Breathing and Exchange of Gases: volumes, capacities, answers

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 174 questions in this chapter are in the book and in practice access.

1. Q1 Multi-statement analysis

   Regarding the volume changes in inspiration: (i) diaphragm contraction increases the thoracic volume in the antero-posterior axis (ii) external inter-costal contraction increases it in the dorso-ventral axis (iii) the increase in thoracic volume causes a similar increase in pulmonary volume (iv) the increase in pulmonary volume raises the intra-pulmonary pressure. 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; an increase in pulmonary volume DECREASES the intra-pulmonary pressure, so (iv) is wrong.

   What this is testing: the chain of events during inspiration, ending with the pressure change.

   (i) is correct. Diaphragm contraction increases thoracic volume along the antero-posterior axis. (ii) is correct. Contraction of the external intercostals increases it along the dorso-ventral axis. (iii) is correct. Since the lungs sit in an air-tight chamber, a rise in thoracic volume raises pulmonary volume too. (iv) is the trap. A bigger pulmonary volume LOWERS intra-pulmonary pressure, it does not raise it — that drop below atmospheric pressure is exactly what pulls air in.

   So three are correct.

   Volume up, pressure down, air in. Breathing is pressure difference, and the muscles only change the volume.

   NCERT Class 11 Biology, page 186

2. Q2 Multi-statement analysis

   The pleura: (i) the lungs are covered by a double-layered pleura (ii) pleural fluid lies between the layers (iii) it reduces friction on the lung surface (iv) the inner pleural membrane is in close contact with the thoracic lining. 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 OUTER pleural membrane contacts the thoracic lining and the INNER one contacts the lung surface, so (iv) is wrong.

   What this is testing: the structure of the pleura and which layer touches what.

   (i) is correct. The lungs sit inside a double-layered pleura. (ii) is correct. Pleural fluid fills the space between the two layers. (iii) is correct. This fluid cuts down friction on the lung surface as it moves. (iv) is the trap. It is the INNER pleural membrane that touches the lung surface — the OUTER membrane is the one in contact with the thoracic lining.

   So three are correct. Inner-lung, outer-chest wall: swap them and you get the trap in (iv).

   Inner pleura on the lung, outer on the chest wall, fluid between. That film is what lets the lung move with the ribs without tearing.

   NCERT Class 11 Biology, page 184

3. Q3 Multi-statement analysis

   Regarding CO2 solubility and diffusion: (i) the solubility of CO2 is 20-25 times higher than that of O2 (ii) the amount of CO2 diffusing per unit difference in partial pressure is much higher than that of O2 (iii) all the factors in our body favour diffusion of O2 from alveoli to tissues (iv) the solubility of O2 is higher than that of CO2. 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; CO2 is far MORE soluble than O2, so (iv) is wrong.

   What this is testing: why CO2 diffuses faster than O2 despite similar partial-pressure gradients.

   (i) is correct. CO2 is 20 to 25 times more soluble than O2. (ii) is correct. Because of that, more CO2 diffuses per unit partial-pressure difference than O2. (iii) is correct. In the body, every factor favours O2 diffusing from alveoli into the blood and tissues. (iv) is the trap. It is the reverse of (i): O2 is NOT more soluble than CO2 — CO2 is far more soluble.

   So three are correct. Solubility favours CO2, not O2; do not let the statement flip that around.

   CO2 is far more soluble than O2, which is why it needs a much smaller gradient to move. Solubility compensates for the gentler pressure difference.

   NCERT Class 11 Biology, page 188

4. Q4 Multi-statement analysis

   Cartilaginous support: (i) the trachea is supported by incomplete cartilaginous rings (ii) the primary, secondary and tertiary bronchi are so supported (iii) the initial bronchioles are so supported (iv) the alveoli are supported by cartilaginous rings. 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; alveoli are thin, irregular-walled sacs with NO cartilage, so (iv) is wrong.

   What this is testing: which parts of the airway are held open by cartilage, and which are not.

   (i) is correct. The trachea is supported by incomplete cartilaginous rings. (ii) is correct. So are the primary, secondary and tertiary bronchi. (iii) is correct. Even the initial bronchioles retain some cartilaginous support. (iv) is the trap. Alveoli are thin, irregular sacs with NO cartilage at all — rigid support would stop them from being flexible enough for gas exchange.

