photosynthesis

• the two stages of photosynthesis are light-dependent and light-independent reactions
• the first stage of photosynthesis is the light-dependent reaction and this consists of non-cyclic photophosphorylation, photolysis and cyclic photophosphorylation
• non-cyclic photophosphorylation

  1. light is absorbed at PS11 and excites the electrons, these electrons are then passed onto the electron transport chain which produces ATP trough chemiosmosis.
  2. excited electrons at PS1 are released and passed onto another electron transport chain which produces more ATP
  3. the electrons leaving the second electron transport chain are accepted with hydrogen by NADP
• electrons lost from PS11 are replaced by electrons from molecules broken down by the sun
• electrons lost from PS1 are replaced by electrons from the first electron transport chain
• photolysis

  1. water is split into hydrogen ions, electrons and oxygen using energy from the sun
  2. the oxygen protons are then released into the thylakoids and increase the proton concentration and as they move down the gradient they produce more ATP
• cyclic photophosphorylation is when the electrons from PS1 can be returned to PS1 and lead to more ATP produced meaning NADph isn't produced
• the second stage of photosynthesis is the light-independent reaction
• light-independent stage consists of the Calvin cycle
• Calvin cycle

  1. carbon dioxide enters the intracellular spaces with spongy mesophyll by diffusion
  2. carbon dioxide combines with ribose biphosphate (RuBp) and becomes fixed
  3. ribulose biphosphate carboxylase (RuBisco) catalyses the reaction and forms an unstable 6C molecule
  4. 6C is immediately broken down into 2 3C glycerate phosphate
  5. each GP molecule converts into triode phosphate using hydrogen ions from NADP and energy from ATP
  6. most TP can be converted into RuBp to carry on the Calvin cycle
  7. the rest of the TP can be used for lipids, amino acids and glucose
• for one glucose to be produced, 6C molecules have to enter which forms 12ATP and 2 are used for glucose. The remaining 10 ATP are recycled int 6 RuBp