5.5.2 C4 Plants and CAM Plants

Question 1

C4 and CAM plants

Answer 1

• have special adaptations that allow them to avoid the problem of photorespiration

Question 2

C4 plants

Answer 2

• are able to avoid photo-respiration by using an
  alternative form of carbon fixation.
• Bundle sheath cells line the veins of C4 plants. The
  Calvin cycle takes place in chloroplasts of the bundle sheath cells, while carbon fixation takes place in the mesophyll cells.
• In C4 plants carbon dioxide is fixed to a molecule called
  phosphoenolpyruvate (PEP) by the enzyme PEP carboxylase within the mesophyll cells. This reaction
  forms the molecule oxaloacetate, which is converted into
  malate. Malate then diffuses into the bundle sheath cells were it is broken down into carbon dioxide and pyruvate. The CO2 that is released enters the Calvin cycle, while the pyruvate returns to the mesophyll cells and is converted back into PEP.

Question 3

CAM plants

Answer 3

• While C4 plants avoid photorespiration by fixing CO2
  in separate location from the Calvin cycle, CAM plants fix their CO2 at a different time than the Calvin cycle.
• CAM plants have their stomata closed during the day and open at night. By having their stomata closed during the day, water loss by evaporation is minimized. When their stomata are opened at night, CO2 is taken up and incorporated into acids. During the day the acids release the CO2, which then enters the Calvin cycle.

Question 4

True or false?
During the C4 pathway, carbon dioxide is fixed in the mesophyll cells and enters the Calvin cycle in the bundle-sheath cells.

Answer 4

• true

Question 5

Which takes place when a C4 plant first fixes carbon dioxide?

Answer 5

• PEP carboxylase is required

Question 6

True or false?
The C4 and C3 pathways differ in that they take place at different times, whereas CAM and C3 pathways differ in that they occur at different locations within the leaf.

Answer 6

• false

Question 7

How are C4 and CAM plants similar?

Answer 7

• Both cases employ an enzyme other than rubisco to initially fix carbon

Question 8

In what way do CAM plants and C4 plants differ?

Answer 8

• Carbon fixation is not separated from the Calvin cycle in CAM plants, while it is in C4 plants