Hemoglobin unlike myoglobin showsa) Sigmoid curve of oxygen dissociationb) Positive cooperativityc) Hills coefficient of oned) None of above
Hb-O2 dissociation curve- Sigmoid shape
Co-operativity- Hb is a tetramer. If one molecule of O2 binds to the tetramer more easily if other O2 is already bound. 
 
Hills coefficient of Hb- 2.8
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