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Photosynthesis This Powerpoint is hosted on www.worldofteaching.com Please visit for 1000+ free powerpoints Supramolecular Chemistry, UAF, 2005 Photosynthesis Where does the energy come from that sustains all life? The Sun!! Well most of it anyway…… Supramolecular Chemistry, UAF, 2005 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 O2 and forms CO2 from the same carbon atoms that had been taken up as CO2 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 O2 was released to create an atmosphere rich in oxygen. (The earth's atmosphere presently contains 20% O2.) Supramolecular Chemistry, UAF, 2005 Cellular Respiration -vs- Photosynthesis Exergonic and endergonic reactions of metabolism… Exergonic: C6H12O6 + 6O2 6CO2 + 6H2O G = -686 kcal/mole Cellular respiration! Provides the energy to run cell processes Endergonic: 6CO2 + 6H2O C6H12O6 + 6O2 G = +686 kcal/mole Photosynthesis! Allows plants to make energy rich sugars from energy poor molecules Supramolecular Chemistry, UAF, 2005 Overview of Photosynthesis 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O G = + 686 kcal/mol • Photosynthesis, like cellular respiration, is a series of redox reactions! What is being oxidized and what is being reduced in the summarizing equation above? Supramolecular Chemistry, UAF, 2005 Historical perspective Early thinking: O2 released came from the CO2 CO2 C + O2 C + H2O CH2O sugar Water was added to the carbon to make sugar van Neil’s experiments with the sulfur bacteria showed that the bacteria used CO2 but did NOT release O2 ...he suggested that plants split water as a source of e- and H+ Scientists used radioactive isotopes to test this idea Supramolecular Chemistry, UAF, 2005 18Oxygen (Heavy Oxygen) Isotope Experiment… Experiment #2 Experiment #1 CO2 CO2 CO2 CO2 CO2 CO2 CO2 C18O C18O2 C18O H218O 2 2 C18O2 C18O2 C18O2 C18O2 H2O Supramolecular Chemistry, UAF, 2005 18O Isotope Experiment Hypothesis: If CO2 is being oxidized C18O2 H218O 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O 18O 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O 18O Can you predict where the heavy oxygen will end up in each case? Supramolecular Chemistry, UAF, 2005 18O Isotope Experiment Hypothesis: If H2O is being oxidized C18O2 H218O 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O 18O 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O 18O Can you predict where the heavy oxygen will end up in each case? Supramolecular Chemistry, UAF, 2005 The Actual Results!! C18O2 H218O 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O 18O 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O 18O So..it’s the water that’s being oxidized! Supramolecular Chemistry, UAF, 2005 Tracking Atoms in Photosynthesis… Reactants 6 CO2 12 H2O Products C6H12O6 6H2O 6O2 Supramolecular Chemistry, UAF, 2005 What does this suggest about photosynthesis? The sugars that result from photosynthesis are produced by adding the hydrogen ions and electrons from water to carbon dioxide, NOT by splitting CO2 and adding water! H+ and e- oxidized 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O reduced Supramolecular Chemistry, UAF, 2005 Plant Photosynthesis internal leaf structure outer membrane inner membrane thylakoid chloroplasts Supramolecular Chemistry, UAF, 2005 The stages of photosynthesis… Light Dependent Reactions • Occurs along the thylakoid membrane • this is where H2O is oxidized. • chemiosmotic production of ATP! • electron carrier (NADPH) is synthesized Supramolecular Chemistry, UAF, 2005 The stages of photosynthesis… Light Independent Reactions • Occurs in the stroma of the chloroplast. • Where CO2 is “fixed” into sugars! Supramolecular Chemistry, UAF, 2005 How plants harness energy from sunlight… Photosynthetic pigments Chlorophylls a – the “main” photosynthetic pigment Accessory pigments.. Chlorophyll b Carotenoids Supramolecular Chemistry, UAF, 2005 Photosynthetic pigments are arranged as “photosystems” Supramolecular Chemistry, UAF, 2005 What wavelengths of light do you think plants use the least in photosynthesis? Supramolecular Chemistry, UAF, 2005 Photosystems use some wavelengths of light but reflect others… Supramolecular Chemistry, UAF, 2005 Photosystem From the Photosystem, e- are passed along an Electron Transport Chain.. The Photosynthetic Electron Transport Chain (PETC) Photon Reaction Center Light Harvesting Pigments Supramolecular Chemistry, UAF, 2005 Photosystem Photon PETC Supramolecular Chemistry, UAF, 2005 Photosynthetic Electron Transfer Chain (PETC) • series of electron carriers which take electrons from photosystem, and.. • ultimately carry electrons to NADP+ Supramolecular Chemistry, UAF, 2005 Photosystems • Experiments in the 1940’s suggested that light photons are absorbed at 2 different points along the same PETC.… • In fact, there are two Photosystems in operation Supramolecular Chemistry, UAF, 2005
