Transcript Alternative Pathways to Cellular Respiration!

Alternative Pathways
to Cellular
Respiration!
By: Julia Sigman, Izzie Gall, Kalah
Haley, Valencia Watson
C4 Pathway
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C4 stands for 4 carbon
In order for the Calvin Cycle to take place,
Rubisco must carry carbon dioxide to a 5
carbon molecule (Ribulose bisphosphate)
during carbon fixation
OH NO!
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When carbon dioxide levels are low, rubisco
has a hard time finding the carbon dioxide and
needs assistance
Without the carbon dioxide, the calvin cycle
cannot occur
In such cases, CO2 goes through stoma and
goes to the mesophyll cell
So what do we do about it?
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Once in the mesophyll cell, we find PEP
carboxylase, a 3C molecule
The CO2 then comes in and forms a 4C
molecule (oxaloacetate)
The molecule rearranges to make the CO2 able
to be broken off easier.
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From there, the CO2 breaks off and a 3C molecule
(pyruvate) is left to go through the cycle again
What the what?
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Basically, without rubisco carrying the CO2 the calvin
cycle cannot fuction thus photosynthesis cannot
occur.
When CO2 levels are low and rubisco has trouble
finding it the CO2 travels through the stomata into
the mesophyll cell and PEP carboxylase finds it and
gives the CO2 to rubisco
Once the rubsico has the CO2 it travels to the bundlesheath cell, where it surrounds the vein, thus the
calvin cycle can continue
What could go wrong?
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The problem with the C4 pathway is that it
uses ATP in addition to the ATP used in the
calvin cycle
When pyruvate is left after the CO2 breaks off
the malate, it takes ATP to rearrange the pyruvate into
PEP.
Who would do this?
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Organisms that perform the calvin cycle are
corn and sugar cane.
CAM Pathway
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CAM stands for Crassulacean Acid
Metabolism
The CAM pathway is specific for day and
night
The CAM pathway is utilized by plants that
close their stomata during the day in order to
prevent evaporation of their water
Sleepover!!
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Plants close their stomata during the day
As in C4 plants, the CAM Pathway uses PEP
Carboxylase to fix a carbon molecule to a 4
Carbon molecule forming oxaloacetate
The oxaloacetate is rearranged and converted
into malate, which is stored in cell vacuoles
overnight (aka there is a CO2 slumber party)
Ba-BAM!
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Because the plants close their stomata during
the day the CO2 gets backed up in the plant
The CO2 is stored overnight in the malate
During the day, when the stoma are closed,
CO2 is removed from the stored malate and
enters the Calvin Cycle and photosynthesis can
continue
What are examples of CAM plants?
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Pineapples and cacti
The problem with the CAM cycle is, like the
C4 pathway, it uses additional ATP.