20.1 Photosynthesis Flashcards
what is the function of the chloroplast envelope?
selective permeability
inner membrane - has embedded transport proteins + is less permeable than outer
why do chloroplasts contain their own circular DNA and 70Svedberg ribosomes?
{cpDNA}
for producing their own photosynthetic proteins
what is the function of a starch grain in a chloroplast?
storage of photosynthetic products
what is the function of a photosynthetic pigment?
the absorption of specific wavelengths of light and converting it to CPE
how is the observed colour of a plant determined?
the wavelength of light that is reflected by the photosynthetic pigments
what is the advantage of having multiple photosynthetic pigments?
move wavelengths can be absorbed
∴ more light is absorbed
more light-dependent reactions (LDRs) can occur
∴ more CPE
which mineral ion is required for chlorophyll?
Mg2+
what are the features of photosystem II?
P680
absorbs 450nm (blue)
peak absorption at 680nm
granal lamellae
what are the features of photosystem I?
P700
absorbs 450nm (blue)
peak absorption at 700nm
intergranal lamellae
where are photosystems located?
in the thylakoid membranes of lamellae and grana
what is the structure of a photosystem?
funnel shaped structures
held in place by extrinsic proteins embedded in PPL bilayer
where does photolysis occur?
photosystem II in granal lamellae
what are the products of photolysis? what is their fate?
4 H+ ions - used in chemiosmosis to produce ATP + to reduce NADP
4 e- - oxidises the Mg in the chlorophyll to Mg2+
O(2) - used for aerobic respiration + excreted as a waste gas
what are other uses of water?
maintaining turgidity
translocation of sucrose
opening/closing stomata via turgidity of guard cells
transpiration
outline the process of photophosphorylation
photon of light hits a chlorophyll molecule in PSII
E from photon transferred to 2 e-
e- can leave Mg atom –> Mg2+
e- accepted by e- acceptor
e- passed along series of e- carriers embedded in thylakoid membrane to PSI (e- transport change)
e- received by NADP+ reductase
e- lost from chlorophyll replaced from a water molecule
2H+ from water molecule combine with e- to reduce NADP+ to red. NADP
outline the process of chemiosmosis
E released from e- transport chain used to pump H+ against concentration gradient across thylakoid membrane into thylakoid space
H+ concentration increases inside thylakoid –> proton electrochemical gradient generated
H+ diffuse back down gradient through ATP synthase
ATP produce from ADP and P(i)
why can’t plants use ATP from the LDR as their only source of ATP?
PHS only occurs in the light
rate of production is insufficient for needs
some plant cells (e.g. root hair) have no chloroplasts ∴ cannot generate ATP
where does the Calvin cycle/light-independent reaction take place?
the stroma of the chloroplast
outline the process of the Calvin cycle
CO(2) diffuses into the leaf into the stroma of the chloroplast
CO(2) fixed to RuBP in the presence of RuBisCO to form a 6C intermediate
6C breaks down into 2x glycerate-3-phosphate
ATP and red. NADP used to convert G3P into triose phosphate
1 TP exits the cycle; 6 TP regenerated to RuBP
what happens to G3P?
reduced to RuBP
converted to aCoA –> fatty acids and a.a. synthesis
what happens to TP?
5/6 recycled to allow continuation of Calvin cycle
2x TP can be converted to hexoses
glucose can be isomerased into fructose –> G + F can be condensed to sucrose
can be polymerised into other polysaccharides
can be converted to glycerol and combined with fatty acids to form trigylcerides
outline some specialisations of a palisade mesophyll cell
closely packed and arranged vertically - max light absorption
large vacuole - pushes chloroplasts to the edge of the cell
cylindrical with air spaces - circulation of gases
large SA - increased gas diffusion
thin cell walls - increased light penetration/gas diffusion
outline the features of RuBisCO
globular protein –> enzyme
has 4 prosthetic groups (∴ quaternary structure)
optimum pH = 8
has 8 active sites
what is the action of RuBisCO in the presence of high concentrations of O(2)?
O(2) binds with active site instead of CO(2)
different chemical reactions –> fully oxygenated product
produces toxic H(2)O(2)
increased temperature –> increased oxygenase activity
what is the light compensation point (LCP)?
the amount of light intensity on the light curve where the rate of photosynthesis exactly matches the rate of respiration
when is the LCP achieved normally?
at dawn and dusk
how can limiting CO(2) be corrected?
paraffin burners (although also increases gas exchanges –> increase transpiration)
what is the effect of light on controlling the rate of photosynthesis?
causes stomata to open
photolysis of water
excitation of e- in chlorophyll molecule
how does temperature affect the rate of photosynthesis?
above 25.C, RuBisCO increases oxygenase activity –> photorespiration > photosynthesis
if too high, increased H(2)O loss ∴ stomata close ∴ CO(2) available decreases
what are the variables that affect the rate of transpiration?
light intensity
temperature
CO(2) availability
how can the rate of photosynthesis be measured?
uptake rate of CO(2)
rate of increase of dry mass of plants
rate of O(2) production
how is light intensity calculated?
1 / (distance from light source)^2
