Light Reactions

• Important steps in overall light reaction

  • Transfer of electrons
  • Generation of ATP
• Photosynthetic transfer of electron from H2O to NADP+ which occurs in the thylakoid membrane

  Light reaction phase
• 4 supramolecular membrane complex

  • Photosystem 1
  • Photosystem 2
  • Cytochrome b6/f
  • ATP synthase
• T or F: Photosystem 2 can perform photochemical reactions independently of Photosystem 1

  True
• T or F: in the z-scheme, molecules at the top of the scale have a higher tendency to extract electrons from neighboring compounds whereas those at the bottom have a higher tendency to give off electrons

  False
• T or F: Photosystem 2 also increases the proton gradient between the stroma and the lumen during electron transfer

  True
• T or F: Upon absorption of light energy. P680 becomes a strong oxidizing agent that is capable of oxidizing water

  False
• T or F: The significance of cytochrome b6f complex is to obligately couple electron flow with proton movement

  True
• T or F: P700+ reduces ferredoxin which eventually reduces NADP+ to NADPH with the help of the enzyme FNR

  False
• T or F: NADPH is the final electron acceptor during noncyclic electron flow

  False
• T or F: Photoinhibition occurs when the rate of damage by excess light exceeds the rate of repair of photosynthetic machinery

  True
• The majority of the chlorophyll pigment is found in the antenna complex of photosystems
• Molecules with a more positive redox potential are more?

  Oxidizing
• Pigment tat generally absorb longer wavelengths are found nearer the reaction center
• A more oxidized plastoquinone pool acts as a signal to slow down the rate of the reactions in PS1
• Water is oxidized after PS2 performs 4 photochemical reactions
• During photophosphorylation, ATP synthase moves protons into the stroma
• When there is a high NADPH/NADP+ ratio in the chloroplast, the rate of cyclic electron flow increases
• Light-harvesting unit in the thylakoid membrane

  Photosystem
• Contain large numbers of specifically bound chlorophyll molecules and other co-factors

  Photosystem
• Harvest light and independently evolve O2 (PS2/PS1) and reduce NADP+ (PS2/PS1)

  PS2 & PS1
• Photosystem consists of reaction center, light harvesting complex, and primary electron acceptor
• It is the minimum unit where photochemical reactions takes place

  Reaction center
• Light harvesting complex is also known as antenna complex
• T or F: the difference in the structure of PS1 and PS2 is that the latter has water oxidation complex

  True
• T or F: Primary electron acceptor of PS1 is A0

  True
• T or F: Primary electron acceptor of PS2 is pheophytin
• T or F: LHC of PS1 is 250 CHl a+b (1:1)

  False
• T or F: LHC of PS1 is 100 Chl a+b (4:1)

  True
• T or F: PS1 and PS2 are spatially separated

  True
• Collects light and transfers the energy to the reaction center complex

  Antenna Complex
• it is the process of energy transfer in the antenna complex

  resonance transfer
• T or F: Efficiency of energy transfer depends on the distance and orientation

  True
• T or F: Resonance transfer has 95%-99% efficiency rate which is explained by the red shift theory wherein high requiring energy pigments found near RC while those low energy pigments are found at the outer parts

  False
• T or F: Resonance transfer is purely physical

  True
• T or F: Red shift explains the resonance transfer's no backflow in the energy transfer

  True
• T or F: Reaction center contains a special pair

  True
• Where the chemical oxidation and reduction reactions leading to long-term energy storage take place

  Reaction center
• T or F: the reason why the electron carrier is farm from the special pair in RC is to prevent the reuptake of energy that is why transferring of electrons to the thylakoid membrane need to be quick

  true
• T or F: P680 is very important oxidizing agent since it is capable of drawing electrons from water which is super stable

  True