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  1. 1. Photosynthesis The Sun is the main source of energy for life on earth
  2. 2. <ul><li>Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water </li></ul>AN OVERVIEW OF PHOTOSYNTHESIS
  3. 3. During Photosynthesis… <ul><li>Organisms (plants  ) absorb light energy from the sun and store it in organic compounds. </li></ul><ul><li>Energy is crucial to all life, without it work could not be done. </li></ul>
  4. 4. An example of basic photosynthesis…
  5. 5. Photosynthesis consists of two stages <ul><li>Light dependent reactions </li></ul><ul><li>Take place in the chloroplasts </li></ul><ul><li>Depends on sunlight for activation energy </li></ul><ul><li>Responsible for the absorbing of light in Photosynthesis </li></ul><ul><li>Water is split, giving off oxygen </li></ul><ul><li>H2O   O2 + ATP + NADPH2 </li></ul><ul><li>Non-light dependent (dark) reactions </li></ul><ul><li>Takes place in the Stroma </li></ul><ul><li>Includes the Calvin cycle </li></ul><ul><li>Does not literally occur in the dark, but requires no light to occur </li></ul><ul><li>Separated into three steps </li></ul><ul><li>Carbon dioxide is split, providing carbon to make sugars </li></ul><ul><li>  ATP + NADPH2 + CO2   C6H12O6 </li></ul>
  6. 6. Chloroplasts <ul><li>The site of Light Dependent Reactions </li></ul><ul><li>These organelles are surrounded by a double membrane and contain an inner membrane separate into disk like sacs called thylakoids </li></ul><ul><li>Thylakoid are arranged into granum , or neat stacks </li></ul><ul><li>Each thylakoid contains the green pigment chlorophyll </li></ul><ul><li>The light absorbing pigments are organized into photosystems , which transfer energy during the light reactions </li></ul>
  7. 8. Pigments in chloroplasts <ul><li>Chloroplasts absorb all other color pigments, leaving green to be reflected resulting in a plant’s color. </li></ul><ul><li>Chlorophyll a and b are </li></ul><ul><li>two are the 2 most </li></ul><ul><li>common types of chlorophyll </li></ul><ul><li>Chlorophyll  b  absorbs colors or </li></ul><ul><li>light energy NOT absorbed by </li></ul><ul><li>chlorophyll a </li></ul>Light Reflected light Absorbed light Transmitted light Chloroplast
  8. 9. The Calvin Cycle – Step one <ul><li>CO2 diffuses into the stroma from surrounding cytosol </li></ul><ul><li>An enzyme combines a CO2 molecule with a five-carbon carbohydrate called  RuBP </li></ul><ul><li>The six-carbon molecule produced then splits immediately into a pair of three-carbon molecules known as PGA </li></ul>
  9. 10. The Calvin Cycle – Step two <ul><li>Each PGA molecule receives a phosphate group from a molecule of ATP </li></ul><ul><li>This compound then receives a proton from NADPH  and releases a phosphate group producing  PGAL </li></ul><ul><li>These reactions produce ADP, NADP+, and phosphate which are used again in the Light Reactions </li></ul>
  10. 11. The Calvin Cycle – Step three <ul><li>Most PGAL is converted back to RuBP to keep the Calvin cycle going </li></ul><ul><li>Some PGAL leaves the Calvin Cycle and is used to make other organic compounds including amino acids, lipids, and carbohydrates </li></ul><ul><li>PGAL serves as the starting material for the synthesis of glucose and fructose </li></ul><ul><li>Each turn of the Calvin cycle fixes One  CO2 molecule so it takes six turns to make one molecule of glucose </li></ul>
  11. 12. Photosystems & Electron Transport Chain <ul><li>Only 1 in 250 chlorophyll molecules (chlorophyll  a ) actually converts light energy into usable energy; these molecules are called reaction-center chlorophyll </li></ul><ul><li>Antenna pigments - the other molecules (chlorophyll b, c, & d and carotenoids) tha absorb light energy and deliver it to the reaction-center molecule </li></ul><ul><li>Photosystem- unit of several hundred antenna pigment molecules plus a reaction center </li></ul><ul><li>There are 2 types of photosystems- photosystem I & photosystem 2 </li></ul><ul><li>Light is absorbed by the antenna pigments of photosystems II and I </li></ul><ul><li>NADPH is used in the Calvin cycle </li></ul><ul><li> </li></ul>
  12. 13. Chemiosmosis <ul><li>Synthesis of ATP (energy) </li></ul><ul><li>Depends on the concentration gradient of protons ( H+) across the thylakoid membrane </li></ul><ul><li>Protons (H+) are produced from the splitting of water in Photosystem II </li></ul><ul><li>Concentration of Protons is HIGHER in the thylakoid than in the stroma </li></ul><ul><li>Enzyme, ATP synthetase in the thylakoid membrane, makes ATP by adding a phosphate group to ADP </li></ul>
  13. 14. Alternate Pathways <ul><li>  C3 Plants are the most common users of the Calvin Cycle </li></ul><ul><li>Stomata are small openings on the underside of leaves used for gas exchange (O2 & CO2) </li></ul><ul><li>Guard cells help to open and close the stomata </li></ul><ul><li>Plants also lose H2O through stoma so they are closed during the hottest part of the day </li></ul>
  14. 15. Review: Photosynthesis uses light energy to make food molecules Sugar used for  Cellular respiration  Cellulose  Starch  Other organic compounds Chloroplast Light Stack of thylakoids ADP + P NADP  Stroma Light reactions Calvin cycle