Respiration in Plants: 30 solved questions on the ATP ledger

Free questions

30 solved MCQs, answer marked and reasoning written out

Every question below is free to read — no sign-up, no email. 2 of them are real questions from past NEET papers. The other 209 questions in this chapter are in the book and in practice access.

1. Q1 Multi-statement analysis

   Regarding fermentation: (i) less than seven per cent of the energy in glucose is released (ii) not all of it is trapped as high energy bonds of ATP (iii) the processes are hazardous, since acid or alcohol is produced (iv) yeasts poison themselves when alcohol reaches about 13 per cent. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.Three
   4. 4.FourCorrect answer

   Why option 4 is the answer

   The trap: All four are correct.

   What this is testing: how inefficient and risky fermentation is compared with aerobic respiration.

   (i) is correct. Fermentation releases less than seven per cent of the energy stored in glucose. (ii) is correct. Not all of even that fraction ends up trapped in ATP's high-energy bonds. (iii) is correct. Fermentation is hazardous to the organism itself, since acid or alcohol builds up as a product. (iv) is correct. Yeast poisons itself once the alcohol it makes reaches about 13 per cent.

   So all four are correct. This chapter leans on this exact pair of numbers — under 7 per cent energy, about 13 per cent alcohol — because they are easy to mix up.

   Less than seven per cent of glucose's energy, and the product poisons the organism that made it. Fermentation is a poor bargain taken only when oxygen is absent.

   NCERT Class 11 Biology, page 157

2. Q2 Multi-statement analysis

   The crucial events of aerobic respiration are: (i) the complete oxidation of pyruvate by stepwise removal of all the hydrogen atoms, leaving three molecules of CO2 (ii) passing the electrons to molecular O2 with simultaneous synthesis of ATP (iii) the first process takes place in the matrix of the mitochondria (iv) the second process is located on the outer membrane of the mitochondria. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; the ETS is on the INNER mitochondrial membrane, so (iv) is wrong.

   What this is testing: where each of the two major mitochondrial events happens.

   (i) is correct. Pyruvate is completely oxidised by removing all its hydrogens step by step, leaving three CO2 molecules behind. (ii) is correct. Those electrons are finally passed to O2, with ATP made alongside. (iii) is correct. This oxidation of pyruvate happens in the mitochondrial matrix. (iv) is the trap. Electron transport runs on the INNER mitochondrial membrane, not the outer one — the outer membrane is a simple, freely permeable boundary.

   So three are correct. Mixing up inner and outer membrane is the single most common slip in this chapter.

   Three CO2 out, electrons to oxygen, ATP alongside. Aerobic respiration is the complete version of what fermentation leaves half-done.

   NCERT Class 11 Biology, page 158

3. Q3 Multi-statement analysis

   The strategy of a cell in catabolising glucose: (i) glucose is oxidised in several small steps, not in one step (ii) some steps are just large enough that the released energy can be coupled to ATP synthesis (iii) not all the liberated energy goes out as heat (iv) complete combustion releases most of the energy as usable chemical energy. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; in complete combustion most energy is given out as HEAT, so (iv) is wrong.

   What this is testing: why glucose is broken down in small steps rather than all at once.

   (i) is correct. The cell oxidises glucose in several small steps instead of one. (ii) is correct. Some of these steps release just enough energy to be coupled to ATP synthesis. (iii) is correct. Not all of the energy escapes as heat. (iv) is the trap. Complete, one-step combustion would release most of the energy as HEAT, not as usable chemical energy — exactly the fate step-wise oxidation avoids.

   So three are correct. (iii) and (iv) point in opposite directions, which is the giveaway.

   Many small steps, each releasing a usable amount. One big step would waste the energy as heat, which is exactly why the cell does not take it.

   NCERT Class 11 Biology, page 155

4. Q4 Multi-statement analysis

   Comparing fermentation and aerobic respiration: (i) fermentation accounts for only a partial breakdown of glucose (ii) in aerobic respiration glucose is completely degraded to CO2 and H2O (iii) fermentation gives a net gain of only two ATP per glucose (iv) NADH is oxidised to NAD+ more vigorously in fermentation than in aerobic respiration. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; NADH oxidation is SLOW in fermentation and vigorous in aerobic respiration, so (iv) is wrong.

