Humans are just fancy plants

One of the most interesting aspects of the evolutionary divergence of life is that the essentials of it exist in very similar forms whether the life that we are talking about is a human or even a plant.

One fine example of this is in the way that a life form maintains respiration. This is the cyclic metabolic process occurring in the mammalian blood stream which facilitates the transport of oxygen and carbon dioxide to and from the cells. The plant also has a complex process which we call photosynthesis but which involves the transport of carbon dioxide and oxygen to and from the cells, but in a reverse sequence compared to the mammal.

The heme molecule in mammals and the chlorophyll molecule in plants perform this action. The molecular nucleus in both of these molecules is called a porphyrin molecule and resides in both heme and chlorophyll. The image below is of porphyrin at the centre of the heme molecule and the red atom at its centre is an iron ion. Simply replacing the iron ion with a magnesium atom makes this porphyrin molecule the nucleus of chlorophyll.

The iron ion at the center of heme gives the blood its red color. The magnesium atom at the center of chlorophyll contributes to a plant's green coloration. While chlorophyll is a strong absorber, it reflects the green part of the visible spectrum.