   So three are correct. Cartilage supports the conducting tubes; the alveoli, built for exchange, have none.

   Cartilage everywhere except the alveoli. Rings keep the tubes open; a rigid alveolus could not expand.

   NCERT Class 11 Biology, page 184

5. Q5 Multi-statement analysis

   The thoracic chamber: (i) is anatomically an air-tight chamber (ii) is formed dorsally by the vertebral column (iii) is formed ventrally by the sternum and laterally by the ribs (iv) is bounded below by the dome-shaped diaphragm. 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 anatomy of the thoracic chamber that houses the lungs.

   (i) is correct. The thoracic chamber is anatomically air-tight. (ii) is correct. It is bounded dorsally by the vertebral column. (iii) is correct. It is bounded ventrally by the sternum and laterally by the ribs. (iv) is correct. Its floor is the dome-shaped diaphragm.

   So all four are correct. This airtight box is exactly why a change in thoracic volume forces an identical change in pulmonary volume — there is no gap for that coupling to leak through.

   Air-tight is the key word. Ribs, sternum, vertebrae and diaphragm seal a box whose volume the muscles change.

   NCERT Class 11 Biology, page 185

6. Q6 Multi-statement analysis

   Respiration in different groups: (i) most aquatic arthropods and molluscs use gills (branchial respiration) (ii) terrestrial forms use lungs (pulmonary respiration) (iii) fishes use gills (iv) amphibians respire only through lungs. 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; amphibians can also respire through the moist skin (cutaneous respiration), so (iv) is wrong.

   What this is testing: which respiratory organ different animal groups actually use.

   (i) is correct. Most aquatic arthropods and molluscs breathe through gills. (ii) is correct. Terrestrial forms use lungs. (iii) is correct. Fishes use gills. (iv) is the trap. Amphibians do not respire ONLY through lungs — they also breathe through their moist skin, cutaneous respiration, especially in water.

   So three are correct. The word 'only' is what breaks (iv); amphibians have two routes, not one.

   Amphibians use lungs and skin together. The word 'only' is what makes the fourth statement fail.

   NCERT Class 11 Biology, page 183

7. Q7 Multi-statement analysis

   The trachea: (i) is a straight tube extending up to the mid-thoracic cavity (ii) divides at the level of the 5th thoracic vertebra (iii) gives rise to a right and left primary bronchi (iv) divides at the level of the 2nd thoracic vertebra. 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 division occurs at the FIFTH thoracic vertebra, so (iv) is wrong.

   What this is testing: the trachea's path and exactly where it splits.

   (i) is correct. The trachea runs as a straight tube down to the mid-thoracic cavity. (ii) is correct. It divides at the level of the fifth thoracic vertebra. (iii) is correct. This division gives rise to the right and left primary bronchi. (iv) is the trap. It contradicts (ii) directly: the split happens at the FIFTH thoracic vertebra, not the second.

   So three are correct. Two statements that cannot both be true about the same division point is the signal that one is planted.

   Trachea divides at the fifth thoracic vertebra into two primary bronchi. The level is asked directly often enough to memorise.

   NCERT Class 11 Biology, page 184

8. Q8 Multi-statement analysis

   Regarding tidal volume: (i) it is the volume of air inspired or expired during a normal respiration (ii) it is approximately 500 mL (iii) a healthy man can inspire or expire approximately 6000 to 8000 mL of air per minute (iv) it is the volume remaining after a forcible expiration. 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 volume remaining after forcible expiration is the RESIDUAL VOLUME, so (iv) is wrong.

   What this is testing: the definition of tidal volume and what it is not.

   (i) is correct. Tidal volume is the air inspired or expired during ordinary, normal breathing. (ii) is correct. It is about 500 mL. (iii) is correct. A healthy adult can move roughly 6000 to 8000 mL of air per minute this way. (iv) is the trap. The air left after a forcible expiration is the RESIDUAL volume, not tidal volume — tidal volume never touches that leftover air at all.

   So three are correct.

