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  1. 1. Photosynthesis Chapter 8 pp160-175
  2. 2. Review <ul><li>What is photosynthesis? </li></ul><ul><ul><li>Process by which energy from sunlight is used to convert water and carbon dioxide into high-energy carbohydrates (sugars and starches) and oxygen as a waste product </li></ul></ul><ul><li>Who uses photosynthesis? </li></ul><ul><ul><li>Plants and other producers </li></ul></ul>
  3. 4. Key contributors <ul><li>Big Question: </li></ul><ul><ul><li>When a tiny seed grows into a tall tree with a mass of several tons, where does the tree’s increase in mass come from? From the soil? From the water? From the air? </li></ul></ul>
  4. 5. Jan van Helmont <ul><li>1643 </li></ul><ul><li>Belgian physician </li></ul><ul><li>Do plants grow by taking material out of the soil? </li></ul><ul><li>Mass of soil </li></ul><ul><li>Mass of seed </li></ul><ul><li>Watered regularly </li></ul><ul><li>@ end of 5 yrs, tree was 75 g, soil the same </li></ul><ul><li>Conclusion: Mass came from water </li></ul><ul><li>Accounts to the “hydrate” portion of carbohydrate produced but what made the “carbo-” portion </li></ul>
  5. 6. Joseph Priestly <ul><li>1771 </li></ul><ul><li>English minister </li></ul><ul><li>Bell jar, candle, plant </li></ul><ul><li>Jar over candle  flame died out </li></ul><ul><li>Jar over candle with live sprig of mint  flame didn’t die </li></ul><ul><li>Conclusion: Plant releases oxygen </li></ul>
  6. 7. Jan Ingenhousz <ul><li>1779 </li></ul><ul><li>Dutch scientist </li></ul><ul><li>Aquatic plants produce bubbles only when light is present </li></ul><ul><li>Conclusion: Plants need sunlight to produce oxygen </li></ul>
  7. 8. Julius Robert Mayer <ul><li>1845 </li></ul><ul><li>German scientist </li></ul><ul><li>Proposed that plants convert light into energy into chemical energy </li></ul>
  8. 9. Melvin Calvin <ul><li>1948 </li></ul><ul><li>American chemist </li></ul><ul><li>Traces the chemical pathway that carbon follows to form glucose…reactions known as the Calvin Cycle </li></ul>
  9. 10. Rudolph Marcus <ul><li>1992 </li></ul><ul><li>Canadian chemist </li></ul><ul><li>Won Nobel Prize for describing process in which electrons are transferred from one molecule to another in the electron transport chain </li></ul>
  10. 11. <ul><li>The experiments performed by van Helmont, Priestly, and Ingenhousz led to work by other scientists who finally discovered that in the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen </li></ul>
  11. 12. Review Sunlight <ul><li>White light </li></ul><ul><ul><li>ROYGBIV </li></ul></ul><ul><ul><li>Combo of all colors </li></ul></ul><ul><li>Pigments </li></ul><ul><ul><li>Chemicals that absorb electromagnetic radiation (visible light) </li></ul></ul><ul><ul><li>Light absorbing molecules </li></ul></ul><ul><li>Electromagnetic spectrum </li></ul><ul><ul><li>Electrons=energy </li></ul></ul>
  12. 13. Structures and molecules <ul><li>Chloroplast </li></ul><ul><li>Chlorophyll </li></ul><ul><li>Thylakoids </li></ul>
  13. 14. Chloroplast (found in cells in leaves) <ul><li>Concentrated in the cells of the mesophyll (inner layer of tissue) in leaf </li></ul><ul><li>Stomata </li></ul><ul><ul><li>Tiny pores on surface of leaf </li></ul></ul><ul><ul><li>Allows carbon dioxide and oxygen in and out of the leaf </li></ul></ul><ul><li>Veins </li></ul><ul><ul><li>Carry water and nutrients from roots to leaves </li></ul></ul><ul><ul><li>Deliver organic molecules produced in leaves to other parts of the plant </li></ul></ul>
