#7: Alternative Mechanisms to Carbon Fixation

Question 1

Explain Normal Plants

Answer 1

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

Question 2

Problem with RuBisCo

Answer 2

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)

Question 3

Challenge with Plants in hot, dry climates

Answer 3

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

Question 4

Alternative 1: C4 Plants

Sugar cane, corn

Answer 4

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

Question 5

1. Bundle-sheath (photosynthetic cell)

Answer 5

surrounding a vein - where the Calvin Cycle occurs

Question 6

2. Mesophyll cells (photosynthetic cell)

Answer 6

located around the bundle sheath - barrier for Oxygen

Question 7

Alternative 2: CAM plants

Cacti, pineapple

Answer 7

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