In plants, these proteins are held inside organelles called chloroplasts, which are most abundant in leaf cells, while in bacteria they are embedded in the plasma membrane.
In most cases, oxygen is also released as a waste product.
Most plants, most algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs.
Photosynthesis maintains atmospheric oxygen levels and supplies all of the organic compounds and most of the energy necessary for life on Earth.
Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centres that contain green chlorophyll pigments.
In the Calvin cycle, atmospheric carbon dioxide is incorporated into already existing organic carbon compounds, such as ribulose bisphosphate (Ru BP).
Using the ATP and NADPH produced by the light-dependent reactions, the resulting compounds are then reduced and removed to form further carbohydrates, such as glucose.
The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen or hydrogen sulfide, rather than water, as sources of electrons.
Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and terrestrial vegetation.
Dark red and blue-green indicate regions of high photosynthetic activity in ocean and land respectively.