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December 5, 2008

December 5, 2008. Objectives: - Discuss how different factors affect the rate of photosynthesis - Describe alternative pathways plants use to make sugars Drill: List 2 factors that can affect the rate of photosynthesis. Online Simulation.

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December 5, 2008

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  1. December 5, 2008 • Objectives: - Discuss how different factors affect the rate of photosynthesis - Describe alternative pathways plants use to make sugars • Drill: List 2 factors that can affect the rate of photosynthesis

  2. Online Simulation • Examined the effect of varying colors of light, light intensity, and amount of carbon dioxide on the rate of photosynthesis • Measured the number of bubbles (oxygen) after 30 seconds

  3. Factors Affecting Rate of Photosynthesis & Alternative Pathways

  4. Factors that affect photosynthesis • The rate at which plants carry out photosynthesis is affected by the plant’s environment. • Three very important factors that can affect the rate of photosynthesis: • Light intensity • Level of CO2 • Temperature

  5. Light Intensity • As the light intensity increases, the rate of photosynthesis increases, and then levels off. • Leveling off represents maximum rate of photosynthesis.

  6. Level of CO2 The Effect of the Level of Carbon Dioxide on the Rate of Photosynthesis • As the level of CO2 increases, the rate of photosynthesis increases, and then levels off. • Leveling off represents maximum rate of photosynthesis.

  7. Temperature • Initially, as temperature increases, the rate of photosynthesis increases. • The rate peaks and then starts to decreases because: • Enzymes that catalyze the reactions become ineffective. • Stomata start to close, limiting water loss and entry of carbon dioxide. The Effect Temperature on the Rate of Photosynthesis

  8. C3 Plants • REVIEW: During the Calvin cycle, CO2 is used to build sugars • C3 plants (soybeans, wheat, rice) only use the Calvin Cycle to fix CO2 • Given this name because CO2 is initially made into a three carbon compound. • These plants operate during the day

  9. Alternative Pathways • Some plants that are found in hot, dry environments have adaptations that minimize water loss while still allowing photosynthesis to take place: • C4 plants • CAM plants • They do not immediately enter into the Calvin cycle like C3 plants

  10. C4 Plants • Stomata partially closed during the day • Have a specialized pathway that captures low levels of CO2 & build 4 carbon compounds that enter the Calvin cycle • Examples: sugarcane, corn, crabgrass

  11. CAM Plants • CAM plants open stomata at night and close them during the day • Have a specialized pathway that takes in CO2 at night and makes a variety of organic acids • Then during the day, enzymes break down these organic acids, releasing CO2 that enters into the Calvin cycle • Examples: cacti and pineapples

  12. Chemosynthesis • Some bacteria that live on the floor of the ocean are autotrophs, but do not make food by photosynthesis • Use a process called chemosynthesis- the process by which energy is obtained from inorganic sources such as sulfur to make food

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