  14. 15. Chloroplast <ul><li>Cellular organelle where photosynthesis takes place </li></ul><ul><ul><li>Double membrane </li></ul></ul><ul><ul><li>Outer membrane </li></ul></ul><ul><ul><li>Stroma (fluid filled space) </li></ul></ul><ul><ul><li>Inner membrane </li></ul></ul><ul><ul><li>Thylakoids </li></ul></ul><ul><ul><li>Granum </li></ul></ul><ul><ul><li>Intermembrane space </li></ul></ul><ul><li>Contain chemical compound called Chlorophyll </li></ul><ul><ul><li>This molecule gives chloroplast its green color </li></ul></ul>
  15. 16. Structure of Chloroplast <ul><li>Structures organize the many reactions that take place in photosynthesis </li></ul><ul><li>Stroma </li></ul><ul><ul><li>Thick fluid enclosed by the inner membrane </li></ul></ul><ul><li>Thylakoids </li></ul><ul><ul><li>Disc-like sacs suspended in the stroma </li></ul></ul><ul><ul><li>Has membrane that surrounds inner thylakoid space </li></ul></ul><ul><li>Grana (sing. Granum) </li></ul><ul><ul><li>Stacks of thylakoids </li></ul></ul>
  16. 19. Chlorophyll <ul><li>Plants principle pigment </li></ul><ul><li>2 types </li></ul><ul><ul><li>Chlorophyll a </li></ul></ul><ul><ul><ul><li>Absorbs light in the blue-violet and red regions of visible spectrum </li></ul></ul></ul><ul><ul><li>Chlorophyll b </li></ul></ul><ul><ul><ul><li>Absorbs light in the blue and red regions of the visible spectrum </li></ul></ul></ul><ul><li>Chlorophyll does NOT absorb light well in the green portion of the visible spectrum </li></ul><ul><li>Green light reflected by leaves </li></ul><ul><ul><li>This is why plants look green…they reflect green light </li></ul></ul><ul><li>Carotene </li></ul><ul><ul><li>Secondary plant pigment </li></ul></ul><ul><ul><li>Red and orange pigments </li></ul></ul><ul><ul><li>Absorb light in other regions of the spectrum other than red and orange </li></ul></ul>
  17. 20. 2 main stages <ul><li>Light Dependent Rxn </li></ul><ul><li>Light-Independent or Calvin Cycle </li></ul>
  18. 21. Photosynthesis Overview <ul><li>#1 “Light-Dependent” reactions </li></ul><ul><ul><ul><li>Convert the E in sunlight to chemical energy </li></ul></ul></ul><ul><ul><ul><li>Rxns depend on molecules made in membranes of thylakoids </li></ul></ul></ul><ul><ul><ul><ul><li>Chlorophyll in membr. captures light E </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Chloroplast use E to remove e- from water </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Splits water into oxygen (waste) and hydrgen ions </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>e- taken are used to make high-E molecule NADPH (similar to NADH) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Chloroplast also use captured E to make ATP </li></ul></ul></ul></ul><ul><ul><ul><li>Overall Product: convert light E into chemical energy stored in compounds ATP and NADPH </li></ul></ul></ul>
  19. 22. Photosynthesis Overview <ul><ul><li># 2 “Light- Independent” Reactions aka </li></ul></ul><ul><ul><li>The Calvin Cycle </li></ul></ul><ul><ul><ul><li>Makes sugar from atoms of CO2 and H+ ions and High-E e- carried by NADPH </li></ul></ul></ul><ul><ul><ul><li>Enzymes for these reactions are dissolved in the stroma (outside thylakoid) </li></ul></ul></ul><ul><ul><ul><li>ATP made by light Rxns provides E to make sugar (glucose) </li></ul></ul></ul><ul><ul><ul><li>Called light independent, b/c unlike unlike the light reactions, these do NOT require light tp begin </li></ul></ul></ul><ul><ul><ul><li>However, this cycle does require two things made by the light reactions: ATP and NADPH </li></ul></ul></ul><ul><ul><ul><ul><li>This means that the calvin cycle cannot necessarily continue in the dark </li></ul></ul></ul></ul>