1. Photosynthesis: Harvesting Light Energy
Chapter 7
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Created by C. Ippolito Jan 11, 2003
updated Jan 17, 2006
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2. Organisms and Photosynthesis
Chapter 7.1 – 7.4
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Created by C. Ippolito Jan 11, 2003
updated Jan 17, 2006
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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
Updated 2/1/04
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4. Created by C. Ippolito Jan 11, 2003
Leaf Structure
Cuticle – forms water barrier
Epidermis – protection
Palisade – capture sunlight
Spongy – capture CO2 & H2O
Stomates – gas exchange
Guard Cells – control transpiration
Created by C. Ippolito Jan 11, 2003
Updated Jan 17, 2006
Updated 2/1/04
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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
Updated 2/1/04
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6. Created by C. Ippolito Jan 11, 2003
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
Updated 2/1/04
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7. Created by C. Ippolito Jan 11, 2003
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
Updated 2/1/04
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8. Check and Challenge Questions on page 162
Homework
Check and Challenge Questions on page 162
2-3 1/ /7
Created by C. Ippolito Jan 11, 2003
updated Jan 17, 2006
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9. The Process of Photosynthesis
Chapter 7.5 – 7.8
Pages 164 – 170
Created by C. Ippolito Jan 11, 2003
updated Jan 17, 2006
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10. Created by C. Ippolito Jan 11, 2003
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
Updated 2/1/04
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11. Created by C. Ippolito Jan 11, 2003
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
Updated 2/1/04
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12. Overview of Photosynthesis
Created by C. Ippolito Jan 11, 2003
Updated Jan 17, 2006
Updated 2/1/04
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13. Created by C. Ippolito Jan 11, 2003
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
Photosystem II – P680 reaction center
Created by C. Ippolito Jan 11, 2003
Updated Jan 17, 2006
Updated 2/1/04
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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
Updated 2/1/04
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15. Cyclic Photophosphorylation
Photosystem I
Excited e- moves down electron transport chain
ADP changed into ATP
Low energy e- returns to photosystem
2-3 1/15/03
Created by C. Ippolito Jan 11, 2003
Updated Jan 17, 2006
Updated 2/1/04
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16. Non Cyclic Photophosphorylation
Created by C. Ippolito Jan 11, 2003
Updated Jan 17, 2006
Updated 2/1/04
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17. Light Reactions in Grana
Created by C. Ippolito Jan 11, 2003
Updated Jan 17, 2006
Updated 2/1/04
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18. Summary of Light Reaction
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 NADPH this keeps H+ outside low
NADPH and ATP go to the Dark Reactions
Created by C. Ippolito Jan 11, 2003
Updated Jan 17, 2006
Updated 2/1/04
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19. Created by C. Ippolito Jan 11, 2003
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 NADPH formed 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 2 PGAL to form glucose.
Rubisco – enzyme that catalyzes initial reaction of carbon fixation.
8/9 1/14
Created by C. Ippolito Jan 11, 2003
Updated Jan 17, 2006
Updated 2/1/04
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20. Check and Challenge Questions on page 170
Homework
Check and Challenge Questions on page 170
Created by C. Ippolito Jan 11, 2003
updated Jan 17, 2006
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21. Photosynthesis and the Environment
Chapter 7.9 – 7.12
Pages
Created by C. Ippolito Jan 11, 2003
updated Jan 17, 2006
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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
Updated 2/1/04
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23. Created by C. Ippolito Jan 11, 2003
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
Updated 2/1/04
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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
Updated 2/1/04
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25. Created by C. Ippolito Jan 11, 2003
Photorespiration
Created by C. Ippolito Jan 11, 2003
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Updated 2/1/04
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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
Updated 2/1/04
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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
Updated 2/1/04
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28. Created by C. Ippolito Jan 11, 2003
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
Updated 2/1/04

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