It is through photosynthesis that Earth's biosphere derives its energy from sunlight. Photosynthetic organisms—plants, algae and photosynthetic bacteria—have developed efficient systems to harvest the light of the Sun and to use its energy to drive their metabolic reactions, such as the reduction of carbon dioxide to sugar. The ubiquitous green color of plants is testimony to the key molecular participant in the light harvesting of plants, chlorophyll. More hidden in this respect, but no less widespread, is a second participating molecule, carotenoid. In green leaves, the color of the carotenoids is masked by the much more abundant chlorophylls, whereas in ripe tomatoes or the petals of yellow flowers, the carotenoids predominate. Chlorophyll molecules exist in slightly different chemical structures in various photosynthetic organisms, as chlorophyll a or b in plants or algae, and as bacteriochlorophyll a or b in photosynthetic bacteria. Molecules such as chlorophyll and carotenoid that absorb light and impart color to living matter and other materials are called pigments.
Skip Nav Destination
Article navigation
August 1997
August 01 1997
How Nature Harvests Sunlight
Specialized molecular aggregates in purple bacteria exploit subtle quantum physics to collect and convert light energy for photosynthesis.
Physics Today 50 (8), 28–34 (1997);