Photosynthesis

Adaptations of Chloroplast

  • Grana has a large surface area for the attachment of chlorophyll, electrons and enzymes

  • Granal membrane has ATP synthase channels and are selectively permeale so a proton gradient can be formed and ATP can be synthesised

  • Chloroplasts contain DNA and ribosomes allowing them to synthesise proteins needed in the light dependent reaction

Light Dependent Reaction

  1. Photoionisation: Light hits chlorophyll molecules in PSII, exciting electrons

  2. Photolysis of water: H2O β†’ 2H+ + 2e- + 0.5O2

  3. Electron transport chain (E.T.C.): Excited electrons move from chlorophyll in PSII to PSI

  4. Active transport of H+ ions: H+ ions are actively transported from the stroma to the thylakoid membrane

  5. Chemiosmosis: H+ ions diffuse back into the stroma via ATP synthase channels, forming ATP from ADP ad Pi

  6. NADP is reduced: Acting as the final electron acceptor of the E.T.C., NADP is reduced to NADPH (NADP + H+ + e- β†’ NADPH)

Light Independent Reaction (Calvin Cycle)

  1. CO2 is added to a 5C ribulose biphosphate (RuBP) using rubisco enzym

  2. RuBP splits into 2 3C glycerate-3-phosphate molecules (GP)

  3. Each GP molecule is reduced to a 3C triose phosphate (TP) using energy from ATP hydrolysis and oxidation of NADPH

  4. The 2 TP molecules re-form RuBP. One C is kept for forming organic molecules

  5. Every 6 turns, 1 glucose molecule is formed

Order of compounds in Calvin cycle: RuBP β†’ GP β†’ TP β†’ RuBP