Photosynthesis Flashcards
How is light harvested?
Photosynthetic pigments catch sunlight energy. Chlorophyll a is the main photosynthetic pigment.
What is the antennae?
The organised group of all the pigments which transmit energy from sunlight to chlorophyll a in the reaction center.
What are the photosystems made of?
An antenna complex and protein machinery embedded in the thylakoid membrane. They power the light reactions.
What reaction happens at PSII?
Photolysis:
H2O –> H+, e-, O2
What happens at the electron transport train?
Electrons are transferred via several carriers in the electron transport chain from photosystem II to photosystem I, losing reducing power on the way.
What happens at PS1?
The excitation by light of PSI reaction center powers more electron movement across another electron transport chain, ending up in the reduction of NADP+ into NADPH.
What reduces NADP+ into NADPH in the light dependent reaction?
Ferradoxin reductase
How is ATP made in the light dependent reaction?
The electron transport generates a proton gradient necessary for the synthesis of ATP.
How can high light levels damage a plant?
Generation of reactive oxygen species. Excess energy/electrons end up on oxygen.
Where do the light dependent reactions take place?
In the lumen of the thylakoids.
Where to the light independent/carbon fixing reactions take place?
In the chloroplast stroma.
How is 3-PGA produced?
A carboxylation where CO2 is added to RuBP.
How is G3P produced?
A reduction of PGA, ATP -> ADP + Pi
NADPH -> NADP+ + H+
How many carbons does it take to produced one G3P for biosynthesis and energy?
How many G3Ps carry on in the cycle?
3 carbons.
5 G3Ps.
How is RuBP formed?
5 G3Ps are regenerated.
ATP -> ADP + Pi
What is G3P used for?
To make sucrose to be transported to other parts of the plant, or stored temporarily in starch granules. (which can then be hydrolysed to make sucrose at night)
What is photorespiration?
Rubisco can catalyse oxygenation as well as carboxylation of RuBP.
This produces 1 3-PGA and 1 2-phosphoglycolate (2PG). Recycling 2PG takes energy and releases fixed CO2.
What is C4 photosynthetic metabolism?
C4 plants fix CO2 in mesophyll cells and carry out the Calvin-Benson cycle in bundle sheath cells. Reducing photorespiration.
What is CAM photosynthetic metabolism?
CAM plants fix CO2 at night and carry out the Calvin-Benson during the day.
What are the consequences of C4 and CAM metabolisms?
Cost of C4: ATP is needed for pyruvate transport back to mesophyll cells
Disadvantage to CAM: the quantity of CO2 fixed at night isn’t enough for a full day of the Calvin-Benson cycle.
Why are C4 and CAM beneficial in hot conditions?
Photorespiration increases with temperature.