   What this is testing: comparing fermentation with aerobic respiration on how fast NADH gets reoxidised.

   (i) is correct. Fermentation only partially breaks glucose down. (ii) is correct. Aerobic respiration completely degrades glucose to CO2 and H2O. (iii) is correct. Fermentation nets only two ATP per glucose. (iv) is the trap. NADH is oxidised back to NAD+ SLOWLY in fermentation, not more vigorously than in aerobic respiration — the ETS reoxidises NADH far faster.

   So three are correct. Fermentation is the slower, not the more vigorous, route for regenerating NAD+.

   Two ATP against thirty-eight. The difference is the price of having no oxygen to finish the job.

   NCERT Class 11 Biology, page 162

5. Q5 Multi-statement analysis

   ATP in respiration: (i) the energy released by oxidation cannot be used directly (ii) it is used to synthesise ATP (iii) ATP is broken down wherever energy needs to be utilised (iv) ATP acts as the energy currency of the cell. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.Three
   4. 4.FourCorrect answer

   Why option 4 is the answer

   The trap: All four are correct.

   What this is testing: why cells need ATP as an intermediate rather than using oxidation energy directly.

   (i) is correct. The energy released by oxidation cannot be used directly by the cell. (ii) is correct. Instead it is used to make ATP. (iii) is correct. ATP is broken down wherever and whenever energy is needed. (iv) is correct. This makes ATP the energy currency of the cell.

   So all four are correct. This chain — oxidation, ATP synthesis, ATP breakdown, energy currency — is the whole logic of why respiration exists.

   Oxidation cannot be spent directly, so the cell banks it as ATP. That conversion is the entire point of respiration.

   NCERT Class 11 Biology, page 154

6. Q6 Multi-statement analysis

   Reducing equivalents in the TCA cycle: (i) there are three points where NAD+ is reduced to NADH + H+ (ii) there is one point where FAD+ is reduced to FADH2 (iii) the cycle requires continued replenishment of oxaloacetic acid (iv) it requires regeneration of NAD+ and FAD+. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.Three
   4. 4.FourCorrect answer

   Why option 4 is the answer

   The trap: All four are correct.

   What this is testing: the electron-carrying coenzymes generated by one turn of the TCA cycle.

   (i) is correct. NAD+ is reduced to NADH + H+ at three points in the cycle. (ii) is correct. FAD+ is reduced to FADH2 at one point. (iii) is correct. The cycle needs oxaloacetic acid continually replenished to keep accepting new acetyl groups. (iv) is correct. It also needs NAD+ and FAD+ regenerated, which is what the ETS does downstream.

   So all four are correct. Three NADH and one FADH2 per turn is worth fixing firmly in memory.

   Three NADH, one FADH2, one ATP per turn - and the cycle turns twice per glucose. Oxaloacetate comes back at the end to start again.

   NCERT Class 11 Biology, page 159

7. Q7 Multi-statement analysis

   The TCA cycle: (i) starts with the condensation of the acetyl group with oxaloacetic acid and water to yield citric acid (ii) the reaction is catalysed by citrate synthase (iii) a molecule of CoA is released (iv) citrate is then isomerised to isocitrate. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.Three
   4. 4.FourCorrect answer

   Why option 4 is the answer

   The trap: All four are correct.

   What this is testing: the opening reaction of the TCA cycle.

   (i) is correct. The cycle starts when the acetyl group condenses with oxaloacetic acid and water to give citric acid. (ii) is correct. Citrate synthase catalyses this reaction. (iii) is correct. A molecule of CoA is released, free to pick up another acetyl group. (iv) is correct. Citrate is then isomerised to isocitrate.

   So all four are correct. This opening sequence — condensation, CoA release, isomerisation — is worth learning as a fixed first block of the cycle.

