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Photosynthesis: Harvesting Light Energy

Photosynthesis: Harvesting Light Energy. Chapter 7 pages 157 - 179. Slide 1. Organisms and Photosynthesis. Chapter 7.1 – 7.4 pages 157 - 162. Slide 2. Importance of Photosynthesis. sunlight (radiant energy)  chemical energy removes carbon dioxide from atmosphere

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Photosynthesis: Harvesting Light Energy

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  1. Photosynthesis: Harvesting Light Energy Chapter 7 pages 157 - 179 Created by C. Ippolito Jan 11, 2003 updated Jan 17, 2006 Slide 1

  2. Organisms and Photosynthesis Chapter 7.1 – 7.4 pages 157 - 162 Created by C. Ippolito Jan 11, 2003 updated Jan 17, 2006 Slide 2

  3. Importance of Photosynthesis • sunlight (radiant energy)  chemical energy • removes carbon dioxide from atmosphere • carbon dioxide and water to make glucose • adds oxygen gas to atmosphere • original source of fossil fuels Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 3

  4. Leaf Structure • Cuticle – forms water barrier • Epidermis – protection • Palisade – capture sunlight • Spongy – capture CO2 & H2O • Epidermis – protection • Stomates – gas exchange • Guard Cells – control transpiration Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 4

  5. Chloroplast Structure • Thylakoids – folds of inner membrane • Grana – stacked sac of thylakoids • Stroma – space around grana • Grana has chlorophyll Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 5

  6. Pigments • Chemicals that absorb light • Phycocyanins - blues • Chlorophylls - greens • Xanthophylls - yellows • Carotenes - oranges • Phycoerythrins - reds • Each pigment has a specific absorption spectrum Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 6

  7. How Pigments Work • Light hits free electrons moving them from their ground state (low energy) to an excited state (high energy) absorbing energy. • Three possible outcomes: • energy gained released as heat • energy gained released as light (fluoresce) • energy gained powers subsequent chemical reaction • Pigment captures light; excited electrons of grana move energy captured into other reactions Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 7

  8. Homework Check and Challenge Questions on page 162 Created by C. Ippolito Jan 11, 2003 updated Jan 17, 2006 Slide 8

  9. The Process of Photosynthesis Chapter 7.5 – 7.8 Pages 164 – 170 Created by C. Ippolito Jan 11, 2003 updated Jan 17, 2006 Slide 9

  10. Discoveries • Van Helmont – plants need water for growth • Priestly (1772)– plants release material (oxygen) that keeps flame burning, mice alive • Lavoisier - proved that oxygen is removed from air when animals breathe or something is burned • Ingenhousz - discovered that plants need light to correct bad air Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 10

  11. Discoveries • de Saussure (1804) – plant growth results from taking up water and carbon dioxide • Meyer (1845) – light is absorbed and transformed into chemical energy • Engelmann - discovered which wavelengths (colours) of light are used by plants in photosynthesis Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 11

  12. Overview of Photosynthesis Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 12

  13. Light Reactions • Photosystems – groups of pigment that absorb light energy and “channel” energy into one pigment molecule that passes it to cytochrome chains to form ATP. • Photosystem I – P700 reaction center • PhotosystemII – P680 reaction center Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 13

  14. Photophosphorylation • light energy  chemical energy of ATP • Cyclic Photophosphorylation • water or carbon dioxide not available • Dark Reactions not involved • Forms only ATP for immediate use by cell • Non Cyclic Photophosphorylation • H2O and CO2 available • products to Dark Reactions Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 14

  15. Cyclic Photophosphorylation • Photosystem I • Excited e- moves down electron transport chain • ADP changed into ATP • Low energy e- returns to photosystem Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 15

  16. Non Cyclic Photophosphorylation Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 16

  17. Light Reactions in Grana Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 17

  18. Photosystem II Photolysis replaces excited electron by spitting water to release H+ and ½O2 Excited electron passes down cytochromes pumping H+ into grana H+ diffuses out through ATP synthase to form ATP Low energy electron passes to photosystem I Photosystem I Low energy electron replaces excited electron Excited electron accepted by NAD+ and joined with H+ forming NADPHthis keeps H+ outside low NADPH and ATP go to the Dark Reactions Summary of Light Reaction Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 18

  19. Dark Reactions • Consists of 3 pathways: • Carbon Fixation – adds six carbon dioxide from environment to six existing 5C sugars named RuBP (ribulose bisphosphate) to form six 6C sugars. This step uses energy from the ATP and NADPHformed in Light Reactions • Calvin Cycle – the 6C sugars break into 12 PGAL (3C) which regenerates the six 5C RuBPs and forms 2 PGAL • Hexose Shunt – joins the 2PGAL to form glucose. • Rubisco – enzyme that catalyzes initial reaction of carbon fixation. Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 19

  20. Homework Check and Challenge Questions on page 170 Created by C. Ippolito Jan 11, 2003 updated Jan 17, 2006 Slide 20

  21. Photosynthesis and the Environment Chapter 7.9 – 7.12 Pages 170 - 177 Created by C. Ippolito Jan 11, 2003 updated Jan 17, 2006 Slide 21

  22. Rate of Photosynthesis • Four environmental factors can act as limiting factors which affect the amount (rate of reaction) of photosynthesis: • Light Intensity • Temperature • Concentration of CO2 • Concentration of O2 Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 22

  23. As light intensity increases the rate of reaction increases and then levels off • Rate of photosynthesis is best at an optimum temperature between 15°C and 35°C Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 23

  24. Oxygen Affect on Photosynthesis • As concentration of O2 increases rate of reaction decreases • When there is an excess of O2 it will combine with Rubisco to form PGA and glycolate which will form CO2 in process called photorespiration Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 24

  25. Photorespiration Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 25

  26. Special Adaptations – C4 plants • C4 plants evolved special system to increase CO2 concentration to limit photorespiration • C4 plants can close their stomates in high light and temperature environments to prevent the rate of reaction from decreasing. • More efficient than C3 plants, fast growing. • Sugar, crabgrass, corn Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 26

  27. Special Adaptations – CAM plants • CAM (crassulacean acid metabolism) plants evolved special system to absorb CO2 at night when open stomates will not cause water loss • CAM plants store the CO2 in a 4C acid that releases the CO2 to Calvin cycle in day light. • Inefficient process plants very slow growing Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006 Slide 27

  28. Chemoautotrophs • Bacteria use chemical energy and H2S (hydrogen sulfide) to form glucose • 6H2S + 6CO2→ C6H12O6 + 6S2 • Symbiotic with vent tube worms Created by C. Ippolito Jan 11, 2003 Updated Jan 17, 2006

  29. Homework Check and Challenge Questions on page 177 Created by C. Ippolito Jan 11, 2003 updated Jan 17, 2006 Slide 29

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