MCQs on Breathing and Exchange of Gases – Class 11 Biology
MCQs on Breathing and Exchange of Gases – CBSE Class 11 Biology (Unit V | NCERT-Based)
CBSE Class 11 Biology – MCQs with Answers and Explanations
Unit V: Human Physiology
Topic: Breathing and Exchange of Gases
Section A: Breathing Mechanism & Respiratory Organs (Q1–Q10)
Q1. Breathing is the process of:
A. Oxidation of food
B. Exchange of oxygen and carbon dioxide between lungs and atmosphere
C. Transport of gases in blood
D. Cellular respiration
Answer: B
Explanation: Breathing (ventilation) involves inhalation and exhalation, exchanging gases between lungs and the environment.
Q2. The organ of respiration in humans is:
A. Skin
B. Trachea
C. Lungs
D. Alveoli
Answer: C
Explanation: Lungs are the primary respiratory organs where gas exchange occurs.
Q3. The functional unit of lungs is:
A. Bronchiole
B. Alveolus
C. Trachea
D. Pleura
Answer: B
Explanation: Alveoli provide a large surface area for gaseous exchange.
Q4. Which structure prevents collapse of trachea?
A. Smooth muscles
B. Cartilage rings
C. Ligaments
D. Pleural fluid
Answer: B
Explanation: C-shaped cartilaginous rings keep the trachea open.
Q5. The nasal chamber helps in respiration by:
A. Digesting food
B. Warming and humidifying air
C. Absorbing oxygen
D. Producing sound
Answer: B
Explanation: Nasal hairs, mucus, and blood vessels filter, warm, and moisten air.
Q6. The epiglottis prevents food from entering the:
A. Oesophagus
B. Pharynx
C. Trachea
D. Bronchi
Answer: C
Explanation: Epiglottis closes the glottis during swallowing.
Q7. Which muscles are involved in normal inspiration?
A. Abdominal muscles
B. Internal intercostals
C. Diaphragm and external intercostals
D. Smooth muscles of lungs
Answer: C
Explanation: Contraction of diaphragm and external intercostals increases thoracic volume.
Q8. Normal breathing is also called:
A. Apnoea
B. Eupnoea
C. Dyspnoea
D. Tachypnoea
Answer: B
Explanation: Eupnoea refers to normal, quiet breathing.
Q9. Pleural fluid is present between:
A. Lungs and heart
B. Alveoli and capillaries
C. Visceral and parietal pleura
D. Bronchi and bronchioles
Answer: C
Explanation: Pleural fluid reduces friction during lung movement.
Q10. Breathing movements are regulated by:
A. Cerebellum
B. Hypothalamus
C. Medulla oblongata and pons
D. Cerebrum
Answer: C
Explanation: Respiratory rhythm is controlled by respiratory centres in the brainstem.
Section B: Mechanism of Breathing & Lung Volumes (Q11–Q20)
Q11. Inspiration is an:
A. Active process
B. Passive process
C. Voluntary process only
D. Chemical process
Answer: A
Explanation: Inspiration requires muscle contraction, hence active.
Q12. Expiration during normal breathing is:
A. Active
B. Passive
C. Voluntary
D. Energy consuming
Answer: B
Explanation: Normal expiration occurs due to elastic recoil of lungs.
Q13. Increase in thoracic volume during inspiration leads to:
A. Increase in lung pressure
B. Decrease in lung pressure
C. No change in pressure
D. Lung collapse
Answer: B
Explanation: Lower pressure inside lungs causes air to enter.
Q14. Tidal volume refers to:
A. Maximum air inhaled
B. Air inhaled and exhaled in normal breathing
C. Residual air in lungs
D. Air exchanged during forceful breathing
Answer: B
Explanation: Tidal volume is about 500 mL in adults.
Q15. Inspiratory reserve volume (IRV) is:
A. Air left after expiration
B. Additional air inhaled after normal inspiration
C. Air exchanged during tidal breathing
D. Maximum air exhaled
Answer: B
Explanation: IRV increases oxygen intake during deep breathing.
