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One haemoglobin molecule can carry a maximum of how many oxygen molecules?

A1 O₂, only one heme functional
B2 O₂, since α and β bind separately
C4 O₂, one per heme
D8 O₂, two per heme
Answer & Solution
Correct answer: C. 4 O₂, one per heme
Haemoglobin has 4 polypeptide subunits (2α + 2β), each with a heme group containing one Fe²⁺. Each heme binds one O₂, so a fully saturated Hb carries 4 O₂. The cooperative binding gives the sigmoid dissociation curve.
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