Breathing Gas Transport

8 MCQs9-step worked example
Source: NCERT Morphology of Flowering PlantsPYQ coverage: NEET 2020, 2021, 2022, 2023, 2024, 2025Official key: NTA-verifiedLast reviewed: May 2026

Lesson

The high-frequency trap in gas transport questions is confusing the direction of the oxyhaemoglobin dissociation curve shift with its physiological consequence. A right shift does not mean "more oxygen in blood" — it means haemoglobin releases oxygen more readily to tissues.

Oxygen transport. About 97% of O₂ is carried as oxyhaemoglobin (HbO₂); ~3% dissolves in plasma. Each haemoglobin molecule binds up to 4 O₂ molecules. Binding is cooperative — the sigmoid shape of the dissociation curve reflects this. At alveolar pO₂ (~104 mmHg), saturation is ~98%. At tissue pO₂ (~40 mmHg), saturation drops to ~75%, releasing O₂ for cellular respiration (NCERT Class 11 Biology Chapter 17, page 324).

The Bohr effect. In active tissues: ↑pCO₂, ↑H⁺ (lower pH), ↑temperature, ↑2,3-BPG → curve shifts right → haemoglobin's O₂ affinity decreases → more O₂ unloaded. In the lungs: low CO₂, higher pH, lower temperature → curve shifts left → Hb binds O₂ tightly.

CO₂ transport. Three modes: (1) ~70% as bicarbonate ions (HCO₃⁻) formed via carbonic anhydrase in RBCs (CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻); (2) ~23% as carbaminohaemoglobin (CO₂ bound to Hb's amino groups); (3) ~7% dissolved in plasma.

Chloride shift. As HCO₃⁻ exits RBCs into plasma, Cl⁻ enters to maintain electrical neutrality — this is the chloride shift (Hamburger phenomenon).

Watch-out: NEET distractors frequently swap the percentages (placing bicarbonate at 23% and carbamino at 70%) or state that CO₂ binds to the iron of haemoglobin (it binds to amino groups, not the haem iron).

Practice MCQs

Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.

MCQ 1Easy RecallPractice

What percentage of oxygen transported in blood is carried as oxyhaemoglobin?

MCQ 2Easy RecallPractice

The majority of carbon dioxide in blood is transported as:

MCQ 3Easy RecallPractice

The chloride shift (Hamburger phenomenon) involves movement of which ion into the RBC?

MCQ 4Direct ApplicationPractice

During vigorous exercise, which of the following changes in active muscle tissue causes a RIGHT shift of the oxyhaemoglobin dissociation curve?

MCQ 5Direct ApplicationPractice

In the lungs, the oxyhaemoglobin dissociation curve shifts LEFT compared to tissues. Which factor in the alveolar environment is responsible?

MCQ 6Direct ApplicationPractice

CO₂ binds to haemoglobin to form carbaminohaemoglobin. To which part of the haemoglobin molecule does CO₂ attach?

MCQ 7Concept TrapPractice

A patient with chronic obstructive pulmonary disease (COPD) shows chronically elevated blood CO₂. Regarding the oxyhaemoglobin dissociation curve, which statement is correct?

MCQ 8CalculationPractice

In an exercising individual, pO₂ in active muscles drops to 20 mmHg. At this pO₂, haemoglobin saturation is approximately 25%. If each 100 mL of fully oxygenated blood carries 20 mL O₂ (bound to Hb), approximately how much O₂ is released per 100 mL blood passing through these muscles?

Worked Example

Pattern: Dissociation curve interpretation + quantitative O₂ release (anchored to NEET pattern: unit bundle)

  1. 1

    Given

    - Blood entering tissue capillaries: Hb saturation = 97%, carrying 19.4 mL O₂ per 100 mL blood (bound to Hb) - Blood leaving resting tissue: Hb saturation = 75% - Blood leaving exercising muscle: Hb saturation = 30% - O₂ carrying capacity at 100% saturation = 20 mL O₂ per 100 mL blood

  2. 2

    Required

    Calculate (a) O₂ delivered to resting tissue per 100 mL blood, and (b) O₂ delivered to exercising muscle per 100 mL blood.

