Easy Biology question! 10 points~!?

The green part of plants consists of a pigment named CHLOROPHYLL. The leaves also consist of another pigment named ETIOLIN(which is supposed to be an antecedent condition of chlorophyll). When you close the box due to lack of sunlight the chlorophyll synthesis stops and the pigment etiolin kicks in for food production. Thus as etiolin is a yellowish pigment the leaves turn yellow.