What is photosynthesis?


Photosynthesis is the process used by plants, algae and certain bacteria to turn sunlight, carbon dioxide (CO2) and water into food (sugars) and oxygen. Here's a look at the general principles of photosynthesis and related research to help develop clean fuels and sources of renewable energy.  

TYPES OF PHOTOSYNTHESIS

There are two types of photosynthetic processes: oxygenic photosynthesis and anoxygenic photosynthesis. They both follow very similar principles, but oxygenic photosynthesis is the most common and is seen in plants, algae and cyanobacteria. 

OXYGENIC

During oxygenic photosynthesis, light energy transfers electrons from water (H2O) taken up by plant roots to CO2 to produce carbohydrates. In this transfer, the CO2 is "reduced," or receives electrons, and the water is "oxidized," or loses electrons. Oxygen is produced along with carbohydrates.The process of oxygenic photosynthesis, in which solar energy is converted into chemical energy, underpins life on earth and is the principal producer of both oxygen and organic matter on earth.

ANOXYGENIC

The emergence of oxygenic photosynthesis created a new niche with dramatic potential to transform energy flow through Earth's biosphere. However, more primitive forms of photosynthesis that fix CO2 into biomass using electrons from reduced species like Fe(II) and H2 instead of water would have competed with Earth's early oxygenic biosphere for essential nutrients. Here, we combine experimental microbiology, genomic analyses, and Earth system modeling to demonstrate that competition for light and nutrients in the surface ocean between oxygenic phototrophs and Fe(II)-oxidizing, anoxygenic photosynthesizers (photoferrotrophs) translates into diminished global photosynthetic O2 release when the ocean interior is Fe(II)-rich. These results provide a simple ecophysiological mechanism for inhibiting atmospheric oxygenation during Earth's early history. We also find a novel positive feedback within the coupled C-P-O-Fe cycles that can lead to runaway planetary oxygenation as rising atmospheric pO2 sweeps the deep ocean of the ferrous iron substrate for photoferrotrophy