of $O_2$ consumed
B. Volume of $O_2$ consumed / Volume of $CO_2$ evolved
C. Weight of glucose oxidized / Weight of $CO_2$ produced
D. Number of ATP produced / Number of $O_2$ molecules used
Answer: A. Volume of $CO_2$ evolved / Volume of $O_2$ consumed
Explanation: $RQ = \frac{\text{Volume of } CO_2 \text{ evolved}}{\text{Volume of } O_2 \text{ consumed}}$. It depends on the type of respiratory substrate used.
22. What is the Respiratory Quotient (RQ) value when carbohydrates are used as respiratory substrate?
A. 1.0
B. 0.7
C. 0.9
D. More than 1
Answer: A. 1.0
Explanation: When carbohydrates are completely oxidized, equal amounts of $CO_2$ and $O_2$ are evolved and consumed ($C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$), making $RQ = 6/6 = 1.0$.
23. What is the approximate Respiratory Quotient (RQ) value when fats (e.g., tripalmitin) are respired?
A. 0.7
B. 1.0
C. 0.9
D. 1.3
Answer: A. 0.7
Explanation: Fats contain less oxygen relative to carbon and hydrogen, so more $O_2$ is consumed during oxidation. For tripalmitin, $RQ = 102 CO_2 / 145 O_2 = 0.7$.
24. Respiration is considered an **amphibolic pathway** because it involves:
A. Both catabolism (breakdown) and anabolism (synthesis)
B. Both aerobic and anaerobic steps in equal proportions
C. Both light and dark reactions
D. Both intra-cellular and extra-cellular digestion
Answer: A. Both catabolism (breakdown) and anabolism (synthesis)
Explanation: Respiratory intermediates serve as precursors for the synthesis of fats, proteins, and other compounds (anabolism) as well as energy production (catabolism).
25. Fatty acids enter the respiratory pathway after being broken down into:
A. Acetyl CoA
B. Pyruvic acid
C. PGAL
D. Oxaloacetic acid
Answer: A. Acetyl CoA
Explanation: Fats are first broken down into glycerol and fatty acids. Fatty acids undergo beta-oxidation to form Acetyl CoA before entering the Krebs cycle.
This page contains a chapter-wise objective practice set. Try the questions without checking the answer first, then use the explanation to understand the point you missed. The current page contains 25 questions, so you can practise in smaller sets when you are revising.
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