Photosynthesis

• Chloroplast structure

  
• Thylakoid membrane


  folded membranes which contain photosynthetic proteins (chlorophyll) and electron carrier proteins are embedded within these membranes which are both involved in LDR
• Stroma


  Fluid centre which contains enzymes involved in the LIR
• inner and outer membrane

  control what can enter and leave the organelle (think plasma membranes)
• Chlorophyll

  • located in the photosystems on the thylakoid membrane + mix of coloured proteins that can absorb light.
  • there are 5 types of closely related
• what colour is chlorophyll a?

  blue/green
• what colour is chlorophyll b?

  yellow/green
• what colour is carotenoids?

  orange
• what colour is xanthophylls?

  yellow
• what colour phaeophytins?


  grey
• Chlorophyll -

  • the different proportions of each pigment in leaves which gives leaves slightly different colours due to the amount of light energy absorbed
• • chlorophyll b, xanthophyll's, phaeophytin's and carotenoids embedded within the thylakoid membrane and form a light harvesting system
  • light harvesting system is where light energy of different wavelengths is absorbed this is then transferred to the reaction centre
  • reaction centre contains chlorophyll a and is where light dependent reaction occur . The light harvesting system and the reaction centre make up a photosystem
• what are the four key stages of the light dependent reaction?

  • non cyclic phosphorylation
  • cyclic phosphorylation
  • photolysis
  • chemiosmosis
• what happens in non-cyclic phosphorylation?

  • both photosystems (PS), PSI and PSII are involved
  • PSII is first used and it absorbs light at 700nm
  • PSI is then used and it absorbs light at 680nm
• • light energy absorbed causes electrons with reaction centres become excited + released
  • electron released from PSI and PSII move along electron transport chain (ETC)
  • electrons lost replaced by photolysis and the electrons are accepted by ETC from PSII
  • electrons are then accepted by the coenzyme NADP, this then makes reduced NADP
  • reduced NADP and ATP made and used in next stage of photosynthesis
• PSI + PSII

  
• what happens in cyclic photophosphorylation?

  • some electrons are released from PSI are not picked up by NADP instead are recycled back into PSI
  • transport of electrons still results in ATP production though chemiosmosis
  • cyclic photophosphorylation results in the production of ATP, but not the production of reduced NADP
• what happens in photolysis of water?

  • light energy is absorbed by chlorophyll and splits water into oxygen H+ and e-
  • h2O = 1/2 O2 + 2e- + 2H+
  • the H= is picked up by NADP to form NADPH and is used in the LIR
  • the e- are passed along a chain of electron carrier proteins
  • the oxygen = respiration or diffuses out of leaf through the stomata
• what happens in chemiosmosis?

  • electrons gained energy and left the chlorophyll move along proteins embedded within thylakoid membrane
  • they as they move along energy is released some electrons pump the proton across chloroplast
  • an electrochemical gradient is created enzyme ATP synthase creates ATP
• Light independent reaction is a cycle (Calvin cycle)

  • occurs in stroma contains the enzyme RuBisCo which catalyses reaction
  • temperature sensitive due to enzymes being involved
• Chemiosmosis

  
• what is used in the light-independent reaction?

  carbon dioxide, reduced NADP and ATP = hexose sugar
• Calvin cycle

  • CO2 reacts with RuBP to form 2 molecules of GP this is catalysed by Rubisco
  • GP is reduced to TP using ATP and accepting H+ from reduced NADP
  • some TP leaves to make useful organic substance (hexose)
  • the rest is used to regenerate RuBP with ATP energy
• Calvin cycle

  
• what are limiting factors for photosynthesis?

  Light intensity, temperature and carbon dioxide.