MCQ on Respiratory System

🟢 Easy Level (1–20)

1. What is the primary organ of the respiratory system?
   A) Heart
   B) Lung ✅
   C) Kidney
   D) Liver
   Explanation: Lungs are the primary organs responsible for gas exchange.
2. What gas do we inhale to survive?
   A) Carbon dioxide
   B) Oxygen ✅
   C) Nitrogen
   D) Hydrogen
   Explanation: Oxygen is essential for cellular respiration and energy production.
3. Which structure connects the throat to the lungs?
   A) Esophagus
   B) Bronchi
   C) Trachea ✅
   D) Larynx
   Explanation: The trachea (windpipe) conducts air to the bronchi.
4. Where does gas exchange occur in the lungs?
   A) Trachea
   B) Bronchioles
   C) Alveoli ✅
   D) Pleura
   Explanation: Alveoli are tiny sacs where oxygen and carbon dioxide exchange.
5. Which muscle helps in breathing?
   A) Biceps
   B) Diaphragm ✅
   C) Hamstring
   D) Deltoid
   Explanation: The diaphragm contracts and relaxes to allow inhalation and exhalation.
6. What is the process of taking air into the lungs called?
   A) Exhalation
   B) Respiration
   C) Inhalation ✅
   D) Circulation
   Explanation: Inhalation is the act of breathing in air.
7. How many lungs does a human have?
   A) 1
   B) 2 ✅
   C) 3
   D) 4
   Explanation: Humans have two lungs – one on each side of the chest.
8. What protects the lungs inside the chest cavity?
   A) Skull
   B) Vertebral column
   C) Rib cage ✅
   D) Pelvic girdle
   Explanation: The rib cage encloses and protects the lungs and heart.
9. Which part of the respiratory system filters dust and microbes?
   A) Alveoli
   B) Trachea
   C) Nasal cavity ✅
   D) Lungs
   Explanation: The nasal cavity has mucus and cilia to trap particles.
10. What gas is expelled from the body during exhalation?
    A) Oxygen
    B) Hydrogen
    C) Carbon dioxide ✅
    D) Nitrogen
    Explanation: Carbon dioxide is a waste product of respiration.
11. What is the tube that carries air from the trachea into the lungs?
    A) Bronchi ✅
    B) Esophagus
    C) Diaphragm
    D) Larynx
    Explanation: The bronchi branch off the trachea and enter the lungs.
12. Which structure is also called the voice box?
    A) Trachea
    B) Pharynx
    C) Larynx ✅
    D) Epiglottis
    Explanation: The larynx contains the vocal cords and produces sound.
13. Which structure covers the trachea during swallowing?
    A) Uvula
    B) Epiglottis ✅
    C) Tongue
    D) Soft palate
    Explanation: The epiglottis prevents food from entering the windpipe.
14. Which gas is necessary for cellular respiration?
    A) Nitrogen
    B) Carbon dioxide
    C) Oxygen ✅
    D) Helium
    Explanation: Oxygen is required to break down glucose for energy.
15. The windpipe is also known as the:
    A) Larynx
    B) Trachea ✅
    C) Pharynx
    D) Bronchi
    Explanation: Trachea is the medical term for windpipe.
16. Which lung is slightly smaller to accommodate the heart?
    A) Right lung
    B) Left lung ✅
    C) Both are equal
    D) None
    Explanation: The left lung has a cardiac notch to accommodate the heart.
17. Breathing rate is controlled by which part of the brain?
    A) Cerebellum
    B) Cerebrum
    C) Medulla oblongata ✅
    D) Thalamus
    Explanation: The medulla regulates involuntary breathing.
18. Respiration is essential for:
    A) Photosynthesis
    B) Energy production ✅
    C) Digestion
    D) Excretion
    Explanation: Respiration releases energy needed for body functions.
19. Which part of the respiratory tract warms and moistens the air?
    A) Alveoli
    B) Nasal cavity ✅
    C) Bronchi
    D) Pharynx
    Explanation: The nasal passage warms and humidifies incoming air.
20. What happens to the diaphragm when we inhale?
    A) It relaxes
    B) It contracts ✅
    C) It remains still
    D) It thickens
    Explanation: The diaphragm contracts and flattens to expand lung volume.

