Assertion A: Yeast fermentation continues whatever the alcohol level in the medium. Reason R: Yeasts poison themselves to death when the alcohol level reaches about 13 per cent. Choose the correct answer.

A is not correct but R is correct

Both A and R are correct and R is the correct explanation of A

A is correct but R is not correct

Both A and R are correct but R is not the correct explanation of A

Respiration in Plants

27 NEET-UG practice questions on Respiration in Plants, part of Botany. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
Arrange these Krebs' cycle intermediates in the order of their formation, starting after acetyl CoA joins oxaloacetic acid. A. α-ketoglutaric acid B. Malic acid C. Citric acid D. Succinic acid
1. AC, A, B, D
2. BC, A, D, B
3. CC, D, A, B
4. DA, C, D, B
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Answer: B · C, A, D, B
Acetyl CoA and oxaloacetic acid condense to form citric acid (6C). Citric acid gives α-ketoglutaric acid (5C), then succinyl CoA and succinic acid (4C), then malic acid, which forms oxaloacetic acid again.
- A: Malic acid forms after succinic acid, on the way to oxaloacetic acid.
- C: This places a 4C acid before the 5C acid.
- D: Citric acid is the first product, before α-ketoglutaric acid.
Remember this
Carbon count falls 6C, 5C, 4C; oxaloacetic acid is regenerated and joins the next acetyl CoA.
Mnemonic: Citrate Is Krebs' Starting Substrate For Making Oxaloacetate (citrate, isocitrate, α-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, oxaloacetate).
Question 2 · Medium
Assertion A: Yeast fermentation continues whatever the alcohol level in the medium. Reason R: Yeasts poison themselves to death when the alcohol level reaches about 13 per cent. Choose the correct answer.
1. ABoth A and R are correct and R is the correct explanation of A
2. BA is correct but R is not correct
3. CA is not correct but R is correct
4. DBoth A and R are correct but R is not the correct explanation of A
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Answer: C · A is not correct but R is correct
Yeast cells die once alcohol reaches about 13 per cent, so fermentation cannot continue at any level. R is a true fact, and it contradicts A.
- A: A is false, so R cannot explain it.
- B: This reverses the truth of A and R.
- D: A is false, so both cannot be correct.
Remember this
Fermentation is self-limiting in yeast at about 13 per cent alcohol, and yields under 7 per cent of glucose energy.
Question 3 · Medium
In a respirometer, a germinating seed uses 20 mL of O₂ and gives out 18 mL of CO₂ in the same time. What are its respiratory quotient and its most likely respiratory substrate?
1. A0.9; fat
2. B1.11; protein
3. C0.9; protein
4. D1.0; carbohydrate
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Answer: C · 0.9; protein
RQ = volume of CO₂ evolved / volume of O₂ consumed = 18/20 = 0.9. Proteins give an RQ of about 0.9, whereas fats give about 0.7 and carbohydrates give exactly 1.
- A: The value is right, but fats give about 0.7.
- B: This divides O₂ by CO₂, inverting the formula.
- D: An RQ of 1 needs equal volumes of the two gases.
Remember this
RQ is CO₂ out divided by O₂ in; carbohydrate is 1, protein about 0.9, fat about 0.7.
Question 4 · Medium
Match List-I with List-II. List-I (ETS complex) A. Complex I B. Complex II C. Complex III D. Complex V List-II (name or role) I. Cytochrome bc₁ II. ATP synthase III. NADH dehydrogenase IV. Passes reducing equivalents of FADH₂ to ubiquinone
1. AA-III, B-IV, C-I, D-II
2. BA-III, B-I, C-IV, D-II
3. CA-II, B-IV, C-I, D-III
4. DA-IV, B-III, C-I, D-II
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Answer: A · A-III, B-IV, C-I, D-II
NADH is oxidised at complex I, NADH dehydrogenase. FADH₂ feeds ubiquinone through complex II. Ubiquinol passes electrons to cytochrome c through complex III, cytochrome bc₁. Complex V, with F₁ and F₀, makes ATP.
- B: This swaps complexes II and III.
- C: This swaps complexes I and V.
- D: This swaps the NADH and FADH₂ entry points.
Remember this
FADH₂ enters after complex I, so it yields 2 ATP compared with 3 from NADH.
Question 5 · Easy
In the electron transport system of plant mitochondria, electrons finally pass to
1. Acytochrome c
2. BNAD⁺
3. Coxygen
4. Dubiquinone
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Answer: C · oxygen
Electrons travel through the complexes and reach cytochrome c oxidase, which passes them to oxygen. Oxygen, with protons, forms water.
- A: Cytochrome c is a mobile carrier before complex IV.
- B: NAD⁺ brings electrons to the chain as NADH, and is not the final acceptor.
- D: Ubiquinone is a mobile carrier in the middle of the chain.
Remember this
Oxygen is the terminal electron acceptor, so removing it stops the whole ETS and its ATP supply.
Question 6 · Medium
Study these statements on the respiratory pathway. A. Glycerol enters after conversion to PGAL. B. Fatty acids enter after breakdown to acetyl CoA. C. Amino acids can enter only through glycolysis. D. The pathway is amphibolic because its intermediates can also be withdrawn for synthesis. Which of these are correct?
1. AA, C and D only
2. BB, C and D only
3. CA, B and D only
4. DA and B only
Answer and explanation in LearnFree account
Question 7 · Easy
Which stage of the aerobic breakdown of glucose takes place in the cytoplasm?
1. ALink reaction
2. BElectron transport system
3. CKrebs' cycle
4. DGlycolysis
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Question 8 · Hard
Given below are two statements: Statement I: During glycolysis, four ATP are formed directly and two are used per glucose, giving a net gain of two ATP. Statement II: The NADH of glycolysis is formed when phosphoenol pyruvate changes to pyruvic acid. Choose the correct answer.
1. AStatement I is incorrect but Statement II is correct
2. BBoth Statement I and Statement II are incorrect
3. CStatement I is correct but Statement II is incorrect
4. DBoth Statement I and Statement II are correct
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Question 9 · Hard
Take 3 ATP per NADH and 2 ATP per FADH₂. How many ATP are formed when one pyruvic acid is fully oxidised in the mitochondrion, counting the link reaction and Krebs' cycle?
1. A14
2. B30
3. C12
4. D15