   Tidal volume 500 mL, times 12 to 16 breaths, gives 6000 to 8000 mL a minute. The arithmetic links the two figures.

   NCERT Class 11 Biology, page 186

9. Q9 Assertion and Reason

   AssertionThe trachea and bronchi are supported by incomplete cartilaginous rings.

   ReasonThe larynx is a cartilaginous box that helps in sound production.

   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 cartilaginous structures in the airway running in parallel; the larynx's role does not explain the tracheal rings.

   What this is testing: whether two true facts about cartilage in the airway are connected to each other.

   A is true. The trachea and bronchi are supported by incomplete cartilaginous rings. R is true too: the larynx is a cartilaginous box that helps produce sound.

   Both are genuine facts about cartilage in the respiratory passage, but R does not explain A — the larynx's sound-producing role has nothing to do with why the trachea's rings are incomplete. So this is code (2).

   The trap: two statements sharing the word 'cartilaginous' can feel linked when they are simply parallel facts about different structures.

   NCERT Class 11 Biology, page 184

10. Q10 Assertion and Reason

    AssertionCigarette smoking is a major cause of emphysema.

    ReasonAsthma causes difficulty in breathing and wheezing due to inflammation of the bronchi and bronchioles.

    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 about respiratory disorders running in parallel; asthma does not explain emphysema.

    What this is testing: whether one respiratory disorder explains the cause of a different one.

    A is true. Cigarette smoking is a major cause of emphysema. R is true too: asthma causes difficulty in breathing and wheezing from inflamed bronchi and bronchioles.

    Both are genuine facts about respiratory disorders, but R describes asthma, a separate disease, and gives no reason for emphysema. So this is code (2).

    The trap: two true statements about the same organ system can look connected purely because they sit in the same paragraph of the book.

    NCERT Class 11 Biology, page 190

11. Q11 Assertion and Reason

    AssertionThe conducting part brings the inspired air to body temperature.

    ReasonThe conducting part also clears the air of foreign particles and humidifies it.

    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 functions of the conducting part running in parallel; cleaning and humidifying do not explain the warming of the air.

    What this is testing: whether two separate functions of the conducting part explain each other.

    A is true. The conducting part brings inspired air to body temperature. R is true too: it also clears the air of foreign particles and humidifies it.

    Both are genuine jobs of the conducting part, but R does not explain why the air gets warmed — cleaning and humidifying are separate actions from temperature regulation. So this is code (2).

    The trap: three true functions of the same structure can be mistaken for a chain of cause and effect when they are really just a list.

    NCERT Class 11 Biology, page 185

12. Q12 Assertion and Reason

    AssertionVital capacity includes the residual volume.

    ReasonVital capacity is the maximum volume of air a person can breathe in after a forced expiration and includes ERV, TV and IRV.

    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 — vital capacity does NOT include the residual volume; R is true.

    What this is testing: whether vital capacity includes the residual volume.

    A is false. Vital capacity does NOT include the residual volume — residual air can never be forced out, so it falls outside vital capacity entirely. R is true: vital capacity is the maximum air breathed in after a forced expiration and equals ERV plus TV plus IRV, none of which is residual volume.

    So A is false and R is true, code (4).

    The trap: R itself is accurate and even proves A wrong, since its own formula has no RV term — read R carefully before assuming it backs up A.

    NCERT Class 11 Biology, page 187

13. Q13 Assertion and Reason

    AssertionTidal volume is the volume of air a person can inspire by a forcible inspiration.

    ReasonTidal volume is the volume of air inspired or expired during a normal respiration and is approximately 500 mL.

    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 — that describes the inspiratory reserve volume; R is true.

    What this is testing: telling tidal volume apart from inspiratory reserve volume.

    A is false. Tidal volume is NOT the air a person can inspire by a forcible inspiration — that description belongs to inspiratory reserve volume. R is true: tidal volume is the air moved during normal, quiet breathing and is about 500 mL.

    So A is false and R is true, code (4).

    The trap: A borrows the 'forcible' language that belongs to IRV and attaches it to tidal volume, which is really just ordinary breathing.

    NCERT Class 11 Biology, page 186

14. Q14 Assertion and Reason

    AssertionAlveoli are the primary sites of exchange of gases.

