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  1. 1. A Historical Perspective of Photosynthesis Is this always the way photosynthesis has been understood?
  2. 2. Aristotle – 350 BC <ul><li>“ Green plants obtain their nourishment from the soil. Leaves are mere ‘shading devices’ that provide a level of comfort for the roots.” </li></ul>
  3. 3. Jan Baptista van Helmont (1643) <ul><li>He performed the classic ‘willow tree experiment ’ </li></ul><ul><li>He studied plant growth by weighing a small tree, some soil, and a pot. Then he planted the small tree in the dirt (in the pot). </li></ul><ul><li>He watered the tree regularly  after several years, he removed the tree and reweighed the tree, soil, and pot. </li></ul><ul><li>What did he discover? </li></ul><ul><li>The weight of the pot did not change. </li></ul><ul><li>The weight of the soil decreased. (very small change - lost several ounces from 200 lbs) </li></ul><ul><li>The weight of the tree increased. (very large change – gained 165 pounds) </li></ul><ul><li>What did he conclude? </li></ul><ul><li>Plants only need water to grow. (We now know that plants also need CO 2 – in 1600, no one had any idea of what air consisted of, let alone any way to measure the weight of gases… </li></ul>
  4. 4. Joseph Priestly (1771) <ul><li>He performed the classic ‘bell jar’ experiments. </li></ul><ul><li>He observed that when lit candles are placed in a closed container, they soon go out… </li></ul><ul><li>But, if a living plant was put in the container, the candle would stay lit longer… </li></ul><ul><li>He was the first person to show that plants produce oxygen gas. </li></ul><ul><li>For this discovery, the King of England awarded him a medal as he exclaimed – “We are assured that no vegetable grows in vain…but cleanses and purifies our atmosphere!” </li></ul><ul><li>He confirmed his findings by showing that a mouse will live considerable longer in a bell jar with a plant than without a plant…(and the plant will live longer as well…) </li></ul>
  5. 5. Joseph Priestly Experiments
  6. 6. Jan Ingenhousz (1779) <ul><li>He was a trained doctor from Holland. </li></ul><ul><li>He finds that aquatic plants produce oxygen bubbles in the light but not in the dark. </li></ul><ul><li>He concludes that plants need sunlight to produce oxygen. </li></ul>
  7. 7. T.W. Engelmann (1843-1909) <ul><li>German Botanist – Built and developed the ideas of Ingenhousz in more depth. </li></ul><ul><li>In 1883, he used an alga that has long spiral chloroplasts. ( Spirogyra ) </li></ul><ul><li>He illuminated the alga with light shown through a prism  He placed oxygen loving bacteria on the alga. He proposed that oxygen production would be the greatest in regions where light of a given color was absorbed the most. He therefore expected to see the most bacteria in those regions. </li></ul><ul><li>The bacteria were most concentrated where red light fell, and also where blue light fell. </li></ul><ul><li>He concluded that plants absorb the light they need (red and blue) and reflect the rest (green) </li></ul>
  8. 8. Wavelengths of light that are used by plants
  9. 9. Melvin Calvin (1948) <ul><li>Traces the chemical pathway that carbon follows to form glucose. (Calvin Cycle) </li></ul>
  10. 10. Rudolph Marcus (1992) <ul><li>Wins the Nobel Prize in Chemistry for describing the process by which electrons are transferred from one molecule to another in the electron transport chain. </li></ul>
  11. 11. So, what do we know today photosynthesis to be?... <ul><li>Light, water, and carbon dioxide are used to make sugar (usually glucose). As by-products, oxygen gas and a small bit of water are also produced… </li></ul><ul><li>CO 2 + H 2 O + light energy  CH 2 O + O 2 + H 2 O </li></ul><ul><li>Photosynthesis is when light energy is changed to chemical energy which is stored in glucose molecules…(remember the whole usable vs. unusable relationship?) </li></ul><ul><li>unusable usable </li></ul><ul><li>[light -------------------------- glucose ------------------------- ATP] </li></ul>