   Two carbons in from acetyl CoA, two carbons out as CO2, and oxaloacetate regenerated. The cycle balances exactly, which is what lets it run indefinitely.

   NCERT Class 11 Biology, page 158

8. Q8 Multi-statement analysis

   Regarding respiration: (i) it is the breaking of C-C bonds of complex compounds through oxidation within cells (ii) it releases a considerable amount of energy (iii) the compounds oxidised are called respiratory substrates (iv) all the energy is released free in a single step. How many are correct?

   1. 1.One
   2. 2.Two
   3. 3.ThreeCorrect answer
   4. 4.Four

   Why option 3 is the answer

   The trap: (i)–(iii) correct; energy is released in a series of slow, step-wise, enzyme-controlled reactions, so (iv) is wrong.

   What this is testing: whether respiration releases its energy all at once or gradually.

   (i) is correct. Respiration breaks the C-C bonds of complex compounds through oxidation inside cells. (ii) is correct. It releases a considerable amount of energy overall. (iii) is correct. The compounds oxidised are called respiratory substrates. (iv) is the trap. Energy is NOT released all in a single step — it comes out through a series of slow, step-wise, enzyme-controlled reactions.

   So three are correct. This is the same "single step versus step-wise" trap seen earlier, now asked about respiration as a whole.

   Respiration breaks C-C bonds by oxidation inside a cell. Burning does the same chemistry in one uncontrolled step and wastes it all as heat.

   NCERT Class 11 Biology, page 154

9. Q9 Assertion and Reason

   AssertionFour H+ pass through F0 for each ATP produced in the mitochondrion.

   ReasonThe F1 headpiece is a peripheral membrane protein complex containing the site for the synthesis of ATP.

   1. 1.Both A and R are true and R is the correct explanation of A
   2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
   3. 3.A is true but R is false
   4. 4.A is false but R is true

   Why option 2 is the answer

   The trap: Both are true of the mitochondrial ATP synthase; the location of the catalytic site is a parallel fact and does not explain the proton stoichiometry.

   What this is testing: two separate facts about mitochondrial ATP synthase running side by side.

   Both statements are true of ATP synthase: four H+ do cross F0 per ATP made, and the F1 headpiece is indeed the peripheral complex holding the catalytic site. But the second fact is a parallel description of the enzyme's structure — it does not explain why exactly four protons are needed.

   Both A and R are true but R is not the correct explanation of A — option 2.

   The proton count and the structure are two separate facts about one enzyme. Describing the machine never explains its exchange rate.

   NCERT Class 11 Biology, page 161

10. Q10 Assertion and Reason

    AssertionGlucose is the favoured respiratory substrate.

    ReasonFats and proteins can also be respired, but they do not enter the respiratory pathway at the first step.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of respiratory substrates; the entry points of fats and proteins are a parallel fact and do not explain why glucose is favoured.

    What this is testing: why glucose, rather than fat or protein, is the favoured respiratory substrate.

    Both statements are true: glucose is indeed favoured, and fats and proteins can be respired but enter the pathway partway rather than at the first step. However, the reason describes the entry points of the alternative substrates; it does not itself explain why glucose is preferred.

    Both A and R are true but R is not the correct explanation of A — option 2.

    Where the alternatives join is not why glucose is preferred. Two true facts about substrates, unconnected by cause.

    NCERT Class 11 Biology, page 162

11. Q11 Assertion and Reason

    AssertionThe electron transport system is located on the inner mitochondrial membrane.

    ReasonThe oxidative decarboxylation of pyruvate and the TCA cycle occur in the mitochondrial matrix.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true statements of mitochondrial compartmentation running in parallel; the matrix location of the TCA cycle does not explain the membrane location of the ETS.

    What this is testing: keeping the locations of different respiratory stages straight.

    Both statements are true: the ETS does sit on the inner mitochondrial membrane, and pyruvate oxidation plus the TCA cycle do occur in the matrix. But these are two separate, parallel facts about mitochondrial geography — the matrix location of one stage does not explain the membrane location of another.

