Explain the process of light dependent stage of photosynthesis and state the products formed.
- Photoionisation: Chlorophyll in photosystem II absorbs light energy which excites electrons to a higher energy level, releasing them from chlorophyll.2) Some energy from electrons released during photoionisation is conserved in the production of ATP and reduced NADP.3) Photolysis: splitting of water using light energy. Produces protons, electrons and oxygen (2H2O → O2 + 4e- + 4H+). 4) Production of ATP: Electrons pass down electron transfer chain (electron carriers) from PSII to PSI via redox reactions, losing energy at each step. This energy is used to actively transport protons from stroma into thylakoid, creating a proton / electrochemical gradient across the thylakoid membrane (higher in thylakoid than stroma). Protons move by facilitated diffusion down the electrochemical gradient into the stroma via the enzyme ATP synthase embedded in the thylakoid membrane. Energy from this allows ADP + Pi → ATP (photophosphorylation) This is called the chemiosmotic theory.5) Production of reduced NADP: In PSI electrons are excited and transferred to NADP (with a proton from photolysis) to reduce NADP to form reduced NADP.
