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Respiration: NEET MCQs with answers

115 questions on this topic of Plant Physiology (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. Which of the following compounds is the first member of the TCA cycle to be regenerated at the end of each cyclic turn?

  1. Citric acid
  2. Succinic acid
  3. Malic acid
  4. Oxaloacetic acid (OAA)
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Answer: (D) Oxaloacetic acid (OAA)

Oxaloacetic acid (OAA, a 4-carbon compound) condenses with acetyl CoA to form citric acid at the start of the cycle, and is regenerated at the end after the oxidation of malate by malate dehydrogenase.

medium

2. Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Oxidation of one molecule of NADH + H⁺ via ETS yields 3 ATP, whereas oxidation of one molecule of FADH₂ yields 2 ATP. Reason (R): NADH + H⁺ transfers its electrons to Complex I, allowing protons to be pumped across three complexes, while FADH₂ transfers its electrons to Complex II, bypassing the first proton-pumping site. In the light of the above statements, choose the correct answer:

  1. Both (A) and (R) are true and (R) is the correct explanation of (A)
  2. Both (A) and (R) are true but (R) is not the correct explanation of (A)
  3. (A) is true but (R) is false
  4. (A) is false but (R) is true
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Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A)

Electrons from NADH enter at Complex I (NADH dehydrogenase) and pass through Complexes III and IV, generating a proton gradient across three sites to produce 3 ATP. In contrast, electrons from FADH₂ enter at Complex II (succinate dehydrogenase) which does not pump protons, thereby bypassing the first proton-pumping site and yielding only 2 ATP. Thus, Reason correctly explains Assertion.

hard

3. Reduced ubiquinone (ubiquinol) is oxidised with transfer of electrons to cytochrome c via:

  1. Cytochrome bc1 complex (complex III)
  2. Complex I
  3. ATP synthase
  4. Complex IV
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Answer: (A) Cytochrome bc1 complex (complex III)

Ubiquinol passes electrons to cytochrome c through the cytochrome bc1 complex (complex III). Cytochrome c then carries them to complex IV.

NCERT Class 11

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4. In glycolysis, glucose is partially oxidised to form:

  1. One molecule of acetyl CoA
  2. Two molecules of pyruvic acid
  3. Two molecules of lactic acid only
  4. Six molecules of CO2
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Answer: (B) Two molecules of pyruvic acid

Glucose undergoes partial oxidation to two molecules of pyruvic acid in the cytoplasm.

easy

5. The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof, and J. Parnas, and is often referred to as the EMP pathway. In plants, the sucrose derived from photosynthesis is converted into glucose and fructose by the enzyme:

  1. Invertase
  2. Hexokinase
  3. Zymase
  4. Aldolase
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Answer: (A) Invertase

According to NCERT, sucrose is converted into glucose and fructose by the enzyme invertase, and these two monosaccharides readily enter the glycolytic pathway.

hard

6. Assertion (A): Fermentation releases much less energy than aerobic respiration from the same amount of glucose. Reason (R): In fermentation glucose is only partially oxidised. Choose the correct option.

  1. Both A and R are true and R is the correct explanation of A
  2. Both A and R are true but R is not the correct explanation of A
  3. A is true but R is false
  4. A is false but R is true
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Answer: (A) Both A and R are true and R is the correct explanation of A

In fermentation, less than seven per cent of the energy in glucose is released because it is only partially oxidised.

medium

7. Match List-I with List-II to choose the correct option: List-I (Process / Site) (A) Site of EMP pathway (B) Site of Krebs cycle (C) Proton accumulation in ETS (D) Terminal electron acceptor List-II (Location / Molecule) (I) Intermembrane space (II) Molecular oxygen (III) Cytoplasm (IV) Mitochondrial matrix

  1. A-IV, B-III, C-I, D-II
  2. A-III, B-IV, C-I, D-II
  3. A-III, B-I, C-IV, D-II
  4. A-II, B-IV, C-I, D-III
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Answer: (B) A-III, B-IV, C-I, D-II

Glycolysis occurs in the cytoplasm (A-III); Krebs cycle takes place in the mitochondrial matrix (B-IV); protons accumulate in the intermembrane space during ETS (C-I); and oxygen acts as the final hydrogen/electron acceptor in ETS (D-II).

medium

8. The electron transport system (ETS) of mitochondria is present in the:

  1. Inner mitochondrial membrane
  2. Outer mitochondrial membrane
  3. Mitochondrial matrix
  4. Cytoplasm
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Answer: (A) Inner mitochondrial membrane

The ETS is located in the inner mitochondrial membrane; electrons pass from one carrier to another, releasing energy for ATP synthesis.

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9. The respiratory quotient (RQ) is the ratio of:

  1. ATP produced to glucose used
  2. Volume of O2 consumed to CO2 evolved
  3. Volume of CO2 evolved to volume of O2 consumed
  4. Water produced to CO2 evolved
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Answer: (C) Volume of CO2 evolved to volume of O2 consumed

RQ = volume of CO2 evolved / volume of O2 consumed; it depends on the respiratory substrate.

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10. Match the stage of respiration with its site in a eukaryotic cell. Column-I: (A) Glycolysis (B) Link reaction (C) Krebs cycle (D) Electron transport system Column-II: (i) Inner mitochondrial membrane (ii) Cytoplasm (iii) Mitochondrial matrix (iv) Mitochondrial matrix (pyruvate dehydrogenase)

  1. A-(iii), B-(ii), C-(iv), D-(i)
  2. A-(ii), B-(iv), C-(iii), D-(i)
  3. A-(ii), B-(i), C-(iii), D-(iv)
  4. A-(i), B-(iv), C-(iii), D-(ii)
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Answer: (B) A-(ii), B-(iv), C-(iii), D-(i)

Glycolysis is cytoplasmic; the link reaction and Krebs cycle occur in the matrix; the ETS is in the inner membrane.

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11. When proteins are used as respiratory substrates, each amino acid, after deamination:

  1. Enters the pathway as pyruvate, acetyl CoA or within the Krebs cycle
  2. Is converted to glucose directly in the cytoplasm only
  3. Is excreted unchanged
  4. Enters glycolysis as glucose-6-phosphate
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Answer: (A) Enters the pathway as pyruvate, acetyl CoA or within the Krebs cycle

Proteins are degraded by proteases into amino acids. Depending on its structure, each deaminated amino acid enters the pathway at some stage within the Krebs cycle or as pyruvate or acetyl CoA.

NCERT Class 11

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12. Given below are two statements: Statement I: The inner mitochondrial membrane is relatively impermeable to protons (H⁺). Statement II: The passage of protons through the F₀ channel of ATP synthase is coupled to the catalytic synthesis of ATP in the F₁ subunit. In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
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Answer: (A) Both Statement I and Statement II are correct

The inner mitochondrial membrane maintains a proton gradient because it is impermeable to protons, preventing spontaneous backflow. Protons can only traverse back into the matrix through the specialized F₀ transmembrane channel of ATP synthase, driving ATP synthesis at the F₁ catalytic headpiece.

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