The light dependent and light independent stages- Photosynthesis

Question 1

Where does the LDR occur?

Answer 1

• in the thylakoid membrane

Question 2

What is photophosphorilation?

Answer 2

• process where light energy is used to produce ATP, either cyclic or non-cyclic

Question 3

Explain non-cyclic photophosphorylation:

Answer 3

• At PS2, light energy is absorbed which excites electrons and causes them to enter electron transport chain–> electrons lost are replaced by photolysis
• This releases energy which helps ATP formation via chemiosmosis
• At the same time, light energy excites electrons in PS1, causes them to enter electron transport chain (also releasing energy for ATP production)
• These electrons bind, along with H+ IONS, TO NADP+ to form reduced NADP. —-> this then passes to the stroma where it is used in the LIR

Question 4

What is photolysis (include an equation)?

Answer 4

2 H20——> 4H + 02
, releases 4H+ and 4e-

Used to replace e- lost from PS2

This also releases protons into thylakoid lumen which increases proton conc of membrane, movement of these protons down conc gradient to stroma results in ATP formation

Question 5

What is cyclic photophosphorylation?

Answer 5

• The excited electrons that leave PS1 move through electron transport chain
• they then come back to the chlorophyll molecule they were lost from

—-> there’s no photolysis of water or generation of NADPH involved

• A small amount of ATP is made due to energy released as electrons travel through electron transport chains, this ATP can then be used in LIR

Question 6

Where does the light independent reaction take place?

what are the 3 processes involved?

Answer 6

• in the stroma
• FIXATION, REDUCTION, REGENERATION

Question 7

Explain the 1st step of the Calvin cycle

And what enzyme catalyses this?

Answer 7

• Atmospheric C02 forms 1 carbon atom, which binds with RuBP 95 carbon molecule) to form an unstable intermediate (6 carbon chain)
• Catalysed by RuBisCO

Question 8

Explain the second step of the Calvin cycle

Answer 8

• 6 carbon intermediate splits to form 2 GP molecules (each with 3 Carbons)

Question 9

Explain the 3rd step of the Calvin cycle.

Answer 9

• GP molecules are reduced to form 2 TP molecules (each with 3 carbons)
• Use the Hydrogen atom from reduced NADP and energy from ATP for this to happen

Question 10

Explain the 4th step of Calvin cycle (what happens to TP?)

Answer 10

• TP can do 2 things:
• Form large organic molecules like lipids, glucose and amino acids
• Can REGENERATE RuBP so that the Calvin cycle can continue ( 5 of every 6 TP molecules are regenerated to RuBP)