  3. 3

    Concept

    The oxyhaemoglobin dissociation curve relates pO₂ to Hb saturation. O₂ released = O₂ arriving − O₂ remaining. The Bohr effect shifts the curve right in active tissue, dropping saturation further at the same venous pO₂.

  4. 4

    Formula

    O₂ released = (saturation_arterial − saturation_venous) × O₂ capacity at 100%

  5. 5

    Substitution

    (a) Resting: (0.97 − 0.75) × 20 mL = 0.22 × 20 (b) Exercise: (0.97 − 0.30) × 20 mL = 0.67 × 20

  6. 6

    Calculation

    (a) 0.22 × 20 = 4.4 mL O₂ per 100 mL blood (resting) (b) 0.67 × 20 = 13.4 mL O₂ per 100 mL blood (exercising)

  7. 7

    Final answer

    - Resting tissue receives ~4.4 mL O₂ per 100 mL blood - Exercising muscle receives ~13.4 mL O₂ per 100 mL blood — approximately 3× more, due to the rightward Bohr shift Note: The percentage values (97%, 75%, 30%) are given-data treated as exact for this calculation; they do not limit significant figures.

  8. 8

    Common trap

    Confusing the SHIFT DIRECTION with the CONSEQUENCE. A right shift does NOT mean "more O₂ in blood." It means lower affinity → O₂ unloads more readily → lower venous saturation → more O₂ delivered to tissue. The curve shifting right REDUCES Hb saturation at any given pO₂.

  9. 9

    Similar NEET-style question

    "At a tissue pO₂ of 40 mmHg, Hb saturation is 75%. If the patient has a fever (raising tissue temperature), would Hb saturation at the same pO₂ be higher or lower than 75%? Explain using the Bohr effect." Answer: Lower. Fever → ↑temperature → right shift → lower affinity → saturation drops below 75% at 40 mmHg → more O₂ released. ---

Before solving, remember these

Key Fact

Gas transport

O2 transport: 97% by haemoglobin (4 O2 per Hb); 3% dissolved. O2-Hb dissociation curve: sigmoid; right shift with high CO2/H+/temperature/2,3-BPG (Bohr effect). CO2: 70% as bicarbonate, 23% by Hb, 7% dissolved.

-- NCERT Class 11 Biology, Ch. 17, p. 324

Formulas

Cardiac output

Volume of blood pumped per minute = heart rate × stroke volume. Normal ~5 L/min at rest.

SymbolQuantitySI Unit
COcardiac outputL/min
HRheart rate/min
SVstroke volumemL

Valid when

  • At rest

Respiratory volumes and capacities

Defines lung volumes and their sums (capacities). TV ~500 mL, IRV ~3000 mL, ERV ~1100 mL, RV ~1200 mL.

SymbolQuantitySI Unit
TVtidalmL
IRVinspiratory reservemL
ERVexpiratory reservemL
RVresidualmL

Valid when

  • Normal adult resting
  • Spirometry-measured (RV indirect)

Exam Traps & Common Mistakes

These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.

Trap

Lung capacity includes which volumes

Category: Similar Terms

Capacities are SUMS of volumes. VC = TV+IRV+ERV (excludes RV); TLC = VC+RV.

When it triggers

Question asks which capacity equals sum of which volumes.

How to avoid

VC excludes RV (residual is unmeasurable directly); TLC includes everything.

Trap

Oxyhaemoglobin curve shift direction

Category: Graph Interpretation

Right shift (lower affinity, more O2 release) caused by ↑CO2, ↑H+, ↑temperature, ↑2,3-BPG (Bohr effect). Left = opposite.

When it triggers

Question on tissue-vs-lung haemoglobin behaviour, exercise effect.

How to avoid

In tissues (high CO2/low pH/high T) → right shift → release O2. In lungs → left → bind O2.

Past Year Questions

57 questions from NEET 2020, 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.

