Chapter 10: Photosynthesis Flashcards
What are photons?
Discrete particles with a fixed amount of energy but no mass
What does the electron transport chain create in the light rxns?
Creates a buildup of H+ inside the cell which flow through ATP synthase to generate ATP
Where is chlorophyll found?
In the thylakoid membranes of the chloroplasts
What are the 3 phases of the Calvin cycle?
Carbon fixation, reduction, and regeneration of CO2 acceptor
What are C3 plants?
Plants that use rubisco for initial carbon fixation. Standard photosynthesis because a 3 carbon product is formed
Path of travel through the photosystems
Photosystem II to electron transport chain to photosystem I
How many tons carbohydrate are produced by a plant each year?
160 billion tons
What becomes oxidized in photosynthesis? What does it oxidized to?
H2O oxidized to O2
How do pigments act as protection?
Act as buffers to absorb excess energy from the sun so the plant isn’t damaged
What is white light?
Reflecting all visible light wavelengths
What is the range for the visible light spectrum?
380nm - 750 nm
What is it called when the cell generates ATP from the light rxns? What is it called when the equivalent happens in cellular respiration?
Photophosphorylation. Oxidative phosphorylation
Overview of regeneration of CO2 acceptor in Calvin cycle
Series of steps which utilize ATP to rearrange 5 molecules of G3P to regenerate 3 molecules of RuBP
What is the product of 3 rounds of the Calvin cycle?
6 G3P but only 1 net G3P
What types of plants have alternate methods of carbon fixation to minimize photorespiration?
C4 plants (4 carbon products) and CAM plants (crassulacean acid metabolism)
Where does the energy come from for photosynthesis?
Light
Light rxns equation
Light + H2O –> NADPH + ATP + O2
What do different pigments do?
Absorb different wavelengths of light
How do CAM plants work?
Stomata close during day to conserve H2O but open at night and take in CO2 and fix it in organic acids which are stored in vacuoles. During the day, CO2 is released from organic acids to enter the Calvin cycle with the supply of ATP and NADPH
Why do leaves change colors?
Presence of additional pigments like carotenoids. Plants stop producing chlorophyll when getting ready to lose leaves, so carotenoids are no longer masked
What occurs in the Calvin cycle?
Uses the chemical energy stored in ATP and NADPH to reduce CO2 to sugar (G3P)
What is chlorophyll a? What wavelength does it absorb?
Contains CH3. Absorbs highest around 430 nm
What does the z scheme mean in the photosystems?
Linear flow of electrons. They follow a z shape
What are granums?
Stacks of thylakoids in chloroplasts
What are the two parts of the photosystems that capture light in the light rxns?
Antenna complexes and run-center complexes
What do the light rxns do?
Convert light energy into chemical energy
What happens at the electron transport chain in the light rxns?
Electrons come with H+ from P680 in photosystem II into the electron transport chain. The electron transport chain provides energy for ATP synthesis by chemiosmosis. The electrons move into photosystem I
What do the light rxns do at the molecular level?
H2O split to provide electrons and H+, NADP+ reduced to NADPH, ATP produced, O2 given off
Overview of reduction in Calvin cycle
Carbon intermediate phosphorylated by ATP. Reduced by NADPH and loses the phosphate creating G3P
What are stomata?
A part of a plant that is an opening
What key step occurs in photosystem II?
H2O is split into O2 (which is a product) and H+ (electron)
What is light a form of?
Energy. Electromagnetic radiation
How many times must the Calvin cycle occur for one G3P and why?
3 times for one G3P because 3CO2 must be fixed per G3P
What do plants have to do with the sugar products of photosynthesis?
Transport in throughout the cell because only the green parts are photosynthetic
What does fixing O2 cause for photosynthesis?
Consumes ATP and reduces photosynthesis by siphoning off material from the Calvin cycle
Why do chlorophyll a and b appear green?
They don’t absorb wavelengths in that part of the spectrum (green)
What is photorespiration?
When rubisco fixes O2 instead of CO2
What is reduced in photosynthesis? What is it reduced to?
CO2 reduced to C6H12O6
What two products of the light rxns move to the Calvin cycle?
NADPH and ATP
What problems occur with carbon fixation in hot dry climates?
Plants close stomata to minimize H2O loss but this reduces the amount of CO2 available so the concentration of O2 released from the light rxns increases which favors rubisco fixing O2 instead of CO2
What type of rxn is photosynthesis?
Redox
Is photosynthesis endergonic or exergonic and why?
Endergonic because building a more complex molecule (glucose) requires energy
What does the Calvin cycle need?