    Both A and R are true but R is not the correct explanation of A — option 2.

    Matrix for the TCA cycle, inner membrane for the ETS. Two neighbouring addresses, and neither explains the other.

    NCERT Class 11 Biology, page 158

12. Q12 Assertion and Reason

    AssertionStomata and lenticels allow gaseous exchange in plants.

    ReasonRoots, stems and leaves of plants respire at rates far lower than animals do.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of plant gas exchange running in parallel; the low respiratory rate does not explain the presence of stomata and lenticels.

    What this is testing: the structures plants use for gas exchange, and their respiration rate.

    Both statements are true: stomata and lenticels do allow gas exchange, and plant tissues do respire more slowly than animal tissue. But the slow respiration rate is a separate fact about plant metabolism — it does not explain why stomata and lenticels exist as gas-exchange structures.

    Both A and R are true but R is not the correct explanation of A — option 2.

    How fast plants respire and where the gas gets in are separate facts. Rate never explains anatomy.

    NCERT Class 11 Biology, page 154

13. Q13 Assertion and Reason

    AssertionThe synthesis of GTP during the conversion of succinyl-CoA to succinic acid is a substrate level phosphorylation.

    ReasonIn a coupled reaction the GTP formed is converted to GDP with the simultaneous synthesis of ATP from ADP.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of this TCA step; the coupled GTP-to-ATP conversion is a parallel fact and does not explain why the phosphorylation is substrate-level.

    What this is testing: what kind of phosphorylation makes GTP in the TCA cycle.

    Both statements are true: the GTP made when succinyl-CoA converts to succinic acid is indeed substrate-level phosphorylation, and that GTP is indeed coupled to make ATP from ADP. But the coupled GTP-to-ATP conversion is a separate downstream fact — it does not itself explain why the original phosphorylation is classed as substrate-level.

    Both A and R are true but R is not the correct explanation of A — option 2.

    Substrate-level means made directly in a reaction, not by a proton gradient. What happens to the GTP afterwards is a separate step.

    NCERT Class 11 Biology, page 159

14. Q14 Assertion and Reason

    AssertionThe respiratory quotient depends upon the type of respiratory substrate used.

    ReasonIn living organisms the respiratory substrates are often more than one, and pure proteins or fats are never respired alone.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of respiratory substrates; the mixed nature of real substrates is a parallel fact and does not explain why the RQ varies with substrate type.

    What this is testing: why the respiratory quotient varies with the substrate used.

    Both statements are true: RQ does depend on the substrate, and real organisms do respire mixtures rather than pure protein or pure fat. But that mixed-substrate reality is a separate fact about living systems — it does not itself explain why RQ varies with substrate type in principle.

    Both A and R are true but R is not the correct explanation of A — option 2.

    What organisms actually burn and why RQ varies are different claims. The reason adds a complication rather than a cause.

    NCERT Class 11 Biology, page 164

15. Q15 Assertion and Reason

    AssertionGlycolysis is often referred to as the EMP pathway.

    ReasonIn glycolysis a chain of ten enzyme-catalysed reactions converts glucose into pyruvate.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true of glycolysis; the ten-step sequence is a parallel fact and does not explain the EMP abbreviation.

    What this is testing: the name EMP pathway and the ten-step structure of glycolysis.

    Both statements are true: glycolysis is indeed called the EMP pathway, and it is a ten-step enzymatic sequence converting glucose to pyruvate. But the ten-step detail is a separate fact about the pathway's length — it does not itself explain why the pathway carries the initials EMP.

    Both A and R are true but R is not the correct explanation of A — option 2.

    The name honours three scientists; the ten steps are a separate fact. Length never explains a name.

    NCERT Class 11 Biology, page 155

16. Q16 Assertion and Reason

    AssertionFatty acids enter the respiratory pathway as acetyl CoA.

    ReasonGlycerol enters the respiratory pathway after being converted to PGAL.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of ACorrect answer
    3. 3.A is true but R is false
    4. 4.A is false but R is true

    Why option 2 is the answer

    The trap: Both are true entry points for the components of a fat, running in parallel; one does not explain the other.