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Question 10 · Medium
During glycolysis of one glucose molecule, how many ATP molecules are used, and how many are formed directly by the pathway?
1. A1 used and 2 formed
2. B2 used and 2 formed
3. C2 used and 4 formed
4. D4 used and 2 formed
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Question 11 · Medium
Given below are two statements: Statement I: In the electron transport system, oxidation of one NADH gives 3 ATP, while that of one FADH₂ gives 2 ATP. Statement II: Cytochrome c is a small protein attached to the outer surface of the inner mitochondrial membrane and carries electrons between complex III and complex IV. Choose the correct answer.
1. AStatement I is incorrect but Statement II is correct
2. BBoth Statement I and Statement II are incorrect
3. CStatement I is correct but Statement II is incorrect
4. DBoth Statement I and Statement II are correct
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Question 12 · Easy
Under anaerobic conditions, yeast converts pyruvic acid into
1. AEthanol and CO₂
2. BAcetyl CoA and CO₂
3. CLactic acid
4. DOxaloacetic acid
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Question 13 · Medium
When fats are used as respiratory substrates, glycerol enters the respiratory pathway after being converted to
1. APGAL
2. BPyruvic acid
3. Cα-Ketoglutaric acid
4. DAcetyl CoA
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Question 14 · Hard
Read these statements about respiration in plants. A. In alcoholic fermentation, less than 7% of the energy in glucose is released. B. Lactic acid fermentation in muscle releases CO₂ along with lactic acid. C. Pyruvic acid is converted to acetyl CoA in the mitochondrial matrix, with NADH being formed. D. Yeasts poison themselves to death when the alcohol concentration reaches about 13%. Which statements are correct?
1. AA, B and C only
2. BA, C and D only
3. CC and D only
4. DA, B, C and D
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Question 15 · Medium
A substrate is completely oxidised in a tissue according to the balanced equation C₄H₆O₅ + 3O₂ → 4CO₂ + 3H₂O. What is the respiratory quotient?
1. A0.75
2. B1.33
3. C0.7
4. D1.0
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Question 16 · Medium
Arrange these stages of aerobic respiration of glucose in the order in which they occur. A. Oxidative decarboxylation of pyruvic acid to acetyl CoA in the mitochondrial matrix B. Glycolysis in the cytoplasm C. Oxidation of NADH and FADH₂ through the electron transport system, with ATP synthesis D. Condensation of the acetyl group with oxaloacetic acid to form citric acid Choose the correct order.
1. AA, B, D, C
2. BB, A, D, C
3. CB, A, C, D
4. DB, D, A, C
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Question 17 · Easy
In which of these is pyruvic acid reduced to lactic acid?
1. AGerminating seeds with plenty of oxygen
2. BYeast cells growing without oxygen
3. CAnimal muscle cells during exercise when oxygen is inadequate
4. DLeaf cells respiring aerobically
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Question 18 · Hard
Consider these statements about the respiratory pathway as an amphibolic pathway. A. Fatty acids are broken down to acetyl CoA before entering the respiratory pathway. B. Proteins enter the respiratory pathway only after their amino acids are converted into glucose. C. When an organism needs to make fatty acids, acetyl CoA is withdrawn from the respiratory pathway. D. The pathway is called amphibolic because it can run both with and without oxygen. Which statements are correct?
1. AA and C only
2. BA, C and D only
3. CA, B and C only
4. DC and D only
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Question 19 · Medium
Why is the respiratory pathway described as amphibolic rather than purely catabolic?
1. AIts intermediates serve both breakdown and synthesis
2. BIt runs only when oxygen is absent from the cell
3. CIt can break down glucose but no other substrate at all
4. DIt releases all the energy of glucose in a single step
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Question 20 · Easy
When fats are used as respiratory substrates, in what form do their fatty acids enter the respiratory pathway?
1. AOxaloacetic acid
2. BAcetyl CoA
3. CPGAL
4. DPyruvic acid
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Question 21 · Hard
A yeast culture ferments two glucose molecules to ethanol and fully oxidises a third glucose aerobically. Using the net yields given in NCERT, how many ATP are gained and how many CO₂ molecules released in all?
1. A42 ATP and 10 CO₂
2. B42 ATP and 8 CO₂
3. C40 ATP and 10 CO₂
4. D46 ATP and 10 CO₂
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Question 22 · Medium
Given below are two statements: Statement I: Oxygen acts at the beginning of the electron transport system by accepting electrons from NADH. Statement II: The F₁ headpiece of complex V is the site of ATP synthesis, while F₀ forms the channel for protons. Choose the correct answer.
1. AStatement I is incorrect but Statement II is correct
2. BBoth Statement I and Statement II are incorrect
3. CStatement I is correct but Statement II is incorrect
4. DBoth Statement I and Statement II are correct
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Question 23 · Easy
In the mitochondrial matrix, pyruvic acid undergoes oxidative decarboxylation to acetyl CoA. Which enzyme complex catalyses this?
1. APyruvic acid decarboxylase
2. BPyruvate dehydrogenase
3. CCitrate synthase
4. DAlcohol dehydrogenase
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Question 24 · Medium
In alcoholic or lactic acid fermentation, roughly what share of the energy in glucose is released?
1. AAbout forty per cent
2. BNearly all of it
3. CAbout fifty per cent
4. DLess than seven per cent
Answer and explanation in LearnFree account
Question 25 · Medium
Arrange these components of the mitochondrial electron transport system in the order electrons pass through them after leaving complex I. A. Complex III B. Ubiquinone C. Cytochrome c D. Complex IV Choose the correct order.
1. AA, B, C, D
2. BB, A, C, D
3. CB, C, A, D
4. DC, B, A, D
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Respiration in Plants

