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Chapter 4 - Photosynthesis

Chapter 4 - Photosynthesis. 6CO 2 + 6H 2 O + light  C 6 H 12 O 6 + 6O 2. The capture and conversion of solar energy to chemical bond energy. Photosynthesis occurs in land plants, algae, cyanobacteria. How is photosynthesis important?. Universal energy source

judith-lynn
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Chapter 4 - Photosynthesis

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  1. Chapter 4 - Photosynthesis 6CO2 + 6H2O + light  C6H12O6 + 6O2 The capture and conversion of solar energy to chemical bond energy • Photosynthesis occurs in • land plants, • algae, • cyanobacteria

  2. How is photosynthesis important? • Universal energy source • 100-200 billion metric tons/yr. • Humans use 40% entire output

  3. Photosynthesis produces oxygen

  4. Photosynthesis & the carbon cycle

  5. Summary of photosynthesis See Figure 4-12 Light-dependent reactions Light-independent reactions

  6. Chlorophyll absorbs some wavelengths of light

  7. Accessory pigments

  8. What happens when light is absorbed by a molecule? “Free” electrons are a source of kinetic energy

  9. Summary of photosynthesis See Figure 4-12 Light-dependent reactions

  10. Light-dependent reactions • Photosystems embedded in the thylakoid membranes consist of chlorophyll molecules (100s) and electron transport systems • Light energy captured and stored in energy carriers (ATP & NADPH) via chemiosmosis

  11. Light absorption by chlorophyll Photolysis replaces electrons removed from chlorophyll

  12. NADP+ NADPH H+ ions Fig. 4-10 H20 →2H+ + 2e- + O e- Moving electrons provide the energy to move H+ ions inside the thylakoid membrane

  13. Summary of photosynthesis Light-dependent reactions Light-independent reactions

  14. Light-independent reactions (Calvin Cycle) • Occurs in the stroma • Several enzyme-catalyzed steps • Requires energy • Produces sugars

  15. 1940s-50s – Melvin Calvin Nobel prize in chemistry - 1961

  16. Calvin’s experiment (see Fig. 4-6)

  17. Calvin’s results

  18. Photosynthesis animation

  19. Rate of photosynthesis varies with environmental conditions • What is meant by the “rate of photosynthesis”? • What environmental conditions affect the rate of photosynthesis?

  20. Factors influencing the rate of photosynthesis • Carbon dioxide concentration • Water availability • Light intensity • Temperature

  21. Photorespiration and rubisco • Rubisco – Ribulose 1,5-bisphosphate carboxylase/oxygenase • Most abundant protein on earth (25-40% of total plant protein) • Activity depends on carbon dioxide concentration in the leaf

  22. Rubisco as a carboxylase

  23. Rubisco as a carboxylase

  24. Rubisco activity and CO2 concentration • If [CO2] > 50ppm, carboxylase activity • If [CO2] < 50ppm, oxygenase activity

  25. When would photorespiration occur and why? • When are CO2 concentrations low? • When stomata close • Hot days • Moisture stress

  26. Variations of photosynthesis • 85% of plants use “C3” photosynthesis • C3 cycle = Calvin cycle • C4 photosynthesis • C4 plants include many tropical monocots, other grasses (0.4% of plants) • Crassulacean Acid Metabolism (CAM) • CAM plants – cacti, orchids, bromeliads, succulents (~10% of plants)

  27. C4 photosynthesis is more efficient than C3 under certain conditions

  28. C4 photosynthesis

  29. C4 plants reduce photorespiration by concentrating CO2 in the bundle sheath cells

  30. Crassulacean Acid Metabolism • Evolved in areas of high light intensity, little precipitation • Stomata closed during the day, open at night

  31. Photosynthesis research • Why study photosynthesis?

  32. Photosynthesis Research • Photosynthesis Center at Arizona State • Oak Ridge National Laboratory • Photosynthesis Research Unit

  33. Photosynthesis Research • Photosynthesis and temperature tolerance • Photosynthesis at high CO2 levels • CO2 Science Magazine • Engineering C4 genes in C3 plants • Production of pharmaceuticals in chloroplasts

  34. Cellular respiration • Plants utilize aerobic respiration as do animals

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