MCQs on Respiration in Plants – NCERT Biology Class 11

MCQs on Respiration in Plants – CBSE Class 11 Biology (Unit IV | NCERT-Based)

CBSE Class 11 Biology – MCQs with Answers and Explanations

Unit IV: Plant Physiology

Topic: Respiration in Plants

Section A: Basics of Respiration & Glycolysis (Q1–Q10)

Q1. Respiration in plants refers to:

A. Release of oxygen
B. Breakdown of glucose to release energy
C. Absorption of carbon dioxide
D. Photosynthesis

Answer: B
Explanation: Respiration is a catabolic process in which glucose is oxidized to release energy in the form of ATP.

Q2. The site of glycolysis is:

A. Mitochondria
B. Chloroplast
C. Cytoplasm
D. Nucleus

Answer: C
Explanation: Glycolysis occurs in the cytoplasm and does not require oxygen.

Q3. Glycolysis is also known as:

A. Krebs cycle
B. EMP pathway
C. HMP pathway
D. Calvin cycle

Answer: B
Explanation: Glycolysis is called the Embden–Meyerhof–Parnas (EMP) pathway.

Q4. The end product of glycolysis is:

A. Acetyl-CoA
B. Pyruvic acid
C. Lactic acid
D. Ethanol

Answer: B
Explanation: One glucose molecule is converted into two molecules of pyruvate.

Q5. Glycolysis requires:

A. Oxygen
B. Mitochondria
C. ATP and enzymes
D. Chlorophyll

Answer: C
Explanation: ATP is invested in early steps of glycolysis.

Q6. Net gain of ATP in glycolysis per glucose molecule is:

A. 1 ATP
B. 2 ATP
C. 4 ATP
D. 6 ATP

Answer: B
Explanation: Glycolysis produces 4 ATP but consumes 2 ATP, giving a net gain of 2 ATP.

Q7. Which enzyme catalyzes phosphorylation of glucose in glycolysis?

A. Hexokinase
B. Rubisco
C. ATP synthase
D. Dehydrogenase

Answer: A
Explanation: Hexokinase catalyzes the first step of glycolysis.

Q8. Glycolysis is common to:

A. Only plants
B. Only animals
C. Only aerobic organisms
D. Both aerobic and anaerobic organisms

Answer: D
Explanation: Glycolysis occurs in all living organisms.

Q9. ATP in glycolysis is formed by:

A. Oxidative phosphorylation
B. Photophosphorylation
C. Substrate-level phosphorylation
D. Chemiosmosis

Answer: C
Explanation: ATP is formed directly from substrates.

Q10. Glycolysis does not directly produce:

A. ATP
B. NADH
C. CO₂
D. Pyruvate

Answer: C
Explanation: CO₂ is released during later stages, not glycolysis.

Section B: Fermentation & Anaerobic Respiration (Q11–Q20)

Q11. Anaerobic respiration occurs in absence of:

A. Water
B. CO₂
C. Oxygen
D. Glucose

Answer: C
Explanation: Anaerobic respiration takes place without oxygen.

Q12. In plants, anaerobic respiration results in formation of:

A. Lactic acid
B. Ethanol and CO₂
C. Acetic acid
D. Acetyl-CoA

Answer: B
Explanation: Plant cells produce ethanol and carbon dioxide.

Q13. Alcoholic fermentation occurs in:

A. Yeast
B. Muscle cells
C. Leaves only
D. Roots only

Answer: A
Explanation: Yeast cells carry out alcoholic fermentation.

Q14. Enzyme involved in conversion of pyruvate to ethanol is:

A. Dehydrogenase
B. Pyruvate decarboxylase
C. ATP synthase
D. RuBP carboxylase

Answer: B
Explanation: Pyruvate decarboxylase converts pyruvate to acetaldehyde.

Q15. Lactic acid fermentation occurs in:

A. Plant roots
B. Yeast
C. Animal muscle cells
D. Chloroplast

Answer: C
Explanation: Muscle cells produce lactic acid under anaerobic conditions.

