7. Photosynthesis Where does the energy come from that sustains all life? The Sun!! Well most of it anyway……
8. Respiration vs. Photosynthesis Photosynthesis and respiration as complementary processes in the living world. Photosynthesis uses the energy of sunlight to produce sugars and other organic molecules. These molecules in turn serve as food. Respiration is a process that uses O 2 and forms CO 2 from the same carbon atoms that had been taken up as CO 2 and converted into sugars by photosynthesis. In respiration, organisms obtain the energy that they need to survive. Photosynthesis preceded respiration on the earth for probably billions of years before enough O 2 was released to create an atmosphere rich in oxygen. (The earth's atmosphere presently contains 20% O 2 .)
11. Early thinking: O 2 released came from the CO 2 CO 2 C + O 2 C + H 2 O CH 2 O sugar Water was added to the carbon to make sugar van Neil’s experiments with the sulfur bacteria showed that the bacteria used CO 2 but did NOT release O 2 ...he suggested that plants split water as a source of e - and H + Historical perspective Scientists used radioactive isotopes to test this idea
12. Experiment #1 H 2 18 O CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 H 2 O C 18 O 2 C 18 O 2 C 18 O 2 C 18 O 2 C 18 O 2 C 18 O 2 C 18 O 2 Experiment #2 18 Oxygen (Heavy Oxygen) Isotope Experiment…
13. 18 O Isotope Experiment 6C O 2 + 12H 2 O C 6 H 12 O 6 + 6O 2 + 6H 2 O C 18 O 2 Hypothesis: If CO 2 is being oxidized H 2 18 O 18 O Can you predict where the heavy oxygen will end up in each case? 6CO 2 + 12H 2 O C 6 H 12 O 6 + 6O 2 + 6H 2 O 18 O
14. 18 O Isotope Experiment 6C O 2 + 12H 2 O C 6 H 12 O 6 + 6O 2 + 6H 2 O C 18 O 2 Hypothesis: If H 2 O is being oxidized H 2 18 O 18 O Can you predict where the heavy oxygen will end up in each case? 6CO 2 + 12H 2 O C 6 H 12 O 6 + 6O 2 + 6H 2 O 18 O
15. The Actual Results!! 6C O 2 + 12H 2 O C 6 H 12 O 6 + 6O 2 + 6H 2 O C 18 O 2 H 2 18 O 18 O 6CO 2 + 12H 2 O C 6 H 12 O 6 + 6 O 2 + 6H 2 O 18 O So..it’s the water that’s being oxidized!
16. Tracking Atoms in Photosynthesis… 6 CO 2 12 H 2 O Reactants Products C 6 H 12 O 6 6H 2 O 6O 2
17. What does this suggest about photosynthesis? 6CO 2 + 12H 2 O C 6 H 12 O 6 + 6O 2 + 6H 2 O The sugars that result from photosynthesis are produced by adding the hydrogen ions and electrons from water to carbon dioxide, NOT by splitting CO 2 and adding water! oxidized reduced H + and e -
21. How plants harness energy from sunlight… Photosynthetic pigments Chlorophylls a – the “main” photosynthetic pigment Chlorophyll b Accessory pigments.. Carotenoids
25. From the Photosystem, e - are passed along an Electron Transport Chain.. The Photosynthetic Electron Transport Chain (PETC) Light Harvesting Pigments Reaction Center Photon Photosystem