    ReasonThe exchange of gases also occurs between the blood and the tissues.

    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 sites of gas exchange running in parallel; the tissue exchange does not explain the alveolar role.

    What this is testing: whether tissue-level gas exchange explains why the alveoli are the primary exchange site.

    A is true. Alveoli are indeed the primary sites of gas exchange. R is true too: exchange of gases also happens between blood and tissues.

    Both are correct facts about gas exchange, but R does not explain why the alveoli specifically hold the primary role — tissue exchange is a separate, later step. So this is code (2).

    The trap: two true statements about exchange at different sites can look linked simply because they share the phrase 'exchange of gases'.

    NCERT Class 11 Biology, page 187

15. Q15 Assertion and Reason

    AssertionThe partial pressure of oxygen in the alveoli is 159 mm Hg.

    ReasonThe partial pressure of oxygen in atmospheric air is 159 mm Hg while in the alveoli it is 104 mm Hg.

    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; R is true.

    What this is testing: keeping the atmospheric and alveolar pO2 figures apart.

    A is false. The partial pressure of oxygen in the alveoli is 104 mm Hg, not 159 — 159 mm Hg is the atmospheric value. R is true: it correctly states that atmospheric pO2 is 159 mm Hg while alveolar pO2 is 104 mm Hg.

    So A is false and R is true, code (4).

    The trap: A takes the atmospheric figure and mislabels it as the alveolar one, even though R right next to it states the correct pair.

    NCERT Class 11 Biology, page 187

16. Q16 Assertion and Reason

    AssertionIn emphysema the bronchi and bronchioles are inflamed causing wheezing.

    ReasonIn asthma there is difficulty in breathing causing wheezing due to inflammation of the bronchi and bronchioles.

    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 — that describes asthma, not emphysema; R is true.

    What this is testing: telling emphysema and asthma apart by their described symptoms.

    A is false. Inflamed bronchi and bronchioles causing wheezing describes ASTHMA, not emphysema — emphysema instead damages the alveolar walls. R is true: it correctly describes asthma's cause of wheezing.

    So A is false and R is true, code (4).

    The trap: A borrows asthma's description and mislabels it as emphysema, even though R, right beside it, states the true asthma definition.

    NCERT Class 11 Biology, page 190

17. Q17 Assertion and Reason

    AssertionEvery 100 mL of oxygenated blood delivers around 5 mL of O2 to the tissues.

    ReasonEvery 100 mL of deoxygenated blood delivers approximately 4 mL of CO2 to the alveoli.

    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 transport figures running in parallel; one does not explain the other.

    What this is testing: whether the O2-delivery and CO2-delivery figures are connected causes or simply parallel facts.

    A is true. Every 100 mL of oxygenated blood delivers about 5 mL of O2 to the tissues. R is true too: every 100 mL of deoxygenated blood delivers about 4 mL of CO2 to the alveoli.

    Both are correct transport figures, but R does not explain A — the CO2 figure at the alveoli says nothing about why the O2 figure at the tissues is 5 mL. So this is code (2).

    The trap: two true numbers from the same paragraph can look like cause and effect when they are simply a matched pair of facts.

    NCERT Class 11 Biology, page 190

18. Q18 Statement I and Statement II

    Statement IIn the tissues, low pO2 and high pCO2 favour the dissociation of oxygen from oxyhaemoglobin.

    Statement IIIn the alveoli, high pO2 and low pCO2 favour the formation of oxyhaemoglobin.

    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 opposite partial-pressure conditions at the tissues and the alveoli.

    Statement I is correct. Low pO2 and high pCO2 at the tissues do favour oxyhaemoglobin dissociation. Statement II is correct too. High pO2 and low pCO2 at the alveoli favour oxyhaemoglobin formation.

    So both statements are correct, code (1).

    The trap: none — this mirror-image pair, tissues unload while alveoli load, is worth fixing as a single rule rather than two separate facts.

    NCERT Class 11 Biology, page 189

19. Q19 Statement I and Statement II

    Statement ICarbonic anhydrase is present in very high concentration in the RBCs.

    Statement IICarbonic anhydrase is completely absent from the plasma.

