NCERT states that tidal volume is about 500 mL and a healthy man can inspire or expire approximately 6000 to 8000 mL of air per minute. The Assertion says inspire and expire, which may imply both together, so it is not NCERT-accurate. The Reason is correct.

Pedagogical value: This question tests precision in biological wording. It shows how “or” and “and” can change the meaning of a numerical NCERT statement.

NCERT states that oxygen is transported mainly by RBCs . Mature human RBCs lack mitochondria and hence rely on anaerobic glycolysis for their energy requirements. Thus, although humans are aerobic organisms, not all of their cells are aerobic. The Reason correctly exemplifies and explains the Assertion.

Pedagogical value: This question addresses the misconception that all cells in an aerobic organism must themselves be aerobic. It highlights the distinction between the metabolic nature of an organism and that of its constituent cells. The question also rewards students who correlate respiratory physiology with cell biology.

NCERT states that O₂ binds reversibly with haemoglobin and that its dissociation is influenced by pO₂, pCO₂, H⁺ concentration and temperature . Mature human RBCs lack mitochondria and therefore rely exclusively on anaerobic glycolysis for ATP production. Thus, the Assertion is true. The Reason is also true, but the fact that oxygen binds tightly to haemoglobin does not explain why RBC cytoplasm exhibits only anaerobic respiration.

Pedagogical value: This question addresses a common misconception that RBCs, being oxygen carriers, must themselves perform aerobic respiration. It reinforces the distinction between transporting oxygen and utilising oxygen. The question also highlights that the presence of oxygen within a cell does not necessarily imply aerobic metabolism.

NCERT states that the pleural fluid present between the double-layered pleura reduces friction on the lung surface . In the absence of this fluid, the pleural layers would rub against each other during breathing, leading to irritation and impaired lung movements.

Pedagogical value: This question encourages students to ask why pleural fluid is necessary rather than merely memorising its presence. It provides a mechanistic basis for the NCERT statement and illustrates how lubrication prevents friction-related injury. Such questions train students to seek explanations behind generalized anatomical descriptions.

NCERT states that about 20–25% of CO₂ is transported by haemoglobin as carbaminohaemoglobin, indicating that haemoglobin can bind CO₂ . Carboxyhaemoglobin, however, is formed when carbon monoxide binds to haemoglobin and is unrelated to the transport of CO₂. Therefore, while the formation of carboxyhaemoglobin may be observed under appropriate conditions, it does not explain the binding of CO₂ to haemoglobin.

Pedagogical value: This question addresses the common confusion between carbaminohaemoglobin and carboxyhaemoglobin. Students may instinctively associate the prefix “carbo-” with carbon dioxide and conclude that carboxyhaemoglobin is the product of CO₂ binding. The question rewards precision in biochemical nomenclature and discourages superficial pattern recognition.

NCERT states that exchange of gases occurs both between alveoli and blood and between blood and tissues . Thus, lungs are not the only site of gaseous exchange. NCERT also states that humans respire through lungs, whereas amphibians like frogs can additionally respire through their moist skin . Therefore, the Reason is true. However, the fact that lungs are the only respiratory organ in humans does not explain why gaseous exchange also occurs at tissue sites.

Pedagogical value

This question addresses the common misconception that gaseous exchange is exclusive to the respiratory system. Students often associate the phrase “gaseous exchange” only with the lungs because lungs are the sole respiratory organs in humans. The question reinforces that, although humans possess only lungs as respiratory organs, gaseous exchange also occurs at the tissue level. Thus, respiratory organs and sites of gaseous exchange are not synonymous.

NCERT states that the tidal volume during normal respiration is approximately 500 mL . This amount of ventilation, together with the normal breathing rate, is sufficient to meet the oxygen demands of the body’s tissues under resting conditions. Thus, the Reason correctly explains why the tidal volume of a healthy person is around 500 mL.

