light dependent and independent reactions

• State what happens generally in the light independent stage. Where does it take place?

  • Take place in the stroma
  • Enzymes are present, carbon dioxide is fixed
  • ATP and NADPH2 from light dependent reactions needed
• What is photolysis?

  • Splitting of water using light energy into two protons, two electrons and an oxygen atom
  • The electeons enter photo system two for photophosohorylation and replace the electrons lost from the reaction centre of photosystem II. They meet up with the protons at the end of this process to reduce NADP
• Describe what happens to the protons after photolysis

  • Protons pumped into thylakoid membranes
  • This increases proton conc across membrane
  • then they diffuse back out down electrochemical gradient, which drives formation of ATP (chemiosmosis)
  • Then hydrogen ions returned to stroma, combine with NADP and one electron (from transport chain in light dependent reaction) to form NADPH2, used in LIR
• describe the process of cyclic phosphorylation and state the differences between it and non cyclic

  • Electrons leaving transport chain after PS1 can be returned to PS1, instead of forming reduced NADP
  • PS1 can still lead to prodcution of ATP without using any new electrons supplied from PSII

  DIFFERENCES: in cyclic photophosphorylation-

  • reduced NADP not produced
  • produces smaller amounts of ATP
  • No photolysis
  • Only uses PS1
  • no oxygen produced- PSII produces oxygen
• true or false? chlorophyll B, xanthophils, carotenoids and other pigments absorb different wavelengths of light to chlorophyll A

  TRUE
• State what happens generally in the light dependent stage. Where does it take place?

  • Takes place in chloroplasts, in the thylakoid membranes
  • Chlorophyll embedded within thylakoids absorbs light, light is used to form ATP
  • Hydrogen from water (from photolysis) used to reduce NADP (NADPH2) using NADP reductase
  • oxygen is also produced
  • NADPH2 and ATP are needed for the light independent reaction
  • in this process cyclic and non-cyclic photophosphorylation take place

  
• State what happens generally in the light independent stage. Where does it take place?

  • Takes place in the stroma
  • Enzymes are present, carbon dioxide is fixed
  • ATP and NADPH2 from light dependent reactions needed to build organic molecules like glucose- ATP supplies the required energy for this

  
• true or false? the Calvin cycle is the light dependent reaction

  FALSE- it's the light independent reaction
• describe what happens during photophosphorylation (light dependent reaction)

  • Water splits during photolysis into two protons, two electrons and oxygen as a by product (1/2 O2)
  • Two electrons enter photosystem II and are taken up by electron carriers
  • electrons that leave reaction centre of photosystem two are replaced by further splitting of water molecules
  • Travel through electron transport chain and lose energy as they do so, energy which is used for chemiosmosis
  • light strikes photo system 1, it absorbs this light and electrons (the ones which had lost energy prior) get excited again and leave through another electron carrier, replaced in the reaction centre by electrons coming again from photosystem 2
  • Can enter cyclic or non cyclic photophosphorylation, in non cyclic- meet the protons in stroma and one electron and 2 protons reduce NADP using NADP reductase enzyme (oxygen also produced)

  
• describe the process of the Calvin cycle

  • carbon dioxide (1C compound) fixed with RuBP, enzyme rubisco is used to do this (RuBP = 5C, + 1C = 6C compound formed) this is called fixation
  • 6C intermediate is unstable so splits immediately into 2 GP molecules (3C each). GP molecules can be used to make amino acids and fatty acids
  • GP is converted or reduced to TP using a hydrogen atom from reduced NADP (NADPH2 -> NADPH) and hydrolysing ATP to ADP. this process is called reduction
  • TP is capable of making hexose sugars, amino acids and lipids
  • or RuBP is regenerated from TP by hydrolysis of another ATP molecule, ATP to ADP.
  • The cycle repeats with a continuous supply of ATP driving the energy for the reactions to take place
• state what energy sources the LDR and LIR use to carry out their respective processes

  • LDR- light energy from the sun
  • LIR- hydrolysis of ATP