5) Energy Transfers In and Between Organisms

• Light dependant reaction takes place in the thylakoid membrane of the chloroplast
• Light independent reaction takes place in the stroma of the chloroplast
• The chloroplast contains a double membrane. The thylakoid membrane has stacks called grana which creates a large surface area which increases the number of light-dependent reactions that can take place
• Photoionisation, photophosphorylation and photolysis take place in the light dependant reaction
• In photoionisation, a chlorophyll molecule absorbs light energy, this boosts the energy of its electrons, raising them to a higher energy level

  The electrons become excited and are emitted from the chlorophyll molecule

  This causes the chlorophyll to become ionised
• In photophosphorylation, the excited electrons pass down the electron transfer chain in the thylakoid membranes. They lose energy as they move down the chain.

  
  

  This energy is used to make ATP in a process catalysed by ATP synthase in the chemiosmotic theory
• In photolysis light energy is used to split water

  Water → protons + electrons + oxygen

  Electrons – replace those lost by the chlorophyll molecule

  Oxygen is released into the atmosphere (or used in respiration),
• The electrons that were passed down the electron transfer chain, together with the protons from photolysis, are now finally picked up by an electron carrier called NADP, to become reduced NADP
• Light Independant Reaction

  RuBP → 2 gylycerate-3-phosphate (GP) → triosephosphate

  1/6 triosphosphate is converted to organic substances like glucose

  5/6 is regenerated into RuBP
• RuBP (5C) combines with CO2 from the air to form 2GP. This reaction is catalysed by a Rubisco catalyst

  RuBP + CO2 + rubisco catalyst → 2 gylycerate-3-phosphate (GP)
• GP is reduced to triosphosphate using reduced NADP and energy from ATP

  2GP + reduced NADP + energy from ATP → triosephosphate