#7: Alternative Mechanisms to Carbon Fixation Flashcards Preview

Bio 4U- Unit 2: Photosynthesis > #7: Alternative Mechanisms to Carbon Fixation > Flashcards

Flashcards in #7: Alternative Mechanisms to Carbon Fixation Deck (7)
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Explain Normal Plants

Plants have to regulate their water loss, and respond to water availability.

Stomata are small openings that control the gas exchange with the atmosphere.

Stomata are open during the day, to allow gas exchange (needed for photosynthesis)
Let CO2 in
Let O2 out


Problem with RuBisCo

Very slow enzyme (though there is lots)

Will also bind to O2 if [CO2] decreases, or O2 increases.

When it binds with O2 it creates a useless molecule for the cell
The recovery of this molecule is long, takes energy (ATP) and produces CO2 (opposite of its job)

Called photorespiration (waste of resources for cell)


Challenge with Plants in hot, dry climates

How to let in carbon dioxide without losing all the plants water


Alternative 1: C4 Plants
(Sugar cane, corn)

Mesophyll acts as a barrier to reduce Rubisco’s exposure to O2

CO2 is continually pumped from mesophyll to the bundle-sheath cells to enter the Calvin cycle

CO2 is converted to a 4C (oxaloacetate and malate), before giving off CO2 and forming pyruvate (3C)

Keeps [CO2] high so it can outcompete O2 – minimize photorespiration

Extra ATP is used as compared with C3


1. Bundle-sheath (photosynthetic cell)

surrounding a vein - where the Calvin Cycle occurs


2. Mesophyll cells (photosynthetic cell)

located around the bundle sheath - barrier for Oxygen


Alternative 2: CAM plants
(Cacti, pineapple)

These plants open their stomata at night, and close them during the day (opposite of other plants)

CO2 is converted again to 4C (oxaloacetate and malate), stored in the vacuole before being releasing CO2 throughout the day

Helps conserve water, but prevents CO2 from entering leaves during day