Regarding primary and secondary sites of gas exchange, consider the following statements:
I. Alveoli are the primary sites of exchange of gases. II. Exchange of gases also occurs between blood and tissues. III. O2 and CO2 are exchanged in these sites by simple diffusion. IV. Exchange at alveoli occurs by active transport against concentration gradient.
Explanation: Statements I, II, and III are correct. Alveoli are the primary exchange sites, blood-tissue interface is the secondary site, and gas exchange occurs by simple diffusion based on concentration/partial pressure gradients. Statement IV is incorrect because gas exchange occurs by passive diffusion, not active transport.
Question 62 of 100
📘 CLASS XI
Which factors directly affect the rate of diffusion across the respiratory membrane?
I. Partial pressure/concentration gradient of gases. II. Solubility of the gases. III. Thickness of the diffusion membrane. IV. Active ATP hydrolysis by alveolar epithelial cells.
Explanation: Statements I, II, and III are correct because diffusion depends on pressure gradient, gas solubility, and membrane thickness. Statement IV is incorrect because diffusion is a passive process requiring no ATP.
Question 63 of 100
📘 CLASS XI
Consider the partial pressure of oxygen (pO2) at different sites in the human body (in mm Hg):
I. Atmospheric air = 159 mm Hg II. Alveoli = 104 mm Hg III. Oxygenated blood = 95 mm Hg IV. Deoxygenated blood and tissues = 40 mm Hg
Explanation: All four statements correctly represent the standard pO₂ values at different physiological sites.
Question 64 of 100
📘 CLASS XI
Consider the partial pressure of carbon dioxide (pCO2) at different sites in the human body (in mm Hg):
I. Atmospheric air = 0.3 mm Hg II. Alveoli = 40 mm Hg III. Oxygenated blood = 40 mm Hg IV. Deoxygenated blood and tissues = 45 mm Hg
Explanation: All four statements correctly represent the standard pCO₂ values at different physiological sites.
Question 65 of 100
📘 CLASS XI
Analyze the concentration gradient for oxygen diffusion from environment to tissues:
I. pO2 is highest in atmospheric air (159 mm Hg) and drops to 104 mm Hg in alveoli. II. pO2 in alveoli (104 mm Hg) is higher than in deoxygenated blood entering pulmonary capillaries (40 mm Hg). III. pO2 in oxygenated blood (95 mm Hg) is higher than in tissue cells (40 mm Hg). IV. Gradient forces O2 to diffuse from tissues into oxygenated blood.
Explanation: Statements I, II, and III are correct. Oxygen diffuses along the partial pressure gradient from atmosphere to alveoli, alveoli to blood, and blood to tissues. Statement IV is incorrect because oxygen diffuses from blood into tissues.
Question 66 of 100
📘 CLASS XI
Analyze the concentration gradient for carbon dioxide diffusion from tissues to atmosphere:
I. pCO2 is highest in tissues and deoxygenated blood (45 mm Hg). II. pCO2 in alveoli (40 mm Hg) is lower than in deoxygenated blood entering alveolar capillaries (45 mm Hg). III. pCO2 in atmospheric air (0.3 mm Hg) is much lower than in alveolar air (40 mm Hg). IV. Gradient forces CO2 to diffuse from alveoli into deoxygenated blood.
Explanation: Statements I, II, and III are correct. Carbon dioxide diffuses from tissues and blood into alveoli and finally into the atmosphere. Statement IV is incorrect because diffusion is from blood to alveoli.
Question 67 of 100
📘 CLASS XI
Regarding gas solubility and diffusion efficiency across alveolar membranes, consider the statements:
I. Solubility of CO2 is 20-25 times higher than that of O2. II. Amount of CO2 that can diffuse through diffusion membrane per unit difference in partial pressure is much higher compared to O2. III. Solubility of O2 is 20-25 times higher than that of CO2. IV. CO2 cannot diffuse across the alveolar membrane due to low solubility.
Explanation: Statements I and II are correct because CO₂ is 20–25 times more soluble than O₂ and therefore diffuses much more readily. Statements III and IV are incorrect.
Question 68 of 100
📘 CLASS XI
Which three major layers constitute the respiratory diffusion membrane?
I. Thin squamous epithelium of alveoli II. Endothelium of alveolar capillaries III. Basement substance in between them IV. Thick ciliated columnar epithelium of bronchioles
Explanation: Statements I, II, and III are correct. The respiratory membrane consists of alveolar squamous epithelium, fused basement substance, and capillary endothelium. Statement IV is incorrect because bronchioles are not part of the diffusion membrane.
Question 69 of 100
📘 CLASS XI
Regarding the basement substance of the alveolar diffusion membrane, analyze the statements:
I. Lies between alveolar squamous epithelium and capillary endothelium. II. Composed of thin basement membrane supporting squamous epithelium. III. Composed of basement membrane surrounding single-layer endothelial cells of capillaries. IV. Its thickness exceeds 5 millimetres to prevent fluid leakage.
Explanation: Statements I, II, and III are correct. The basement substance lies between alveolar epithelium and capillary endothelium. Statement IV is incorrect because the respiratory membrane is extremely thin, not several millimetres thick.
Question 70 of 100
📘 CLASS XI
Consider the total thickness of the diffusion membrane in human lungs:
I. Total thickness is much less than a millimetre. II. Allows rapid simple diffusion of gases between alveoli and capillaries. III. Total thickness is approximately 5 to 10 millimetres. IV. Thinness provides significant resistance to oxygen transport.
Explanation: Statements I and II are correct because the diffusion membrane is much less than a millimetre thick, allowing rapid diffusion of respiratory gases. Statements III and IV are incorrect because the membrane is extremely thin and minimizes resistance to gas diffusion.
