Question

why does light absorbtion only occur when there is green chlorophyll? all colors absorb light too .

Answer 1

Photosynthesis requires maximum extent of sunlight to be absorbed. Each plant has different kinds of chlorophyll, which differ only slightly in their structure. When light falls on them, these pigments get excited and absorb radiation to trigger a chemical reaction. The pigments absorb blue and red lights sufficiently to satisfy their energy requirements. There is a large spectral region between 500 to 600nm which is reflected and hence plants appear green.