Chapter 10 Photosynthesis

1. Chapter 10 Photosynthesis

2. Warm-Up • Compare and contrast heterotrophs to autotrophs. • Write the balanced equation for photosynthesis. • Why is the leaf shaped and structured as it is? (think structure  function)

3. Warm-Up • A photon of which color of light would contain more energy: • Orange (620 nm) or Blue (480 nm)? • Why? • How did Engelmann determine the absorption spectrum for algae? What were his results? • What are the components of a photosystem?

4. Warm-Up Write a short synopsis of the light reaction. What is its function? Where does it occur? What purpose does cyclic e- flow serve? What is the main function of the Calvin Cycle?

5. Warm-Up • What are the products of the Calvin cycle that are utilized in the light cycle? • What are the reactants of the Calvin cycle? • Where does the Calvin cycle take place?

6. Warm-Up • Describe the differences between cyclic and noncyclic e- flow. Why does each occur? • What occurs during photophosphorylation? Where does it occur? • What is the purpose of the light reaction? The Calvin cycle?

7. Warm-Up • Why do C4 plants photosynthesize without photorespiration? • What is the purpose of the proton gradient? • State the differences and similarities between C4 and CAM plants.

8. Warm-Up • Draw the chloroplast and label it. Where does the light reaction, Calvin cycle, chemiosmosis occur? • What is RuBP, rubisco and G3P? • Compare the Light Reactions to the Calvin Cycle.

9. Chapter 10Photosynthesis

10. What you need to know: The summary equation of photosynthesis including the source and fate of the reactants and products. How leaf and chloroplast anatomy relates to photosynthesis. How photosystems convert solar energy to chemical energy. How linear electron flow in the light reactions results in the formation of ATP, NADPH, and O2. How chemiosmosis generates ATP in the light reactions. How the Calvin Cycle uses the energy molecules of the light reactions to produce G3P. The metabolic adaptations of C4 and CAM plants to arid, dry regions.

11. Photosynthesis in Nature Plants and other autotrophs are producers of biosphere Photoautotrophs: use light E to make organic molecules Heterotrophs: consume organic molecules from other organisms for E and carbon

12. Photoautotrophs

13. Photosynthesis converts light energy to chemical energy of food Thylakoid space Chloroplasts: sites of photosynthesis in plants

15. Sites of Photosynthesis • mesophyll: chloroplasts mainly found in these cells of leaf • stomata: pores in leaf (CO2 enter/O2 exits) • chlorophyll: green pigmentin thylakoid membranes of chloroplasts

16. Photosynthesis 6CO2 + 6H2O + Light Energy  C6H12O6 + 6O2 • Redox Reaction: water is split  e- transferred with H+ to CO2  sugar Remember: OILRIG Oxidation: lose e- Reduction: gain e-

17. Tracking atoms through photosynthesis 12 H2O 6 CO2 Reactants: 6 O2 6 H2O C6H12O6 Products: Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis (C.B. van Niel)

18. Photosynthesis = Light Reactions + Calvin Cycle “photo” “synthesis”

19. The light reactions convert solar E to chemical E of ATP and NADPH Nature of sunlight • Light = energy = electromagnetic radiation • Shorter wavelength (λ): higher E • Visible light - detected by human eye • Light: reflected, transmitted or absorbed

20. Electromagnetic Spectrum

21. Interaction of light with chloroplasts

22. Photosynthetic pigments • Pigments absorb different λ of light • chlorophyll – absorb violet-blue/red light, reflect green • chlorophyll a (blue-green): light reaction, converts solar to chemical E • chlorophyll b (yellow-green): conveys E to chlorophyll a • carotenoids (yellow, orange): photoprotection, broaden color spectrum for photosynthesis

23. Absorption Spectrum: determines effectiveness of different wavelengths for photosynthesis

25. Action Spectrum: plots rate of photosynthesis vs. wavelength (absorption of chlorophylls a, b, & carotenoids combined) Engelmann: used bacteria to measure rate of photosynthesis in algae; established action spectrum Which wavelengths of light are most effective in driving photosynthesis?

26. Light Reactions

27. Electrons in chlorophyll molecules are excited by absorption of light

28. Photosystem: reaction center & light-harvesting complexes (pigment + protein)

29. Light Reactions Two routes for electron flow: A. Linear (noncyclic) electron flow B. Cyclic electron flow

30. Light Reaction (Linear electron flow) • Chlorophyll excited by light absorption • E passed to reaction center of Photosystem II (protein + chlorophyll a) • e- captured by primary electron acceptor • Redox reaction  e- transfer • e- prevented from losing E (drop to ground state) • Water is splitto replace e-  O2 formed

31. MAIN IDEA: Use solar E to generate ATP & NADPH to provide E for Calvin cycle e- passed to Photosystem I via ETC E transfer pumps H+ to thylakoid space ATP produced by photophosphorylation e- moves from PS I’s primary electron acceptor to 2nd ETC NADP+ reduced to NADPH

37. Mechanical analogy for the light reactions

38. Cyclic Electron Flow: uses PS I only; produces ATP for Calvin Cycle (no O2 or NADPH produced)

39. Both respiration and photosynthesis use chemiosmosis to generate ATP

40. Proton motive force generated by: • H+ from water • H+ pumped across by cytochrome • Removal of H+ from stroma when NADP+ is reduced

41. Calvin Cycle

42. The Calvin cycle uses ATP and NADPH to convert CO2 to sugar • Uses ATP, NADPH, CO2 • Produces 3-C sugar G3P(glyceraldehyde-3-phosphate) Three phases: • Carbon fixation • Reduction • Regeneration of RuBP (CO2 acceptor)

43. Phase 1: 3 CO2 + RuBP (5-C sugar ribulosebisphosphate) • Catalyzed by enzyme rubisco (RuBPcarboxylase)

44. Phase 2: Use 6 ATP and 6 NADPH to produce 1 net G3P

45. Phase 3: Use 3 ATP to regenerate RuBP

46. Alternative mechanisms of carbon fixation have evolved in hot, arid climates Photorespiration • Metabolic pathway which: • Uses O2 & produces CO2 • Uses ATP • No sugar production (rubisco binds O2  breakdown of RuBP) • Occurs on hot, dry bright days when stomata close (conserve H2O) • Why? Early atmosphere: low O2, high CO2?

47. Evolutionary Adaptations • C3 Plants: • CO2 fixed to 3-C compound  Calvin cycle • Ex. Rice, wheat, soybeans • Hot, dry days: • partially close stomata, ↓CO2 • Photorespiration • ↓ photosynthetic output (no sugars made)

48. C4 Plants: • CO2 fixed to 4-C compound • Ex. corn, sugarcane, grass • Hot, dry days  stomata close • 2 cell types = mesophyll & bundle sheath cells • mesophyll : PEP carboxylase fixes CO2 (4-C), pump CO2 to bundle sheath • bundle sheath: CO2 used in Calvin cycle • ↓photorespiration, ↑sugar production • WHY? Advantage in hot, sunny areas

49. C4 Leaf Anatomy

50. CAM Plants: • Crassulacean acid metabolism (CAM) • NIGHT: stomata open  CO2 enters  converts to organic acid, stored in mesophyll cells • DAY: stomata closed  light reactions supply ATP, NADPH; CO2 released from organic acids for Calvin cycle • Ex. cacti, pineapples, succulent (H2O-storing) plants • WHY? Advantage in arid conditions