what are the four types of photosynthetic pigments
chlorophyll a, chlorophyll b, carotenoids, phaeophytin
where in the chloroplast does the light independant reaction take place?
the stroma
where does the light dep take place?
thylakoid (lumen)
why do chlorophyll look green to the human eye?
chlorophyll absorbs blue and read light and reflects green light.
- reflected light is visible to eye
chlorophyll a
- where is it found?
- what colour is it?
- what colour does it absorb?
- mainly in PS2 and is the most abundant pigment
- it is blue/green
- it absorbs red light
chlorophyll b
- where is it found?
- what colour is it?
- what colour does it absorb?
- mainly in PS1
- it is yellow/green
- absorbs bluer light
two types of carotenoids
carotene (orange)
xanthophyll (yellow)
what is the absorption spectrum
amount of light absorbed by a pigment against the wavelength of light
(represents the range of wavelengths that a pigment can absorb)
what is the action spectrum
rate of photosynthesis against the wavelength of light
- show that the R.O.P is closely related to the combined absorption spectrum of all the photosynthetic pigments
- the range of the pigments makes up a large portion of the wavelength of light available to plants - allow them to have options for photosynthesis for different conditions
(show the pigment that actually work)
what two processes are in the L.D.R
- cyclic and non cyclic
how does cyclic photophosphorylation work and what are the products?
-involves only PS1
when there is not enough NADP+ to accept electron along the etc
- this is why the electrons are given back to the proton pump (because it still has light energy and doesn’t want to waste that)…
so when the electrons are passed to the proton pump, more H+ ions actively transported, so more atp eventually generated.
product : only ATP produced
how does non-cyclic photophosphorylation
- water molecules split (photolysis), provide h+ ions to reduce NADPH and producing ATP. involves PS2 and PS1
- light hits PS2 - electron excited (reach reaction centre) and passed along e.t.c.
- photolysis happens again because the PS2 short of electron (continues to happen - like a little cycle)
- light hits PS1 and electron excited again (reach reaction centre)
- travel to FNR, make NADPH
- proton pump : hydrogens actively transport but then due to conc gradient, travels down electrochemical gradient in the `ATP synthase
- phosphorylation of adp to form atp
products : atp, nadph (and oxygen)
what is the equation for phtolysis?
2H2O -> 4OH- + 4e- +4H+
and then this will again become 2H2o and O2 (because all of the hydrogen ions wont be used, so it will mix with the OH to make H2O)
where does the oxygen made in photolysis go?
it gets released into the atmosphere and it is let out through the stomata.
how does the light-independent stage (calvin cycle) work?
(basically describe the process)
- uses the NADPH and ATP produced by L.D.R to make glucose
- CO2 from air combines with RuBP ( 5c molecule) - this is carbon fixation
- this forms a 6 carbon molecule
- immediately splits to form 2 molecules of 3GP
- GP is reduced (H added) to form GALP (needs NADPH and ATP)
- most (5/6) of galp goes through steps to replace RUBP needed in the 1st step of the cycle
- (some is synthesised into glucose)
- atp is needed to regenerate RuBP. then, rubisco fixes the CO2 to to RuBP again.
what is the primary product of photosynthesis and what happens to this molecule?
GALP is the primary product of photosynthesis - also synthesise biomass of the plant
- some GALP in glycolysis, some used to produce glucose in gluconeogenesis.
- converted to disaccharides for transport and polysaccharides for energy storage/structure.
- GALP in glycolysis and Krebs provides ATP and compounds that can be used as building blocks of amino acids when combined with nitrates
- can also be used to make nucleic acid when combined with phosphates
- some also made into acetyl-CoA
how can light be a limiting factor?
- affects the amount of electrons excited –> also affects the production of NADPH and ATP
- in low levels of light - insufficient NADPH and ATP produced for L.I.R
how can carbon dioxide be a limiting factor?
- if not enough for the Calvin cycle, the reactions can’t proceed at the maximum rate
how can temp be a limiting factor?
- all the calvin cycle and most of L.D.R are controlled by enzymes
- even when the light and CO2 levels are good, plant can’t take advantage of conditions if temp not ideal (enzymes denature or not work)
what other factors could be limiting?
- height, spreading of leaves, climbing and large leaves are how plants get as much light as possible
