Photosynthesis notes


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Photosynthesis notes

  1. 1. Photosynthesis Chapter 6
  2. 2. The Light Reactions• Almost all of the energy in living systems comes from the sun• Sunlight energy enters living systems when plants and some other organisms absorb light and use it to make sugars
  3. 3. Obtaining Energy• Organisms can be classified by how they get energy• Autotrophs use energy from sunlight to make sugars (their own food) – Most use photosynthesis to convert sunlight energy into chemical energy• Heterotrophs get energy from food
  4. 4. Obtaining Energy
  5. 5. Overview of Photosynthesis • The products of photosynthesis are the reactants for cellular respiration • The products of cellular respiration are the reactants for photosynthesis
  6. 6. Overview of Photosynthesis• Photosynthesis can be divided into 2 stages – Light Reactions – light energy is converted to chemical energy, which is temporarily stored in ATP and NADPH – Calvin Cycle – Sugars are formed using CO2 and the chemical energy stored in ATP and NADPH
  7. 7. Overview of Photosynthesis• Overall photosynthesis equation: Light energy6CO2 + 6H2O C6H12O6 + 6O2 Light energyCarbon dioxide + water sugars + oxygen
  8. 8. Capturing Light Energy• The first stage of photosynthesis is called the light reactions because they require light• Photosynthesis begins with the absorption of light in the chloroplast
  9. 9. Parts of the chloroplast • Chloroplasts – organelles found in the cells of plants and algae • Thylakoids – membranes arranged as flattened sacs • Grana – stacks of thylakoids • Stroma – solution surrounding the grana
  10. 10. Light and Pigments• Light from the sun appears white, but it is made of a variety of colors
  11. 11. Light and Pigments• Pigments are compounds that absorb light• Many objects contain pigments that absorb some colors of light and reflect others• The colors that are reflected are the ones you see
  12. 12. Chloroplast Pigments• There are several pigments in the thylakoid membranes – Most important are chlorophylls • Chlorophyll a absorbs mostly red and blue light and reflects mostly green light – Accessory pigments • Chlorophyll b assists chlorophyll a in capturing light energy • Carotenoids are the yellow, orange, and brown pigments
  13. 13. Chloroplast Pigments
  14. 14. Chloroplast Pigments• In plant leaves, chlorophylls are the most abundant pigments and therefore mask the colors of the other pigments• During the fall, many plants lose their chlorophylls and become the color of the carotenoids
  15. 15. Light Reactions• The first set of reactions – the light reactions take place in the thylakoid membranes
  16. 16. Light dependent reactions1. Light energy is absorbed by chlorophyll in photosystem II2. Electrons in chlorophyll are energized, or “excited” and leave the chlorophyll3. These electrons are passed to the primary electron acceptor
  17. 17. Light Dependent Reactions4. The electrons move down the electron transport chain (series of molecules that transport electrons) a. As the electrons move down the chain, the energy is used to move H+ ions into the thylakoid
  18. 18. Light-Dependent Reactions5. Light is absorbed by chlorophyll in Photosystem I6. Electrons are energized and passed on to a different electron transport chain7. NADP+ accepts these electrons and is converted to NADPH
  19. 19. Replacing Electrons in Light Reactions• To replace the electrons lost from chlorophyll in photosystem II, an enzyme splits water molecules• 2H2O 4H+ + 4e- + O2
  20. 20. Making ATP in Light Reactions• Hydrogen ions move from the inside of the thylakoid to the outside through ATP Synthase, an enzyme• As this happens, ATP is produced
  21. 21. Summary• The light-dependent reactions use: – Sunlight – Water• And produce: – NADPH – ATP
  22. 22. The Calvin Cycle• Second set of reactions in photosynthesis• Uses the energy stored in ATP and NADPH to produce sugars
  23. 23. The Calvin Cycle1. Carbon atoms from carbon dioxide in the air enter the plant2. This carbon joins with sugars in the plant3. Energy from ATP and NADPH converts these compounds into sugar for the plants to use4. Using 3 ATP the remaining sugars are converted back to the original carbon compounds to begin the cycle again
  24. 24. A Summary of Photosynthesis• Happens in two stages 1. The light reactions – Energy is absorbed from sunlight and converted into chemical energy, which is temporarily stored in ATP and NADPH 2. The Calvin cycle – Carbon dioxide and the chemical energy stored in ATP and NADPH are used to form sugars
  25. 25. Summary of Photosynthesis
  26. 26. Factors That Affect Photosynthesis• Light Intensity• Carbon Dioxide Levels
  27. 27. Factors that Affect Photosynthesis• Temperature