Photosystem
A photosystem is a complex of proteins and Pigments found in the Thylakoid Membrane of chloroplasts that plays a crucial role in the Light-Dependent Reactions of Photosynthesis. Photosystems absorb light energy, which is then used to excite electrons, initiating the process of energy conversion into chemical forms. There are two main types of photosystems:
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Photosystem II (PSII):
- PSII is the first photosystem in the Light-Dependent Reactions. It absorbs light at a wavelength of 680 nm and excites electrons, which are then passed down the Electron Transport Chain (ETC).
- This process involves the splitting of water molecules (Photolysis) to replenish the lost electrons, producing Oxygen as a Byproduct. The energy released during electron transfer helps establish a Proton Gradient used to generate ATP through Photophosphorylation.
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Photosystem I (PSI):
- PSI absorbs light at a wavelength of 700 nm and is responsible for the reduction of NADP+ to NADPH, which is essential for the Calvin Cycle.
- The excited electrons from PSI travel through another part of the Electron Transport Chain and are transferred to NADP+, forming NADPH, which provides the reducing power needed for Carbon Fixation in the dark reactions.
2 Main Components:
Light Harvesting Complex or Antenna Complex
- Directly absorbs photons
- Energy transferred via resonance energy transfer
Reaction Center
Together, PSII and PSI work in tandem to convert light energy into ATP and NADPH, which are required for the synthesis of sugars during the Calvin Cycle.