Read How Blood Carries Respiratory Gases
Haemoglobin carries most oxygen, while carbon dioxide travels mainly as bicarbonate.
Gas Transport is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Know the proportions
About 97% of O2 is haemoglobin-bound and about 3% dissolved. Roughly 70% of CO2 is carried as bicarbonate, 20–25% bound to globin, and about 7% dissolved.
Increase delivery during exercise
At rest, about 5 mL O2 per 100 mL oxygenated blood is delivered to tissues. Active muscle extracts more. Bohr and Haldane effects link CO2/H+ conditions with O2 binding and CO2 carriage.
Identify gases from their pressure profile
In inspired air, oxygen is high and carbon dioxide is almost absent. By alveolar air, oxygen falls as it diffuses into blood while carbon dioxide rises as it enters the alveoli. Water vapour rapidly equilibrates with humid airways, and nitrogen remains the largest relatively unchanged fraction. Match those patterns before naming each gas. Choose C.
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- ✓O2: mostly haemoglobin-bound.
- ✓CO2: mostly bicarbonate; smaller carbamino and dissolved fractions.
- ✓O2 extraction rises with tissue activity.
- ✓Alveolar gas exchange lowers oxygen and raises carbon dioxide relative to inspired air.
A resting O2-delivery figure should not be applied unchanged to strenuous exercise.
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