Photosynthesis Process

Study Notes

Photosynthesis is a system of biological processes that convert light energy into chemical energy necessary for organisms to fuel their activities.
Photosynthetic organisms, such as plants, algae, and cyanobacteria, store chemical energy in organic compounds like sugars, glycogen, cellulose, and starches.
Oxygenic photosynthesis produces oxygen and is the most common type of photosynthesis.

Anoxygenic photosynthesis uses bacteriochlorophyll to split hydrogen sulfide, producing sulfur instead of oxygen.
Archaea, such as Halobacterium, perform a type of non-carbon-fixing anoxygenic photosynthesis, using retinal and its derivatives to absorb green light and produce ATP.

Light energy is absorbed by reaction centers, proteins that contain photosynthetic pigments or chromophores.
In plants, these proteins are chlorophylls, held inside chloroplasts, abundant in leaf cells.
In bacteria, they are embedded in the plasma membrane.
Light-dependent reactions strip electrons from suitable substances, such as water, producing oxygen gas.
Hydrogen freed by the splitting of water is used to create NADPH and ATP.
In plants, algae, and cyanobacteria, sugars are synthesized by the Calvin cycle, incorporating atmospheric carbon dioxide into existing organic carbon compounds.

Photosynthesis plays a critical role in producing and maintaining the oxygen content of the Earth's atmosphere.
It supplies most of the biological energy necessary for complex life on Earth.
The average rate of energy captured by photosynthesis globally is approximately 130 terawatts.
Photosynthetic organisms convert around 100–115 billion tons of carbon into biomass per year.
Photosynthesis is vital for climate processes, capturing carbon dioxide from the air and binding it in plants, harvested products, and soil.

Photosynthesis was first discovered in 1779 by Jan Ingenhousz.
He showed that plants need light, not just air, soil, and water.
Cyanobacteria appeared later, contributing to the oxygenation of the Earth, which rendered the evolution of complex life possible.