🟡 Moderate Level (21–40)

21. What lines the respiratory tract to trap particles and microbes?
    A) Mucus and cilia ✅
    B) Capillaries
    C) Alveoli
    D) Cartilage
    Explanation: Mucus traps particles, and cilia move them out of the tract.
22. How many lobes are in the right lung?
    A) 1
    B) 2
    C) 3 ✅
    D) 4
    Explanation: The right lung has 3 lobes; the left has 2.
23. What is the function of surfactant in the lungs?
    A) Increase friction
    B) Reduce surface tension ✅
    C) Absorb oxygen
    D) Trap dust
    Explanation: Surfactant prevents alveoli from collapsing by reducing surface tension.
24. Where is the respiratory center located?
    A) Hypothalamus
    B) Medulla oblongata ✅
    C) Cerebellum
    D) Pituitary
    Explanation: The medulla oblongata regulates the rhythm of breathing.
25. Which phase of respiration involves the intake of air?
    A) Exhalation
    B) Inhalation ✅
    C) Diffusion
    D) Osmosis
    Explanation: Inhalation is the process of drawing air into the lungs.
26. What part of the pharynx conducts air to the larynx?
    A) Nasopharynx
    B) Oropharynx
    C) Laryngopharynx ✅
    D) Hypopharynx
    Explanation: Laryngopharynx is the lowest part of the pharynx and directs air into the larynx.
27. The exchange of gases in the lungs is facilitated by:
    A) Active transport
    B) Diffusion ✅
    C) Osmosis
    D) Filtration
    Explanation: Gases move across alveolar membranes by passive diffusion.
28. What type of epithelial tissue lines the alveoli?
    A) Columnar
    B) Cuboidal
    C) Squamous ✅
    D) Transitional
    Explanation: Alveoli are lined by simple squamous epithelium for rapid gas exchange.
29. What is tidal volume?
    A) Total lung volume
    B) Volume during forced inhalation
    C) Air exchanged in normal breathing ✅
    D) Residual air left after exhalation
    Explanation: Tidal volume is the air exchanged during normal, quiet breathing.
30. What is the function of pleural fluid?
    A) Transport gases
    B) Aid blood flow
    C) Lubricate lungs ✅
    D) Trap bacteria
    Explanation: Pleural fluid reduces friction between lung surfaces and chest wall.
31. Which condition involves inflammation of bronchi?
    A) Asthma
    B) Pneumonia
    C) Bronchitis ✅
    D) Emphysema
    Explanation: Bronchitis is the inflammation of the bronchial tubes.
32. What is the primary stimulus for breathing?
    A) Low oxygen
    B) High carbon dioxide ✅
    C) Low blood pressure
    D) High pH
    Explanation: Rising CO₂ levels in the blood stimulate the respiratory center.
33. Which muscle group assists the diaphragm during deep breathing?
    A) Abdominal muscles ✅
    B) Quadriceps
    C) Biceps
    D) Gluteals
    Explanation: Abdominal muscles help forcefully expel air during deep or forced breathing.
34. Vital capacity is the sum of:
    A) Residual and tidal volume
    B) Tidal, inspiratory, and expiratory reserve volumes ✅
    C) Total and residual volume
    D) None of the above
    Explanation: Vital capacity includes all air that can be inhaled and exhaled.
35. What is the main function of the respiratory system?
    A) Produce energy
    B) Transport nutrients
    C) Exchange gases ✅
    D) Filter blood
    Explanation: The system exchanges oxygen and carbon dioxide with the environment.
36. What percentage of oxygen is transported in hemoglobin?
    A) 98% ✅
    B) 75%
    C) 50%
    D) 25%
    Explanation: Most oxygen in blood is carried bound to hemoglobin.
37. Carbon monoxide is dangerous because it:
    A) Blocks oxygen entry
    B) Binds to hemoglobin tightly ✅
    C) Causes lung infection
    D) Destroys alveoli
    Explanation: CO binds to hemoglobin more strongly than oxygen, reducing oxygen delivery.
38. What is residual volume?
    A) Extra air inhaled
    B) Air exhaled forcibly
    C) Air remaining after full exhalation ✅
    D) Air used in speech
    Explanation: Residual volume is the air that stays in lungs after maximum exhalation.
39. Which disease destroys alveoli and reduces surface area for gas exchange?
    A) Asthma
    B) Tuberculosis
    C) Emphysema ✅
    D) Bronchitis
    Explanation: Emphysema breaks down alveoli walls, impairing gas exchange.
40. Hyperventilation causes:
    A) Decreased CO₂ levels ✅
    B) Oxygen depletion
    C) Lung collapse
    D) Alkalosis prevention
    Explanation: Rapid breathing removes too much CO₂, leading to respiratory alkalosis.

