Fototrofie

Fototrofie is a metabolic strategy used by organisms to acquire energy. These organisms, known as phototrophs, harness light energy and convert it into chemical energy in the form of ATP through a process called photophosphorylation. This chemical energy is then used to fix inorganic carbon, typically carbon dioxide, into organic compounds, a process called carbon fixation. Therefore, phototrophs are autotrophs, meaning they can produce their own food.

There are two main types of phototrophy: oxygenic and anoxygenic. Oxygenic phototrophs, such as plants, algae, and cyanobacteria, use water as the electron donor and release oxygen as a byproduct. This process involves two photosystems, Photosystem I and Photosystem II, which work in tandem to absorb light energy and split water molecules. Anoxygenic phototrophs, found in bacteria like purple bacteria and green sulfur bacteria, do not produce oxygen. They utilize a wider range of electron donors, including hydrogen sulfide, sulfur, or organic molecules. These organisms typically possess only one photosystem.

The light-dependent reactions of phototrophy occur in specialized membrane structures within the cell, such as chloroplasts in eukaryotes or the cell membrane in prokaryotes. The light energy absorbed by pigments like chlorophyll excites electrons, which then flow through an electron transport chain, generating a proton gradient across the membrane. This gradient drives the synthesis of ATP by ATP synthase. The subsequent light-independent reactions, also known as the Calvin cycle, utilize this ATP and reducing power to convert carbon dioxide into sugars.