    What this is testing: the separate entry routes of the two halves of a triglyceride.

    Both statements are true: fatty acids do enter as acetyl CoA, and glycerol does enter after conversion to PGAL. But these describe two different, parallel entry points for the two halves of a fat molecule — one does not explain the other.

    Both A and R are true but R is not the correct explanation of A — option 2.

    A fat splits into glycerol and fatty acids, and the two halves enter at different points. Parallel entries, neither explaining the other.

    NCERT Class 11 Biology, page 162

17. Q17 Assertion and Reason

    AssertionGlycolysis occurs in the mitochondrial matrix of the cell.

    ReasonGlycolysis is present in all living organisms, including prokaryotes that lack mitochondria.

    1. 1.Both A and R are true and R is the correct explanation of A
    2. 2.Both A and R are true but R is not the correct explanation of A
    3. 3.A is true but R is false
    4. 4.A is false but R is trueCorrect answer

    Why option 4 is the answer

    The trap: A is false — glycolysis occurs in the CYTOPLASM; R is true and indeed implies it.

    What this is testing: the location of glycolysis and why it can run in organisms without mitochondria.

    The assertion is false: glycolysis occurs in the CYTOPLASM, not the mitochondrial matrix. The reason is true, and it is exactly why the assertion cannot be right — glycolysis is present in all living organisms, including prokaryotes with no mitochondria, so it cannot depend on a mitochondrial location.

    So A is false but R is true — option 4.

    Prokaryotes have no mitochondria and still perform glycolysis. That alone places the pathway in the cytoplasm.

    NCERT Class 11 Biology, page 155

18. Q18 Statement I and Statement II

    Statement IThe net gain of ATP in aerobic respiration of one glucose is 38.

    Statement IIIn fermentation there is a net gain of only two ATP per glucose.

    1. 1.Both Statement I and Statement II are correctCorrect answer
    2. 2.Both Statement I and Statement II are incorrect
    3. 3.Statement I is correct but Statement II is incorrect
    4. 4.Statement I is incorrect but Statement II is correct

    Why option 1 is the answer

    The trap: Both statements are correct.

    What this is testing: the contrast between the ATP yield of aerobic respiration and that of fermentation.

    Statement I is correct. Complete aerobic respiration of one glucose molecule nets about 38 ATP.

    Statement II is correct. Fermentation nets only two, because the glucose is never fully broken down and most of its energy stays locked in the alcohol or lactic acid produced.

    Both are correct, so the answer is option 1.

    The trap: the gap between the two figures is so large that a student who half-remembers one of them doubts the other. Anchor them together — the whole point of breathing oxygen is that 38 against 2.

    NCERT Class 11 Biology, page 162

19. Q19 Statement I and Statement II

    Statement IFatty acids enter the respiratory pathway after being degraded to acetyl CoA.

    Statement IIGlycerol enters the respiratory pathway after being converted to PGAL.

    1. 1.Both Statement I and Statement II are correctCorrect answer
    2. 2.Both Statement I and Statement II are incorrect
    3. 3.Statement I is correct but Statement II is incorrect
    4. 4.Statement I is incorrect but Statement II is correct

    Why option 1 is the answer

    The trap: Both statements are correct.

    What this is testing: how the two components of a fat enter the respiratory pathway separately.

    Both statements are correct. Fatty acids do enter after being degraded to acetyl CoA, and glycerol does enter separately, after being converted to PGAL.

    Both Statement I and Statement II are correct — option 1.

    Glycerol and fatty acids take different routes into the same pathway. A fat is dismantled before any of it can be burnt.

    NCERT Class 11 Biology, page 162

20. Q20 Statement I and Statement II

    Statement IThe respiratory pathway is purely a catabolic pathway.

    Statement IIThe respiratory pathway is involved in both anabolism and catabolism.

