Alternative Pathways Alternative Pathways to Cellular to Cellular

Respiration!Respiration!By: Julia Sigman, Izzie Gall, Kalah By: Julia Sigman, Izzie Gall, Kalah

Haley, Valencia WatsonHaley, Valencia Watson

C4 PathwayC4 Pathway C4 stands for 4 carbonC4 stands for 4 carbon In order for the Calvin Cycle to take place, In order for the Calvin Cycle to take place,

Rubisco must carry carbon dioxide to a 5 Rubisco must carry carbon dioxide to a 5 carbon molecule (Ribulose bisphosphate) carbon molecule (Ribulose bisphosphate) during carbon fixationduring carbon fixation

OH NO!OH NO! When carbon dioxide levels are low, rubisco When carbon dioxide levels are low, rubisco

has a hard time finding the carbon dioxide and has a hard time finding the carbon dioxide and needs assistanceneeds assistance

Without the carbon dioxide, the calvin cycle Without the carbon dioxide, the calvin cycle cannot occurcannot occur

In such cases, COIn such cases, CO22 goes through stoma and goes through stoma and goes to the mesophyll cellgoes to the mesophyll cell

So what do we do about it?So what do we do about it? Once in the mesophyll cell, we find PEP Once in the mesophyll cell, we find PEP

carboxylase, a 3C moleculecarboxylase, a 3C molecule The COThe CO22 then comes in and forms a 4C then comes in and forms a 4C

molecule (oxaloacetate)molecule (oxaloacetate) The molecule rearranges to make the COThe molecule rearranges to make the CO2 2 able able

to be broken off easier.to be broken off easier. From there, the From there, the COCO2 2 breaks off and a 3C molecule breaks off and a 3C molecule

(pyruvate) is left to go through the cycle again(pyruvate) is left to go through the cycle again

What the what?What the what? Basically, without rubisco carrying the COBasically, without rubisco carrying the CO22 the calvin the calvin

cycle cannot fuction thus photosynthesis cannot cycle cannot fuction thus photosynthesis cannot occur.occur.

When COWhen CO22 levels are low and rubisco has trouble levels are low and rubisco has trouble finding it the COfinding it the CO22 travels through the stomata into travels through the stomata into the mesophyll cell and PEP carboxylase finds it and the mesophyll cell and PEP carboxylase finds it and gives the COgives the CO2 2 to rubiscoto rubisco

Once the rubsico has the COOnce the rubsico has the CO2 2 it travels to the bundle-it travels to the bundle-sheath cell, where it surrounds the vein, thus the sheath cell, where it surrounds the vein, thus the calvin cycle can continuecalvin cycle can continue

What could go wrong?What could go wrong? The problem with the C4 pathway is that it The problem with the C4 pathway is that it

uses ATP in addition to the ATP used in the uses ATP in addition to the ATP used in the calvin cyclecalvin cycle

When pyruvate is left after the COWhen pyruvate is left after the CO2 2 breaks off breaks off the malate, it takes ATP to rearrange the pyruvate the malate, it takes ATP to rearrange the pyruvate into PEP.into PEP.

Who would do this?Who would do this? Organisms that perform the calvin cycle are Organisms that perform the calvin cycle are

corn and sugar cane.corn and sugar cane.

CAM PathwayCAM Pathway CAM stands for Crassulacean Acid CAM stands for Crassulacean Acid

MetabolismMetabolism The CAM pathway is specific for day and The CAM pathway is specific for day and

nightnight The CAM pathway is utilized by plants that The CAM pathway is utilized by plants that

close their stomata during the day in order to close their stomata during the day in order to prevent evaporation of their water prevent evaporation of their water

Sleepover!!Sleepover!! Plants close their stomata during the dayPlants close their stomata during the day As in C4 plants, the CAM Pathway uses PEP As in C4 plants, the CAM Pathway uses PEP

Carboxylase to fix a carbon molecule to a 4 Carboxylase to fix a carbon molecule to a 4 Carbon molecule forming oxaloacetateCarbon molecule forming oxaloacetate

The oxaloacetate is rearranged and converted The oxaloacetate is rearranged and converted into malate, which is stored in cell vacuoles into malate, which is stored in cell vacuoles overnight (aka there is a COovernight (aka there is a CO2 2 slumber party) slumber party)

Ba-BAM!Ba-BAM! Because the plants close their stomata during Because the plants close their stomata during

the day the COthe day the CO2 2 gets backed up in the plantgets backed up in the plant The COThe CO2 2 is stored overnight in the malateis stored overnight in the malate During the day, when the stoma are closed, During the day, when the stoma are closed,

COCO22 is removed from the stored malate and is removed from the stored malate and enters the Calvin Cycle and photosynthesis can enters the Calvin Cycle and photosynthesis can continue continue

What are examples of CAM plants?What are examples of CAM plants?

Pineapples and cacti Pineapples and cacti The problem with the CAM cycle is, like the The problem with the CAM cycle is, like the

C4 pathway, it uses additional ATP. C4 pathway, it uses additional ATP.