Chlorophyll is a _________ protein.

Chlorophyll is the molecule that traps this 'most elusive of all powers' - and is called a photoreceptor. It is found in the chloroplasts of green plants, and this is what makes,  green plants, green. The basic structure of a chlorophyll molecule is a porphyrin ring, co-ordinated to a central atom, Mg. This is very similar in structure to the heme group found in hemoglobin, except that in heme, the central atom is iron, whereas in chlorophyll,  it is magnesium.