5.7 Photosynthesis Flashcards
(23 cards)
Describe the structure of a chloroplast
- usually disc shaped
- double membrane (envelope)
- thylakoids: flattened discs that stack up to form grana
- intergranal lamellae: tubular extensions attcth thylakoids in adjacent grana
- stroma: fluid filled matrix high enzume and substrate concentration
Describe the structure of chloroplasts in relation to their roles in photosynthesis
- The chloroplast is a membrane bound organelle so create a seperate environment (compartment) for photosynthetic reactions
- thylakoid (membranes) are the site of (light dependent reaction/photophosphorylation/chemiosmosis)
- idea that (thylakoid) membrane provide a space for accumulation of H+
- stroma is site of (light-independent reaction/calvin cycle/carbon fixation)
Where do the light dependent and light indendependent reactions occur in plants?
- light-dependent: in the thylakoids of chloroplasts
- light-independent: stroma of chloroplasts
What processes occur in the light dependent reaction?
-photoionisation
-electron transfer chain
-chemiosmosis
non-cyclic only:
-reduction of NADP
-photolysis of water
what is photoionisation
the process where light energy excites e- in a chlorophyll molecule, causing them to gain so much energy that they leave the molcule completely. (so the chlorophyll is ionised)
why is photoionisation important
- the lost electrons enter the ECT
- which drives the formation of ATP and NADPH
- In PSII electrons lost through photoionisation are replaced by e- from water (photlysis)
describe the formation of ATP by chemiosmosis
- there is a higher concentration of of H+ ions in the lumen of the thylakoid compared to the stroma because of cyclic and non clycic photophorylation
- H+ therefore move back across the membrane towards the stroma down the concentration gradient
- the thylakoid membrane is impermeable to H+ so they move through a special transport protein
- this protein uses the energy released by the movement down the conc/elelectrochemical gradient to build up ATP with the help of enzyme ATPase
is non-cyclic photophosphorylation or cyclic phosphorylation the main pathway?
non cyclic
which photosystems are involved in non cyclic photophosphorylation
PSII and PSI
breifly describe non cyclic photophosphorylation
electrons are excited in PSII and go through the ECT to make ATP and end up in PSI which re excited them and they are finally used to reduce NADP+ to NADPH
why is non clyclic Photophosphorylation called that
electrons are NOT recylced - instead they are replaced with e- from with photolysis
products of non-clyclic photophosphorylation
- ATP
- NADP
(used in calvin cycle) - O2 (waste)
what photosystem does cyclic photophosphorylation involve?
PSI only
briefly decribe cyclic photophosphorylation
electrons get excited in PSI, pass through part of the ETC then return to PSI
why is cyclic photophosphorylation called that
electrons are recylcled!! (not replaced by e- from photolysis)
products of cyclic photophosphorylation
ATP only
why do plants do cyclic photophosphorylation
- when more ATP is needed than NADPH
- the calvin cyclle needs more ATP than it gets from non-cyclic photophosphorylation alone
what is the light independent and where does it happen?
Calvin cycle - stroma
what are the 3 parts of the calvin cycle?
- carbon fixation
- reduction
- regeneration
what does carbon fixation involve?
carbon dioxide joins with 5C RuBP to form 2 molcules of GP (glycerate phosphate). Catalysed by enzyme RuBisCo
what does reduction (calvin cycle) involve?
GP is reduced to glyceraldeghyde phosphate (GALP) using H+ by NADPH and energy from the breakdown of ATP
what does regeneration involve?
for every six molecules of GALP made, 1 molcule leaves the cycle to be used as the product of photosynthesis and 5 stay in the cycle to regenerate RuBP
what can GALP become
(regenerates RuBP)
- monosaccharides –> carbohydrates
- 6C sygar phosphate –> glycerol
- pyruvate –> fatty acids
- amino acids (with addition of minerals) –> proteins
