Topic 8.3: Photosynthesis Flashcards
Site of light dependent reactions
Intermembrane space of thylakoids
Function of light dependent reactions
Convert light energy from the Sun into chemical energy (ATP + NADPH)
Overall process of light dependent reactions
a) Excitation of Photosystems by light
b) Production of ATP via ETC
c) Reduction of NADP+ and the Photolysis of Water
Excitation of Photosystems by light
a) Photosystem II absorbs light energy
b) Delocalized electrons within the pigments become excited
c) Excited e- are transferred to carrier molecules within the thylakoid membrane
Production of ATP via an Electron Transport Chain
a) Excited electrons from Photosystem II are transferred to an ETC within the thylakoid membrane
b) As the e- are passed through the chain, they lose energy to translocate H+ ions into the thylakoid
c) This builds up of protons within the thylakoid creates an electrochemical gradient
d) H+ ions return to the stroma along the H+ gradient via ATP synthase
e) Photophosphorylation
f) The newly de-energized electrons from Photosystem II are taken up by Photosystem I
Reduction of NADP+ and the Photolysis of Water
a) Excited e- from Photosystem I are transferred to reduce NADP+ into NADPH
b) e- lost from Photosystem I are replaced by de-energized electrons from Photosystem II
c) H2O is split by light energy into H+ ions (used in chemiosmosis) and O2 (released as a by-product)
d) e- lost from Photosystem II are replaced by electrons released from H2O via photolysis
Types of photophosphorylation
a) Cyclic
b) Non-cyclic
Cyclic phosphorylation (Steady supply of ATP)
a) Only chlorophyll in PS I are photoactivated
b) e- move through ETC before returning to their original location
c) ETC produces ATP
a) NADPH is not synthesized
Non-cyclic phosphorylation (Synthesis of organic molecules)
a) Chlorophyll in PS I and II are photoactivated
b) Electrons from PS I reduce NADP to produce NADPH
c) Electrons from PS II move through ETC before replacing those from PS I
d) ETC produces ATP
e) Electrons lost from PS II are replaced by water (Photolysis)
Site of light independent reactions
Stroma
Function of light independent reactions
Use the chemical energy to synthesize organic compounds (Glucose)
Overall process of light independent reactions
a) Carbon fixation
b) Reduction of GP
c) Regeneartion of RuBP
Carbon fixation
a) Rubisco catalyzes the attachment of a CO2 of ribulose bisphosphate
b) Unstable 6C compound breaks down into two glycerate-3-phosphates
Reduction of GP
a) GP is phosphorylated by ATP and reduced by NADPH
b) This converts each GP molecule into a triose phosphate
Regeneration of RuBP
a) One molecule of the six of TP is used to produce half a sugar
b) Remaining TP molecules are used to regenerate stocks of RuBP
c) ATP is required for the regeneration of RuBP
Aim of lollipop experiment
Elucidate the carbon compounds involved in the light independent reactions
Process of lollipop experiment
a) Radioactive carbon-14 is added to a ‘lollipop’ apparatus containing green algae
b) Light is shone on the apparatus to induce photosynthesis
c) Algae is killed by running it into a solution of heated alcohol
d) Dead algal samples are analyzed using 2D chromatography to separate out different carbon compounds
e) Radioactive carbon compounds on the chromatograph were identified using autoradiography
f) By comparing different periods of light exposure, the order by which carbon compounds are generated was determined
Function of chloroplast
Convert light energy into chemical energy (ATP / Organic compounds)
Structure of chloroplast
a) Double membrane
b) Stroma
c) Thylakoids
d) Grana
e) Lamella
f) Starch granules
Double membrane
Evidence for endosymbiosis
Stroma
Has appropriate enzymes and a suitable pH for the Calvin cycle
Thylakoids
a) Have ETC and ATP synthase for phosphorylation
b) Have a small internal volume to maximize H+ gradient
Grana
Arranged into stacks to increase SA:Vol ratio
Lamella
Connects and separates thylakoid stacks
Similarities between Photosynthesis and Cell Respiration
a) ATP production
b) ETC / Chemiosmosis
Differences between photosynthesis and cell respiration (
a) Water is broken down to oxygen to release electrons for ETC
a) Electrons from ETC are taken up by oxygen to form water
b) Electrons are taken up by electron carriers
b) Hydrogen carriers release electrons for ETC
c) Uses Calvin cycle to synthesize glucose
c) Uses Kelvin cycle to break down glucose
