Chlorophyll is a chlorin pigment, related to the porphyrin containing iron compound known as Heme. At the center of the ring is a magnesium ion. The side chains vary somewhat between the different forms of chlorophyll found in different organisms - chlorophyll a is always present, but chlorophylls b and c also occur in various groups.
Evidence for chorophyll
It can be shown that chlorophyll is vital for photosynthesis by destarching a variegated plant's leaves and exposing it to light for several hours. Variegated plant leaves have green areas which contain chlorophyll and white areas that have none. When tested with iodine solution[?] a colour change showing starch present is only evident in regions of the plant that were green and therefore contained chlorophyll. This shows that photosynthesis does not occur in areas where chlorophyll is absent, and therefore supports the theory that the presence of chlorophyll is a requirement for photosynthesis to take place.