    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 incorrectCorrect answer
    4. 4.Statement I is incorrect but Statement II is correct

    Why option 3 is the answer

    The trap: I correct; minute quantities occur in the plasma too, so II is incorrect.

    What this is testing: whether carbonic anhydrase is found only in RBCs or in plasma as well.

    Statement I is correct. RBCs do carry a very high concentration of carbonic anhydrase. Statement II is incorrect: the enzyme is not completely absent from plasma — minute quantities are present there too.

    So I is correct and II is incorrect, code (3).

    The trap: statement II turns 'mostly in RBCs, a little in plasma' into 'never in plasma at all', overstating a true fact into a false absolute.

    NCERT Class 11 Biology, page 190

20. Q20 Statement I and Statement II

    Statement IThe respiratory rhythm centre is in the medulla.

    Statement IIThe pneumotaxic centre in the pons can reduce the duration of inspiration.

    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: which brain region houses the rhythm centre and what the pneumotaxic centre can do to inspiration.

    Statement I is correct. The respiratory rhythm centre is indeed in the medulla. Statement II is correct too. The pneumotaxic centre in the pons can reduce the duration of inspiration.

    So both statements are correct, code (1).

    The trap: none — medulla for the rhythm centre and pons for its moderator is the pairing other questions in this chapter try to mix up.

    NCERT Class 11 Biology, page 190

21. Q21 Match the columns

    Match the muscle action with the phase of breathing:

    Column I	Column II
    (a) Contraction of diaphragm	(ii) expiration
    (b) Contraction of external intercostals	(iii) expiration
    (c) Relaxation of diaphragm	(i) inspiration
    (d) Relaxation of intercostals	(iv) inspiration

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

    Why option 2 is the answer

    The trap: Contraction drives inspiration; relaxation drives expiration.

    What this is testing: matching each muscle action to the breathing phase it produces.

    The correct pairing is diaphragm contraction with inspiration, external intercostal contraction with inspiration, diaphragm relaxation with expiration, and intercostal relaxation with expiration. That is option 2.

    Why the others are wrong: options 1, 3 and 4 all cross-wire at least one action, most often attaching a contraction to expiration.

    The trap: contraction drives inspiration and relaxation drives expiration for both muscles; do not let one muscle's contraction get paired with expiration by mistake.

    NCERT Class 11 Biology, page 186

22. Q22 Match the columns

    Match the condition with its site:

    Column I	Column II
    (a) High pO2, low pCO2	(ii) tissues
    (b) Low pO2, high pCO2	(iii) alveoli
    (c) Formation of oxyhaemoglobin	(i) tissues
    (d) Dissociation of oxyhaemoglobin	(iv) alveoli

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

    Why option 3 is the answer

    The trap: Alveoli favour loading; tissues favour unloading of oxygen.

    What this is testing: matching each partial-pressure condition and haemoglobin event to its correct site.

    The correct pairing is 'high pO2, low pCO2' with the alveoli, 'low pO2, high pCO2' with the tissues, formation of oxyhaemoglobin with the alveoli, and dissociation of oxyhaemoglobin with the tissues. That is option 3.

    Why the others are wrong: options 1, 2 and 4 all swap at least one row, most often attaching formation of oxyhaemoglobin to the tissues instead of the alveoli.

    The trap: alveoli load oxygen onto haemoglobin, tissues unload it; keeping loading and unloading tied to the right site is the entire test.

    NCERT Class 11 Biology, page 189

23. Q23 Match the columns

    Match the term with its definition:

    Column I	Column II
    (a) Breathing	(iii) estimates respiratory volumes
    (b) Partial pressure	(iv) sigmoid plot of saturation against pO2
    (c) Spirometer	(i) pressure contributed by an individual gas in a mixture
    (d) Oxygen dissociation curve	(ii) exchange of atmospheric O2 with CO2 produced by cells

    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: Breathing, partial pressure, spirometer and the oxygen dissociation curve defined.

    What this is testing: matching four respiratory terms to their exact definitions.

    The correct pairing is breathing with the exchange of atmospheric O2 with CO2 produced by cells, partial pressure with the pressure contributed by one gas in a mixture, spirometer with estimating respiratory volumes, and oxygen dissociation curve with the sigmoid plot of saturation against pO2. That is option 4.

