Light-dependant stage

Question 1

What is the light-dependant stage?

Answer 1

• E from sunlight absorbed and used to form ATP
  
  • add a phosphate groups to form ATP, and to reduce NADP
• hydrogen from water used to reduce coenzyme NADP to reduced NADP
• water oxidised

Question 2

What is the difference between cyclic and non-cylic photophosphorylation?

Answer 2

• cyclic
  
  • electrons leaving the electron transport chain after PSI can be returned to PSI instead of being used to form reduced NADP
  • leads to production of ATP w/o any electrons being supplied from PSII
  • reduced NADP not produced when this happens

Question 3

What happens as light is aborbed in photosysten II?

Answer 3

• excited electrons are released from the reaction centre of PSII
• passed to an electron transport chain
• ATP produced by the process of chemiosmosis

Question 4

What happens at PSI?

Answer 4

• excited electrons released from reaction centre at PS1
  
  • passed to another electron transport chain
• ATP produced by chemiosmosis
• electrons leaving the electron transsport chain are accepted along with H+ by the coenzyme NADP
• forming reduced NADP

Question 5

Why is reduced NADP important?

Answer 5

• Provides the hydrogen or reducing power in the production of organic molc such as glucose in light-independant stage which follows

Question 6

WHat is photolysis/

Answer 6

• splitting H₂O into:
  
  • O₂
  • H⁺
  • e^-
• using energy from the sun

Question 7

How are the electrons replaced in PSI and PSII

Answer 7

• PSI
  
  • electrons replaced by those travelled along the transport chain from PSII
• PSII
  
  • electron released due to photolusis used to replace those lost in the reaction centre
  • this is why water is a raw material for photosynthesis

Question 8

What happens to the rest of the products of photolysis?

Answer 8

• O2 released as a by-product
• protons released into lumen of the thylakoid
  
  • increasing proton conc across the membrane
  • drive formation of ATP as they move down an electrochemical gradient

Question 9

What happens the the H+ returns to the stroma?

Answer 9

• combine with NADP and an electron from PSI to form reduced NADP
• removes H+ from stroma to maintain conc gradient

Question 10

What is the oxygen-evolving complex?

Answer 10

• forms part of PSII
• catalyses break down of water
• using energy released by transport chain

Question 11

Where does the light–dependant reaction take place?

Answer 11

thylakoid membranes

Question 12

What is NADP?

Answer 12

• transfers hydrogen and electrons to other molecules