Partial Pressure and Gas Diffusion — NEET Biology
✅ Asked in NEET 2021What are the partial pressures (in mmHg) of O₂ and CO₂ in alveoli? NEET 2021
What are the partial pressures (in mmHg) of O₂ and CO₂ in alveoli? NEET 2021
The partial pressure of oxygen in the alveoli of the lungs is [NEET Phase II – 2016]
Answer & NCERT explanation
Correct answer: D — pO₂ = 104, pCO₂ = 40
According to NCERT, in alveoli the partial pressure of oxygen (pO₂) is 104 mmHg and partial pressure of carbon dioxide (pCO₂) is 40 mmHg. These values create favorable gradients for gas exchange - oxygen moves from alveoli to blood, CO₂ moves from blood to alveoli. Option d gives the correct alveolar gas pressures.
Read more NCERT concept on the PYQ
Pressure contributed by an individual gas in a mixture of gases is called partial pressure and is represented as pO₂ for oxygen and pCO₂ for carbon dioxide. Partial pressures of these two gases in the atmospheric air and the two sites of diffusion are given in Table 14.1 and in The data given in the table clearly indicates a concentration gradient for oxygen from alveoli to blood and blood to tissues. Similarly,
NTA tests your understanding of partial pressure gradients that drive gas exchange. Partial pressure (pO₂ and pCO₂) determines the direction and rate of gas diffusion across concentration gradients. Students commonly confuse partial pressure with total atmospheric pressure or forget that O₂ moves from alveoli to blood because pO₂ is higher in alveoli. The critical concept: gases always diffuse from higher to lower partial pressure. Remember the gradient sequence—alveoli (high pO₂) → blood (lower pO₂) → tissues (lowest pO₂). This principle explains why gases move in specific directions without any active transport, making it a fundamental mechanism NTA frequently tests.
What does NCERT say about Pressure contributed by individual?
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Through deep analysis of NEET and NTA, 88 of 90 questions from the NEET 2026 paper were matched straight from the MedicNEET Biology question bank.
88/90MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.