A2 photosynthesis (topic 5)

Question 1

what type of plant does PHS

Answer 1

photoautotrophs (green plants)

Question 2

4 adaptations of leaves for PHS

Answer 2

large SA:V ratio

airspaces in spongey mesophyll

stomata

thin

Question 3

3 things that affect rate of PHS

Answer 3

CO2 conc
light intensity
temperature

Question 4

how are chloroplasts adapted for PHS

Answer 4

stacks of thylakoid membranes called grana => provide large SA for attachment of chlorophyll, e- and enzymes

network of proteins in the grana hold chlorophyll in specific place to absorb max light

granal membrane has ATP synthase channels allowing ATP to be synthesised as well as being selectively permeable so a proton gradient can be established

DNA and ribosomes to synthesise proteins needed in the LDR

Question 5

light dependent reaction

Answer 5

photoionisation: photons of light hit chlorophyll molecules in PSII, e- become excited

photolysis: splitting water with light. one molecule of water needs 4 photons to split. produces 1mol O2, 4 protons and 4 electrons. (o2 diffuses out through stomata or used in respiration) the 4e- replace those lost from the chlorophyll, and 4p move into stroma to create a proton gradient

excited e- moves down a series of protein complexes. at one, the energy from the e- is used to pump 4 protons from the stroma to the thylakoid space

e- then moves down the chain to PSI. here more photons are absorbed causing e- to move back up to a high energy level

e- moves along chain to another complex where the e- combined with a proton to form hydrogen atom. this is used to reduce NADP

the pumping of protons across the membrane means there is a greater P conc in the thylakoid space than stroma. protons diffuse across proton gradient through a stalked particle protein. this drives process of photophosphorylation (ATP synthase phosphorylates ATP from ADP and Pi)

Question 6

PSI and PSII

Answer 6

photo system => pigments arranged in light harvesting clusters

Question 7

Light Independent Reaction

Answer 7

carboxylation: co2 that has diffused in from stomata combines with RuBP (ribulose biphosphate) using enzyme rubisco. produces an unstable 6C compound which then forms 2 x 3C glycerate 3-phosphate

reduction: GP molecules contain COOH- so are acids. reduced by NADPH using ATP from LDR and forms triose phosphate

regeneration: 5 molecules of triose phosphate used to regenerate 3 RuBP which uses ATP from LDR. 1 goes to make glucose (therefore 6 turns of calvin cycle for 1 glucose molecule)

Question 8

limiting factors of photosynthesis

Answer 8

light intensity => light compensation point is where co2 given out = co2 taken in
co2 conc
temperature