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Photosynthesis

Photosynthesis. The Light Reactions. Obtaining Energy Autotrophs - organisms that use energy from sunlight or from chemical bonds in inorganic substances to make organic compounds like sugar

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Photosynthesis

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  1. Photosynthesis

  2. The Light Reactions • Obtaining Energy • Autotrophs- organisms that use energy from sunlight or from chemical bonds in inorganic substances to make organic compounds like sugar • Photosynthesis- process used to convert light energy from the sun into chemical energy in the form of organic compounds, primarily carbohydrates • Heterotrophs- organisms that must get energy from food instead of directly from sunlight or inorganic substances • https://wps.prenhall.com/wps/media/objects/486/498596/CDA7_1/CDA7_1b/CDA7_1b.htm

  3. Overview of photosynthesis • Can be divided into 2 stages • Light reactions: light energy is converted to chemical energy, which is temporarily stored in ATP and the energy carrier molecule NADPH • Calvin Cycle: organic compounds formed using CO2 and chemical energy stored in ATP and NADPH • Photosynthesis equation • https://wps.prenhall.com/wps/media/objects/486/498596/CDA7_1/CDA7_1d/CDA7_1d.htm

  4. Capturing light energy • Light reactions occur in the thylakoids of chloroplasts • Inside the chloroplast is a system of membranes called thylakoids that are arranged as flattened sacs • Grana- stacks of thylakoids • Stroma- fluid that surrounds grana

  5. Capturing light energy • Pigments- compounds that absorb light • Chloroplast pigments • Chlorophyll a- directly involved in light reactions • Chlorophyll b- assists chlorophyll a in capturing light energy (accessory pigment) • Carotenoids- yellow, orange, brown accessory pigments

  6. Converting light energy into chemical energy • Photosystem- cluster of pigment molecules and the proteins that the pigment molecules are embedded in • Steps of light reactions • 1. light energy forces electrons to enter higher energy level in photosystem II • 2. These e- move along thylakoid membrane to primary e- acceptor

  7. 3. e- move through electron transport chain, losing energy; protons (H+) pumped into thylakoid • 4. light energy forces electrons to enter higher energy level in photosystem I; e- from phtotsystem II replace photosystem I electrons: Photosystem II e- replaced by splitting water

  8. 5. e- from photosystem I move through a primary electron acceptor and then through another electron transport chain; e- combine with NADP+ to form NADPH • https://wps.prenhall.com/wps/media/objects/486/498596/CDA7_1/CDA7_1f/CDA7_1f.htm

  9. Making ATP • Chemiosmosis- process used to make ATP in the light reaction • The gradient of protons (H+) inside the thylakoid represent potential energy • These protons diffuse through ATP synthase, which uses this energy to add a phosphate to ADP to make ATP

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