Arrange these Krebs' cycle intermediates in the order of their formation, starting after acetyl CoA joins oxaloacetic acid. A. α-ketoglutaric acid B. Malic acid C. Citric acid D. Succinic acid

Assertion A: Yeast fermentation continues whatever the alcohol level in the medium. Reason R: Yeasts poison themselves to death when the alcohol level reaches about 13 per cent. Choose the correct answer.

In a respirometer, a germinating seed uses 20 mL of O₂ and gives out 18 mL of CO₂ in the same time. What are its respiratory quotient and its most likely respiratory substrate?

Match List-I with List-II. List-I (ETS complex) A. Complex I B. Complex II C. Complex III D. Complex V List-II (name or role) I. Cytochrome bc₁ II. ATP synthase III. NADH dehydrogenase IV. Passes reducing equivalents of FADH₂ to ubiquinone

In the electron transport system of plant mitochondria, electrons finally pass to

Which stage of the aerobic breakdown of glucose takes place in the cytoplasm?

Given below are two statements: Statement I: During glycolysis, four ATP are formed directly and two are used per glucose, giving a net gain of two ATP. Statement II: The NADH of glycolysis is formed when phosphoenol pyruvate changes to pyruvic acid. Choose the correct answer.

Take 3 ATP per NADH and 2 ATP per FADH₂. How many ATP are formed when one pyruvic acid is fully oxidised in the mitochondrion, counting the link reaction and Krebs' cycle?

During glycolysis of one glucose molecule, how many ATP molecules are used, and how many are formed directly by the pathway?

Under anaerobic conditions, yeast converts pyruvic acid into

When fats are used as respiratory substrates, glycerol enters the respiratory pathway after being converted to

A substrate is completely oxidised in a tissue according to the balanced equation C₄H₆O₅ + 3O₂ → 4CO₂ + 3H₂O. What is the respiratory quotient?

In which of these is pyruvic acid reduced to lactic acid?

Why is the respiratory pathway described as amphibolic rather than purely catabolic?

When fats are used as respiratory substrates, in what form do their fatty acids enter the respiratory pathway?

A yeast culture ferments two glucose molecules to ethanol and fully oxidises a third glucose aerobically. Using the net yields given in NCERT, how many ATP are gained and how many CO₂ molecules released in all?

Given below are two statements: Statement I: Oxygen acts at the beginning of the electron transport system by accepting electrons from NADH. Statement II: The F₁ headpiece of complex V is the site of ATP synthesis, while F₀ forms the channel for protons. Choose the correct answer.

In the mitochondrial matrix, pyruvic acid undergoes oxidative decarboxylation to acetyl CoA. Which enzyme complex catalyses this?

In alcoholic or lactic acid fermentation, roughly what share of the energy in glucose is released?

Arrange these components of the mitochondrial electron transport system in the order electrons pass through them after leaving complex I. A. Complex III B. Ubiquinone C. Cytochrome c D. Complex IV Choose the correct order.