Q16. Energy yield of anaerobic respiration is:

A. Higher than aerobic
B. Equal to aerobic
C. Lower than aerobic
D. Zero

Answer: C
Explanation: Anaerobic respiration yields only 2 ATP per glucose.

Q17. Fermentation occurs in which cellular compartment?

A. Mitochondria
B. Cytoplasm
C. Nucleus
D. Chloroplast

Answer: B
Explanation: Fermentation takes place in the cytoplasm.

Q18. Which compound is regenerated during fermentation?

A. ATP
B. NAD⁺
C. FAD
D. ADP

Answer: B
Explanation: NAD⁺ is regenerated to allow glycolysis to continue.

Q19. Anaerobic respiration is less efficient because:

A. Glucose not used fully
B. Oxygen absent
C. Fewer ATP formed
D. Enzymes inactive

Answer: C
Explanation: Incomplete oxidation results in less ATP.

Q20. Which condition favors anaerobic respiration in plants?

A. High oxygen
B. Waterlogged soil
C. High light intensity
D. Low temperature

Answer: B
Explanation: Roots in waterlogged soil face oxygen deficiency.

Section C: Aerobic Respiration – Krebs Cycle (Q21–Q35)

Q21. Aerobic respiration occurs in presence of:

A. Nitrogen
B. Oxygen
C. Carbon dioxide
D. Water

Answer: B
Explanation: Oxygen acts as the final electron acceptor.

Q22. Pyruvate enters mitochondria in the form of:

A. Acetyl-CoA
B. Oxaloacetate
C. Citrate
D. Lactate

Answer: A
Explanation: Pyruvate is converted to Acetyl-CoA.

Q23. Krebs cycle occurs in:

A. Cytoplasm
B. Inner mitochondrial membrane
C. Mitochondrial matrix
D. Outer membrane

Answer: C
Explanation: Enzymes of Krebs cycle are in the matrix.

Q24. The first stable compound of Krebs cycle is:

A. Citric acid
B. Oxaloacetic acid
C. Succinic acid
D. Malic acid

Answer: A
Explanation: Acetyl-CoA combines with oxaloacetate to form citrate.

Q25. Krebs cycle is also known as:

A. EMP pathway
B. TCA cycle
C. HMP pathway
D. Glyoxylate cycle

Answer: B
Explanation: Krebs cycle is the Tricarboxylic Acid (TCA) cycle.

Q26. Number of CO₂ molecules released per glucose in Krebs cycle is:

A. 2
B. 4
C. 6
D. 8

Answer: B
Explanation: Each acetyl-CoA releases 2 CO₂; glucose produces 2 acetyl-CoA.

Q27. Which compound is regenerated at the end of Krebs cycle?

A. Citrate
B. Malate
C. Oxaloacetate
D. Succinate

Answer: C
Explanation: Oxaloacetate is regenerated to continue the cycle.

Q28. Which reduced coenzyme is formed in Krebs cycle?

A. NADH
B. NADPH
C. FADH₂
D. Both A and C

Answer: D
Explanation: Both NADH and FADH₂ are produced.

Q29. Direct ATP formation in Krebs cycle occurs at:

A. Succinyl-CoA → Succinate
B. Citrate → Isocitrate
C. Malate → Oxaloacetate
D. Pyruvate → Acetyl-CoA

Answer: A
Explanation: One ATP (or GTP) is formed by substrate-level phosphorylation.

Q30. Krebs cycle is amphibolic because it:

A. Produces ATP only
B. Is aerobic
C. Participates in both anabolic and catabolic pathways
D. Occurs in mitochondria

Answer: C
Explanation: Intermediates are used in biosynthesis.

Q31. Complete oxidation of one glucose molecule releases:

A. 2 CO₂
B. 4 CO₂
C. 6 CO₂
D. 8 CO₂

Answer: C
Explanation: Total of 6 CO₂ molecules are released.

Q32. Which step links glycolysis and Krebs cycle?

A. Oxidative phosphorylation
B. Pyruvate oxidation
C. Fermentation
D. Glyoxylate cycle

Answer: B
Explanation: Conversion of pyruvate to acetyl-CoA is the link reaction.