    1. 1.Both Statement I and Statement II are correct
    2. 2.Both Statement I and Statement II are incorrect
    3. 3.Statement I is correct but Statement II is incorrect
    4. 4.Statement I is incorrect but Statement II is correctCorrect answer

    Why option 4 is the answer

    The trap: I incorrect (it is amphibolic); II correct.

    What this is testing: whether the respiratory pathway is purely catabolic or also anabolic.

    Statement I is incorrect: the respiratory pathway is not purely catabolic — it is amphibolic. Statement II is correct: it is indeed involved in both anabolism and catabolism, which is exactly why "purely catabolic" is the wrong description.

    Statement I is incorrect but Statement II is correct — option 4.

    Amphibolic, not catabolic. The pathway both dismantles and supplies the parts for building.

    NCERT Class 11 Biology, page 162

21. Q21 Match the columns

    Match the gas exchange structure with its site:

    Column I	Column II
    (a) Stomata	(i) network of air spaces
    (b) Lenticels	(ii) leaves
    (c) Loose parenchyma	(iii) dead, mechanical support
    (d) Interior stem cells	(iv) stems

    1. 1.(a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)
    2. 2.(a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)Correct answer
    3. 3.(a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
    4. 4.(a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)

    Why option 2 is the answer

    The trap: Stomata-leaves, lenticels-stems, parenchyma-air spaces, interior cells-dead support.

    What this is testing: which gas-exchange structure sits where, and the state of the deepest stem cells.

    The correct pairing is stomata in leaves, lenticels in stems, loose parenchyma forming the network of air spaces, and the interior stem cells being dead and providing mechanical support — option 2.

    Option 1 is the tempting wrong pick. It swaps stomata and lenticels, putting stomata in stems and lenticels in leaves — the reverse of where each structure is actually found.

    NCERT Class 11 Biology, page 155

22. Q22 Match the columns

    Match the process with its net ATP:

    Column I	Column II
    (a) Glycolysis (net)	(i) 2 ATP
    (b) Fermentation (net)	(ii) 38 ATP
    (c) Aerobic respiration	(iii) 2 ATP
    (d) TCA cycle (per glucose, direct)	(iv) 2 ATP

    1. 1.(a)-(i), (b)-(iv), (c)-(ii), (d)-(iii)
    2. 2.(a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)
    3. 3.(a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)Correct answer
    4. 4.(a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)

    Why option 3 is the answer

    The trap: Glycolysis and fermentation-2 ATP net; aerobic-38 ATP; TCA direct-2 ATP.

    What this is testing: matching each process to its correct net ATP figure, including the one genuine outlier.

    The correct pairing gives glycolysis, fermentation and the TCA cycle's direct output all 2 ATP net, with aerobic respiration alone reaching 38 ATP — option 3.

    Option 2 is the tempting wrong pick, and the dangerous one. It pairs fermentation with 38 ATP — fermentation never gets anywhere close to that; its net gain stops at the 2 ATP made in glycolysis.

    NCERT Class 11 Biology, page 162

23. Q23 Match the columns

    Match the decarboxylation with the compound formed:

    Column I	Column II
    (a) Pyruvate decarboxylated	(iii) succinyl-CoA
    (b) Isocitrate decarboxylated	(iv) GTP formed
    (c) α-ketoglutarate decarboxylated	(i) α-ketoglutaric acid
    (d) Succinyl-CoA to succinate	(ii) acetyl CoA

    1. 1.(a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
    2. 2.(a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)Correct answer
    3. 3.(a)-(ii), (b)-(iii), (c)-(i), (d)-(iv)
    4. 4.(a)-(iv), (b)-(i), (c)-(iii), (d)-(ii)

    Why option 2 is the answer

    The trap: The three decarboxylations and the substrate-level GTP step of the mitochondrial phase.

    What this is testing: which decarboxylation step produces which compound in the mitochondrial phase.

    The correct pairing is pyruvate decarboxylated to acetyl CoA, isocitrate decarboxylated to α-ketoglutaric acid, α-ketoglutarate decarboxylated to succinyl-CoA, and succinyl-CoA to succinate forming GTP — option 2.