Pedagogical value: This question encourages students to think about the physiological significance of tidal volume rather than treating 500 mL as a number to be memorised. It raises the natural question, “Why 500 mL and not 100 mL or 1000 mL?” and emphasizes that tidal volume is tuned to satisfy the metabolic demands of the body under normal conditions.

NCERT states that an increase in thoracic volume causes a similar increase in pulmonary volume, decreasing intrapulmonary pressure below atmospheric pressure. This pressure gradient forces air from outside into the lungs, resulting in inspiration . Thus, human breathing is a form of negative-pressure breathing, where air enters the lungs due to a lower intrapulmonary pressure relative to atmospheric pressure.
Pedagogical value

This question is intended primarily for students who seek a deeper understanding beyond the immediate NCERT text. Although the terms negative-pressure breathing and positive-pressure breathing are not explicitly mentioned in NCERT, they are commonly encountered in NEET and other competitive examinations. The question demonstrates that many seemingly out-of-syllabus terms are often just labels for mechanisms already described in NCERT. By understanding that inspiration occurs because intrapulmonary pressure falls below atmospheric pressure , students can readily appreciate the concept of negative-pressure breathing without memorising additional facts.

Thus, the question encourages top-level students to bridge terminology and concepts, recognising that advanced terminology often represents a natural extension of NCERT principles rather than entirely new knowledge. It also helps students remain confident when confronted with unfamiliar terms in competitive examinations, relying on conceptual understanding instead of rote memorisation.

NCERT states that the pO₂ of oxygenated blood is about 95 mmHg and that every 100 mL of oxygenated blood can deliver around 5 mL of O₂ to the tissues under normal physiological conditions . In strenuous muscles, where pO₂ is low and pCO₂, H⁺ concentration and temperature are high, conditions favour dissociation of O₂ from oxyhaemoglobin . However, neither NCERT nor physiology supports the statement that 95% of oxygen is delivered to strenuous muscle. Also, the Reason is false because 95 mmHg refers to the pO₂ of oxygenated blood, not the partial pressure of oxyhaemoglobin itself.

Pedagogical value

This question addresses the tendency to associate familiar numbers with incorrect concepts. Students may instinctively connect the 95 mmHg pO₂ of oxygenated blood with 95% oxygen delivery. The question tests whether students distinguish between partial pressure, percentage saturation, and oxygen delivery, which are related but distinct concepts.

NCERT states that the alveoli are the primary sites of exchange of gases and that the alveoli and their ducts constitute the respiratory or exchange part . Thus, gaseous diffusion does not occur in many distinct parts of the respiratory system but mainly in the alveolar region. The Reason is true because the lungs contain millions of alveoli, providing a vast surface area for gas exchange.

Pedagogical value: This question addresses the tendency to equate many alveoli with many parts. Students may intuitively infer that because there are millions of alveoli, gas exchange occurs in many parts of the respiratory system. The question helps distinguish between numerous repeated units within a single exchange region and multiple distinct anatomical parts.

Humans exhibit double circulation, comprising pulmonary and systemic circulations. Gaseous exchange occurs not only in the lungs during pulmonary circulation but also between blood and tissues during systemic circulation. NCERT states that exchange of gases occurs between alveoli and blood as well as between blood and tissues . Therefore, the statement that gaseous exchange occurs only in pulmonary circulation is false.

Pedagogical value: This question addresses the common tendency to equate gaseous exchange exclusively with the lungs. Students often overlook the fact that oxygen and carbon dioxide are exchanged not only between alveoli and blood but also between blood and tissues. Thus, the question reinforces the distinction between pulmonary gas exchange and tissue gas exchange.

NCERT states that CO₂ produced at the tissues combines with water to form carbonic acid in a reversible reaction catalysed by carbonic anhydrase. Since CO₂ is continuously supplied at tissue sites, the forward reaction is favoured there, whereas the reverse reaction is favoured in the lungs.

Pedagogical value: This question tests the dynamic nature of reversible reactions in physiology and reinforces the principle that the direction of a reversible reaction depends on the continuous addition or removal of reactants and products.