    Why the others are wrong: options 1 to 3 all shuffle at least one term to the wrong definition.

    The trap: 'partial pressure' and 'oxygen dissociation curve' both involve pO2, so it is easy to swap their definitions if you read quickly.

    NCERT Class 11 Biology, page 187

24. Q24 Match the columns

    Match the delivery figure with the blood:

    Column I	Column II
    (a) 100 mL oxygenated blood	(i) formed in the alveoli
    (b) 100 mL deoxygenated blood	(ii) formed in the tissues
    (c) Oxyhaemoglobin	(iii) delivers about 4 mL CO2 to the alveoli
    (d) Carbamino-haemoglobin	(iv) delivers about 5 mL O2 to the tissues

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

    Why option 4 is the answer

    The trap: 5 mL O2 delivered per 100 mL oxygenated blood; 4 mL CO2 per 100 mL deoxygenated blood.

    What this is testing: matching the volume of oxygenated and deoxygenated blood to what each delivers, and where each haemoglobin form is made.

    The correct pairing is 100 mL oxygenated blood with delivering about 5 mL O2 to the tissues, 100 mL deoxygenated blood with delivering about 4 mL CO2 to the alveoli, oxyhaemoglobin with being formed in the alveoli, and carbamino-haemoglobin with being formed in the tissues. That is option 4.

    Why the others are wrong: options 1 to 3 all cross-wire at least one row, most often swapping where the two haemoglobin forms are made.

    The trap: oxyhaemoglobin forms where oxygen is picked up, the alveoli, while carbamino-haemoglobin forms where CO2 is picked up, the tissues — keep each pigment tied to its own site.

    NCERT Class 11 Biology, page 190

25. Q25 Exception / incorrect

    Identify the INCORRECT transport figure:

    1. 1.97 per cent of O2 by RBCs
    2. 2.3 per cent of O2 dissolved in plasma
    3. 3.70 per cent of CO2 as carbamino-haemoglobinCorrect answer
    4. 4.70 per cent of CO2 as bicarbonate

    Why option 3 is the answer

    The trap: 20-25 per cent of CO2 is carried as carbamino-haemoglobin.

    What this is testing: the correct percentage figure for carbamino-haemoglobin.

    97 per cent of O2 carried by RBCs, 3 per cent of O2 dissolved in plasma, and 70 per cent of CO2 carried as bicarbonate are all correct figures, so options 1, 2 and 4 are accurate and not the answer. Option 3 is the exception: carbamino-haemoglobin carries 20 to 25 per cent of CO2, not 70 per cent, which is the bicarbonate figure.

    So option 3 is correct.

    The trap: option 3 takes the bicarbonate percentage and pastes it onto carbamino-haemoglobin instead.

    NCERT Class 11 Biology, page 189

26. Q26 Exception / incorrect

    Identify the INCORRECT pairing (centre – location):

    1. 1.Respiratory rhythm centre – medulla
    2. 2.Pneumotaxic centre – pons
    3. 3.Pneumotaxic centre – medullaCorrect answer
    4. 4.Chemosensitive area – adjacent to the rhythm centre

    Why option 3 is the answer

    The trap: The pneumotaxic centre lies in the pons.

    What this is testing: which brain region actually houses the pneumotaxic centre.

    Respiratory rhythm centre in the medulla, pneumotaxic centre in the pons, and the chemosensitive area sitting adjacent to the rhythm centre are all correct pairings, so options 1, 2 and 4 are accurate and not the answer. Option 3 is the exception: the pneumotaxic centre lies in the PONS, not the medulla, so this pairing is wrong.

    So option 3 is correct.

    The trap: option 3 directly contradicts option 2, giving the pneumotaxic centre two different locations in the same question — trust the pons.

    NCERT Class 11 Biology, page 190

27. Q27 Sequence / ordering

    Correct order of increasing pCO2:

    1. 1.tissues → alveoli → atmospheric air
    2. 2.atmospheric air (0.3) → alveoli (40) → tissues (45)Correct answer
    3. 3.alveoli → atmospheric air → tissues
    4. 4.tissues → atmospheric air → alveoli

    Why option 2 is the answer

    The trap: pCO2 rises from the atmosphere through the alveoli to the tissues.

