Chlorophyll is the photoreceptive molecule that uses the light energy to break apart the hydrogen and oxygen atoms. There is a magnesium atom in the center of the porphyrin ring which makes chlorophyll and that is what absorbs the light energy. Chlorophyll is also the thing that gives plants their green color; it absorbs blue and red light and reflect green light, which is what we see. There are actually two types of chlorophyll: chlorophyll a and b. They only differ by their structure, and chlorophyll b acts as an accessory chlorophyll to help chlorophyll a. Chlorophyll a directly participates in the light reactions which are a part of photosynthesis.