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Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Photosynthesis: Harvesting Light Energy Chapter 7 pages 157 - 179 Slide 1.

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Presentation on theme: "Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Photosynthesis: Harvesting Light Energy Chapter 7 pages 157 - 179 Slide 1."— Presentation transcript:

1 Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Photosynthesis: Harvesting Light Energy Chapter 7 pages Slide 1

2 Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Organisms and Photosynthesis Chapter 7.1 – 7.4 pages Slide 2

3 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 importance of photosynthesis sunlight energy  chemical energy carbon dioxide  sugars removes carbon dioxide from atmosphere adds oxygen to atmosphere source of fossil fuels

4 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Leaf Structure Cuticle – barrier Epidermis – protect Palisade – light Spongy – gases Epidermis – protect Stomates – gas exchange Guard Cells – control stomate

5 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Chloroplast Structure Thylakoids – folds of inner membrane Grana – stacked sac of thylakoids Stroma – space around grana Grana has chlorophyll

6 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Pigments Chemicals that absorb light Phycocyanins - blue Chlorophylls – green Xanthophylls - yellow Carotenes - orange Phycoerythrins - red Each has a specific absorption spectrum

7 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Pigment’s Function Light hits free electrons that move from ground state to excited state. Three possible outcomes: 1. energy gained released as heat 2. energy gained released as light (fluoresce) 3. energy gained powers subsequent chemical reaction Chlorophyll captures light; components of grana channel light into other reactions

8 Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 The Process of Photosynthesis Chapter 7.5 – 7.8 Pages 164 – 170

9 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Discoveries Van Helmont – water necessary for plant growth Priestly (1772)– plants give off material (oxygen) that keeps flame burning, mice alive de Saussure (1804) – plant growth results from intake of water and carbon dioxide Meyer (1845) – light absorbed and transformed into chemical energy

10 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Overview of Photosynthesis Photosynthesis 6CO2 + 6H2O  C6H 12 O6 + 6O2 Light Reactions (grana) 1.Requires sunlight 2.Splits water (photolysis) 3.Forms ATP and NADPH2 4.Releases oxygen Dark Reactions (stroma) 1.Does not require sunlight 2.Uses ATP and NADPH2 3.Takes in CO2 4.Forms sugars

11 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Light Reactions Photosystems – pigments that absorb light energy and “channel” energy into one pigment molecule that passes it to substrates to form ATP. Photosystem I – P700 reaction center Photosystem II – P680 reaction center

12 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Photophosphorylation light energy  chemical energy of ATP 1. Non Cyclic Photophosphorylation  H 2 O and CO 2 available  products to Dark Reactions 2. Cyclic Photophosphorylation  H 2 O or CO 2 not available  Dark Reactions not involved  Forms only ATP for immediate use by cell

13 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Non Cyclic Photophosphorylation

14 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Light Reactions in Grana

15 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Summary of Light Reaction Photosystem II 1. Photolysis replaces excited e - releases H + and ½O 2 2. Excited e - passes down cytochromes releases energy to form ATP 3. Low energy e - passes to photosystem I Photosystem I Low energy e - replaces excited electron Excited e - accepted by NADP + and joined with H + forming NADPH NADPH 2 and ATP go to the Dark Reactions

16 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Dark Reactions Consists of 3 pathways: 1. Carbon Fixation – adds CO 2 from environment to existing 5 carbon sugar RuBP (ribulose bisphosphate). 2. Calvin Cycle – regenerates 5 carbon sugar RuBP and forms PGAL 3. Hexose Shunt – joins 2 PGAL to form glucose. Rubisco – enzyme that catalyzes initial reaction.

17 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Dark Reactions

18 Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Photosynthesis and the Environment Chapter 7.9 – 7.12 Pages

19 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Rate of Photosynthesis Four environmental factors can act as limiting factors on the speed with which photosynthesis occurs: 1. Light intensity 2. Temperature 3. Concentration of CO 2 4. Concentration of O 2

20 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 As light intensity increases rate increases and levels off Rate of photosynthesis is best at optimum temperature between 15°C and 35°C

21 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Oxygen Affect on Photosynthesis As concentration of O2 increases rate of photosynthesis declines Excess O 2 combines with Rubisco to form PGA and glycolate which forms CO 2 in process of photorespiration

22 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Photorespiration

23 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Special Adaptations – C 4 plants C 4 plants evolved special system to increase CO 2 concentration to limit photorespiration C 4 plants can close stomates in high light and high temperature environments and not slow down photosynthesis rate.

24 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Special Adaptations – CAM plants CAM plants evolved special system to absorb CO 2 at night when open stomates will not cause water loss CAM plants store the CO 2 in a 4C acid that releases the CO 2 to Calvin cycle in day light.

25 Updated 1/20/05Created by C. Ippolito Jan 11, 2003 Updated Feb 2, 2004 Chemoautotrophy Bacteria use chemical energy and H 2 S (hydrogen sulfide) to form glucose 6H 2 S + 6CO 2 → C 6 H 12 O 6 + 6S 2 Symbiotic with vent tube worms


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