Photosynthesis Flashcards
what is the greatest source of light input
sun
what is the foundation of all terrestrial ecosystems
solar energy
how is oil formed
former plant material compressed over time
what is photosynthesis
the biological system that acquires energy from the sun
energy is used to produce sugar from CO2 and H2O
also releases oxygen
how was energy before photosynthesis
all energy was conserved
how is energy with photosynthesis
solar energy is a new and endless supply of new energy for life to consume
what is the photosynthesis equation
6 CO2 + 6 H2O + E –> 6 O2 + 2 C3H6O3 (3c sugar)
in photosynthesis what is reduced
carbon dioxyde
in photosynthesis what is oxidized
water
where does photosynthesis take place
in the chloroplast
what are the 2 processes in photosynthesis
- light dependant reactios
- carbon fixation
what are the components of light dependant reactions
- photosystem complexes
- electron transport pathways
- cytochrome
- ATP synthase
what do photosynthesis complexes consist of
- pigments
- reaction center
- antenna complex
what are the 2 photosystem complexes
PS II
PS I
what is in the antenna complex
250-400 individual pigment compounds
reaction center
what is the role of the antenna complex
capture light through pigments
funnel energy derived from light to reaction center
what are pigments
compounds in a plant that produce visually observable colour
what are the 2 main classes of pigments
- light responsive pigments
- secondary pigments
what are the light responsive pigments
chlorophyll a
accessory pigments
how is energy transfered to the organism
pigments absorb light
what is the colour we see
the wavelength that is reflected and NOT absorbed
what is the most important pigment
chlorophyll a
why is chlorophyll a the most important pigment
it is the only photosynthetic pigment common to all photosynthesizers
how is light captured
a photon of energy from light is absorbed by the pigment
the energy from the photon excites an electron and energy is held in the chlorophyll
why are different photosynthesizers found in different habitats
not all wavelengths can penetrate all habitats
what are accessory pigments
they absorb light energy and transfer energy to chlorophyll a for carbon capture
what is the role of accessory pigments
to broaden the range of wavelengths of light that can be used for photosynthesis
why are they called accessory pigments
they are accessory to the more critical function of chlorophyll a
what are types of accessory pigments
chlorophyll b
carotenoids
phycobiliprotein
what is chlorophyll a essential for
O2 generation in photosynthesis
what is chlorophyll b used for
absorb light and has excited electron and must transfer the energy to chlorophyll a to be used for photosynthesis
what are carotenoids
red, orange, yellow lipid soluble pigments embedded in the thylakoid membrane that absorb light and transfer it to chlorophyll a
what are the groups of carotenoids
carotenes
xanthophylls
when are carotenoids visible in leaves
when chlorophyll is absent
where are carotenes produces
only in plants
what colours are reflected and what colours are absorbed in carotenes
reflected: red, orange, yellow
absorbed: UV, violet, blue
what colours are reflected and what colours are absorbed in xanthophylls
reflecetd: yellow
absorbed: orange/red
where can we find phycobiliprotein
in cyanobacteria in red algae
what colour is absorbed in phycobiliprotein
green
when are phycobiliproteins necessary
for organisms that live in deep marine environments where other wavelengths dont penetrate
how can energy be transferred from the pigments
- fluorescence
- resonance energy transfer
- transfer of excited electron
what is fluorescence
when energy is released as a less energetic photon with a slightly longer wavelength
(loses energy)
what is resonance energy transfer
when energy is transferred from an excited chlorophyll molecule to a neighbouring chlorophyll molecule
what is transfer of excited electrons
when electron is transferred to a neighouring molecules that is part of an electron carrier
what is the consequence of electron transfer
oxidation of chlorophyll molecule
electron is replaced by oxidation of water molecule
what compounds can convert light to chemical energy
chlorophylls
what is in PS II
P680 chlorophyll that absorbs 680nm light
what is in PS I
P700 chlorophyll that absorb 700nm light
where is the site of light absorption
PS II and PS I
what are light dependant reactions
a series of coupled reactions driven by light energy
how do light dependant reactions function
electrons move down a chain of proteins
what are the consequences of light dependant reactions
- proton gradient created by releasing H+ ions into the thylakoid
- synthesis of ATP
- synthesis of NADPH
explain step 1 in PS II
- light energy is absorbed by a pigment in the antenna complex
- resonance energy transfer of E to P680 chlorophyll in the reaction center
- P680 loses electron
what happens when P680 loses an electron