NEET 2025

Given below are two statements : Statement I : The DNA fragments extracted from gel electrophoresis can be used in construction of recombinant DNA. Statement II : Smaller size DNA fragments are observed near anode while larger fragments are found near the wells in an agarose gel. In the light of the above statements, choose the most appropriate answer from the options given below :

1Statement I is incorrect but statement II is correct
2Both statement I and statement II are correct
3Both statement I and statement II are incorrect
4Statement I is correct but statement II is incorrect
NTA Answer: Option 2(final)
NEET 2025

The blue and white selectable markers have been developed which differentiate recombinant colonies from non- recombinant colonies on the basis of their ability to produce colour in the presence of a chromogenic substrate. Given below are two statements about this method: Statement I : The blue coloured colonies have DNA insert in the plasmid and they are identified as recombinant colonies. Statement II : The colonies without blue colour have DNA insert in the plasmid and are identified as recombinant colonies. In the light of the above statements, choose the most appropriate answer from the op

1Statement I is incorrect but Statement II is correct
2Both Statement I and Statement II are correct
3Both Statement I and Statement II are incorrect
4Statement I is correct but Statement II is incorrect
NTA Answer: Option 1(final)
NEET 2025

Match List-I with List-II. List-I List-II A. Emphysema I. Rapid spasms in muscle due to low Ca++ in body fluid B. Angina Pectoris II. Damaged alveolar walls and decreased respiratory surface C. Glomerulonephritis III. Acute chest pain when not enough oxygen is reaching to heart muscle D. Tetany IV. Inflammation of glomeruli of kidney Choose the correct answer from the options given below :

1A-II, B-III, C-IV, D-I
2A-III, B-I, C-IV, D-II
3A-III, B-I, C-II, D-IV
4A-II, B-IV, C-III, D-I
NTA Answer: Option 1(final)
NEET 2025

Find the correct statement : (A) In human pregnancy, the major organ systems are formed at the end of 12 weeks. (B) In human pregnancy the major organ systems are formed at the end of 8 weeks. (C) In human pregnancy heart is formed after one month of gestation. (D) In human pregnancy, limbs and digits develop by the end of second month. (E) In human pregnancy the appearance of hair is usually observed in the fifth month. Choose the correct answer from the options given below :

1A, C, D and E only
2A and E only
3B and C only
4B, C, D and E only
NTA Answer: Option 1(final)
NEET 2024

Match List I with List II List I List II A. Expiratory capacity I. Expiratory reserve volume + Tidal volume + Inspiratory reserve volume B. Functional residual II. Tidal volume + Expiratory reserve volume capacity C. Vital capacity III. Tidal volume + Inspiratory reserve volume D. Inspiratory capacity IV. Expiratory reserve volume + Residual volume Choose the correct answer from the options given below :

1A-II, B-IV, C-I, D-III
2A-III, B-II, C-IV, D-I
3A-II, B-I, C-IV, D-III
4A-I, B-III, C-II, D-IV
NTA Answer: Option 1(final)
NEET 2024

Given below are two statements : Statement I : In the nephron, the descending limb of loop of Henle is impermeable to water and permeable to electrolytes. Statement II : The proximal convoluted tubule is lined by simple columnar brush border epithelium and increases the surface area for reabsorption. In the light of the above statements, choose the correct answer from the option given below :

1Both statement I and Statement II are true
2Both statement I and Statement II are false
3Statement I is true but Statement II is false
4Statement I is false but Statement II is true
NTA Answer: Option 2(final)
NEET 2024

Choose the correct statement given below regarding juxta medullary nephron.

1Juxta medullary nephrons are located in the columns of Bertini.
2Renal corpuscle of juxta medullary nephron lies in the outer portion of the renal medulla.
3Loop of Henle of juxta medullary nephron runs deep into medulla.
4Juxta medullary nephrons outnumber the cortical nephrons.
NTA Answer: Option 3(final)
NEET 2024

Given below are two statements: Statement I: The cerebral hemispheres are connected by nerve tract known as corpus callosum. Statement II: The brain stem consists of the medulla oblongata, pons and cerebrum. In the light of the above statements, choose the most appropriate answer from the options given below:

1Both Statement I and Statement II are correct.
2Both Statement I and Statement II are incorrect.
3Statement I is correct but Statement II is incorrect.
4Statement I is incorrect but Statement II is correct.
NTA Answer: Option 3(final)
NEET 2024

