Photosynthesis Flashcards
Photosynthesis equation
6 CO2 + light + 6H20 -> C6H12O6 + 6 O2 + 6 H20
G= 686 kcal/mol
Mesophyll cell
Cell that contains chloroplasts; site of photosynthesis
Stroma
Fluid inside mesophyll cell; site of Calvin cycle
Thylakoid
Stacked chlorophyll-containing sacs inside of mesophyll cell
Thylakoid membrane: site of light reactions
Thylakoid space: site of proton gradient
Stomata
Pores in leaf through which CO2 enters and O2 leaves
Granum
Stack of thylakoids
Light absorption by pigment
Light stays in that state for a short amount of time, then dissipates
Dissipation- some energy is lost as heat
After absorption: fluorescence, heat, or resonance transfer
Fluorescence
Emitting a photon lower in energy than what was absorbed
Structure of chlorophyll
Porphyrin ring: absorbs photons
Hydrocarbon tail: anchored to thylakoid membrane
Absorption spectra
Light waves that are absorbed
Action spectrum
Light waves that are used for photosynthesis
Endosymbiotic theory
Chloroplasts and mitochondria are of prokaryotic origin
Chloroplasts and mitochondria have their own…
DNA, DNA polymerase, RNA polymerase, Ribosomes, Ribosomal RNA
Non-cyclic electron transport (light cycle)
H20 split to form 2 electrons -> 2 photons of light excite electrons in photosystem II -> electrons are transferred from P680 to primary acceptor -> plastiquinone -> cytochrome complex, pumping through membrane H+ needed to make ATP -> plastocyanin -> 2 photons of light excite electrons in photosystem I -> electrons are transferred from P700 to primary acceptor -> ferredoxin -> NADP+ reductase reduces NADP+ to NADH
Cyclic electron flow
Electrons in PS I -> primary acceptor -> ferredoxin -> cytochrome complex (creates ATP) -> plastocyanin -> PS I
Used when NADP+ is low (plant has been doing lots of photosynthesis)
2 H+ instead of 4 from cytochrome complex: less efficient than non-cyclic transport
Amounts of products produced in light reaction
1.5 H+/ photon 4 H+/ ATP 4 photon/ NADPH Per light reaction: 4 photons, 2 electrons, 6 protons 3 ATP created (2 light cycles)
Calvin cycle
Phase 1 (carbon fixation): Rubisco turns 3 CO2 into 3-phosphoglycerate (3PG)
Phase 2 (reduction): 3PG + 6 ATP -> 1,3-bisphosphoglycerate
1,3-BPG + 6 NADPH -reduction> glyceraldehyde 3-phosphate (G3P)
Phase 3 (regeneration): G3P + 3 ATP -> ribulose bisphosphate (RuBP)
Per cycle: 9 ATP and 6 NADH consumed
Primitive bacteria
Developed first ATP-driven proton pump
Photorespiration
Rubisco adds O2 when CO2 is scarce (much more O2 than CO2 in atmosphere)
Occurs under light conditions
Doesn’t make ATP
C3 plants: 1 in 3 times, rubisco fixes O2 instead of CO2
Decreases photosynthesis
Releases CO2
Increases when stomata close (conserve H2O) and temperatures increase
C4 plants
1st stable compound in pathway has 4 carbons
Mesophyll cells, bundle-sheath cells (storage of CO2- impermeable, so it can’t escape), vascular tissue
Spatial separation in pathway
C4 photosynthetic pathway
Mesophyll cell: PEP carboxylase -> oxaloacetate -> malate -> pyruvate -> PEP (ATP used to make)
Bundle sheath cell: malate -> CO2 -> Calvin cycle -> sugar transported to vascular tissue
1 extra ATP is used per fixed CO2- as a result, plants use more cyclic electron flow to create more ATP
CAM plants
Desert plants
Stomata open at night
Temporal separation in pathway
2 mesophyll cells
CAM photosynthetic pathway
Night: PEP carboxylase fixes CO2- creates organic acids
Day: CO2 is used to fuel Calvin cycle and make sugar
Photosynthetic rates of plants
C4 > C3»_space; CAM
C4 = 2*C3
