1. Light-Dependent Reactions:
* Photosystem II (PSII):
* Light energy excites electrons in chlorophyll molecules within PSII.
* These energized electrons are passed to an electron acceptor.
* Water molecules are split, releasing oxygen as a byproduct.
* Electron Transport Chain:
* The excited electrons travel through a series of electron carriers.
* This movement releases energy, which is used to pump protons (H+) across the thylakoid membrane, creating a proton gradient.
* Photosystem I (PSI):
* Electrons reach PSI and are re-energized by light.
* These energized electrons are passed to another electron acceptor, NADP+, which is reduced to NADPH.
2. Light-Independent Reactions (Calvin Cycle):
* Carbon Fixation:
* The Calvin cycle begins with the enzyme RuBisCo capturing carbon dioxide from the atmosphere and attaching it to a 5-carbon sugar (RuBP).
* This forms an unstable 6-carbon molecule that quickly breaks down into two 3-carbon molecules.
* Reduction:
* Using the energy from ATP and the reducing power of NADPH, these 3-carbon molecules are converted into a 3-carbon sugar (glyceraldehyde-3-phosphate).
* Regeneration:
* Some of the 3-carbon sugars are used to regenerate RuBP, which allows the cycle to continue.
Key Points:
* Electron flow starts at PSII and ends at PSI.
* Energy from light is used to move electrons through the electron transport chain.
* The energy released during electron transport is used to create a proton gradient that drives ATP synthesis.
* NADPH is produced at PSI and used to reduce carbon dioxide in the Calvin cycle.
Let me know if you have any other questions about photosynthesis!
