Photosynthetic

Photosynthesis is a process used by plants and other organisms to convert light energy, usually from the sun, into chemical energy that can be later released to fuel the organisms' activities. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water.

Overview

Photosynthesis maintains atmospheric oxygen levels and supplies most of the energy necessary for life on Earth. However, it is not just confined to plants; many types of bacteria also perform photosynthesis. Photosynthesis is vital for life on Earth. As well as maintaining the normal level of oxygen in the atmosphere, nearly all life either depends on it directly as a source of energy, or indirectly as the ultimate source of the energy in their food.

Process

The process of photosynthesis provides the main input of free energy into the biosphere, and is one of four main ways in which radiation is important for plant life. The process of photosynthesis in plants involves a series of steps and reactions that use solar energy, water, and carbon dioxide to produce oxygen and complex carbohydrates.

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

There are three main factors affecting photosynthesis and several corollary factors. The three main are:

• Light intensity and wavelength
• Carbon dioxide concentration
• Temperature.

See also

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

References

Photosynthetic Resources
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