Q33. NADH and FADH₂ are finally oxidized in:

A. Cytoplasm
B. Krebs cycle
C. Electron transport chain
D. Glycolysis

Answer: C
Explanation: They donate electrons to the ETC.

Q34. Which step of respiration produces maximum ATP?

A. Glycolysis
B. Krebs cycle
C. Fermentation
D. Oxidative phosphorylation

Answer: D
Explanation: ETC produces most ATP molecules.

Q35. Respiration in plants differs from animals because plants:

A. Do not respire
B. Respire only at night
C. Lack specialized organs
D. Do not use oxygen

Answer: C
Explanation: Plants lack specialized respiratory organs.

Section D: Electron Transport System & Respiratory Quotient (Q36–Q50)

Q36. Electron transport chain is located in:

A. Outer mitochondrial membrane
B. Inner mitochondrial membrane
C. Matrix
D. Cytoplasm

Answer: B
Explanation: ETC proteins are embedded in inner mitochondrial membrane.

Q37. The final electron acceptor in aerobic respiration is:

A. CO₂
B. NAD⁺
C. Oxygen
D. Water

Answer: C
Explanation: Oxygen accepts electrons and forms water.

Q38. Oxidative phosphorylation occurs due to:

A. Light energy
B. Enzyme action only
C. Proton gradient
D. Substrate-level reaction

Answer: C
Explanation: ATP is synthesized using proton motive force.

Q39. ATP synthase complex is also called:

A. CF₀–CF₁
B. F₀–F₁
C. Rubisco
D. Cytochrome c

Answer: B
Explanation: Mitochondrial ATP synthase is F₀–F₁ complex.

Q40. Total ATP produced per glucose molecule in plants is approximately:

A. 18
B. 28
C. 36
D. 44

Answer: C
Explanation: Net yield is about 36 ATP.

Q41. Respiratory quotient (RQ) is the ratio of:

A. O₂ used / CO₂ released
B. CO₂ released / O₂ consumed
C. ATP formed / glucose used
D. NADH formed / FADH₂ formed

Answer: B
Explanation: RQ indicates the nature of respiratory substrate.

Q42. RQ of carbohydrates is:

A. 0.5
B. 0.7
C. 1.0
D. 1.5

Answer: C
Explanation: Equal CO₂ released and O₂ consumed.

Q43. RQ of fats is:

A. More than 1
B. Equal to 1
C. Less than 1
D. Zero

Answer: C
Explanation: Fats require more oxygen, so RQ < 1.

Q44. RQ greater than 1 indicates respiration of:

A. Proteins
B. Fats
C. Organic acids
D. Carbohydrates

Answer: C
Explanation: Organic acids release more CO₂.

Q45. Which substrate gives RQ = 0.8?

A. Carbohydrates
B. Proteins
C. Fats
D. Organic acids

Answer: B
Explanation: Proteins have RQ ≈ 0.8.

Q46. Cyanide inhibits respiration by blocking:

A. Glycolysis
B. Krebs cycle
C. Electron transport chain
D. Fermentation

Answer: C
Explanation: Cyanide inhibits cytochrome oxidase.

Q47. Pasteur effect refers to:

A. Increase in respiration
B. Inhibition of respiration by oxygen
C. Inhibition of fermentation by oxygen
D. Increase in glycolysis

Answer: C
Explanation: Oxygen suppresses fermentation.

Q48. Respiratory substrates are oxidized to:

A. ATP only
B. CO₂ and H₂O
C. Ethanol
D. Lactic acid

Answer: B
Explanation: Complete oxidation forms CO₂ and water.

Q49. Respiration provides energy mainly for:

A. Growth only
B. Reproduction only
C. Maintenance only
D. All metabolic activities

Answer: D
Explanation: ATP supports all life processes.

Q50. Respiration in plants is continuous because:

A. It occurs only in leaves
B. Energy is always required
C. Light is always present
D. Oxygen is absent

Answer: B
Explanation: Plants need energy at all times.