Products from the light rxns (NADPH and ATP)
What happens at photosystem II?
Light excites, water is split into O2 and H+, P680 moves the electrons from water being split out to the electron transport chain
What is the electron transport chain called in the light rxns?
Cytochrome complex
What do antenna complexes do?
Contain pigment molecules which absorb light and transfer the energy to rxn-center complexes. They are light harvesting complexes
What happens to the 4 carbon product in C4 plants?
It is transported to bundle sheath cells where the CO2 is released and can be added to the Calvin cycle by rubisco
What is the equation of photosynthesis the opposite of?
Cellular respiration. Inputs and outputs are flipped but processes are completely different
How does the Calvin cycle end up proceeding in C4 and CAM plants?
Normally
What is chlorophyll b? What wavelength does it absorb?
Contains CHO. Absorbs highest around 460nm
What does the Calvin cycle (light independent/dark rxns) do?
Fixes carbon from CO2 into organic molecules, reduces fixed carbon into sugar using the NADPH and ATP from light rxns
What does fixing O2 instead of CO2 cause?
O2 is added to the Calvin cycle instead of CO2 creating a 2 carbon compound that is broken down by mitochondria and peroxisomes to release CO2. Consumes ATP and decreases photosynthesis by siphoning off material from the Calvin cycle. Uses resources and energy and doesn’t provide anything useful
How much ATP and NADPH are required for the production of 1 net G3P (3 rounds of Calvin cycle) and why is this not an issue?
9 ATP and 6 NADPH. Not a problem because the sun allows the plant to make a lot of ATP and NADPH
Where does the O2 come from in photosynthesis?
H2O
What is a pigment?
A substance that absorbs visible light
Where does carbon fixation occur in C4 plants?
It is separated spatially from the Calvin cycle. The Calvin cycle takes place in a different place than carbon fixation
Where does carbon fixation occur in CAM plants?
It is temporally separated from the Calvin cycle
What do C4 plants require?
ATP
Where are ATP and NADPH used in the Calvin cycle?
6ATP and 6NADPH used to reduce 3PGA to G3P. 3ATP used to regenerate RuBP from G3P
What is black light?
Absorbing all visible light wavelengths
What initially fixes CO2 in C4 plants and what does it produce?
Fixed by PEP carboxylase in mesophyll cells to form a 4 carbon product
What do rxn-center complexes do?
Contains a special pair of chlorophyll a molecules which can reduce the primary electron acceptor
How is carbon fixed in CAM plants?
At night CO2 is taken in and fixed in organic acids which are stored in vacuoles until the light comes back to supply ATP and NADPH for the Calvin cycle
What happens in C4 plants?
PEP carboxylase fixes CO2 to produce a 4 carbon product that is transported to bundle sheath cells where CO2 is released and can be added to the Calvin cycle by rubisco
What happens during photosynthesis?
Water is split and the electrons (along with H+) are transferred to CO2, reducing it to sugar
What is the equation for photosynthesis?
6H2O + 6CO2 + radiant energy (sunlight) –> C6H12O6 + 6O2
What can rubsico fix in place of CO2 that causes problems?
O2
Where are the photosystems that capture light in the light rxns?
Thylakoid membranes
What do plant mitochondria do in the dark?
Burn stored sugar
What do CAM plants require?
ATP
What are the sugar products also used for?
Linking together to form cellulose and stored in excess as starch
What are the two rxns in photosynthesis?
Light rxns and Calvin cycle (light independent/dark rxns)
What happens in photosystem I?
Light excites, electrons carried with P700, electron moves out and is given to NADP+ to create NADPH
What wavelengths do carotenoids absorb?
460nm - 490nm
What is cyclic electron flow in the light rxns and what does it do?
Electrons from photosystem I are transferred back to the electron transport chain to create a proton gradient to generate ATP instead of NADPH
What is G3P?
A product of photosynthesis that can build glucose or other sugars
What are the parts of a chloroplast?
Stroma, granum, thylakoid, thylakoid space, inner membrane, inter membrane space, outer membrane
What is the electromagnetic spectrum?
The entire range of radiation
What is about 50% of the sugar produced in photosynthesis used for?
Fuel for cellular respiration in the mitochondria
What are the other 5 G3P products used for from 3 rounds of the Calvin cycle?
They are used to regenerate RuBP
Overview of carbon fixation in Calvin cycle
Rubisco (RuBP carboxylase) attaches CO2 molecule to ribulose bisphosphate (RuBP)
Who proved the O2 in photosynthesis came from H2O
C.B. van Niel
