Term
| Place photosynthesis in a broad biological context |
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Definition
Photosynthesis is found in plants, algae and photosynthetic bacteria
Photosynthesis covers all spatial and temporal scales on Earth
100 billion tons of Carbon/year is fixed by photosynthesis
Impact of Earth's atm evolution:
Oxygen level has risen from <1% to ~20%.
CO2level has fallen from >10% to ~0.03 %. |
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Term
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Definition
Carbon is 'fixed' from CO2 into sugars
O2 is released from water |
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Term
| What is cellular respiration? |
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Definition
Sugars are 'burned' in O2 to release energy for cellular metabolism
CO2 and H2O are released as waste products |
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Term
| Explain the main steps through which solar energy is captured as chemical potential energy, using pigments for light harvesting. |
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Definition
Light-dependent reactions split water to extract electrons. The electrons are excited by light and generate reducing power (NADPH) and Energy (ATP)
The energy and reducing power are then used in the light-independent reactions to reduce CO2 to carbohydrates.
Light-dependent Rxns:
2H2O+Light -> 4H+ (ATP) + 4e- (makes NADPH later) + O2
Light independent Rxns:
CO2 + 4H+ + 4e+ -> CH2O + H2O |
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Term
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Definition
Oxidation through splitting water
Releases O2
Transforms energy through high energy electron transfers
Produced ATP and NADPH
on Thylakoid membrane |
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Term
| Light independent reactions |
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Definition
Uses ATP and NADPH
Fixes Co2 to Carbs (stores solar energy as high energy carbon bonds)
Endergonic reaction (non spontaneous)
in stroma |
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Term
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Definition
Derived from free living cyanobacteria
2 membranes, stroma, granum -> thylakoids ->lumen |
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Term
| How do plants capture the energy from sunlight and transfer into chemical energy? |
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Definition
Through Pigments: Chlorophylls (transmit green) and Carotenoids (transmit red and orange and yellow) are the main photosynthetic pigments
When light hits teh pigments, an electron is excited to a higher energy state (blue better than red light)
So what happens to the excited election?
Fluorescence, resonance transfer, or photochemistry |
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Term
| When electron in the pigment is excited, and fluorescence is observed, what happens? |
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Definition
| e drops back down and light is emitted |
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Term
| Why does Chlorophyl have two absorbance peaks? |
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Definition
| some of the blue photons captured are reemitted as red fluorescence and Chla can capture those red photons |
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Term
| When electron in the pigment is excited, and resonance is observed, what happens? |
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Definition
THe energy in e is transferred to e in a nearby pigment (energy moves, not e)
All the energy gets bounced to the reaction center |
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Term
| What is the antenna system? |
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Definition
The antenna complex contains pigment molecules that act as an antenna for the reaction center, directing energy from photons toward the center
relies on resonance activity based on fluorescence emission and coupling among the antenna pigments [image] |
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Term
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Definition
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Term
| After the energy is collected at the reaction center, what happens? |
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Definition
Excited electrons are finally transferred to a new molecule that acts as an electron acceptor( pheophytin, amodified chlorophyll)
When pheophytin becomes reduced,the electromagnetic energy is stored as chemical energy that fuel electron transfer chains (energy transformation) |
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Term
| Why do plants need to split water? |
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Definition
The reaction center needs to replace the electrons transferred to the acceptor
and O2 is released as a waste product |
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Term
| Discuss the pathways of electron flow around PSI and PSII (will pull apart into different cards) |
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Definition
Plants have two reaction centres that acitivate two ps
[image] |
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Term
| Photo acclimation: regulation of the antenna capacity: what is the relationship between amount of chlorophyll and light intensity |
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Definition
| EX cannabis leaves increase chlorophyll levels under low light conditions and deacrease chlorophyll levle under high light conditions |
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Term
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Definition
Electrons fall from high energy to low energy and drive biochemical ‘turbines’
e donated to Pheophytin and Rxn centre is oxidized
Pheophytin outside membrane -> ETC in membrane -> Plastoquinone (PQ) moves e and protons form pheophytim across membrane to cytochrome complex |
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Term
| How is the H+ gradient produced? |
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Definition
| Movement of PQ across the membrane creates H+ gradient |
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Term
| What molecule joins PSII and PSI? |
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Definition
| Plastocyanin (PC) couples |
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Term
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Definition
e moved down ETC full of iron and sulfur containing proteins to ferredoxin
The enzyme NADP+ reductase transfers a proton and two electrons from ferredoxin to NADP+, forming NADPH. NADPH functions as an e-carrier that can donate electrons to other compounds. |
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Term
| Alternative Electron path, cyclic e flow |
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Definition
THrough excited e from PS I flows back to PSII to PQ (via ferredoxin), go to PC and enters back to PSI
Produces ATP
No production of NADPH and O2 |
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Term
| When is cyclic flow advantageous? |
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Definition
Cells require additional ATP, but no NADPH
Not enough NADP+ available for NADPH synthesis
Want to avoid excess O2 accumulation from PSII |
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Term
| Discuss the role of RubisCOin the Calvin cycle and the limitations of this enzyme as they affect C fixation. |
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Definition
[image]
RubisCOcatalyzes two opposite and competing reactions: one side is C3 Carbon fixation (consuming O2 and breaks C-C bonds) and the other side is photorespiration (recylcing phosphoglycolate produced from photorespiration) This may be useful as a means of dissipating excess energy
Very low reaction rate (one of hte slowest) |
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Term
| The Calvin cycle (C3 photosynthesis) |
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Definition
[image]
A co2 molecule reacts with a 5C sugar (Ribulose) to produce 3 carbon compounds (3-phosphoglycerate). |
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Term
| What are some benefits of Photorespiration? |
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Definition
Low light (limits PS)
Excess light can damage cells(accumulation of ROS)
Photorespiration can “burn” excess ATP generated by high light |
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Term
Discuss strategies used by plants to enhance C fixation by RubisCO.
How do photosynthetic organisms cope with a poor C-fixing catalyst? |
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Definition
1. Synthesize lots of the enzyme
2. Concentrating CO2 around RubisCO
C4 and CAM PS |
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Term
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Definition
C4 plants trap CO2 in a chemical form which doesn't diffuse through the air and can be concentrated inside cells
Bundle sheath cells contain rubisco and are isolated form contact with air, so it is shielded from contact with O2, then C4 acids act as a shuttle for CO2
Enzyme PEP-carboxylaseto convert CO2 into a 4C organic acid (e.g. malic/ aspartic acid).This C4 compound can be used as a C shuttle –delivering CO2to internal plant tissues in close vicinity to RubisCO, and concentrating CO2 around Rubisco
[image] |
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Term
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Definition
In arid environments
CO2 is also trapped as an organic (4C) acid, and delivered to RubisCO at high concentrations
CAM plants load CO2 into C4 acids at night, release CO2 from C4 during the day. in this circumstance, C4 compound can be accumulated and used in the same cell
since O2 is only produced when there is light, this works well |
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