photosynthesis

• What is the structure of a chloroplast?

  • Double membrane
  • stroma (fluid where Calvin cycle occurs)
  • Thylakoid (discs with chlorophyll + site of light dependant)
  • Grana/granum (stacks of thylakoids)
  • lamellae (membranes linking grana)
  • DNA + ribosomes
• what are the 4 stages of the light dependant reaction?

  • photolysis
  • photoionization
  • chemiosmosis
  • ATP + NADPH production
• What happens during photolysis?

  • Light energy absorbed by chlorophyll in thylakoid splits water
  • H2O→ ½O2 + 2e- + 2H+
  • Hydrogen ions form NADPH from NADP
  • Electrons replace electrons lost from chlorophyll in photoionization
• What happens in photoionization of chlorophyll?

  • Light energy is absorbed by chlorophyll in PS2 and excites the electrons
  • electrons move down the thylakoid membrane by a series of redox reactions with proteins releasing energy, this is called the electron transport chain
• what happens in chemiosmosis?

  • Energy released form the electron transport chain actively transports hydrogen ions from the stroma into the thylakoid
  • This causes a high electrochemical gradient of hydrogen ions in the thylakoid so they move out by facilitated diffusion across the ATP synthase protein into the stroma
• What happens in NADPH + ATP production?

  • The movement of hydrogen ions across ATP synthase initiates the production of ATP by photophosphorylation
  • NADP combines with hydrogen ions in the stroma and electrons from the electron transport chain to from NADPH
• Where does the Calvin cycle occur?

  • In the stroma a chloroplast
• Where does the light dependent reaction occur?

  • In the thylakoid membranes of a chloroplast
• What happens in the Calvin cycle?

  • 1C carbon dioxide combines with 5C RUBP to make 6C compound
  • 6C compound splits into 2 lots of 3C GP catalysed by rubisco
  • 3C GP is reduced into 3C TP by NADPH and energy from ATP
  • 2 lots of 3C TP can help form a hexose sugar by donating a carbon and leave a 2C compound and a 3C compound
  • ATP will provide the energy to help to regenerate RUBP
  • This happens 6 times to donate 6 carbons to make a hexose sugar, starch etc
• what are the 3 limiting factors of photosynthesis?

  • light intensity
  • Carbon dioxide concentration
  • temperature