it is replaced through the oxidation of water
- oxidation of water releases 2 H+ into the lumen of the thylakoid
- oxygen gas is produced
explain step 2 in between PS II and cytochrome b6f
- electron from P680 travels down a chain of proteins through oxidation/reduction reaction
what are the proteins involved with sending the electron from the PSII to cytochrom b6f
- pheophytin
- plastiquinone a
- plastiquinone b
what is a consequence of the electron traveling from PSII to cytochrome b6f
2H+ are sent to the thylakoid lumen
explain step 3 between cytochrome b6f and plastocyanin
- plastiquinone donates electron through b6/f complex and releases H+
- cytochrome b6f complex gives the electron to plastocyanin (molecule in the lumen)
- plastocyanin carries electron to PS I
explain step 4 in PS I
- plastocyanin gives electron to PS I
- PS I also absorbs light
explain step 5 between PS I and ferredoxin
- electrons oxidized on pS I are used to reduce NADP+ to NADPH
- electrons travel from P700 to ferredoxin
- ferredoxin sends electrons to NADP+ using the catalyst: FNR
what is the consequence of electron going from PSI to ferredoxin
- NADPH produced
- H+ is removed from stroma
explain step 6 of H+ gradient and ATP synthase
- electron train is over
- there is an accumulation of H+ within the thylakoid lumen
- H+ powers phosphorylation of ADP to ATP
what is referred to as noncyclic electron flow
when electrons have passed down the electron transport chain from photosystem complex II and produced NADPH
electron move uni-directionally from the chlorophyll to ferredoxin
How many H+ are released during the noncyclic electron flow
4H+ from the stroma to the thylakoid lumen
3H+ removed from the stroma (1 from reduction of NADP, 2 from transfer of e from plastoquinone to cytochrome)
What does the proton gradient power
the synthesis of ATP from ADP + P
what are the 2 methods for ATP synthesis
- proton gradient created by the electron transport chain
2. PS I functions independently and creates a proton gradient alone
what is the end product of noncyclic electron flow and noncyclic phosphorylation
6 NADPH and 6 ATP
why is cyclic phosphorylation necessary for carbon-fixation
it generates more ATP than NADPH
the carbon fixation require 3ATP:2NADPH
what is carbon fixation
using energy to create sugars
where does carbon fixation take place
calvin benson bassham cycle
what compound begins and ends the C3 photosynthesis (also calvin-benson-bassham cycle)
ribulose 1,5-biphosphate (RuBP)
in what a part of the cell is the calvin cycle
the stroma of the chloroplast
what are the 3 phases of the calvin cycle
- fixation of CO2
- Reduction
- Regeneration of RuBP
what happens in fixation of CO2
CO2 is bonded to 3 molecules of RuBP
fixation is catalyzed by Rubisco
what is the most abundant enzyme on earth
Rubisco
what happens in reduction
6 molecules of 3-phosphoglycerate (PGA) are converted to 6 molecules of glyceraldehyde 3-phosphate (PGAL)
what happens with the PGAL after reduction
5 continue in the cycle
1 is converted into sugar
what is consumed during reduction
6 ATP and 6 NADPH
what happens in the regeneration of RuBP
5 molecules of PGAL reduced to 3 molecules of RuBP
what is consumed during regeneration of RuBP
3 ATP
what is the calvin cycle equation
3 CO2 + 9 ATP + 6 NADPD + 6 H+ –> PGAL + 9 ADP + 8P + 6 NADP+ + 3 H2O
what is the fate of fixed carbon
most PGAL transported to the cytosol and converted into sucrose
some PGAL remain in the chloroplast is converted into starch and stored in the stroma
what is photorespiration
where O2 is fixed by Rubisco instead of CO2
what are the systems that minimize photorespiration
- C4 photosynthesis with/without Kranz anatomy
- C3-C4 intermediates
- CAM photosynthesis
what is C4 photosynthesis
Photosynthesis has an extra step to concentrate CO2 around rubisco
what is Kranz anatomy
when there are bundle sheath cells that surround the vascular bundle and mesophyll cells that surround the bundle sheath cells
what are the steps of C4
- CO2 fixed to PEP and form oxaloacetate in cytosol of mesophyll cells
- Oxaloacetate is converted to malate
- malate moves from mesophyll cell to neighbouring bundle-sheath cell
- malate is converted to form CO2 and pyruvate
- CO2 enters the calvin cycle in the bundle sheath cell
- pyruvate returns to the mesophyll cell, reacts with ATP to regenerate PEP
when is C4 more efficient than C3
high temperatures
What is CAM photosynthesis
an extreme adaptation to high temps and dry environments
can fix carbon in the absence of light
what are the steps of CAM at night
- CO2 is fixed to PEP to form oxaloacetate
- Oxaloactetate is immediately converted to malate
- malate is stored in the vacuole as malic acid
what are the steps of CAM at day
- malic acid is transported out of the vacuole and into the cytosol as malate
- malate is converted and the released CO2 enters the chloroplast
- CO2 fixed to RuBP by Rubisco and calcin cycle begins and sugar and starch can be produced
