Chapter 17: Breathing and Exchange of Gases – MCQs with Answers & Explanations

CBSE Class 11 Biology MCQs – Breathing and Exchange of Gases (NCERT-Based)

Course & Examination Details

• Course: CBSE Class 11 Biology
• Prescribed By: Central Board of Secondary Education
• Based On: NCERT
• Unit: Unit V – Human Physiology
• Chapter: Chapter 17 – Breathing and Exchange of Gases
• Question Type: Multiple Choice Questions (MCQs)
• Exam Relevance: CBSE Class 11 Annual Exam, Unit Tests, School Assessments

Section A: Respiratory Organs (MCQ 1–17)

1. The primary function of nasal hairs is to

A. Warm inhaled air
B. Moisten inhaled air
C. Filter dust particles
D. Increase oxygen content

Correct Answer: C
Explanation:
Nasal hairs trap dust particles and microbes, preventing them from entering deeper parts of the respiratory tract.

2. The respiratory passage common to both air and food is

A. Larynx
B. Pharynx
C. Trachea
D. Bronchus

Correct Answer: B
Explanation:
The pharynx acts as a common passage for air and food before diverging into trachea and esophagus.

3. The voice box in humans is the

A. Pharynx
B. Trachea
C. Larynx
D. Bronchiole

Correct Answer: C
Explanation:
The larynx contains vocal cords that vibrate to produce sound during airflow.

4. Cartilaginous rings are present in trachea to

A. Help in sound production
B. Prevent collapse of airway
C. Increase surface area
D. Aid diffusion of gases

Correct Answer: B
Explanation:
C-shaped cartilaginous rings keep the trachea open and prevent its collapse during breathing.

5. The smallest respiratory units where gaseous exchange occurs are

A. Bronchi
B. Bronchioles
C. Alveoli
D. Trachea

Correct Answer: C
Explanation:
Alveoli are thin-walled sacs surrounded by capillaries and are the primary sites of gas exchange.

6. The left lung is smaller than the right lung because

A. It has fewer alveoli
B. It accommodates the heart
C. It receives less air
D. It has fewer bronchioles

Correct Answer: B
Explanation:
The heart occupies space on the left side, forming a cardiac notch that reduces left lung size.

7. Pleural fluid mainly helps in

A. Gas diffusion
B. Preventing infection
C. Reducing friction
D. Oxygen transport

Correct Answer: C
Explanation:
Pleural fluid reduces friction between lungs and chest wall during breathing movements.

8. Alveoli are best adapted for gas exchange due to

A. Thick walls
B. Cartilaginous support
C. Large surface area and thin walls
D. Presence of mucus

Correct Answer: C
Explanation:
Thin walls and a large surface area facilitate rapid diffusion of gases.

9. Which structure prevents food from entering the trachea?

A. Glottis
B. Epiglottis
C. Pharynx
D. Larynx

Correct Answer: B
Explanation:
The epiglottis closes the glottis during swallowing, preventing aspiration.

10. Bronchioles differ from bronchi because bronchioles

A. Have cartilage
B. Are larger
C. Lack cartilage
D. Are outside lungs

Correct Answer: C
Explanation:
Bronchioles are smaller airways without cartilaginous rings.

11. The membrane covering lungs is called

A. Peritoneum
B. Pericardium
C. Pleura
D. Endothelium

Correct Answer: C
Explanation:
Pleural membranes cover lungs and reduce friction during respiration.

12. Number of lobes in right lung is

A. Two
B. Four
C. Three
D. One

Correct Answer: C
Explanation:
The right lung has three lobes, while the left lung has two.

13. The main function of bronchi is to

A. Exchange gases
B. Conduct air
C. Produce sound
D. Trap dust

Correct Answer: B
Explanation:
Bronchi conduct air from trachea to lungs.

14. Which feature increases efficiency of alveoli?

A. Cartilage
B. Cilia
C. Moist surface
D. Thick epithelium

Correct Answer: C
Explanation:
Moist surface allows gases to dissolve and diffuse easily.

15. Vital capacity is the sum of

A. TV + RV
B. IRV + ERV + TV
C. ERV + RV
D. TV + RV + ERV

Correct Answer: B
Explanation:
Vital capacity includes tidal volume, inspiratory reserve volume, and expiratory reserve volume.

16. Tidal volume in a normal adult is approximately

A. 150 mL
B. 300 mL
C. 500 mL
D. 1000 mL

Correct Answer: C
Explanation:
Tidal volume is about 500 mL during normal breathing.

