Alternate pathways

Calvin cycle - most common pathway for carbon fixation

C3 plants - fix exclusively through Calvin cycle
	3-carbon compound PGA is the 1st stable compound

Some plants fix carbon through alternate pathways- then release it into the Calvin cycle
	often in hot/dry climates
		plants can rapidly lose water to the air
			most water loss is through stomata
				pores on the underside of leaves
				major passageway for CO2 and O2 to enter/leave
				can close
					closed-inhibit carbon fixation by Calvin cycle

C4 pathway
	stomata remain partially closed
	enzyme that can fix CO2 into a 4-carbon compound even when CO2 level is low
	compounds are then transported to other cells where CO2 is released and enters the Calvin cycle
	used by:
		corn
		sugar cane
		marsh grass/crabgrass
	C4 plants lose 1/2 the water as C3 plants while producing the same amount of carbohydrates

CAM pathway
	used by:
		cacti
		pineapples
	open stomata at night, close during the day
		(opposite of other plants)
	night- take in CO2 and fix it into a variety of different compounds
	day- CO2 is released from compounds and enters the Calvin cycle
	grow slowly
	lose less H2O than both C4 and C3

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