Photosynthesis Using light, water and CO 2 to make food for over a billion years

1. Photosynthesis Using light, water and CO2 to make food for over a billion years Newark Science Park High School Mrs. Paulose Joseph Geissler

2. Outline • Hierarchy Photosynthesis • Structure of leaf • Chloroplast • Thylakoid Membrane • Chlorophyll • Photosystems • Light vs Dark Reactions • Review Questions

3. Energy Source • Autotrophs • Plants, algae, and many bacteria • Heterotrops • Animals, fungi and many bacteria • Aerobic vs Anaerobic • The presence of oxygen vs the absence of oxygen

4. Cellular Evolution ~1,500,000,000 years of anaerobic cells 200,000 years of humans The earth is 4.6 billion years old (4,600,000,000 years)

5. What is Photosynthesis? • The process by which green plants make their own food using carbon dioxide and water in the presence of sun light. 6CO2 + 6 H2O + light energy C6H12O6 + 6O2

6. Hierarchy Photosynthesis Palisade Cell Thylakoid Membrane The Leaf Chloroplast Chlorophyll

7. Structure of Leaf Palisade Cell

8. Structure of Chloroplast Thylakoid Membrane Thylakoid Space Stroma

9. Thylakoid Membrane • Stroma • Interior space of the chloroplasts • Contains metabolic enzymes, as well a special set of ribosomes, RNA and DNA • Thylakoid Membrane • Network of flattened disclike sacs (thylakoids) which create a third internal compartment separate from the stroma • The site of the light-capturing systems, the electron-transport chains, and ATP synthase

10. Chlorophyll • Light absorbing pigment that plays a central role in photosynthesis • Long hydrophobic tails (in yellow) anchor chlorophyll to the thylakoid membrane • Light is absorbed by electrons within the bond network (in blue) • Chlorophyll are arranged in and around photosystems embedded in the thylakoid membrane • Electrons in chlorophyll molecules interact with photons from light are raised to a higher energy level

11. Photosystems Cartoon Electron Transport A. (A) Charge separation generated in pigment-protein complex of a chlorophyll molecule to drive (B) the donation of a high-energy electron to the electron-transport chain B.

12. Classic Model of Photosystems Direction of electron flow

13. Photosystem II Photosystem I --Produces high-energy electrons to be propelled along the electron-transport chain --Electron transportation drives H+ pump creating a proton gradient --ATP synthase uses this gradient to drive ATP synthesis (video) --Finally, the high-energy electron arrives at photosystem I --Here, it will fill a positively charged ‘hole’ which has been left in the reaction center of chlorophyll

14. Light and Dark Reactions • Light reactions (photosynthetic electron-transfer reactions) Photosystems • Energy from sun light excites electrons within chlorophyll, enabling electrons to move along an electron transport chain in the thylakoid membrane • Electrons are obtained from the splitting of water molecules, which produces O2 as a byproduct • Dark reactions (carbon-fixation reactions) Calvin Cycle • ATP and NADPH generated from light reactions serve as a source of energy and reducing power, respectively, to drive the conversion of CO2 to carbohydrate, such as sucrose • These organic molecules can then be exported to other tissues as a source of energy

16. High Energy Molecules Direct Energy Molecules ATPGTP Indirect Energy Molecules NADH/NADPH FADH2 http://www.biotek.com/resources/articles/nadh-concentrations -fluorescence-absorbance.html

17. Photosystem II Photosystem I

18. ATP Synthase The ATP Synthase is an enzyme which generates ATP by combining ADP and Pi. ATP synthase + ADP + Pi ATP Synthase + ATP This protein is powered by the movement of H+ down its electrochemical gradient. Are found in both the stroma of chloroplasts and the inter-membrane space of mitochondria. http://www.youtube.com/watch?v=PjdPTY1wHdQ

19. Conditions • Properly functioning chloroplasts • Properly functioning chlorophyll molecules • Well established electron transport chain • Optimum exposure to sun light • Steady supply of water and nutrients and CO2 • Steady removal of waste products O2

20. Review Question #1 • Which of the following is the correct formula which describes photosynthesis? • A) O2 + H2O + light C6H12O6 + CO2 • B) C6H12O6 + light CO2 + H2O • C) CO2 + O2 + light C6H12O6 + O2 • D) CO2 + H2O + light C6H12O6 + O2 + H2O • Balance the equation of your answer D) 6 CO2+ 6 H2O → C6H12O6+ 6 O2

21. Review Question #2 • Which organelle in plants is the site for photosynthesis? • A) Stroma • B) Chlorophyll • C) Chloroplast • D) Mitochondria C) Chloroplast, chlorophyll is the light-absorbing green pigment essential in photosynthesis

22. Review Question #3 • What gas occupies the intercellular space of the mesoderm on a bright sunny day? • A) Nitrogen • B) Carbon Dioxide • C Hydrogen • D) Oxygen • B) Carbon Dioxide

23. Review Question #4 • Which of the following events takes place during light reactions? • A) Combination of H and CO2 • B) Combination of C and CO2 • C) Splitting of H2O • D) Splitting of CO2 • C) Splitting of H2O, Electrons are obtained from the splitting of water molecules, which produces O2 as a byproduct

24. Review Question #6 • From where does the low-energy electron responsible for releasing the high-energy electron come from? • A) CO2 • B) NADPH • C) ATP • D) H2O • E) None of the above D) H20