5.1 - Photosynthesis Flashcards
Where does the light dependent stage occur?
in the thylakoid membranes/grana
Where does the light independent stage occur?
stroma
Describe photolysis
- chlorophyll absorbs light energy to split water into oxygen, H+ and e-
- H+ and electrons used to form NADPH for LIR
- electrons passed along electron transport chain
- oxygen for respiration or diffuses out through stomata
Describe photoionisation
- light energy ‘excites’ electrons in chlorophyll, where they raise up an energy level
- some energy released used to make ATP and reduced NADP in chemiosmosis
Describe chemiosmosis
- electrons move along series of proteins (electron transport chain), releasing energy at each movement
- energy used to actively transport H+ ions across membrane from stroma into intermembrane space
- creates electrochemical gradient
- H+ ions diffuse through ATP synthase back into stroma
- causes ATP synthase to change in shape and energy released catalyses ATP synthesis (ATP will be hydrolysed to release energy for LIR later)
- H+ ion and electrons combine with co-enzyme NADP -> NADPH
Describe the first stage of the Calvin Cycle (LIR)
Carbon fixation: CO2 ‘fixes’ RuBP into 2 molecules of GP
catalysed by the enzyme rubisco
Describe the second stage of the Calvin Cycle
GP is reduced to triose phosphate using ATP hydrolysis and by accepting H from NADPH from LDR
What is triose phosphate used for?
- to regeneration RuBP in Calvin Cycle
- converted to useful organic substances
Describe the third stage of the Calvin Cycle
RuBP is regenerated using energy released from ATP hydrolysis
Name the 3 factors which are limiting factors for photosynthesis
- temperature
- CO2 concentration
- light intensity
(see graphs - temperature is different to other two)
How many turns of the Calvin cycle are required to produce 1 molecule of glucose per molecule of CO2?
6