    Option 1 is the tempting wrong pick. It swaps the products of the first two decarboxylations, giving pyruvate's decarboxylation the α-ketoglutaric acid product and isocitrate's the acetyl CoA product — the reverse of the real sequence.

    NCERT Class 11 Biology, page 159

24. Q24 Match the columns

    Match the condition with the fate of pyruvate:

    Column I	Column II
    (a) Yeast, anaerobic	(i) lactic acid
    (b) Muscle, oxygen inadequate	(iii) acetyl CoA, then TCA cycle
    (c) Aerobic conditions	(iv) lactic acid
    (d) Some bacteria, anaerobic	(ii) ethanol and CO2

    1. 1.(a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
    2. 2.(a)-(ii), (b)-(iii), (c)-(i), (d)-(iv)
    3. 3.(a)-(iv), (b)-(i), (c)-(iii), (d)-(ii)
    4. 4.(a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)Correct answer

    Why option 4 is the answer

    The trap: Yeast-ethanol, muscle and some bacteria-lactic acid, aerobic-acetyl CoA and TCA.

    What this is testing: which organism, under which condition, sends pyruvate down which fermentation or respiratory route.

    The correct pairing is yeast under anaerobic conditions making ethanol and CO2, muscle short of oxygen making lactic acid, aerobic conditions routing pyruvate to acetyl CoA and the TCA cycle, and some bacteria under anaerobic conditions also making lactic acid — option 4.

    Option 3 is the tempting wrong pick. It swaps yeast and the lactic-acid-forming bacteria, sending yeast down the lactic acid route and the bacteria down the ethanol route — the reverse of the textbook's named examples.

    NCERT Class 11 Biology, page 157

25. Q25 Exception / incorrect

    All occur in the TCA cycle EXCEPT:

    1. 1.three FADH2 per acetyl CoACorrect answer
    2. 2.three NADH per acetyl CoA
    3. 3.one FADH2 per acetyl CoA
    4. 4.one GTP per acetyl CoA

    Why option 1 is the answer

    The trap: Only one FAD+ reduction occurs per turn.

    What this is testing: how many times each coenzyme is reduced in one turn of the TCA cycle.

    Three NADH, one FADH2, and one GTP do form per acetyl CoA oxidised through one turn of the cycle. Three FADH2 does not happen.

    So option 1 is the exception — only ONE FAD+ is reduced to FADH2 per turn, at the succinate-to-fumarate step; three is the count for NADH, not FADH2.

    Three NADH but only one FADH2 per turn. The single FAD step is succinate to fumarate.

    NCERT Class 11 Biology, page 159

26. Q26 Exception / incorrect

    Identify the INCORRECT pairing (compound – carbons):

    1. 1.Citric acid – 6
    2. 2.α-ketoglutaric acid – 5
    3. 3.Succinic acid – 4
    4. 4.Oxaloacetic acid – 6Correct answer

    Why option 4 is the answer

    The trap: OAA is a four-carbon acid.

    What this is testing: the carbon count of each TCA intermediate.

    Citric acid with 6 carbons, α-ketoglutaric acid with 5, and succinic acid with 4 are all correctly paired. Oxaloacetic acid does not have 6 carbons.

    So option 4 is the incorrect pairing — oxaloacetic acid is a FOUR-carbon acid; six carbons is the count for citric acid, the compound OAA becomes once it condenses with acetyl CoA.

    Six for citric, five for α-ketoglutaric, four for oxaloacetic. Each decarboxylation drops the count by one.

    NCERT Class 11 Biology, page 159

27. Q27 Sequence / ordering

    Correct order of ATP yield per glucose (increasing):

    1. 1.aerobic respiration → fermentation → glycolysis
    2. 2.fermentation (2) → glycolysis net (2) → aerobic respiration (38)Correct answer
    3. 3.aerobic respiration → glycolysis → fermentation
    4. 4.glycolysis → aerobic respiration → fermentation

    Why option 2 is the answer

    The trap: Fermentation and glycolysis give 2 ATP net; aerobic respiration gives 38.

