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6-2 Calvin Cycle the second biochemical pathway

The Calvin Cycle, the second biochemical pathway, fixes carbon atoms from CO2 into organic compounds in three steps that occur in the stroma of chloroplasts. This process requires CO2, NADPH, and ATP, and takes place in the absence of light. C3, C4, and CAM plants have alternative pathways for carbon fixation, depending on their environmental conditions. The rate of photosynthesis depends on light intensity, carbon dioxide levels, and temperature. The overall equation for photosynthesis is carbon dioxide + water + energy → oxygen + organic molecules.

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6-2 Calvin Cycle the second biochemical pathway

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  1. 6-2 Calvin Cycle the second biochemical pathway

  2. Carbon Fixation by the Calvin Cycle Carbon atoms from CO2 are bonded or “fixed” into organic compounds. 3 steps occur in the stroma of chloroplasts. • requires CO2, NADPH and ATP • Carbon from carbon dioxide are bonded or "fixed" into organic compounds • takes place in the stroma of the chloroplast • end products are PGAL (which can be converted to organic molecules where energy is stored), ADP, NADP, & oxygen • Called dark reactions since light is not needed

  3. Alternative Pathways Modes of Calvin Cycle C3 plants - fix carbon dioxide in the Calvin cycle (most common) C4 plants (corn, sugar cane, crab grass) -can close stomata in extreme heat, thereby allowing less CO2. fix carbon dioxide using an enzyme before the Calvin cycle. CAM plants (cactus, pineapple) - fix carbon dioxide at night when stomata (pores on underside of leaves) open without water loss

  4. Rate of Photosynthesis depends on the environment • 1. Light intensity - as light intensity increases, so does photosynthesis until it plateaus • 2. Carbon dioxide levels - as carbon dioxide increases, so does photosynthesis until it plateaus • 3. Temperature- as temperature increases, photosynthesis increases to a certain temperature, then the rate of photosynthesis decreases

  5. Photosynthesis overall equation______________________________

  6. overall equation carbon dioxide + water + energy → oxygen + organic molecules

  7. Section 6-2 Review In what part of the chloroplast does the Calvin cycle take place? Describe what can happen to PGAL molecules made in the Calvin cycle. How many turns of the Calvin cycle are needed to produce a molecule of PGAL? How many molecules of ATP and NADPH are used in the process? What plant structures control the passage of water out of a plant and carbon dioxide into a plant? What is a C4 plant?

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