Photosynthesis

• Where does photosynthesis take place?

  Chloroplast
• Where does the light dependent reaction take place?

  Thylakoid membrane
• Aims of the light dependent reaction

  -synthesise ATP

  -synthesise NADPH
• What is light energy used for in the light-dependent reactions?

  -split water (photolysis)

  -release oxygen

  -release H+

  -excite electrons
• Photoionisation of chlorophyll

  light energy is absorbed by chlorophyll and the energy excites electrons which leave, chlorophyll becomes ionised

  Some of the energy from the released electrons is used to make ATP + NADPH
• Photolysis of water

  Splitting of water

  H2O --> 2H+ + 2e- + 1/2 O2

  
• Chemiosmosis


  the electrons that left the photosystem move along a series of proteins embedded within the thylakoid membrane

  As they move along they release energy and some this energy is used to pump protons across chloroplast membranes
• Production of ATP

  H+ diffuse through facilitated diffusion down their gradient through the ATP synthase enzyme, changing its shape and producing ATP.

  ADP + Pi --> ATP
• Production of NADPH

  H+ is taken up with electrons by molecules of NADP, reducing it to NADPH

  NADP + H+ + e- --> NADPH
• How are ATP and NADPH used after the LDR

  They move to the stroma for the light-independent reaction
• Where does the light-independent reaction take place

  chloroplast stroma
• What does the LIR need?

  -CO2

  -ATP

  -NADPH
• what does the light independent reaction form?

  a hexose sugar
• Light Independent Reaction (Calvin Cycle)

  
• Carbon fixation

  CO2 binds to RuBP to form 2 molecules of GP, catalysed by the enzyme rubisco
• Reduction

  GP is reduced to form TP using energy from ATP and accepting a H+ from NADPH (ADP, Pi and NADP return to thylakoid membrane (LDR))
• Regeneration of RuBP


  most of the TP continues through a series of reactions to regenerate the RuBP and complete the cycle (needs ATP)
• Formation of glucose


  1 new TP molecule every 3 turns, 2 TP molecules for 1 hexose sugar, 6 turns for 1 hexose sugar
• Factors that limit the speed of photosynthesis

  -light intensity

  -carbon dioxide concentration

  -temperature

  -amount of chlorophyll
• To reduce the effects of limiting factors

  increase CO2 and temperature by burning a fuel

  increase light intensity through artificial lighting