Photosynthesis

Photosynthesis is a process used by plants, algae, and certain bacteria to harness energy from sunlight into chemical energy. There are two types of photosynthetic processes: oxygenic photosynthesis and anoxygenic photosynthesis. The general principles of anoxygenic and oxygenic photosynthesis are very similar, but oxygenic photosynthesis is the most common and is seen in plants, algae and cyanobacteria.

Overview

Photosynthesis maintains atmospheric oxygen levels and supplies most of the energy necessary for life on Earth. However, it is not just about energy. The process also creates the biomass that makes up the organisms in the biosphere.

Process

Photosynthesis occurs in two stages. In the first stage, light-dependent reactions capture the energy of light and use it to make high-energy molecules. In the second stage, the light-independent reactions use these products to capture and reduce carbon dioxide.

Light-dependent reactions

In the light-dependent reactions, one molecule of the pigment chlorophyll absorbs one photon and loses one electron. This electron is passed to a modified form of chlorophyll called pheophytin, which passes the electron to a quinone molecule, starting the flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP to NADPH.

Light-independent reactions

In the light-independent or "dark" reactions, the enzyme RuBisCO captures CO2 from the atmosphere and, in a process called the Calvin cycle, it uses the newly formed NADPH and releases three-carbon sugars, which are later combined to form sucrose and starch.

Factors affecting photosynthesis

Several factors affect the rate of photosynthesis including light intensity, carbon dioxide concentration, temperature, and the availability of water.

Importance

Photosynthesis is essential for life on Earth. As well as maintaining the normal level of oxygen in the atmosphere, nearly all life either directly or indirectly depends on it for nourishment.

See also

• Chloroplast
• Light-dependent reactions
• Calvin cycle
• Carbon fixation
• Photorespiration
• Chemosynthesis

References

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