photosynthesis Flashcards
name 6 components of a chlorplast?
outermembrane
lamellae
grana
thylakoid
stroma
DNA- circular
where does the light dependent stage of photosynthesis take place?
thylakoids
where does the light independent stage of photosynthesis take place?
stroma
what is the light harvesting system?
accessory pigments held by proteins and arranged into a funnel shape
it absorbs light energy and passes the energy to the action centre/ primary pigment
gives energy for electron excitement
what do the light harvesting system and primary pigment together form?
photosystem
what are the 2 main photosystems and what is their maximum absorption?
photosystem I absorbs to 700nm
photosystem II sbosrbs to 680nm
describe the non cyclic photophosphorylation in the light dependent stage of photosynthesis
electrons are excited from PSII, they move down the electron transport chain, forming ATP by chemiosmosis
the electrons lost from PSII are replaced by electrons from photolysis
electrons are excited from PSI and move down electron transport chain producing ATP. electrons lost from PSI are replaced by electrons excited in PSII
electrons excited from PSI with H+ from photolysis reduce NADP
describe the cyclic photophosphorylation in the light dependent stage of photosynthesis
when electrons excited from PSI return to PSI instead of being replaced by electrons from PSII. no reduced NADP is formed
equation for photolysis?
H2O ——–> 2H+ + 2e- + 1/2 O2
what is RuBisCO and what does it do?
Ribulose bisphosphate carboxylase
enzyme that catalyses fixation of carbon dioxide
what is RuBP?
5 carbon compound called Ribulose Bisphosphate
describe the calvin cycle
carbon dioxide fixation
carbon dioxide combines with RuBP, catalysed by RuBisCO
forms a very unstable 6 carbon compound which breaks down immediately into 2 glycerate 3-phosphate molecules
each GP molecule is converted into Triose phosphate by reduction using reduced NADP and energy from ATP, both produced in the light dependent stage
triose phosphate mostly regenerates into RuBP but some used to start the synthesis of complex biological molecules
what are 3 factors limiting the rate of photosynthesis?
light intensity
CO2 concentration
temperature
how does light intensity affect photosynthesis?
it is the energy source of the reaction so increasing light intensity increases ATP and reduced NADP produced in light dependent
how does light intensity affect the levels of GP, TP and RuBP?
low light intensity = less ATP and reduced NADP produced so:
increases GP
decreases TP
decreases RuBP
how does carbon dioxide concentration affect photosynthesis?
its needed as a source of carbon, increase CO2 concentration increases carbon fixation in the calvin cycle
how does carbon dioxide concentration affect the levels of GP, TP and RuBP?
low CO2 concentration:
decreases GP
decreases TP
increases RuBP
how does temperature affect photosynthesis?
it increases the rate of enzyme activity as it increases the frequency of sucessful collisions
RuBisCO which catalyses calvin cycle increases in activity when temperature increases until its too hot and dentures
how does temperature affect the levels of GP, TP and RuBP?
low temperature:
decrease GP
decrease TP
decrease RuBP
What happens during water stress?
stomatal closure
prevents CO2 diffusion into leaf so reduces rate of photosynthesis
why is water not seen as a limiting factor of photosynthesis?
by the time water potential is low enough to be a limiting factor, the stomata have already closed to prevent water loss and photosynthesis has stopped due to low CO2 concentration.
what inhibits RuBisCO?
oxygen, competitive inhibition
what is accesory pigment?
(accessory) other part of photosystem/antenna unit/surround reaction centre;
(accessory) absorb different wavelengths of light (not absorbed by primary);
(accessory pigments) transfer energy to primary pigments;
what is primary pigment?
(primary) act as reaction centres/where electrons are excited;
describe calvin cycle
1 occurs in stroma ;
2 a series of enzyme-controlled reactions ;
3 carbon dioxide fixed by RuBP ;
4 carboxylation ;
5 enzyme is Rubisco ;
6 (unstable) 6C intermediate ;
7 forms (2 molecules) of GP ;
8 forms TP ;
9 using ATP (linked to point 8) ;
10 reduction step ;
11 using reduced NADP ;
12 ref to either ATP or NADP red coming from light dependent reaction ;
13 (most of) TP regenerates RuBP ;
14 rearrangement of carbons to form pentose sugars ;
15 ATP required, for phosphorylation / ribulose phosphate to ribulose
bisphosphate ;
16 AVP ; e.g. TP can be used to form, lipids / amino acids / hexose sugars
/ suitable named example
Outline the ways in which heterotrophic organisms are dependent on plants.
1 animals / heterotrophs (need to) , eat / obtain organic material from / AW , plants / autotrophs ; 2 (plants / autotrophs) produce (named) organic molecules during , photosynthesis / Calvin cycle / light independent stage ; 3 (plants / autotrophs) produce oxygen during , photosynthesis / photolysis / light dependent stage; 4 glucose / carbohydrate / oxygen , (produced in photosynthesis) are used in respiration by , animals / heterotrophs ;
what is an autotroph
can make organic molecules from inorganic molecules
what is a heterotroph
needs to use organic molecules made by other organisms
what are compensation points?
when carbohydrate produced by photosynthesis equals the carbohydrate used in respiration