Q16. Expiratory reserve volume (ERV) is:
A. Air exhaled forcefully after normal expiration
B. Air left after forceful expiration
C. Normal breathing volume
D. Air inhaled forcefully
Answer: A
Explanation: ERV helps in removing extra air.
Q17. Residual volume is important because it:
A. Helps in digestion
B. Prevents lung collapse
C. Stores oxygen for muscles
D. Removes CO₂
Answer: B
Explanation: Residual air keeps alveoli open at all times.
Q18. Vital capacity is the sum of:
A. TV + IRV
B. TV + ERV
C. IRV + ERV
D. TV + IRV + ERV
Answer: D
Explanation: Vital capacity represents maximum usable lung volume.
Q19. Total lung capacity includes:
A. Vital capacity only
B. Residual volume only
C. Vital capacity + residual volume
D. Tidal volume only
Answer: C
Explanation: Total lung capacity includes all lung volumes.
Q20. Spirometer is used to measure:
A. Blood pressure
B. Lung volumes
C. Oxygen content
D. Heart rate
Answer: B
Explanation: Spirometry measures respiratory volumes and capacities.
Section C: Exchange of Gases & Transport (Q21–Q35)
Q21. Exchange of gases in lungs occurs by:
A. Active transport
B. Diffusion
C. Osmosis
D. Mass flow
Answer: B
Explanation: Gases move down their partial pressure gradients.
Q22. Oxygen diffuses from alveoli to blood because:
A. Blood has higher O₂ pressure
B. Alveoli have higher O₂ pressure
C. CO₂ pressure is low
D. Temperature difference exists
Answer: B
Explanation: Oxygen moves from high to low partial pressure.
Q23. The respiratory surface must be:
A. Thick and dry
B. Thin and moist
C. Thick and moist
D. Rigid
Answer: B
Explanation: Thin, moist surfaces allow efficient diffusion.
Q24. Oxygen is transported in blood mainly by:
A. Plasma
B. RBC cytoplasm
C. Hemoglobin
D. WBCs
Answer: C
Explanation: About 97% of oxygen binds with hemoglobin.
Q25. Each hemoglobin molecule can bind with:
A. 1 oxygen molecule
B. 2 oxygen molecules
C. 3 oxygen molecules
D. 4 oxygen molecules
Answer: D
Explanation: Hemoglobin has four heme groups.
Q26. Oxyhemoglobin formation is favored by:
A. High CO₂
B. High temperature
C. High pO₂
D. Low pH
Answer: C
Explanation: High oxygen tension promotes oxygen binding.
Q27. Carbon dioxide is transported mainly as:
A. Dissolved gas
B. Carbaminohemoglobin
C. Bicarbonate ions
D. Carbonic acid
Answer: C
Explanation: About 70% CO₂ is transported as bicarbonates.
Q28. The enzyme carbonic anhydrase is present in:
A. Plasma
B. RBCs
C. Alveoli
D. WBCs
Answer: B
Explanation: Carbonic anhydrase in RBCs catalyzes CO₂ hydration.
Q29. Chloride shift occurs during:
A. Oxygen transport
B. Carbon dioxide transport
C. Inspiration
D. Expiration
Answer: B
Explanation: Chloride shift maintains ionic balance in RBCs.
Q30. Release of oxygen from hemoglobin is promoted by:
A. High pO₂
B. Low CO₂
C. High pCO₂ and low pH
D. Low temperature
Answer: C
Explanation: Bohr effect facilitates oxygen release in tissues.
Q31. Which gas is more soluble in blood?
A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Hydrogen
Answer: C
Explanation: CO₂ is 20 times more soluble than oxygen.
Q32. Partial pressure of oxygen is highest in:
A. Tissues
B. Blood plasma
C. Alveoli
D. Veins
Answer: C
Explanation: Fresh air in alveoli has maximum pO₂.
Q33. Which factor does NOT affect gas exchange?
A. Surface area
B. Thickness of membrane
C. Partial pressure gradient
D. Blood glucose level
Answer: D
Explanation: Glucose level does not directly affect diffusion.
