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Understanding Photosynthesis: Key Concepts and Experiments for Biology Students

Explore the process of photosynthesis, from leaf structure to light reactions and the Calvin cycle. Understand how plants use light energy to produce carbohydrates and study important experiments.

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Understanding Photosynthesis: Key Concepts and Experiments for Biology Students

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  1. Chapter 8 Photosynthesis

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

  3. Attitude of Gratitude Leaf #1: What is something you are proud of that you’ve accomplished this school year so far? Leaf #2: What is something that you are grateful for?

  4. Apply Leaf Pigments to Chromatography Paper

  5. Paper Chromatography

  6. Calculating Rf Values Rf = (distance pigment moved) / (distance solvent front moved) Red Pigment: Rf = 57/66 = 0.86 Purple Pigment: Rf = 32/66 = 0.48

  7. Warm-Up What pigments are found in spinach leaves? Based on the color of the pigments, what wavelengths of visible light are absorbed by each of these pigments? (see Figure 10.7 in textbook for help)

  8. Warm-Up Which wavelengths of light are best absorbed by each pigment shown in the graph?

  9. 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? • Read the article and leaves in the fall. What is happening in the leaves during autumn?

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

  11. 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.

  12. Explain the results of each experiment Experiment A Experiment B Experiment C

  13. Chapter 8Photosynthesis

  14. 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 relate to photosynthesis. How photosystems convert solar energy to chemical energy. How linear electron flow in light reactions results in the formation of ATP, NADPH, and O2. How the formation of a proton gradient in light reactions is used to form ATP from ADP plus inorganic phosphate by ATP synthase. How the Calvin cycle uses energy molecules of the light reactions (ATP and NADPH) to produce carbohydrates (G3P) from CO2.

  15. 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

  16. Photoautotrophs

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

  18. 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

  19. 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-

  20. 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)

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

  22. 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

  23. Electromagnetic Spectrum

  24. Interaction of light with chloroplasts

  25. 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

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

  27. 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?

  28. Warm-Up (Refer to notes / Campbell) What is the main function of the Light Reactions? What are the reactants of the Light Reactions? What are the products? Where does the Light Reactions occur? What were the main pigments present in the leaves tested in class yesterday?

  29. Light Reactions

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

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

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

  33. 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) • H2O is splitto replace e-  O2 formed

  34. 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

  35. Mechanical analogy for the light reactions

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

  37. Both respiration and photosynthesis use chemiosmosis to generate ATP

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

  39. Warm-Up Write a short synopsis of the light reaction. What is its function? Where does it occur? (See Fig. 10.5) What products of the Light Reaction are used for the Calvin Cycle?

  40. Calvin Cycle

  41. 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)

  42. Phase 1: 3 CO2 + RuBP (5-C sugar ribulose bisphosphate) • Catalyzed by enzyme rubisco (RuBP carboxylase)

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

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