17. Residual volume helps in

A. Increasing breathing rate
B. Preventing lung collapse
C. Producing sound
D. Increasing oxygen binding

Correct Answer: B
Explanation:
Residual volume keeps alveoli inflated even after expiration.

Section B: Mechanism of Breathing (MCQ 18–34)

18. Inspiration in humans is

A. Passive process
B. Active process
C. Diffusion process
D. Osmotic process

Correct Answer: B
Explanation:
Inspiration requires muscle contraction and energy expenditure.

19. During inspiration, diaphragm becomes

A. Dome-shaped
B. Relaxed
C. Flattened
D. Rigid

Correct Answer: C
Explanation:
Contraction flattens the diaphragm, increasing thoracic volume.

20. Air enters lungs due to

A. Increase in intrapulmonary pressure
B. Decrease in intrapulmonary pressure
C. Decrease in atmospheric pressure
D. Increase in pleural pressure

Correct Answer: B
Explanation:
Lower intrapulmonary pressure allows air to move into lungs.

21. Expiration at rest is

A. Active
B. Passive
C. Forced
D. Voluntary

Correct Answer: B
Explanation:
Expiration occurs due to relaxation of muscles and elastic recoil.

22. Movement of ribs during expiration is

A. Upward and outward
B. Downward and inward
C. Only upward
D. Only outward

Correct Answer: B
Explanation:
Ribs move downward and inward during expiration.

23. Breathing rhythm is controlled by

A. Cerebellum
B. Hypothalamus
C. Medulla oblongata
D. Cerebrum

Correct Answer: C
Explanation:
Medulla oblongata contains respiratory rhythm center.

24. Which factor primarily regulates breathing rate?

A. Oxygen concentration
B. Carbon dioxide concentration
C. Nitrogen concentration
D. Hemoglobin level

Correct Answer: B
Explanation:
CO₂ concentration strongly influences respiratory centers.

25. Pneumotaxic center is located in

A. Medulla
B. Cerebrum
C. Pons
D. Spinal cord

Correct Answer: C
Explanation:
Pneumotaxic center in pons regulates breathing pattern.

26. Intrapleural pressure is always

A. Positive
B. Zero
C. Negative
D. Variable positive

Correct Answer: C
Explanation:
Negative intrapleural pressure keeps lungs inflated.

27. Functional residual capacity is air remaining after

A. Forced expiration
B. Normal expiration
C. Forced inspiration
D. Normal inspiration

Correct Answer: B
Explanation:
FRC remains after normal expiration.

28. Elastic recoil of lungs helps in

A. Inspiration
B. Expiration
C. Gas exchange
D. Oxygen transport

Correct Answer: B
Explanation:
Elastic recoil aids passive expiration.

29. Which volume prevents sudden lung collapse?

A. Tidal volume
B. Vital capacity
C. Residual volume
D. Inspiratory capacity

Correct Answer: C
Explanation:
Residual volume keeps alveoli open.

30. Increased breathing during exercise is due to

A. Low oxygen
B. High carbon dioxide
C. Low nitrogen
D. High humidity

Correct Answer: B
Explanation:
CO₂ accumulation stimulates faster breathing.

31. Intercostal muscles are involved in

A. Digestion
B. Circulation
C. Breathing
D. Excretion

Correct Answer: C
Explanation:
They move ribs during breathing.

32. Inspiration causes thoracic cavity volume to

A. Decrease
B. Remain constant
C. Increase
D. Collapse

Correct Answer: C
Explanation:
Muscle contraction increases thoracic volume.

33. Which muscle plays the major role in breathing?

A. Biceps
B. Triceps
C. Diaphragm
D. Abdominal muscles

Correct Answer: C
Explanation:
The diaphragm is the primary muscle of respiration.

34. Breathing movements occur due to

A. Diffusion
B. Osmosis
C. Pressure differences
D. Active transport

Correct Answer: C
Explanation:
Pressure gradients drive air movement.

Section C: Transport of Gases (MCQ 35–50)

35. Gas exchange occurs by

A. Active transport
B. Diffusion
C. Osmosis
D. Mass flow

Correct Answer: B
Explanation:
Gases move down their partial pressure gradients.

36. Oxygen is transported mainly as

A. Dissolved oxygen
B. Oxyhaemoglobin
C. Carbaminohaemoglobin
D. Bicarbonate

Correct Answer: B
Explanation:
About 97% oxygen is transported bound to haemoglobin.

