Final answer:
Oxygen is the molecule that binds to the heme group of hemoglobin, enabling the transport of oxygen. Hemoglobin binds carbon dioxide as well, though not at the heme site. Carbon monoxide competes with oxygen for the binding sites on hemoglobin.
Step-by-step explanation:
The molecule that binds to the heme group of hemoglobin is oxygen. Hemoglobin is responsible for the transport of oxygen from the lungs to tissues. The iron ion within the heme group interacts with oxygen, forming oxyhemoglobin. Interestingly, hemoglobin can also bind carbon dioxide, although not at the heme site but rather at the amino groups of the globin chains, creating a form known as carbaminohemoglobin.
It is noteworthy that the affinity of hemoglobin for carbon monoxide (CO) is even higher than for oxygen, which can lead to carbon monoxide poisoning as it competes with oxygen for binding sites. However, in the presence of a sufficiently high concentration of oxygen, it can displace carbon monoxide due to its own binding affinity.