Given below are two statements : Statement I : Bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced. Statement II : Both bone marrow and thymus provide micro environments for the development and maturation of T-lymphocytes. In the light of above statements, choose the most appropriate answer from the options given below :

1Both Statement I and Statement II are correct.
2Both Statement I and Statement II are incorrect.
3Statement I is correct but Statement II is incorrect.
4Statement I is incorrect but Statement II is correct.
NTA Answer: Option 1(final)
NEET 2024

Match List I with List II : List - I List – II A. Exophthalmic goiter I. Excess secretion of cortisol, moon face & hypergylcemia. B. Acromegaly II. Hypo-secretion of thyroid hormone and stunted growth. C. Cushing’s syndrome III. Hyper secretion of thyroid hormone & protruding eye balls. D. Cretinism IV. Excessive secretion of growth hormone. Choose the correct answer from the options given below

1A-I, B-III, C-II, D-IV
2A-IV, B-II, C-I, D-III
3A-III, B-IV, C-II, D-I
4A-III, B-IV, C-I, D-II
NTA Answer: Option 4(final)
NEET 2023

Axile placentation is observed in

1China rose, Beans and Lupin
2Tomato, Dianthus and Pea
3China rose, Petunia and Lemon
4Mustard, Cucumber and Primrose
NTA Answer: Option 3(final)
NEET 2023

Which one of the following statements is NOT correct?

1Algal blooms caused by excess of organic matter in water improve water quality and promote fisheries
2Water hyacinth grows abundantly in eutrophic water bodies and leads to an imbalance in the ecosystem dynamics of the water body
3The amount of some toxic substances of industrial waste water increases in the organisms at successive trophic levels
4The micro-organisms involved in biodegradation of organic matter in a sewage polluted water body consume a lot of oxygen causing the death of aquatic organisms
NTA Answer: Option 1(final)
NEET 2023

Which of the following statements is correct?

1Biomagnification refers to increase in concentration of the toxicant at successive trophic levels.
2Presence of large amount of nutrients in water restricts ‘Algal Bloom’
3Algal Bloom decreases fish mortality
4Eutrophication refers to increase in domestic sewage and waste water in lakes.
NTA Answer: Option 1(final)
NEET 2023

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: Nephrons are of two types: Cortical & Juxta medullary, based on their relative position in cortex and medulla. Reason R: Juxta medullary nephrons have short loop of Henle whereas, cortical nephrons have longer loop of Henle. In the light of the above statements, choose the correct answer from the options given below:

1Both A and R are true but R is NOT the correct explanation of A.
2A is true but R is false.
3A is false but R is true.
4Both A and R are true and R is the correct explanation of A.
NTA Answer: Option 2(final)
NEET 2023

Given below are two statements: Statement I: Vas deferens receives a duct from seminal vesicle and opens into urethra as the ejaculatory duct. Statement Il: The cavity of the cervix is called cervical canal which along with vagina forms birth canal. In the light of the above statements, choose the correct answer from the options given below:

1Both Statement I and Statement II are false.
2Statement I is correct but Statement II is false.
3Statement I is incorrect but Statement II is true.
4Both Statement I and Statement II are true.
NTA Answer: Option 4(final)
NEET 2022

Which of the following is not observed during apoplastic pathway ?

1Apoplast is continuous and does not provide any barrier to water movement
2Movement of water occurs through intercellular spaces and wall of the cells
3The movement does not involve crossing of cell membrane
4The movement is aided by cytoplasmic streaming
NTA Answer: Option 4(final)
NEET 2022

Given below are two statements : Statement I : The coagulum is formed of network of threads called thrombins. Statement II : Spleen is the graveyard of erythrocytes. In the light of the above statements, choose the most appropriate answer from the options given below :

1Statement I is incorrect but Statement II is correct
2Both Statement I and Statement II are correct
3Both Statement I and Statement II are incorrect
4Statement I is correct but Statement II is incorrect
NTA Answer: Option 1(final)
NEET 2022

In-situ conservation refers to:

1Conserve only extinct species
2Protect and conserve the whole ecosystem
3Conserve only high-risk species
4Conserve only endangered species
NTA Answer: Option 2(final)
NEET 2022

Select the incorrect statement regarding synapses :