Q34. The Bohr effect relates to:
A. CO₂ transport
B. Oxygen binding with hemoglobin
C. Lung volumes
D. Breathing rate
Answer: B
Explanation: High CO₂ lowers hemoglobin’s oxygen affinity.
Q35. Exchange of gases at tissue level is called:
A. External respiration
B. Internal respiration
C. Breathing
D. Ventilation
Answer: B
Explanation: Internal respiration occurs between blood and tissues.
Section D: Regulation of Respiration & Disorders (Q36–Q50)
Q36. Normal breathing rate in adults is about:
A. 6–8/min
B. 12–16/min
C. 20–25/min
D. 30–40/min
Answer: B
Explanation: Normal adult breathing rate is 12–16 breaths per minute.
Q37. Increase in CO₂ concentration stimulates breathing because it:
A. Increases oxygen level
B. Lowers blood pH
C. Raises temperature
D. Increases blood pressure
Answer: B
Explanation: CO₂ increases H⁺ concentration, stimulating chemoreceptors.
Q38. Which receptors monitor blood pH and CO₂ levels?
A. Stretch receptors
B. Chemoreceptors
C. Baroreceptors
D. Photoreceptors
Answer: B
Explanation: Chemoreceptors regulate respiratory rate.
Q39. Asthma is characterized by:
A. Infection of alveoli
B. Narrowing of bronchi
C. Collapse of lungs
D. Fluid in pleura
Answer: B
Explanation: Bronchial constriction causes difficulty in breathing.
Q40. Emphysema involves damage to:
A. Bronchi
B. Trachea
C. Alveolar walls
D. Diaphragm
Answer: C
Explanation: Alveolar destruction reduces respiratory surface area.
Q41. Smoking mainly affects respiration by:
A. Increasing oxygen diffusion
B. Increasing lung capacity
C. Damaging cilia and alveoli
D. Increasing hemoglobin
Answer: C
Explanation: Smoking damages cilia and alveolar walls.
Q42. Pneumonia affects breathing due to:
A. Mucus accumulation
B. Fluid-filled alveoli
C. Reduced hemoglobin
D. Weak diaphragm
Answer: B
Explanation: Fluid in alveoli reduces gas exchange efficiency.
Q43. Cyanosis refers to:
A. Excess oxygen in blood
B. Bluish skin due to low oxygen
C. High CO₂ in lungs
D. Normal respiration
Answer: B
Explanation: Cyanosis indicates oxygen deficiency.
Q44. Artificial respiration is required when:
A. Oxygen transport fails
B. Breathing stops
C. Digestion stops
D. Heart rate increases
Answer: B
Explanation: Artificial respiration maintains ventilation.
Q45. Carbon monoxide poisoning is dangerous because CO:
A. Destroys lungs
B. Combines strongly with hemoglobin
C. Increases CO₂
D. Reduces breathing rate
Answer: B
Explanation: CO forms carboxyhemoglobin, blocking oxygen transport.
Q46. Which condition results in difficulty in breathing?
A. Apnoea
B. Dyspnoea
C. Eupnoea
D. Hypoxia
Answer: B
Explanation: Dyspnoea refers to labored breathing.
Q47. Apnoea means:
A. Fast breathing
B. Slow breathing
C. Absence of breathing
D. Deep breathing
Answer: C
Explanation: Apnoea is temporary cessation of breathing.
Q48. High altitude causes breathlessness due to:
A. High CO₂
B. Low atmospheric pressure
C. Low humidity
D. Low temperature
Answer: B
Explanation: Reduced pO₂ at high altitude limits oxygen diffusion.
Q49. Which adaptation increases oxygen delivery to tissues?
A. Decreased hemoglobin
B. Increased RBC count
C. Reduced breathing rate
D. Thick alveolar walls
Answer: B
Explanation: More RBCs enhance oxygen-carrying capacity.
Q50. Breathing and gas exchange are essential because they:
A. Produce glucose
B. Remove waste only
C. Supply oxygen for cellular respiration
D. Maintain body temperature
Answer: C
Explanation: Oxygen is essential for ATP production in cells.