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Understanding Photosynthesis: The Light Reactions and Energy Conversion Process

Learn about photosynthesis, the process converting sunlight into chemical energy. Explore the light reactions, ATP formation, and pigments involved. Understand the Calvin Cycle and the overall equation for photosynthesis. Discover how autotrophs and heterotrophs obtain energy, and how chlorophyll and carotenoids play a crucial role in capturing light energy. Delve into the structure of chloroplasts, including thylakoids and grana. Unravel the steps of the light reactions and the production of ATP using chemiosmosis. For detailed information, visit the provided link.

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Understanding Photosynthesis: The Light Reactions and Energy Conversion Process

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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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