Chapter 10:Photosynthesis

1. Chapter 10:Photosynthesis 6CO2 + 12H2O + Light  C6H12O6 + 6O2 + 6H2O

2. Where does the mass come from? ?

3. Answer: CO2 in the air! • Yes it is true! Gasses have mass!

4. 6CO2 + 12H2O + Light  C6H12O6 + 6O2 + 6H2O

5. Structure of a leaf

6. Organization of photosynthesis and the structure of a chloroplast

7. Photosynthesis and respiration

10. Chlorophyll is a big light antennae Check it out with Rasmol

11. The harvesting of light is through Photosystems (I and II)

12. Non–cyclic electron flow in the light reactions

17. Photophosphorylation

18. Comparison of chemiosmosis and photophosphorylation

19. Cyclic electron flow

21. Why cyclic electron flow? • Non-cyclic flow produces an equal balance of ATP and NADPH. • The Calvin cycle uses ATP more than NADPH, which results in an imbalance. • To generate more ATP and no more NADPH the plant has evolved the cyclic flow which produced ATP and no NADPH.

22. Key steps to the dark reactions

25. See any similarities? Differences?

26. Understanding of photorespiration in C3 plants • Called C3 because Rubisco in the Calvin cycle fixes CO2 into a 3 carbon compound, ribulose bisphosphate, first. • Photorespiration occurs when oxygen levels are high and CO2 levels low. • Rubisco switches gears and incorporates O2 into the first reaction which splits Ribulose bisP into a two-carbon compound • The two carbon compound is exported to the perioxisomes which convert it to CO2.

27. The net result of photorespiration is the consumption of O2 and the production of CO2 (respiration) but no production of ATP. • Results in a siphoning of CO2 from the Calvin cycle • Photorespiration is an evolutionary relic from ancient plants. At that time the atmosphere was much higher in CO2 and much lower in O2. • Under these conditions, the ability of rubisco to exclude O2 from its active site was of little consequence. Essentially CO2 was so abundant that it overwhelmingly “out competed” O2. • Therefore, in today’s plants photorespiration is almost inevitable due to the amount of O2 in the air and the fact that rubisco has retained some of its O2 binding properties.

28. A paradox: Increase photosynthesis for food, open stomates and lose water?What do plants do when they live in arid climates?

29. Simple, evolve special mechanisms for the conservation of water • C4 plants: Mesophyll cells take in CO2 for photosynthesis and convert CO2 to organic acids • The enzymes for the Calvin cycle are only found in specialized cells around the mesophyll called Bundle Sheath cells. • When conditions call for stomates to be closed, the mesophyll cells pump organic acids to the bundle sheath cells which then convert the organic acid to CO2. • This keeps the CO2 concentration around rubisco high and O2 levels low • Thus, Calvin cycle cranks and photorespiration is minimized.

30. C4 plants separate the steps of CO2 uptake and the Calvin Cycle spatially.

31. CAM (Crassulacean Acid Metabolism) plants separate the processes temporally, via keeping CO2 capture and organic acid making at night and light reactions in the day

32. A comparison of C4 and CAM plants

33. Wrapping it all up!