MP9 - Alternative Mechanisms to Carbon Fixation

What is carbon fixation?

the process of converting CO₂ from an unusable inorganic molecule to useable organic molecules

What is the problem with C3 plants?

O₂ binds with RuBisCO instead of CO₂ (photorespiration)

Photoautotrophs must fix …

carbon (from carbon dioxide) to produce glucose)

Describe the C4 pathway.

CO2 + PEP -> oxaloacetate -> malate -> CO2 + pyruvate. This pathway builds up CO2 concentration to enter the Calvin cycle.

Where does the C4 pathway occur in the leaf?

Mesophyll cells.

How do C4 and CAM plants differ in how they separate the C4 pathway and the Calvin cycle?

C4 plants separate them spatially (different cells), while CAM plants separate them temporally (different times).

Describe what happens in CAM plants at night.

Stomata open, CO2 enters, and the C4 cycle fixes CO2 into malate.

Describe what happens in CAM plants during the day.

Stomata close to prevent water loss; malate is oxidized to release CO2 for the Calvin cycle.

What problem occurs when  O2 takes the binding site instead of CO2?

We end up losing CO2 (to the atmosphere) which reduces the amount of carbon fixed

What are the two other problems with C3?

rubisco is slow at fixing carbon; now there is competition for the binding site of rubisco

In C4 photosynthesis plants, the dark reaction occurs in the

bundle-sheath cell

Why does more oxygen that gets into the mesophyll cell?

more closer to the surface of the leaf (through stomata)

What brings CO2 deeper into the cell for carbon fixation (into the bundle-sheath cell) in C4?

Another enzyme

The C₄ pathway occurs in

leaves of the plant

C4 plants preferred habitat are?

hot and dry locations (corn, sugar cane)

Why does C4 plants pathway of carbon fixation occurs in the leaves of plants?

since, their is a higher oxygen concentration near the leaf

The mesophyll cell takes carbon dioxide and combines it with _______ to produce ________ by ______

PEP (3C), oxaloacetate (4C), PEP carboxylase

What happens to oxaloacetate in C4 plants?

reduced by NADPH to form malate

How can malate enter the bundle-sheath cell?

diffusion

What happens to malate in C4 plants?

oxidized and decarboxylated to produce pyruvate

What happens to pyruvate in C4 plants?

hydrolysis of ATP + PPi to AMP to regenerate PEP

Why do C4 plants have their stomata closed?

to prevent water loss

CAM plants complete C4 and Calvin cycle in the ______but during different times

same area

Where do CAM live?

 locations with hot and dry days and cool nights (these are usually cacti)

What happens during the night in CAM plants?

stomata open and allow O2 to be released and CO2 to be brought into the plant. The CO2 is fixed into malate through the C4 cycle and it accumulates in the vacuole during the night (as malic acid)

What happens during the day in CAM plants?

the sun comes out and heats up the temperature, the stomata close to prevent water loss.The malate diffuses from the vacuoles into the cytoplasm where malate is oxidized by NADP+ to form pyruvate and a large concentration of CO2 is released and entered into calvin cycle to fix CO2 into gulcose

Requires more energy to fix carbon but allows plant to work harder at night _______________________.

when its cooler to prevent water loss

Why is it important to prevent water loss by closing the stomata?

so, water can make P680 netural for it to then absorb light energy and facilitate to make glucose