Photosynthesis

Generically, the biological process of photosynthesis captures the energy of the photons in sunlight and through a series of reactions transforms it into the biochemical energy needed to perform the cellular work that maintains a living organism. Nearly all living systems on Earth depend directly or indirectly on photosynthesis, and for us humans it provides essentially all of our food and the bulk of our energy resources.

In the prototypical form of the biological process of photosynthesis in green plants, the leaves capture energy from the photons in sunlight and use that captured energy as the essential primary energy source to drive a set of biochemical reactions that converts carbon dioxide (CO₂) and water (H₂) to oxygen (O₂) and a carbohydrate compound, the sugar, glucose (C₆H₁₂). The process effectively stores energy in the sugar molecule that the photosynthetic organism can metabolize to generate adenosine triphosphate (ATP), the universal energy currency of cells, so-called because it can provide the energy needed to drive biochemical reactions necessary to synthesize the nutrients required to maintain the cell in a living state. Photosynthesizing cells thus convert light energy to the life-sustaining chemical energy that drives cellular processes.

Organisms that photosynthesize, functioning as autotrophs — organisms that generate their own source of food-energy — with their photon-energy-derived complement of carbohydrates, proteins and lipids, directly provide a source of food-energy (e.g., vegetables, fruits) for consumption by us humans and other organisms, so-called heterotrophs — organisms that feed on other organisms or their components — and indirectly provide a source of food-energy in the form of the non-human heterotrophs that we consume (e.g., chickens, fish). Photosynthesizing cells also supply the oxygen we need to generate our own ATP, and they consume the 'waste' CO₂ produced in the process of generating ATP.

This article will classify the differing types of photosynthesizing organisms, and describe the details of the differing photosynthetic mechanisms employed by them. It will also discuss the implications of photosynthesis in the sciences of biology, geology, oceanography, climatology, and other areas of importance to the life of planet Earth.

Preliminarily, the reader might refer to the following: