Photosynthesis

Question 1

what are the two stages of photosynthesis

Answer 1

• Light-dependent reaction (LDR)
• Light-independent reaction (LIR)

Question 2

describe properties of ATP (4)

Answer 2

• releases energy in small manageable amounts
• quickly hydrolysed and resynthesised
• energy is released immediately
• soluble in water where most reactions occur

Question 3

what are the products of the LDR

Answer 3

• ATP
• Reduced NADP (NADPH)
• Oxygen

Question 4

how is NADPH produced during the LDR

Answer 4

• light energy absorbed by chlorophyll causing photoionisation as electrons are released and raised to a higher energy level
• water is split via photolysis releasing electrons which replace the ones in the chlorophyll along with protons and oxygen
• electrons move down the electron transport chain towards the second chlorophyll releasing energy
• photoionisation occurs again at the second chlorophyll causing the electrons to move to a higher energy level and be accepted by NADP
• the protons from the photolysis of water are also accepted by the NADP to form NADPH

Question 5

how is ATP produced during the LDR

Answer 5

• light energy absorbed by chlorophyll causing photoionisation as electrons are released and raised to a higher energy level
• electrons move down the electron transport chain towards the second chlorophyll releasing energy
• energy is used to pump protons from stroma into the thylakoid space inducing an electrochemical gradient
• the protons diffuse back into the stroma via ATP synthase producing energy that is used to phosphorylate ADP to form ATP

Question 6

where does the LDR occur

Answer 6

• in the grana

Question 7

where does the LIR occur

Answer 7

• in the stroma

Question 8

what are the products of the LIR

Answer 8

• 2 molecules of Triose Phosphate
• Oxidised NADP
• ADP and Pi

Question 9

describe the Calvin cycle

Answer 9

• ribulose bisphosphate (5C) accepts CO₂ (1C) to form 2 molecules of Glycerate-3-Phosphate (GP) (2x3C) in a reaction catalysed by the enzyme Rubisco
• 2 molecules of GP is then reduced using NADPH and the energy from the hydrolysis of ATP to form 2 molecules of Triose Phosphate
• most of the Triose Phosphate is used to regenerate the RuBP

Question 10

what is the use of Triose Phosphate

Answer 10

• used to form all photosynthetic products e.g. glucose, fatty acids, glycerol etc etc
• used to regenerate ribulose bisphosphate

Question 11

why does temperature affect photosynthesis

Answer 11

• it affects the functionality of the enzymes used in the LIR (Rubisco)