Photosynthesis

• Light independent stage

  NADPH+ATP+CO2= glucose
• Light dependent stage

  H2O+light= O2+ATP+NADPH
• NADP= a coenzyme molecule that becomes reduced to form NADPH
• Chlorophyll

  = Pigment molecules absorb specific wavelengths of light and reflect others.

  • Different pigments absorb and reflect different wavelengths
  • The primary pigment is chlorophyll, it mainly absorbs red and blue light and reflects green light
• Photosystem

  • Reaction centre (primary pigments like chlorophyll a) is surrounded by the antenna complex (secondary pigments like chlorophyll b, xanthophylls, carotenoids.)
  • The role of the system is to absorb light energy at different wavelength and transfer this energy quickly and efficiently to the reaction centre.
• Where does the light dependent stage occur

  Thylakoid membrane
• Where does the light independent stage occur

  Stroma
• Light dependent stage

  Non-cyclic photophosphorylation

  • Light absorbed excites electrons at the reaction centre of the photosystem. The electrons are released from reaction centre of PS2 and are passed to an electron transport chain. Energy is released.
  • Excited electrons released from PS2 are used to replace those lost from PS1.
  • Electrons lost from PS2 are replaced from water molecules during photolysis.
  • Electrons leaving electrons transport chain following PS1 are accepted along with a hydrogen ion by NADP to form NADPH.
• Cyclic photophosphorylation

  • The electrons leaving the electron transport chain after PS1 can be returned to PS1, instead of being used to form NADPH.
• Photolysis

  • Water molecules are split into hydrogen ions, electrons and oxygen molecules using energy from the sun.
  • The electrons are used to replace those lost from the reaction centre of PS2.
  • Oxygen and hydrogen are released.
• Chemiosmotic theory

  • Hydrogen ions from photolysis are actively transported into the thylakoid using energy from the electron transport chain.
  • A high concentration of hydrogen ions inside the thylakoid causes hydrogen ions to diffuse out through an ATP synthase channel.
  • ATP synthase catalyses the phosphorylation of ADP+Pi= ATP
  • Hydrogen ions bind to NADP to produce NADPH.
• Calvin cycle- light independent reaction

  • Carbon dioxide is combined with a 5-carbon molecule called RuBP, this reaction is catalysed by the enzyme RuBisCO.
  • The carbon is fixed forming a 6 carbon molecule which is quickly broken down into two 3-carbon molecules called GP.
  • GP is converted into TP by the addition of hydrogen from NADPH using energy from ATP (2 lots are needed)
  • 5/6 is recycled back into RuBP and the rest is used to make glucose, lipid and amino acids.