1. Light Energy: This is the primary input for the light-dependent reactions. It is absorbed by chlorophyll and other pigments in the chloroplasts.
2. Water (H2O): Water is split into its components, providing electrons and protons (H+ ions).
3. Photosystems (PSI and PSII): These are complexes of proteins and pigments in the thylakoid membrane of chloroplasts. They capture light energy and use it to excite electrons.
4. Electron Transport Chain: A series of electron carriers embedded in the thylakoid membrane. They transfer excited electrons, releasing energy along the way.
5. ATP Synthase: This enzyme uses the proton gradient created by the electron transport chain to produce ATP (adenosine triphosphate), the energy currency of the cell.
6. NADP+: This molecule acts as an electron carrier, accepting electrons from the electron transport chain and becoming NADPH. NADPH is a reducing agent that will be used in the Calvin cycle.
Here's a summary of the key steps involved:
1. Light Absorption: Light energy is absorbed by chlorophyll and other pigments in photosystems I and II.
2. Electron Excitation: This energy excites electrons in the pigments, which are then passed along the electron transport chain.
3. Water Splitting: Photosystem II uses light energy to split water molecules into oxygen, hydrogen ions (H+), and electrons.
4. Electron Transport: Excited electrons move along the electron transport chain, releasing energy and pumping H+ ions into the thylakoid lumen.
5. ATP Production: The proton gradient created by the electron transport chain drives ATP synthase to produce ATP.
6. NADPH Production: Photosystem I uses light energy to energize electrons, which are then transferred to NADP+ to form NADPH.
In essence, the light-dependent reactions convert light energy into chemical energy in the form of ATP and NADPH, which are used in the Calvin cycle (light-independent reactions) to fix carbon dioxide and produce sugar.
