Free Gaseous Exchange in Lungs MCQs with Answers
47 Gaseous Exchange in Lungs MCQs from Biology, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Gaseous exchange in the lungs occurs across the thin, moist alveolar and capillary surfaces, where oxygen and carbon dioxide diffuse down partial pressure gradients. The topic covers alveolar adaptations, ventilation, the role of haemoglobin in oxygen transport, carbon dioxide carriage, and the difference between external gas exchange and cellular respiration.
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- A. Their supporting rings of cartilage
- B. Their walls, one cell thick, giving an enormous surface area with a dense capillary network
- C. The cilia lining their inner surface
- D. The mucus that coats them
Explanation: Around 300 million alveoli give a surface of roughly 70 square metres, and a wall a single cell thick lying against an equally thin…
Correct answer: Their walls, one cell thick, giving an enormous surface area with a dense capillary network- A. hydrogen carbonate ions dissolved in the plasma
- B. carbaminohaemoglobin
- C. carbon dioxide dissolved in the plasma
- D. carbon monoxide
Explanation: About seventy per cent of carbon dioxide enters the red cells, where carbonic anhydrase converts it with water into carbonic acid, which…
Correct answer: hydrogen carbonate ions dissolved in the plasma- A. one molecule of oxygen
- B. four molecules of oxygen
- C. two molecules of oxygen
- D. an unlimited number of oxygen molecules
Explanation: Haemoglobin has four polypeptide chains, each with an iron containing haem group that binds one oxygen molecule, giving a maximum of four.
Correct answer: four molecules of oxygen- A. the chloride shift
- B. the countercurrent effect
- C. the Bohr effect
- D. the induced fit effect
Explanation: Carbon dioxide lowers the pH of the blood, which alters the shape of haemoglobin and reduces its affinity for oxygen, shifting the…
Correct answer: the Bohr effect- A. oxygen in the alveoli
- B. glucose in the blood
- C. nitrogen in the blood
- D. carbon dioxide in the blood, monitored by the medulla oblongata
Explanation: Chemoreceptors in the medulla and in the great arteries respond to the fall in pH that a rise in carbon dioxide produces, and the…
Correct answer: carbon dioxide in the blood, monitored by the medulla oblongata- A. out of the red cell as oxygen enters
- B. into the red cell to balance the hydrogen carbonate ions leaving it
- C. from the plasma into the alveolar air
- D. into the plasma from the kidney tubules
Explanation: As hydrogen carbonate ions formed inside the red cell diffuse out into the plasma, the cell would be left with a net positive charge, so…
Correct answer: into the red cell to balance the hydrogen carbonate ions leaving it- A. Bronchi
- B. Bronchioles
- C. Alveoli
- D. Trachea
Explanation: Alveoli are the site of gas exchange, with thin walls and large surface area for efficient O2 and CO2 diffusion.
Correct answer: Alveoli- A. Type I alveolar cells
- B. Type II alveolar cells
- C. Goblet cells
- D. Ciliated cells
Explanation: Type II pneumocytes (alveolar cells) produce surfactant, which reduces surface tension to prevent alveolar collapse.
Correct answer: Type II alveolar cells- A. O2 binding to hemoglobin
- B. Effect of CO2/pH on O2 affinity
- C. CO2 transport
- D. Lung compliance
Explanation: The Bohr effect states that increased CO2/decreased pH reduces hemoglobin's affinity for O2, facilitating O2 release to tissues.
Correct answer: Effect of CO2/pH on O2 affinity- A. Dissolved in plasma
- B. Carbaminohemoglobin
- C. Bicarbonate ions
- D. Free CO2
Explanation: About 70% of CO2 is transported as bicarbonate (HCO3-) in plasma, formed by carbonic anhydrase in RBCs.
Correct answer: Bicarbonate ions- A. pH is low
- B. CO2 is high
- C. pH is high
- D. Temperature is high
Explanation: Hemoglobin has highest O2 affinity at high pH, low CO2, and low temperature (in the lungs).
Correct answer: pH is high- A. Maintain electrical neutrality
- B. Increase O2 transport
- C. Decrease CO2
- D. Activate enzymes
Explanation: As HCO3- leaves RBCs, Cl- enters to maintain electrical neutrality (chloride shift or Hamburger shift).
Correct answer: Maintain electrical neutrality- A. 150 millions
- B. 500 millions
- C. 800 millions
- D. 1 billion
Explanation: Human lungs contain roughly 300 to 500 million alveoli, so 500 million is the closest estimate given.
Correct answer: 500 millions- A. Thin
- B. Thick
- C. Soft
- D. Hard
Explanation: In higher animals, the skin is relatively thick and is not sufficient for rapid diffusion over the whole body, so specialised respiratory…
Correct answer: Thick- A. 30%
- B. 20%
- C. 40%
- D. 50%
Explanation: Intercellular air spaces can occupy about 40% of a leaf's total volume, providing pathways for carbon dioxide and oxygen movement between…
Correct answer: 40%- A. 1200
- B. 12000
- C. 100,000
- D. 1000
Explanation: Tobacco leaves may have about 100,000 stomata per square centimetre of leaf surface, allowing substantial exchange of carbon dioxide…
Correct answer: 100,000- A. 50
- B. 1000
- C. 5000
- D. 8000
Explanation: At ordinary temperature, water is approximately 50 times more viscous than air, so gases diffuse much more readily through air than…
Correct answer: 50- A. Air
- B. Water
- C. Soil
- D. None of these
Explanation: Air is a better respiratory medium than water because it contains a much higher concentration of oxygen and gases diffuse more rapidly…
Correct answer: Air- A. Alveoli
- B. Air sacs
- C. Bronchi
- D. Parabronchi
Explanation: Birds exchange gases across the thin walls of parabronchi, where air flows continuously through tubes surrounded by capillaries.
Correct answer: Parabronchi- A. Lungs
- B. Trachea
- C. Bronchus
- D. Body tissue
Explanation: The correct answer is the lungs. In the context of respiratory physiology, the lungs play a crucial role in gas exchange.
Correct answer: LungsGaseous Exchange in Lungs MCQs: common questions
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