5.2.1 Photosynthesis Flashcards
How are photosynthesis and respiration linked ?
•CO2 and H2O are the reactants of photosynthesis and produce C6H12O6 + O2
•C6H12O6 and O2 are the reactants of respiration and produce CO2 + H2O.
Describe the structure of a chloroplast
*Disc shaped
*Double membrane
*Thylakoids ; flattened discs that form grana
*Stroma : fluid filled matrix with high enzyme conc and it’s own loop of DNA
Where do the light dependant and light independent reactions occur in the plant ?
Light dependant : in the thylakoids of the chloroplasts
Light independent : The stroma of the chloroplasts.
What is the role of the photosynthetic pigments ?
Molecules which are embedded within the thylakoid membrane, they absorb different wavelengths of light in order to maximise the rate of photosynthesis
Name two main groups of photosynthetic pigments
•Primary pigments: chlorophyll (made from chlorophyll a + b)
•Accessory pigments : carotenoids (carotene + xanthophylls).
Name the processes in the light dependant reaction
Cyclic
•Photoionisation (excitation of chlorophyll e- for chain)
•Electron transfer chain
•Chemiosmosis
Non cyclic only
•Reduction of NADP
•Photolysis of water
Explain the role of light in photoionisation
•Chlorophyll molecules absorb energy from photons of light
•This excites 2 electrons (raises them to a higher energy level), causing them to be released from the chlorophyll.
What happens in the electron transfer chain ?
•Electrons released from chlorophyll move down a series of carrier proteins in the thylakoid membrane
•Redox reactions occur which release energy
How does chemiosmosis produce ATP in the light dependant stage ?
•Some energy released from the ETC is used for the active transport of H+ from the stroma to the thylakoid space
•H+ ions move down the concentration gradient from thylakoid space into stroma via transmembrane channel protein ATP synthase
•ATP synthase catalysts ADP + Pi -> ATP.
Describe non-cyclic phosphorylation
•Uses photosystems I & II
•Excited electrons enter ETC to produce ATP
•NADP acts as final electron acceptor and is reduced, water is photolysed to release e- and replace those lost in PSI & PSII
•The purpose is to produce ATP and rNADP for the Calvin cycle, which produces biological compounds.
Describe cyclic phosphorylation
•Uses only PS I
•Excited e- enter ETC and produce ATP then return directly to PS, therefore there is no photolysis or reducing of NADP
•Purpose is to produce ATP and to meet surplus energy needs of cell.
What happens in the photolysis of water ?
•Light energy is used to split water molecules into O2 and H+
•2H2O -> O2 + 4H+ + 4e-
What happens to the products of the photolysis of water ?
•H+ ions move out of the thylakoid space via ATP synthase
•e- replace the lost electrons from chlorophyll
•O2 is used in respiration or diffuses out as a waste gas.
How and where is reduced NADP produced in the light dependant reaction ?
•NADP + 2H+ (lysis of water) + 2e- -> reduced NADP
•Catalysed via dehydrogenase enzymes
•Occurs in the stroma of chloroplasts.
Name the 3 main stages in the light independant reaction
•Carbon fixation
•Reduction
•Regeneration
What happens during carbon fixation ?
•Reactions between CO2 and ribulose bisphosphate (RuBP), catalysed between ribulose bisphosphate carboxylase (RuBisCo)
•This forms an unstable 6 carbon intermediate which breaks down into 2x glycerate phosphate.
What happens during reduction in the light independent reaction ?
•2 glycerate phosphate are reduced into 3 triose phosphate
•Requires 2rNADP + 2ATP, forms 2NADP and 2ADP.
Outline the roles of triose phosphate from the light independent reaction
•Raw material : 1C leaves the cycle per rotation to make monosaccharides, amino acids and other bio molecules
•Involved in the regeneration of RuBP, after 1C leaves cycle 5C compound forms: RuP
•1ATP is used to turn it into RuBP.
How many carbons are in the following compounds : RuBP, GP, GALP ?
•RuBP : 5C
•GP : 3C
•GALP : 3C
Define limiting factor
A factor that determines the maximum rate of reaction even if other factors change to become more favourable
Name 4 environmental factors that can limit the rate of photosynthesis
•Light intensity (light dependant stage)
•CO2 levels (light independent stage)
•Temperature (enzyme controller)
•Magnesium levels (chloroplasts).
How does light intensity affect the of reaction of photosynthesis?
•Low light intensity : slower light dependant reaction, less ATP and rNADP produced, less GP able to be converted to TP for light independent