1Impulse transmission across a chemical synapse is always faster than that across an electrical synapse.
2The membranes of presynaptic and postsynaptic neurons are in close proximity in an electrical synapse.
3Electrical current can flow directly from one neuron into the other across the electrical synapse.
4Chemical synapses use neurotransmitters
NTA Answer: Option 1(final)
NEET 2022

Match List-I with List-II with respect to methods of Contraception and their respective actions. List-I List-II (a) Diaphragms (i) Inhibit ovulation and Implantation (b) Contraceptive Pills (ii) Increase phagocytosis of sperm within Uterus (c) Intra Uterine Devices (iii) Absence of Menstrual cycle and ovulation following parturition (d) Lactational Amenorrhea (iv) They cover the cervix blocking the entry of sperms Choose the correct answer from the options given below:

1(a) - (iii), (b) - (ii), (c) - (i), (d) - (iv)
2(a) - (iv), (b) - (i), (c) - (iii), (d) - (ii)
3(a) - (iv), (b) - (i), (c) - (ii), (d) - (iii)
4(a) - (ii), (b) - (iv), (c) - (i), (d) - (iii)
NTA Answer: Option 3(final)
NEET 2021

Assertion (A): A person goes to high altitude and Choose the correct answer from the options given experiences 'altitude sickness' with symptoms like below breathing difficulty and heart palpitations. (a) (b) (c) (d) Reason (R): Due to low atmospheric pressure at

1(ii) (iii) (i) (iv) high altitude, the body does not get sufficent
2(iv) (i) (iii) (ii) oxygen.
3(iii) (iv) (i) (ii) In the light of the above statements, choose the correct answer from the options given below
4(i) (ii) (iv) (iii) (1) (A) is false but (R) is true
NTA Answer: Option 3(final)
NEET 2020

ª‹Ã ∑§ÕŸ ∑§Ê øÈÁŸ∞–

1≈UÒÁŸŸ, ⁄U Á¡Ÿ, Ã‹Ò •ÊÁŒ ∑§ ¡◊Ê „ÊŸ ∑§ ∑§Ê⁄UáÊ •Ã —∑§Êc∆U 93. Identify the incorrect statement. ª„⁄ U ⁄ Uª ∑§Ë „Ê ÃË „Ò– (1) Due to deposition of tannins, resins, oils etc.,
2• ×∑§Êc∆U ¡‹ ∑§Ê øÊ‹Ÿ Ÿ„Ë ∑§⁄UÃË, ¬⁄UãÃÈ ÿÊ ÁòÊ∑§ heart wood is dark in colour. ‚„ÊÿÃÊ ¬˝ŒÊŸ ∑§⁄UÃË „Ò– (2) Heart wood does not conduct water but gives mechanical support.
3⁄U‚ŒÊM§ ¡«∏ ‚ ¬ûÊË Ã∑§ ¡‹ ∑ § øÊ‹Ÿ ◊ •ÊÒ⁄U πÁŸ¡Ê (3) Sapwood is involved in conduction of water ∑ § øÊ‹Ÿ ◊ ‡ÊÊÁ◊‹ „Ê ÃË „Ò– and minerals from root to leaf.
4⁄U‚ŒÊM§ ‚’‚ ÷ËÃ⁄UË ÁmÃËÿ∑§ ŒÊM§ „Ê ÃÊ „Ò •ÊÒ⁄U ÿ„ (4) Sapwood is the innermost secondary xylem •¬ ˇÊÊ∑Χà „À∑ § ⁄ Uª ∑§Ë „Ê ÃË „Ò– and is lighter in colour. H3 22 Hindi+English
NTA Answer: Option 4(final)
NEET 2020

Identify the correct statement with reference to human digestive system. 96. ◊ÊŸfl ¬ÊøŸ à òÊ ‚ ‚ ŒÁ÷¸Ã ‚„Ë ∑§ÕŸ ∑§Ê øÿŸ ∑§⁄UÊ –

