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What is Photosynthesis?

What is Photosynthesis?. The process of capturing light energy‚ converting it to chemical energy‚ and storing it by manufacturing sugar 6CO 2 + 6H 2 O (+ light energy) C 6 H 12 O 6 + 6O 2 3 linked stages: Capturing light energy

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What is Photosynthesis?

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  1. What is Photosynthesis? • The process of capturing light energy‚ converting it to chemical energy‚ and storing it by manufacturing sugar • 6CO2 + 6H2O (+ light energy) C6H12O6 + 6O2 • 3 linked stages: • Capturing light energy • Using the light energy to create chemical energy (ATP and NADPH)  Light Reactions • Using the free energy from ATP and reducing power of NADPH to synthesize organic compounds from atmospheric carbon (carbon fixation)  Light Independent (Calvin Cycle)

  2. Types of Photosynthesis • C3: in most plants. Puts CO2 directly into the Calvin Cycle. More efficient than C4 and CAM plants under cool and moist conditions and under normal light • C4: works well for plants in hot, dry climates (sugar cane) • CAM: for plants in very hot and dry climates (deserts). Stomata are closed during the day to reduce excessive water loss from transpiration (cactus)

  3. C3 Photosynthesis

  4. C4 Photosynthesis • Called C4 because the CO2first binds with Phosphoenolpyruvate to form a 4 carbon compound • Plants that first go through the C4 pathway are better adapted than plants that solely go through the C3 pathway under conditions of drought, high temperatures and low nitrogen or CO2 concentrations

  5. Photosynthesis takes place in a chloroplast of a thin-walled mesophyll cell and a 4-carbon acid is handed off to a thick-walled bundle sheath cell (using ATP) where the Calvin cycle occurs in a chloroplast of that second cell

  6. Photorespiration • Plants, especially C3 plants, face the problem of photorespiration. In hot dry days, these plants tend to close their stomata to prevent excessive loss of water (from transpiration). • Inevitably, the carbon dioxide cannot enter the leaves (via the stomata) resulting in the levels of carbon dioxide within the leaves to become low.

  7. Photorespiration continued • Since there are few carbon dioxide molecules to fix, the oxygen molecules are used as a substitute to produce G3P. • Because of photorespiration, instead of 2 molecules of G3P, only one G3P is produced and a toxic phosphoglycolate (which the plant must get rid of) is also formed.

  8. Examples of C4 Plants

  9. Crassulacean Acid Metabolism (CAM) Photosynthesis • Refers to the Crassulaceaefamily of plants, since the pathway was first discovered in crassulaceaen plants • Stomata open at night (when evaporation rates are usually lower) and are closed during the day. The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released to go into the Calvin Cycle

  10. Examples of CAM plants

  11. Questions

  12. Exit Card • Name a C4 plant • What is the difference between CAM and C4? • What is the enzyme that carbon fixes CAM?

  13. Exit Card • Name a C4 plant • Corn, millet, sorghum, sugar cane • What is the difference between CAM and C4? • In C4 stomata are open during the day, in CAM it is open in the night • What is the enzyme that carbon fixes CAM? • Phosphoenolpyruvate-carboxylase, or PEP-C

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