Light dependent reaction - Photosynthesis

• Light energy is absorbed by chlorophyll molecules in the chloroplast, exciting electrons in these molecules which are emitted from the molecules in a process called photoionisation
• Lost "high-energy" electrons move along carriers of an electron transfer chain in the thylakoid membranes of the chloroplast, releasing energy as they go
• The released energy is used to actively pump protons from the stroma into the thylakoid space against the proton electrochemical gradient
• Protons then move back to the stroma through a channel in an enzyme called ATP synthase by facilitated diffusion, providing energy for ATP synthesis from ADP and Pi in a process called chemiosmosis
• Electrons are used to reduce a molecule called NADP, requiring protons from the stroma
• Water is split by photolysis at the start of the process, producing three products:

  • Electrons from this process replace those lost by chlorophyll
  • Oxygen diffuses out of the plant as a waste product
  • Protons may contribute to chemiosmosis or be used to reduce NADP