🔴 Hard Level (41–50)

41. Bohr effect describes the relationship between:
    A) CO₂ and oxygen release from hemoglobin ✅
    B) Oxygen and pH
    C) CO₂ and pH only
    D) pH and bicarbonate
    Explanation: Bohr effect shows that higher CO₂ lowers hemoglobin’s oxygen affinity.
42. Carbaminohemoglobin forms when:
    A) CO₂ binds with water
    B) CO₂ binds with hemoglobin ✅
    C) Oxygen binds with hemoglobin
    D) CO binds with hemoglobin
    Explanation: CO₂ binds to globin part of hemoglobin forming carbaminohemoglobin.
43. What enzyme helps convert CO₂ into bicarbonate in RBCs?
    A) Trypsin
    B) Catalase
    C) Carbonic anhydrase ✅
    D) Pepsin
    Explanation: Carbonic anhydrase facilitates rapid conversion of CO₂ into bicarbonate.
44. Oxygen-hemoglobin dissociation curve shifts right due to:
    A) Low CO₂
    B) High pH
    C) Low temperature
    D) High CO₂ and temperature ✅
    Explanation: High CO₂, temperature, and low pH decrease hemoglobin’s oxygen affinity.
45. Which part of the respiratory system has the smallest cross-sectional area?
    A) Trachea ✅
    B) Bronchi
    C) Bronchioles
    D) Alveoli
    Explanation: The trachea is a single tube; total alveolar surface is much larger.
46. In which form is most CO₂ transported in the blood?
    A) Dissolved in plasma
    B) Carbaminohemoglobin
    C) Bicarbonate ion ✅
    D) CO₂ gas
    Explanation: ~70% of CO₂ is transported as bicarbonate ions.
47. Which law explains gas diffusion based on pressure gradient?
    A) Boyle’s law
    B) Charles’ law
    C) Dalton’s law
    D) Henry’s law ✅
    Explanation: Henry’s law governs gas diffusion based on partial pressure and solubility.
48. Oxygen is primarily carried in the blood by:
    A) Plasma
    B) Hemoglobin ✅
    C) White blood cells
    D) Platelets
    Explanation: Hemoglobin binds to and transports oxygen in RBCs.
49. The respiratory membrane consists of:
    A) Alveolar and capillary walls ✅
    B) Bronchioles
    C) Cartilage and mucus
    D) Cilia and goblet cells
    Explanation: The respiratory membrane is where alveolar and capillary walls meet for gas exchange.
50. Which condition results in difficulty exhaling air from the lungs?
    A) Asthma ✅
    B) Pneumonia
    C) Tuberculosis
    D) Pleuritis
    Explanation: Asthma causes airway narrowing, making exhalation difficult.