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Biology 102

Biology 102. Photosynthesis 1. Lecture Outline. Back to the dinosaurs… What is photosynthesis (and “who” does it)? The light-dependent reactions. 1. Back to the dinosaurs…. 2. What is photosynthesis?. Photo: “light” Light energy is stored in the energy of chemical bonds.

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Biology 102

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  1. Biology 102 Photosynthesis 1

  2. Lecture Outline • Back to the dinosaurs… • What is photosynthesis (and “who” does it)? • The light-dependent reactions

  3. 1. Back to the dinosaurs…

  4. 2. What is photosynthesis? • Photo: “light” • Light energy is stored in the energy of chemical bonds. • Synthesis: “build” • Organic molecules are built from inorganic molecules • Carbon-carbon bonds are formed! • The formulas for photosynthesis and cellular respiration • Write it down!

  5. The relationship between photosynthesis and cellular respiration

  6. Organisms that photosynthesize • Eukaryotes that photosynthesize • Plants (all!) • Some protists • Marine phytoplankton • Freshwater and marine algae • Prokaryotes that photosynthesize • Example: Cyanobacteria

  7. Leaves (plants only) and chloroplasts (eukaryotes only) • Chloroplasts within mesophyll cells • Epidermis is thin and transparent (why?)

  8. Photosynthesis involves two sets of reactions • The light-dependent reactions (“photo”) • Light energy is captured from the sun and turned into chemical energy • The energy is temporarily stored within energy carrier molecules • The light-independent reactions (“synthesis”) • Temporarily-stored energy is used to build the glucose molecule from carbon dioxide and water • Energy is stored in the carbon-carbon bonds!

  9. 3. The light-dependent reactions • What is accomplished? • Light energy is turned into chemical energy • Overview of what happens • Light is captured by pigments in the chloroplast • Electrons of the pigments “absorb” the energy • Electrons are transferred between compounds • ATP and NADPH are both formed

  10. What is light? • Light is one type of energy within the electromagnetic spectrum • Different wavelengths of light have different amounts of energy

  11. What wavelengths of light do different plant pigments absorb? • Note that the color you see is the color that is not absorbed, but rather reflected!

  12. How is the energy of light actually captured?

  13. Summary of light-dependent reactions • Light energy is “absorbed” by pigments of the light-harvesting complex and passed to a special chlorophyll molecule, the “reaction center” • An electron in the reaction center chlorophyll is excited and “jumps” from the chlorophyll molecule to… • An electron acceptor at a higher energy level

  14. The electron is passed between molecules of the electron transport system • The energy gained (from moving the electron to lower energy compounds) is used to synthesize ATP

  15. The electron ends up in another chlorophyll molecule (Photosystem I) • An electron in the reaction center chlorophyll is excited and “jumps” from the chlorophyll molecule to… • An electron acceptor at a higher energy level

  16. The electrons are transferred along a second electron transport chain (along with an H+ ion…) to a molecule of NADPH

  17. Where did the mysterious H+ come from? What about the missing electron? • It’s all about the water!

  18. Review of light-dependent reactions

  19. End result of light-dependent reactions • Energy from sun was captured and converted to chemical energy • ATP and NADPH • Water was split to provide e- and H+ and generated oxygen as a bi-product!

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