Alternate Carbon Pathways

Question 1

what kind of plants are C3

Answer 1

“normal” plants
approx. 85% of plants
rice, wheat, soybeans, all trees

Question 2

advantages of C3

Answer 2

• stoma can be open all day to take in CO2, release O2

- low energy requirements so fewer steps means less energy needed

Question 3

disadvantages of C3

Answer 3

• stoma being open often means move H2O lost through transpiration
• no separation of Rubisco from O2, so photorespiration is common
• not as productive in warm, sunny, dry conditions

Question 4

what kind of plants are C4

Answer 4

plants well- adapted to high temperatures, light intensities, and dryness
3% of vascular plants
corn, sugarcane, grass

Question 5

advantages of C4

Answer 5

• limited photorespiration (high CO2, low O2)
• because of heat, a lot of H2O is lost, limiting photorespiration less energy is waster per H2O in light reaction
  -more efficient use of CO2
  benefit of reduced photorespiration likely exceeds ATP
• cost of moving CO2 from mesophyll to bundle-sheath

Question 6

Disadvantages of C4

Answer 6

• energy-intensive
• C4 plants need 5 ATP to fix one CO2 whereas C3 plants only need 3 ATP
• does not compete well at lower temperatures

Question 7

what kind of plants are CAM

Answer 7

plants well-adapted to high light intensity and water stress (dry)
7% of plants
pineapple, cacti

Question 8

advantages of CAM

Answer 8

• limited water loss which allows plants to survive where water loss is a major limiting factor to plant growth
• limited photorespiration (high CO2, low O2)

Question 9

disadvantages of CAM

Answer 9

• energy-intensive
• does not compete well at lower temperatures
• stomata closed during the day which means less CO2 entering