1Vermiform appendix arises from duodenum. (1) ∑ΧÁ◊M§¬ ¬Á⁄U‡Ê Á ∑§Ê ª˝„áÊË ‚ ©à¬ÛÊ „Ê ÃÊ „Ò–
2Ileum opens into small intestine. (2) ˇÊÈŒ˝Ê òÊ ¿UÊ ≈UË •Ê à ◊ πÈ‹ÃÊ „Ò–
3Serosa is the innermost layer of the alimentary canal. (3) Á‚⁄UÊ ‚Ê •Ê„Ê⁄U ŸÊ‹ ∑§Ê ‚’‚ •ãŒ⁄U flÊ‹Ë ¬⁄Uà „Ê ÃË „Ò–
4Ileum is a highly coiled part. (4) ˇÊÈŒ˝Ê òÊ •àÿÊÁœ∑§ ∑È §«UÁ‹Ã ÷ʪ „Ê ÃÊ „Ò–
NTA Answer: Option 4(final)
NEET 2020

ÁŸêŸ Sà ÷Ê ∑§Ê Á◊‹ÊŸ ∑§⁄U ‚„Ë Áfl∑§À¬ ∑§Ê øÿŸ ∑§⁄UÊ – 98. Match the following columns and select the correct option. Sà ÷ - I Sà ÷ - II Column - I Column - II (a) ¬ËÿÍ ª˝ ÁÕ (i) ª˝ fl‚ ⁄UÊ ª (a) Pituitary gland (i) Grave’s disease (b) ÕÊÿ⁄UÊÚß«U ª˝ ÁÕ (ii) «UÊÿÊÁ’≈UË¡ ◊ Á‹≈U‚ (b) Thyroid gland (ii) Diabetes mellitus (c) •ÁœflÎÄ∑§ ª˝ ÁÕ (iii) «UÊÿÊÁ’≈UË¡ ßã‚ËÁ¬«U‚ (c) Adrenal gland (iii) Diabetes insipidus (d) •ÇãÿʇÊÿ (iv) ∞«UË‚Ÿ ⁄UÊ ª (d) Pancreas (iv) Addison’s disease (a) (b) (c) (d) (a) (b) (c) (d)

1(ii) (i) (iv) (iii) (1) (ii) (i) (iv) (iii)
2(iv) (iii) (i) (ii) (2) (iv) (iii) (i) (ii)
3(iii) (ii) (i) (iv) (3) (iii) (ii) (i) (iv)
4(iii) (i) (iv) (ii) (4) (iii) (i) (iv) (ii)
NTA Answer: Option 4(final)
NEET 2020

Match the following columns and select the 103. ÁŸêŸ Sà ÷Ê ∑§Ê Á◊‹ÊŸ ∑§⁄U ‚„Ë Áfl∑§À¬ ∑§Ê øÿŸ ∑§⁄UÊ – correct option. Sà ÷ - I Sà ÷ - II Column - I Column - II (a) ÿÍÕ, ’„È„Ê⁄UË ¬Ë«U∑§ (i) ∞S≈ UÁ⁄Uÿ‚ (a) Gregarious, polyphagous (i) Asterias pest (b) √ÿS∑§Ê ◊ •⁄UËÿ ‚◊Á◊Áà ∞fl (ii) Á’ë¿ÈU (b) Adult with radial (ii) Scorpion ‹Êflʸ ◊ Ám¬Ê‡fl¸ ‚◊Á◊Áà symmetry and larva (c) ¬ÈSà »È§å»È§‚ (iii) ≈UËŸÊ å‹ÊŸÊ with bilateral symmetry (d) ¡Ëfl‚ ŒËÁåà (iv) ‹Ê ∑§S≈UÊ (c) Book lungs (iii) Ctenoplana (d) Bioluminescence (iv) Locusta (a) (b) (c) (d)

1(ii) (i) (iii) (iv) (a) (b) (c) (d)
2(i) (iii) (ii) (iv) (1) (ii) (i) (iii) (iv)
3(iv) (i) (ii) (iii) (2) (i) (iii) (ii) (iv)
4(iii) (ii) (i) (iv) (3) (iv) (i) (ii) (iii) (4) (iii) (ii) (i) (iv)
NTA Answer: Option 3(final)

How NEET usually asks this

Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.

Sources

NCERT refs: Class 11 Biology Chapter 17, p.324

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