37. Oxygen dissociation curve is

A. Linear
B. Exponential
C. Sigmoid
D. Parabolic

Correct Answer: C
Explanation:
The S-shaped curve allows efficient loading and unloading.

38. Bohr effect states that

A. High pH increases O₂ binding
B. High CO₂ reduces O₂ binding
C. Low temperature reduces O₂ release
D. Oxygen binds irreversibly

Correct Answer: B
Explanation:
CO₂ and low pH reduce haemoglobin affinity for oxygen.

39. Most CO₂ is transported as

A. Dissolved gas
B. Carbaminohaemoglobin
C. Bicarbonate ions
D. Carbonic acid

Correct Answer: C
Explanation:
Around 70% CO₂ is transported as bicarbonate.

40. Carbonic anhydrase is present in

A. Plasma
B. Alveoli
C. Red blood cells
D. Lungs only

Correct Answer: C
Explanation:
This enzyme is present in RBCs for CO₂ conversion.

41. Chloride shift occurs in

A. Lungs
B. Alveoli
C. RBCs
D. Tissues

Correct Answer: C
Explanation:
It maintains ionic balance during CO₂ transport.

42. Carbaminohaemoglobin is formed by binding of

A. Oxygen
B. Carbon dioxide
C. Nitrogen
D. Hydrogen

Correct Answer: B
Explanation:
CO₂ binds with haemoglobin to form carbaminohaemoglobin.

43. Oxygen release at tissues is favored by

A. Low CO₂
B. High pH
C. Low temperature
D. High CO₂

Correct Answer: D
Explanation:
High CO₂ reduces haemoglobin affinity for oxygen.

44. Partial pressure refers to

A. Total pressure of gases
B. Pressure exerted by individual gas
C. Pressure inside lungs only
D. Blood pressure

Correct Answer: B
Explanation:
Each gas in a mixture exerts its own partial pressure.

45. Internal respiration occurs between

A. Lungs and blood
B. Blood and tissues
C. Alveoli and blood
D. Bronchi and lungs

Correct Answer: B
Explanation:
Internal respiration is exchange between blood and tissues.

46. Exchange of gases in alveoli depends on

A. Thickness of walls
B. Partial pressure gradient
C. Blood pressure
D. Nerve impulses

Correct Answer: B
Explanation:
Diffusion depends on partial pressure differences.

47. Oxygen has lower solubility than CO₂ because

A. It is lighter
B. It is non-polar
C. It is less chemically reactive
D. It has lower chemical solubility

Correct Answer: D
Explanation:
CO₂ is more soluble due to its chemical properties.

48. Which factor shifts oxygen dissociation curve to right?

A. Low temperature
B. Low CO₂
C. High pH
D. High CO₂

Correct Answer: D
Explanation:
High CO₂ favors oxygen release.

49. Haemoglobin is important because it

A. Transports CO₂ only
B. Increases oxygen-carrying capacity
C. Filters blood
D. Produces energy

Correct Answer: B
Explanation:
Haemoglobin binds oxygen efficiently for transport.

50. Gaseous exchange at tissues is facilitated by

A. High pO₂ in tissues
B. Low pO₂ in tissues
C. High pCO₂ in blood
D. Low blood flow

Correct Answer: B
Explanation:
Lower oxygen partial pressure in tissues promotes diffusion from blood.

NCERT & CBSE Compliance Note

✔ Strictly as per NCERT Class 11 Biology
✔ Concept-clearing explanations provided
✔ Fully aligned with CBSE exam pattern
✔ Ideal for school exams and revision

🎯 Targeting Exams

This MCQ set is highly useful for preparation of the following exams:

• CBSE Class 11 Biology Annual Examination

• CBSE School Unit Tests & Periodic Assessments

• NEET (UG) – Human Physiology Basics

• CUET (UG) – Biology Section

• State Board Class 11 Biology Exams

• Foundation Courses for Medical Entrance Exams

🔑 Related & Semantic Keyphrases

• Breathing and Exchange of Gases MCQs Class 11

• CBSE Class 11 Biology Chapter 17 MCQs

• NCERT Biology MCQs Human Physiology

• Breathing and Exchange of Gases Objective Questions

• Class 11 Biology Respiration MCQs

• Human Physiology MCQs Class 11

• Breathing Mechanism and Gas Transport MCQs

• NCERT Class 11 Biology Online Practice Questions