The most prominent of these (and historically the first) is the representation theory of groups, in which elements of a group are represented by invertible matrices in such a way that the group operation is matrix multiplication.
hemoglobin is able to perform this function due to its ability to reversibly bind to oxygen. inside oxygen rich areas of the lungs, hemoglobin picks up oxygen molecules, then it transports the oxygen via red blood cells to bodys tissue, once hemoglobin reached the oxygen poor area of the tissues it releases the oxygen.
Oxygen binds to hemoglobin in the lungs, which increases the affinity for even more oxygen to bind. This is exactly what happens as our blood flows through the lungs. Since there's a lot of oxygen in the lungs, there's a good possibility that hemoglobin will bind to oxygen. Oxygen binding to hemoglobin changes the structure of hemoglobin, and that makes it easier for oxygen to bind. Additional oxygen binding further increases the affinity, resulting in the third and then fourth oxygen molecule binding.