1. Photosynthesis, Environment & Adaptation C3 vs. C4 vs. CAM Photosynthesis

2. How does matter move in and out of plant cells? Think about the process that matter must go through to move in or out of a plant cell. Diffusion

3. What two molecules must enter a plant cell in order for photosynthesis to take place? Carbon dioxide & Water

4. What one molecule must leave a plant cell in order for photosynthesis to take place? Oxygen

5. While molecules move in and out of a plant cell via diffusion, they actually enter and exit the plant through tiny openings in the leaf called stomata.

6. Stomata in Duck Weed

7. When the stomata close, what two molecules can’t exit the leaf?

8. When the stomata close, what molecule (think about photosynthesis) can’t enter the leaf?

9. So, what happens to the rate of photosynthesis when the stomata close?

10. C3 Photosynthesis C3 plants evolved in a high CO 2 environment Examples: Wheat, rice, tomatoes, oak trees

11. Photosynthesis in the Presence of CO 2 Photorespiration in the Presence of O 2

12. When C3 Plants close their stomata, they begin a process called photorespiration The concentration of O 2 builds up inside the leaf. The enzyme rubisco attaches O2 to RuBP instead of CO2. The intermediate product breaks down to one PGA and one glycolate.

13. What are the implications of photorespiration? Only one molecule of PGA enters the Calvin Cycle Glycolate is broken down and releases a CO 2 Photorespiration is inefficient for plants

14. C4 Photosynthesis C4 plants evolved independently in a hot, dry environment where their stomata MUST be partially closed during the day Examples: Corn, sugar cane and grasses

15. What happens in C4 Photosynthesis? C4 plants have a different cell structure than C3 plants. The Calvin Cycle only takes place in bundle sheath cells

16. What happens when the stomata close & O 2 builds up? PEP carboxylase only bonds with CO2, forming oxaloacetate.

17. The intermediate product malate diffuses to adjacent bundle sheath cells where malate breaks down to pyruvate & CO2.

18. The CO2 then enters the Calvin Cycle and rubisco binds to the CO 2 and the Calvin Cycle proceeds as usual. ATP is used in the process, but photorespiration is minimized and sugar production is increased.

19. What is the impact on Carbon fixation?

20. Photorespiration: An Evolutionary Relic? In most plants (C 3 plants), initial fixation of CO 2, via rubisco, forms a three-carbon compound In photorespiration, rubisco adds O 2 instead of CO 2 in the Calvin cycle Photorespiration consumes O 2 and organic fuel and releases CO 2 without producing ATP or sugar

21. Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O 2 and more CO 2 Photorespiration limits damaging products of light reactions that build up in the absence of the Calvin cycle In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle

22. C 4 Plants C 4 plants minimize the cost of photorespiration by incorporating CO 2 into four-carbon compounds in mesophyll cells This step requires the enzyme PEP carboxylase PEP carboxylase has a higher affinity for CO 2 than rubisco does; it can fix CO 2 even when CO 2 concentrations are low These four-carbon compounds are exported to bundle-sheath cells, where they release CO 2 that is then used in the Calvin cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

23. Fig. 10-19 C 4 leaf anatomy Mesophyll cell Photosynthetic cells of C 4 plant leaf Bundle- sheath cell Vein (vascular tissue) Stoma The C 4 pathway Mesophyll cell CO 2 PEP carboxylase Oxaloacetate (4C) Malate (4C) PEP (3C) ADP ATP Pyruvate (3C) CO 2 Bundle- sheath cell Calvin Cycle Sugar Vascular tissue

24. Fig. 10-19a Stoma C 4 leaf anatomy Photosynthetic cells of C 4 plant leaf Vein (vascular tissue) Bundle- sheath cell Mesophyll cell

25. Fig. 10-19b Sugar CO 2 Bundle- sheath cell ATP ADP Oxaloacetate (4C) PEP (3C) PEP carboxylase Malate (4C) Mesophyll cell CO 2 Calvin Cycle Pyruvate (3C) Vascular tissue The C 4 pathway

26. CAM Plants Some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon CAM plants open their stomata at night, incorporating CO 2 into organic acids Stomata close during the day, and CO 2 is released from organic acids and used in the Calvin cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings