Practice tests · NEET

NEET Breathing and Exchange of Gases: 5 practice MCQs

By the PrepMatic team · Updated 9 Oct 2026 · 3 min read

Breathing and Exchange of Gases is a Class 11 Human Physiology chapter that mixes anatomy, pressure gradients and some calculations on lung volumes. The five MCQs below test the partial pressure of oxygen in alveoli, a vital capacity calculation, how CO₂ is carried in blood, the respiratory centres and the enzyme carbonic anhydrase.

What this chapter covers in the NEET syllabus

Breathing is part of the NMC unit Human Physiology and is the Class 11 NCERT chapter Breathing and Exchange of Gases. The topics are:

• The respiratory organs and the human respiratory system.
• The mechanism of breathing: inspiration, expiration, and the role of the diaphragm and intercostal muscles.
• Respiratory volumes and capacities.
• Exchange of gases and the partial pressures involved.
• Transport of gases: oxygen as oxyhaemoglobin, CO₂ as bicarbonate, carbamino-haemoglobin and in solution.
• Regulation of respiration, and disorders such as asthma, emphysema and occupational respiratory disorders.

Five practice MCQs on Breathing and Exchange of Gases

Question 1

The partial pressure of oxygen (pO₂) in alveolar air is about:

• A. 159 mm Hg
• B. 45 mm Hg
• C. 40 mm Hg
• D. 104 mm Hg

Question 2

In a healthy person the tidal volume is 500 mL, inspiratory reserve volume 3000 mL, expiratory reserve volume 1100 mL and residual volume 1200 mL. The vital capacity is:

• A. 3600 mL
• B. 5800 mL
• C. 4600 mL
• D. 4100 mL

Question 3

Approximately what percentage of CO₂ is transported by blood as bicarbonate?

• A. 70%
• B. 7%
• C. 25%
• D. 100%

Question 4

The pneumotaxic centre that moderates the functions of the respiratory rhythm centre is located in the:

• A. medulla oblongata
• B. pons
• C. cerebellum
• D. hypothalamus

Question 5

In red blood cells, the formation of carbonic acid from CO₂ and water is catalysed by the enzyme:

• A. pepsin
• B. amylase
• C. carbonic anhydrase
• D. catalase

Answers and explanations

1. D. NCERT gives the pO₂ of atmospheric air as 159 mm Hg and of alveolar air as 104 mm Hg. Deoxygenated blood and tissues are near 40 mm Hg. The decreasing gradient from 104 to 40 mm Hg drives oxygen into the blood.
2. C. Vital capacity = ERV + TV + IRV = 1100 + 500 + 3000 = 4600 mL. This is the maximum air you can breathe out after a maximum inspiration. Adding the residual volume gives total lung capacity (5800 mL), which is not the vital capacity.
3. A. About 70% of CO₂ is carried as bicarbonate, 20 to 25% as carbamino-haemoglobin and about 7% dissolved in plasma. Carbonic anhydrase in RBCs speeds the conversion.
4. B. The respiratory rhythm centre lies in the medulla. The pneumotaxic centre in the pons can reduce the duration of inspiration, which changes the respiratory rate. The chemosensitive area near the rhythm centre is sensitive to CO₂ and H⁺.
5. C. Carbonic anhydrase, found in high concentration in RBCs, catalyses CO₂ + H₂O ⇌ H₂CO₃, which dissociates into H⁺ and HCO₃⁻. In the alveoli, the same reaction runs in reverse to release CO₂.

How to prepare Breathing and Exchange of Gases

• Memorise the volumes and capacities, with approximate values and the formulas: vital capacity = TV + IRV + ERV; inspiratory capacity = TV + IRV; functional residual capacity = ERV + RV; total lung capacity = VC + RV. Practise rearranging them for calculation questions.
• Learn the partial pressure table (atmospheric air, alveolar air, deoxygenated blood, oxygenated blood, tissues) for both O₂ and CO₂. The direction of every diffusion follows from this table.
• Understand the oxygen dissociation curve. It is sigmoid. The curve shifts right (lower affinity) with higher pCO₂, higher H⁺ and higher temperature, as in tissues. It shifts left (higher affinity) in the alveoli, with low pCO₂, lower H⁺ and lower temperature.
• Keep the mechanism of breathing straight: inspiration needs contraction of the diaphragm and external intercostals, increasing thoracic volume and lowering the pressure inside the lungs. Expiration is mostly passive.
• Revise the disorders as one-line facts: asthma, emphysema, and occupational disorders such as silicosis.

A careful read with the tables, followed by calculation practice, usually covers the chapter in two sittings. For planning, see the NEET Biology preparation guide, and for related physiology, the next chapter Body Fluids and Circulation.

Take a full Breathing and Gas Exchange test on PrepMatic

Calculation questions on lung volumes are quick marks if the formulas are fresh. A PrepMatic topic test (about 15 questions in 30 minutes) is scored with NEET's negative marking and shows your result by subject. The free Basic plan includes topic tests, and the practice hub has the next chapter.

← All practice tests