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Light Reactions of Photosynthesis definitions

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  • Thylakoid
    Green, pancake-shaped structure inside chloroplasts where the light reactions and related processes occur.
  • Chloroplast
    Organelle in plant cells housing thylakoids and stroma, serving as the site for photosynthesis.
  • Photosystem II
    Light-harvesting complex that initiates the light reactions by absorbing photons and energizing electrons from water.
  • Photosystem I
    Light-harvesting complex that re-energizes electrons with photons, enabling their transfer to NADP+.
  • Electron Transport Chain
    Series of molecules in the thylakoid membrane that shuttle electrons, creating a proton gradient for ATP synthesis.
  • Photon
    Unit of solar energy absorbed by photosystems to energize electrons during the light reactions.
  • NADP+
    Final electron acceptor in the light reactions, reduced to a high-energy electron carrier used in the Calvin Cycle.
  • NADPH
    Electron carrier formed by the reduction of NADP+, transporting energized electrons to the Calvin Cycle.
  • ATP
    Molecule produced during chemiosmosis, providing chemical energy for the Calvin Cycle.
  • Chemiosmosis
    Process using a proton gradient across the thylakoid membrane to drive ATP synthesis via ATP synthase.
  • ATP Synthase
    Enzyme embedded in the thylakoid membrane that synthesizes ATP as protons flow through it.
  • Oxygen
    Byproduct released when water molecules are split during the light reactions, often exiting through leaf stomata.
  • Stroma
    Fluid-filled region surrounding thylakoids in chloroplasts, where the Calvin Cycle takes place.
  • Proton Gradient
    Difference in hydrogen ion concentration across the thylakoid membrane, essential for ATP production.
  • Calvin Cycle
    Second stage of photosynthesis that uses ATP and NADPH from the light reactions to fix carbon.