    What this is testing: how the partial pressure of carbon dioxide rises in stages from air to tissue.

    The correct rising order is atmospheric air at 0.3 mm Hg, then alveoli at 40 mm Hg, then tissues at 45 mm Hg. That is option 2.

    Why the others are wrong: option 1 runs the order backwards, starting from the tissues. Option 3 places alveoli before atmospheric air, reversing the first two values. Option 4 places atmospheric air between the tissues and alveoli, breaking the true rising sequence.

    The trap: pCO2 rises the whole way from air to tissue, the mirror image of how pO2 falls; keep the two trends pointed in opposite directions.

    NCERT Class 11 Biology, page 187

28. Q28 Sequence / ordering

    Correct order of the layers a molecule of O2 crosses from alveolus to blood:

    1. 1.alveolar squamous epithelium → basement substance → capillary endotheliumCorrect answer
    2. 2.capillary endothelium → basement substance → alveolar epithelium
    3. 3.basement substance → alveolar epithelium → capillary endothelium
    4. 4.capillary endothelium → alveolar epithelium

    Why option 1 is the answer

    The trap: Oxygen crosses the three layers of the diffusion membrane in this order.

    What this is testing: the order in which an oxygen molecule crosses the three layers of the diffusion membrane.

    The correct order is the alveolar squamous epithelium first, then the basement substance, then the capillary endothelium, moving from the air side into the blood. That is option 1.

    Why the others are wrong: option 2 runs the order backwards, starting from the blood side. Option 3 places the basement substance first, ahead of the alveolar epithelium it actually sits behind. Option 4 skips the basement substance layer altogether.

    The trap: oxygen always moves from air to blood, so the alveolar epithelium, the air-side layer, must come first, not last.

    NCERT Class 11 Biology, page 188

29. Q29 NEET 2020

    Select the correct events that occur during inspiration: (i) contraction of the diaphragm (ii) contraction of the external inter-costal muscles (iii) pulmonary volume decreases (iv) intra-pulmonary pressure increases. How many of the above are correct?

    1. 1.One
    2. 2.TwoCorrect answer
    3. 3.Three
    4. 4.Four

    Why option 2 is the answer

    The trap: (i) and (ii) are correct — both muscles contract during inspiration; pulmonary volume actually INCREASES and intra-pulmonary pressure DECREASES, so (iii) and (iv) are wrong — two statements.

    What this is testing: which muscle actions and pressure changes actually belong to inspiration.

    (i) is correct: the diaphragm does contract during inspiration. (ii) is correct too: the external intercostal muscles also contract. (iii) is the trap: pulmonary volume actually INCREASES during inspiration, not decreases. (iv) is the trap as well: intra-pulmonary pressure actually DECREASES during inspiration, not increases — that drop is what pulls air in.

    So two are correct, option 2.

    The trap: (iii) and (iv) both state the exact reverse of what happens, testing whether you know inspiration is a volume-up, pressure-down event.

    NCERT Class 11 Biology, pages 185-186

30. Q30 NEET 2018

    Which of the following options correctly represents the lung conditions in asthma and emphysema, respectively?

    1. 1.Increased number of bronchioles; increased respiratory surface
    2. 2.Increased respiratory surface; inflammation of bronchioles
    3. 3.Decreased respiratory surface; inflammation of bronchioles
    4. 4.Inflammation of bronchioles; decreased respiratory surfaceCorrect answer

    Why option 4 is the answer

    The trap: Asthma involves inflamed bronchioles causing wheezing; emphysema damages alveolar walls, decreasing the respiratory surface.

    What this is testing: matching asthma and emphysema to their correct lung changes.

    Asthma involves inflammation of the bronchioles causing wheezing, while emphysema damages the alveolar walls and so decreases the respiratory surface — that order matches option 4 exactly.

    The trap: the other options either swap which disorder gets which description or wrongly claim an increased respiratory surface or bronchiole count, when both disorders in fact damage or narrow the airway rather than improving it.

    NCERT Class 11 Biology, page 190