Chlorophyll is vital for photosynthesis, which helps plants get energy from light. Chlorophyll molecules are specifically arranged in and around pigment protein complexes called photosystems, which are embedded in the thylakoid membranes of chloroplasts. In these complexes, chlorophyll serves two primary functions. The energy by resonance energy transfer to a specific chlorophyll pair in the reaction center of the photosystems. Because of function of the vast majority of chlorophyll (up to several hundred per photosystem) is to absorb light and transfer that light chlorophyll’s selectivity regarding the wavelength of light it absorbs, areas of a leaf containing the molecule will appear green. When a leaf was tested using iodine, only the green areas were shown as positive for starch, meaning that photosynthesis will not occur without chlorophyll.