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Breathing and Exchange of Gases
Biology · Class 11NCERT pp. 181–1912 sets × 25 questions
Key facts and formulas for Breathing and Exchange of Gases, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.
Key facts for this chapter
| Idea | Rule or fact |
|---|
| Lung volumes | TV about 500 mL; IRV 2500-3000 mL; ERV 1000-1100 mL; RV 1100-1200 mL |
| Capacities | IC = TV + IRV; FRC = ERV + RV; VC = ERV + TV + IRV; TLC = VC + RV |
| Minute and alveolar ventilation | Minute volume = TV × rate; alveolar ventilation = (TV − dead space) × rate |
| Partial pressures (mm Hg) | Atmosphere 159 and 0.3; alveoli 104 and 40; oxygenated blood 95 and 40; deoxygenated blood 40 and 45 |
| Mechanism of breathing | Diaphragm and external intercostals contract; thorax enlarges; lung pressure falls below atmospheric; air enters |
| Transport of gases | 97% O2 in RBCs; one Hb binds 4 O2; CO2: 70% bicarbonate, 20-25% carbamino-Hb, 7% dissolved |
| Curve shifts | Right shift (more O2 release) by high pCO2, H+, temperature and 2,3-BPG: Bohr effect; Haldane: oxygenated Hb releases CO2 |
| Control of breathing | Rhythm centre in medulla; pneumotaxic centre in pons; chemosensitive area detects CO2 and H+ |
| Disorders and terms | Asthma: inflamed bronchi; emphysema: damaged alveoli; pleurisy: pleura; hypercapnia: high CO2; CO binds Hb 200 times more than O2 |
Three sample questions
Q1. Match the volume with its average value.
a. Tidal volume i. 1100-1200 mL
b. Inspiratory reserve volume ii. 2500-3000 mL
c. Expiratory reserve volume iii. About 500 mL
d. Residual volume iv. 1000-1100 mL
- a-ii, b-iii, c-i, d-iv
- a-iii, b-ii, c-iv, d-i
- a-iii, b-i, c-iv, d-ii
- a-iv, b-ii, c-iii, d-i
Hint and solution
Hint: Tidal volume is the small amount of a normal breath. Reserve volumes are the extra air you can add by forcing the breath in or out.
- TV ≈ 500 mL — Tidal volume is the air in one quiet breath, about 500 mL. So a matches iii.
- IRV ≈ 2500-3000 mL — Inspiratory reserve volume is the extra air taken in by a forced inspiration. It is the largest reserve, so b matches ii.
- ERV ≈ 1000-1100 mL; RV ≈ 1100-1200 mL — Expiratory reserve volume is 1000-1100 mL, so c matches iv. Residual volume left after forced expiration is 1100-1200 mL, so d matches i.
- a-iii, b-ii, c-iv, d-i — The matching is a-iii, b-ii, c-iv, d-i. This is Option B.
Answer: B. TV is about 500 mL, IRV 2500-3000 mL, ERV 1000-1100 mL and RV 1100-1200 mL.
Q2. A person has TV 500 mL, IRV 2800 mL, ERV 1000 mL and RV 1200 mL. The vital capacity is
- 4300 mL
- 5500 mL
- 3300 mL
- 4800 mL
Hint and solution
Hint: Vital capacity is the maximum air you can breathe out after a deepest breath in. Does it include the air that can never leave the lungs?
- VC = ERV + TV + IRV — Vital capacity is the maximum air that can be expelled after a forced inspiration. It is the sum of the three volumes you can move.
- Residual volume is excluded — RV stays in the lungs even after the strongest expiration, so it is not part of VC.
- VC = 1000 + 500 + 2800 = 4300 mL — Adding the three volumes gives 4300 mL.
- Answer: 4300 mL — Vital capacity is 4300 mL. Option A.
Answer: A. VC = ERV + TV + IRV = 1000 + 500 + 2800 = 4300 mL. Adding RV would give TLC, 5500 mL.
Q3. If ERV is 1050 mL and RV is 1150 mL, the functional residual capacity is
- 1050 mL
- 1150 mL
- 1600 mL
- 2200 mL
Hint and solution
Hint: Functional residual capacity is the air still in the lungs after a normal expiration. Which two volumes stay behind?
- FRC = ERV + RV — After a normal quiet expiration the lungs still hold the expiratory reserve volume and the residual volume.
- FRC = 1050 + 1150 — Substitute the given values of ERV and RV.
- = 2200 mL — Adding gives 2200 mL.
- Answer: 2200 mL — So the functional residual capacity is 2200 mL. Option D.
Answer: D. FRC = ERV + RV = 1050 + 1150 = 2200 mL.
How to use this chapter
Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.