8. Photosynthesis Flashcards
What is the photic zone?
surface layer of the ocean, about 100 m deep
- where photosynthesis is able to occur
What are the two stages of photosynthesis?
- light capture: capture energy from sunlight into useable chemical forms
- carbon fixation: convert CO2 into organic molecules
What type of reaction is photosynthesis? what is its end goal?
redox reaction
Use CO2 and sunlight to from high energy carbohydrate molecules
What is the electron donors in the photosynthesis reaction? What are the products?
Water
After oxidation, water becomes:
- electrons
- protons
- O2
Name the parts of a chloroplast
- outer membrane
- inner membrane
- thylakoid: highly folded flattened membrane sacks
- lumen: space inside the thylakoid membrane
- grana: the orderly stacks of thylakoids
- stroma: space surrounding thylakoids (where carbon fixation occurs)
What are pigments? What is the principle pigment in photosynthesis?
pigments: molecules that absorb some or all wavelengths of visible light
photosynthetic pigments:
- absorbs photons and transitions to a higher energy state
- transfers energy to anther molecule to reestablish ground state
chlorophyll is the principle pigment in photosynthesis
- reflects green wavelengths
What is the light dependent reaction in photosynthesis?
- chlorophyll absorbs light energy
- energy is used to power the movement of electrons
- movement of electrons through the photosynthetic electron transport chain creates NADPH and ATP
What is the light independent reaction in photosynthesis?
Calvin cycle
What is the molecule getting oxidized/reduced in the reaction for photosynthesis?
Energy + 6CO2 + 12H2O
->
Glucose C6H12O6 + 6O2 + 6H2O
CO2 reduced to glucose
H2O oxidized to Oxygen
What is the structure of chlorophyll?
Porphyrin ring for light absorption
- Magnesium surrounded by alternating double/single bonds
Phytol side chain
- insertion of chlorophyll in the lipid bilayer (thylakoid membrane)
- positioned within integral membrane proteins
Does the oxygen resulting from photosynthesis come from water or CO2?
water
What is a photosystem
Protein + pigment complexes that absorb light energy and drive electron transport
What are accessory pigments?
Additional pigments other than chlorophyll that photosystems have
- etc. carotenoids (yellow/orange)
What is the difference in the behaviour of chlorophyll absorbing light in the lab vs in a chloroplast
in the lab:
- remits energy as heat
- small amount of fluorescence
in chloroplast:
- transfers energy to adjacent chlorophyll (very efficient!)
What is an antenna chloropyll
the initial chlorophyll molecule that absorbs the light energy (and then passes it on)
T/F antenna chlorophylls transfer electrons
F
they transfer energy
What is the reaction center
- end destination of the chlorophyll’s energy
- at the reaction center, the electron itself (along with energy) is transferred to an adjacent molecule
so the reaction center becomes oxidized and the adjacent electron acceptor becomes reduced
Where does the reaction center get its electron from, after it has donated it?
H2O
What are the roles of the two photosystems?
Photosystem II: Takes in energy to allow electrons to be pulled from water
Photosystem I: Takes in energy to allow electrons to be transfered from NADP+ to NADPH
What is the Z scheme?
The energy trajectory as the electron moves through and between the two photosystems resembles a Z turned on its side (CCW)
- moving through: increase in energy
- moving between: decrease in energy
What are the parts of the photosynthetic electron transport chain?
- Photosystem II
- Pq (plastoquinone)
- b6f complex
- Pc (pastocyanin)
- Photosystem I
- Fd
- NADP reductase
How does the proton gradient get produced in the photosynthetic electron transport chain?
- In photosystem II, by breaking H2O into H+ + O2
- Using the b6f complex to pump H+ from outside the thylakoid membrane (stroma) to inside the lumen
How many molecules of NADPH and ATP are required for each CO2 incorporated into carbohydrates (calvin cycle)?
2 molecules of NADPH
3 molecules of ATP
What is cyclic electron transport?
Electrons from photosystem I are redirected back into the electron transport chain
What has the higher proton concentration
- Lumen
- Stroma
Lumen
What are the three main steps of the calvin cycle?
Carboxylation
- Addition of CO2 to 5-carbon compound RuBP
- Catalyzed by the enzyme rubisco
- Outputs are two 3-carbon compounds (3-phosphoglycerate, PGA)
Reduction
- Increases the potential energy of the PGA
- Energy inputs from ATP and NADPH lead to the synthesis of triose phosphates (G3P)
- NADPH transfers two electrons and one proton
- Outputs are 3-C
Regeneration
- 3-Carbon compounds are reorganized and combined to produce RuBP
- Requires energy (ATP)
What are extra carbohydrates from the Calvin cycle stored as?
starch
- If the carbohydrates were in the form of soluble sugars, it would cause water to enter the cell by osmosis
What are the main inputs and outputs to the carbon cycle?
Main inputs:
- CO2 (from the atmosphere), ATP and NADPH (from the photosynthetic electron transport chain)
Main outputs:
- carbohydrates (triose phosphates, G3P)
- ADP and NADP+
The Calvin cycle requires both ATP and NADPH. Which of these molecules provides the major input o f energy needed to synthesize carbohydrates?
NADPH
What are two hypotheses for why there are two photosystems?
- Horizontal gene transfer (organism 1 gives a gene to organism 2)
- Duplication and divergence (mutation during duplication of the gene)
What were the first organisms to use water as the electron donor?
cyanobacteria
