Plants use chlorophyll, a green pigment responsible for the color of most plants, to absorb light and produce usable chemical energy through photosynthesis. Carbohydrate molecules are created from water and carbon dioxide store in order to store the chemical energy. During this process, oxygen is usually released.
Chloroplasts are cellular organelles that hold specialized proteins called reaction centers. The reaction centers in turn contain chlorophyll pigments. In plants, most chloroplasts are contained in the leaf cells, while in bacteria they are located within the plasma membrane. Additional compounds are created by photosynthesis, including nicotinamide adenine dinucleotide phosphate and adenosine triphosphate. These compounds are involved in energy transfer. Algae also use chlorophyll, but many species are reliant on other pigments, which give algae colors other than green.
It is believed that some of the earliest forms of life on Earth were photosynthetic. The earliest photosynthetic organisms likely used hydrogen or hydrogen sulfide instead of water for the electron donation that is essential in photosynthesis. Cyanobacteria are hypothesized to have contributed the bulk of the oxygen in early history, making it possible for complex life to evolve. Photosynthetic organisms produce approximately six times more energy than all of human civilization annually. Around 100 to 115 million tons of carbon are also converted into biomass per year by these organisms.