The binding of oxygen to hemoglobin is facilitated by changes in protein conformation upon oxygen binding to one subunit that affect the binding of oxygen to another subunit.

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Answer is: The COOPERATIVE binding oxygen to hemoglobin is facilitated by changes in protein conformation upon oxygen binding to one subunit that affect the binding of oxygen to another subunit.

Explanation:

     Hemoglobin, which is a complex protein contained within our red blood cells is an alternative source of transportation of oxygen through our body. With hemoglobin, we can carry 20 ml of oxygen in that same 100 ml of blood.

    The way by which hemoglobin binds oxygen is referred to as cooperative binding. The binding of oxygen to hemoglobin makes it easier for more oxygen to bind.

     For example: during the cooperative binding of oxygen to hemoglobin, using four oxygen molecules. The binding of one oxygen molecule causes a change in conformation allowing the 2nd, 3rd, and 4th molecules to bind more efficiently to the hemoglobin.

     Therefore, the answer to the question is COOPERATIVE.