Photosynthesis

• Definition of photolysis.

  the splitting of a molecules using light energy
• Definition of photoionisation.


  When light energy excites electrons in an atom or molecules, giving them more energy and causing them to be released. The release of electrons causes the atom or molecule to become a positively charged ion.
• Definition of chemiosmosis.

  Using the flow of electrons down an electro-chemical gradient through ATP synthase to make ATP from ADP and Pi.
• What two main processes does photosynethesis have ?

  Light dependent reaction and Calvin cycle
• What is used in the LDR ?

  H2O, NADP, ADP, Pi
• What is produced in the LDR ?

  O2, NADPH, ATP
• What is used in the LIR ?

  CO2, ATP, NADPH
• What is produced in the LIR ?

  Glucose, NADP, ADP, PI
• What are the 3 main parts of LDR ?

  Photophosphorylation, Photolysis and Reduction of NADP
• What is the equation for photophosphorylation in LDR ?

  Light

  ADP + Pi -----> ATP

  Energy
• What is the equation for Photolysis in LDR ?

  light

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

  energy
• What is the equation for Reduction of NADP in LDR ?

  NADP + H+ + e- ---> NADPH
• Describe the process of the LDR. (steps 1 to 3)

  1. Chlorophyll absorbs the light energy, and a pair of electrons become photoexcited and leave the chlorophyll, leading to photoionisation of chlorophyll.
  2. The electrons released are transferred down the electron transport chain - a series of electron carrier proteins embedded in the thylakoid membrane using redox reactions.
  3. As the electrons are transferred down some of the energy is lost as heat, but some is used to actively pump protons from the stroma into the thylakoid lumen.
• Describe the process of LDR. (steps 4 to 6)

  
  

  4. The protons build up in the lumen causing an electrochemical gradient to form across the thylakoid membrane.

  
  

  5. The protons flow back into the stroma by facilitated diffusion through ATP synthase enzyme which also acts as a channel protein.

  
  

  6. The flow of protons through ATP synthase is used to make ATP from ADP + Pi (chemiosmosis). When ATP is made in this way it is called photophosphorylation (as the energy to make ATP originally came from light
• Describe the process of LDR. (steps 7 to 11)

  7. Chlorophyll contains an enzyme that splits water into protons, electrons and oxygen - This is called photolysis.

  8. The electrons released by photolysis replace those lost from the chlorophyll returning it to its original state.

  9. Oxygen is released as a waste product.

  10. The electrons which reach the end of the electron transport chain combine with the protons which have moved through the ATP synthase and a molecule NADP (oxidised co-enzyme) to form NADPH.

  11. NADP is the final electron acceptor in the LDR of photosynthesis.
• What colours does chlorophyll absorb ?

  red and blue light
• What colour does chlorophyll reflect ?

  green light
• What is the roles of a photosystem ?

  To absorb and harvest light energy at different wavelengths and transfer this energy to Chlorophyll.
• What is a photosynthetic pigment ?

  A pigment used in photosynthesis
• Give an example of a photosynthetic pigment ?

  Chlorophyll, carotene
• Where in the chloroplasts does the light dependent reaction take place ?

  thylokoid membrane
• What is photophosphorylation ?

  adding a phosphate group to a molecule with light
• What is the purpose of photolysis in the light-dependent reaction ?

  To replace electrons which have left chlorophyll and return it to its normal state.
• Electrons are transferred down the electron transport chain and ATP is produced. Explain how.

  Energy from the electrons moving down from the ETC is used to actively transport protons from the stroma into the thylakoid lumen. This forms an electrochemical proton gradient across the thylakoid membrane. Protons move down their concentration gradient, into the stroma, via an enzyme called ATP synthase. The energy from this movement combines ADP and Pi to form ATP = chemiosmosis . As the energy to phosphorylate ADP originally came from light, this process is known as photophosphorylation.