UNIT 7 PHOTOSYNTHESIS Flashcards
Primary producers on earth
photo autotroph
photosynthesis
converts the energy from sunlight into chemical energy and use it to assemble simple inorganic raw material into complex organic molecules.
2 parts of photosynthesis
the light-dependant reaction and the Calvin cycle
light dependant reaction
capture light energy by pigment molecules and utilize this energy to synthesize NADPH and ATP.
Calvin cycle
CO2 fixation. The electrons carried by NADPH and ATP are used to convert co2 from inorganic to organic form.
product of the Calvin cycle
it takes 3 turns of the cycle to produce one extra G3P that the cell can use.
Where does photosynthesis take place?
chloroplast
3 fates for the electron possessed by a pigment molecule
- electron returns to it’s ground state. releasing heat to bioluminescence
- the electron returns to it’s ground state and the energy released is transferred to a neighbour molecule.
- the excited electron is accepted by an electron receptor
Inductive resonance
when the electron returns to is ground state and the energy released is transferred to a molecule close by.
fluorescence
emission of light of a longer wavelength than the absorbed light.
chlorophyll
major photosynthetic pigment. Types A and B are most common.
What are accessory pigments?
carotenoids and chlorophyll b
What does accessory pigments do?
After light absorption they donate excitation e energy by inductive resonance of chlorophyll a.
Action spectrum
Plot of the effectiveness of light of particular wavelength in driving photosynthesis. Show the spectrum of light that is most effective for photosynthesis.
Each photosystems is composed of what?
Large antenna complex of pigment proteins that surrounds a central reaction centre.
What is in the reaction centre in photosystems?
Small number of proteins that binds a pair of chlorophyll a as well as the primary electron receptor.
PSI
P700
PSII
P680
Photosystem works?
Once excite p680* can be oxidized to P680+ by the primary electron receptor pheophytin.
Water-splitting complex
The reformation of p680 into p680+ is facilitated by this enzyme subunit.
Linear electron transport
P680 oxidize to P680+, the electron is transferred from the primary acceptor to plastoquinone which migrates through the lipid bilayer and links PSII and the cytochrome complex. From there, the electron pass to plastocyanin which links cytochrome complex and PS1. P700 is oxidized and reduced by the electron donation from plastocyanin, the electrons from P700 is then passed to ferrédoxine which transfer electrons to NADP+ which is reduced to NADPH.
What is used to synthesize ATP by chemiosmosis?
Proton-motive force
How many photons of light needs to be absorbed to make 4 electrons?
8, 4 per photosystem
Cyclic electron transport
When PSI functions independently from PSII
Difference between linear electron transport and cyclic electron transport?
Reduce ferrédoxine donates electrons back to the plastoquinone pool instead of giving it to the NADP+ reductase complex. This allows plastoqunone to move protons across the membrane without the need for PSII so ATP is produced but not NADPH.
Why is the cyclic electron transport so important?
Because the Calvin cycle needs more ATP then NADPH and once we’ve got enough NADPH from the light dependant reaction, ATP can be produced in the cyclic electron transport without energy loss.
Calvin cycle
11 reactions that use NADPH to reduce CO2into sugar, requires energy from ATP
3 phases of the Calvin cycle
- Fixation
- reduction
- regeneration
Fixation phase of the Calvin cycle
incorporation of a carbon atom from CO2 into RUBP to produce 2 3-phosphoglycerate.
Reduction phase of the Calvin cycle
Each two 3-phosphoglycerate gets a phosphate from the hydrolysis of ATP which produces 3-biphosphoglycerate which is reduced, producing G3P
Regeneration phase of the Calvin cycle
Each Calvin cycle turn makes 2 G3P (6atoms) 5 of these atoms makes RuBP which is needed to start the cycle again. So it takes 3 turns to produce one extra G3P.
What is needed to synthesize the G3P from the Calvin cycle?
9 ATP and 6 NADH.
G3P
3-carbon sugar, base of more complex carbs (glucose)
Rubisco
Enzyme that catalyses the first reaction of the Calvin cycle. most abundant enzyme on earth.
Photorespiration
Because rubisco is inefficient at fixing CO2 because it catalyzes O2 into RuBP, making a toxic molecule while loosing a carbon and using ATP.
C4
CO2 combines with PEP producing oxaloacetate, then reduced to malate. It gets to the Calvin cycle site and get oxidized to pyruvate, releasing co2. That pyruvate is then converted back to PEP in a ATP consuming reaction. it prevents photorespiration by a high rate of CO2 at rubisco site and low 02.
CAM plants
Run Calvin cycle and C4 at different times. At night they allow O2 in and is fixed to oxaloacetate, then converted to malate which is store till day. Daytime, malate is transported and release CO2 by breaking it down, it enters the Calvin cycle. It maintains a high co2 at rubisco site and avoir photorespiration.
Where will the light dependant reaction and the Calvin cycle take place in eukaryotes?
Chloroplast
Thylakoid
Closed flat sac
PSI produces
NADPH
Absorption spectrum
The light that is absorbed (blue, red, green)
