system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
The oxygen hemoglobin dissociation curve is sigmoid because
assistant
The correct answer is  Co-operativity- Hb is a tetramer. If one molecule of O2 binds to the tetramer more easily if another O2 is already bound. Since it is most difficult for the first molecule of O2 to bind to Hb, the shape becomes sigmoid.