why do plants need more than one pigment for light absorption?
Pigments are molecules with an array of covalent bonds capable of absorbing a photon of light that has only a certain wavelength. The absorbed wavelength is only a fraction of the continuous range of wavelengths reaching the reaction center of a chloroplast. Each pigment species absorbs a different portion of the spectrum. So most photosynthesis works in combinations of pigments to absorb a across the visible spectrum and somewhat beyond. Some pigments (accessory photosynthesis carotenoid pigments) absorb useful wavelengths to pass the energy to chlorophyll A while the Xanthophyll Cycle pigments absorb potentially harmful high energy wavelengths for dissipation. Accessory pigments provide a range of spectra collection that allowed plants to adapt successfully to environments of differing light conditions. Pigments provide coloration to signal flower or fruit maturity to pollination partners or seed dispersal partners. Anthocyanins and carotenoids perform these communication functions. Phytochrome is a pigment that absorbs one wavelength only to toggle to another shape capable of absorbing at a different wavelength. Algae and plants both use this system to inform them of the time of year so they can synchronize with the best season in their habitat for reproduction efforts to succeed. Plants use phytochrome to regulate the photoperiod of flowering or seed germination.
