Calvin
Named after American biochemist Melvin Calvin
Most commonly used pathway by most plants
Calvin cycle is used by plants that are called C3 because of the 3-Carbon molecules that are made
PhotosynthesisLight-independent reaction
(Dark Reaction)Does not require light
Calvin CycleOccurs in stroma of chloroplastRequires CO2
Uses ATP and NADPH as fuel to runMakes glucose sugar from CO2 and
Hydrogen
The Calvin cycle uses products from the light reactions + CO2 to make sugars and other compounds
What are the products of the light reactions?
Where does the CO2 come from?
Calvin Cycle
Calvin Cycle
CO2 is changed to sugar in a series of chemical reactions:
CO2 + RuBP 6-Carbon molecule RuBP = 5 Carbon sugar
The Enzyme that catalyzes this reaction is rubisco = the most abundant protein in nature(25%)
Step 1CO2 is diffused into the stroma of the
chloroplast
A 5-Carbon molecule named RuBP combines to the CO2
This becomes a 6-Carbon molecule that is
very unstableSplit to become two 3-Carbon molecules
called 3-phosphoglycerate (3-PGA)
6-Carbon Sugar 3-PGA + 3-PGA
Step 2
3-PGA is still unstable3-PGA glyceraldehyde 3-phosphate (G3P)
For this to occur, each3-PGA molecule gets a phosphate from ATP and a proton from NADPH
Once the molecule receives the P and proton it converts into G3P
Step 4
Other G3P molecule gets converted BACK to RuBP due to an addition of another phosphate from ATP G3P + P RuBP
This RuBP goes back to the Calvin cycle to be fixed again
Oxidation Reaction
Loss of electrons from a substance in a chemical reaction
What molecules were oxidized during photosynthesis?
Reduction Reaction
The gain of electrons by a substance in a chemical reaction
Which substances were reduced during photosynthesis?
StomaStoma Open
CO2 can increase
O2 will decrease and leave cells
Stoma ClosedCO2
decreaseO2
increases
C4 Pathway
Plants that use this are called C4 plants and have stomata closed during hot part of day
Enzyme fixes CO2 to a 4-carbon compound when CO2 is low and O2 is high
Corn, sugar cane, & crab grass
Usually tropical climates
CAM Pathway
Water conserving pathway
Hot dry climates
Stoma closed during day & open at nightOpposite of ordinary plants
Pineapples & cactuses
CAM Pathway
During the dayStoma are closedCO2 is released from compounds and
enters Calvin cycle
During the nightStoma are openTake in CO2 and fix into carbon
compounds
PHOTOSYNTHESIS
What affects photosynthesis? Light intensity: as light increases, rate of
photosynthesis increases
PHOTOSYNTHESIS
What affects photosynthesis? Carbon Dioxide: As CO2 increases, rate of
photosynthesis increases