    What this is testing: ranking fermentation, glycolysis and aerobic respiration by ATP yield.

    In increasing order of ATP yield per glucose: fermentation and glycolysis alone both give a net 2 ATP, while full aerobic respiration gives the much larger theoretical 38 ATP. Sequences placing aerobic respiration first, or fermentation ahead of glycolysis as though they differ, misrepresent that fermentation adds nothing beyond glycolysis's own net 2 ATP.

    The trap: fermentation has its own name, but its net ATP yield equals glycolysis's, since fermentation itself makes no additional ATP — it only regenerates NAD+ so glycolysis can keep running.

    NCERT Class 11 Biology, page 162

28. Q28 Sequence / ordering

    Correct order of RQ values (decreasing):

    1. 1.fat (0.7) → protein (0.9) → carbohydrate (1.0)
    2. 2.protein → carbohydrate → fat
    3. 3.fat → carbohydrate → protein
    4. 4.carbohydrate (1.0) → protein (0.9) → fat (0.7)Correct answer

    Why option 4 is the answer

    The trap: Carbohydrate 1.0 > protein 0.9 > fat 0.7.

    What this is testing: ranking carbohydrate, protein and fat by their respiratory quotient, from highest to lowest.

    In decreasing order of RQ: carbohydrate gives 1.0, protein gives about 0.9, and fat gives about 0.7 — this order reflects how oxygen-rich each substrate is, carbohydrate needing the least extra oxygen to fully oxidise. Any sequence starting with fat or protein at the top reverses this real ranking of RQ values.

    The trap: these three numbers, 1.0, 0.9 and 0.7, are reused constantly across this chapter's questions, so the risk is not forgetting the numbers themselves but misordering which substrate owns which value.

    NCERT Class 11 Biology, page 164

29. Q29 NEET 2024

    Which step of the TCA cycle does NOT involve oxidation?

    1. 1.Conversion of isocitrate to α-ketoglutarate
    2. 2.Conversion of succinate to fumarate
    3. 3.Conversion of citrate to isocitrateCorrect answer
    4. 4.Conversion of malate to oxaloacetate

    Why option 3 is the answer

    The trap: Citrate is rearranged to its isomer isocitrate without any change in oxidation state; the other listed steps are oxidative.

    What this is testing: identifying the one TCA cycle step that is NOT an oxidation.

    Citrate rearranging to its isomer, isocitrate, is a simple structural change with no change in oxidation state, the one non-oxidative step among the four listed. Isocitrate to α-ketoglutarate, succinate to fumarate, and malate to oxaloacetate are all genuine oxidation steps, each reducing NAD+ or FAD.

    The trap: every other named TCA cycle conversion in this chapter is tied to an NADH or FADH2 forming, so it is easy to assume EVERY step must be oxidative, overlooking that citrate-to-isocitrate is purely a rearrangement.

    NCERT Class 11 Biology, pages 158-159

30. Q30 NEET 2021

    Identify the INCORRECT statement about the electron transport chain:

    1. 1.Complex IV does not use molecular oxygen as the final electron acceptorCorrect answer
    2. 2.Complex I accepts electrons from NADH
    3. 3.Complex II is succinate dehydrogenase
    4. 4.ATP synthase uses the proton gradient to make ATP

    Why option 1 is the answer

    The trap: Complex IV (cytochrome c oxidase) DOES use molecular oxygen as the final electron acceptor, reducing it to water — the statement denying this is the incorrect one.

    What this is testing: catching a false statement about the electron transport chain.

    Complex I accepting electrons from NADH, complex II being succinate dehydrogenase, and ATP synthase using the proton gradient to make ATP are all correct facts about the ETC. The false statement claims complex IV does NOT use molecular oxygen as final acceptor — complex IV, cytochrome c oxidase, in fact DOES use O2, reducing it to water.

    The trap: the double negative in "does not use...as the final electron acceptor" is easy to skim past, letting a careless reader accept it as true simply because complex IV and oxygen are genuinely linked.

    NCERT Class 11 Biology, page 160