Photosynthesis

• Photosynthesis Simple Equation

  Water + Carbion Dioxide + Energy (Sunlight) → Nutrients + Oxygen
• Anabolism


  Metabolic reactions that build molecules [endergonic reaction].
• Catabolism


  Metabolic reactions that break down molecules [exergonic reaction].
• Energy flow through ecosystems begins when photosynthesizers [plants] capture sunlight and convert it to chemical energy.
• Autotrophs are producers.
• Heterotrophs are consumers.
• Photosynthesis


  Metabolic pathway that uses light energy to turn carbon dioxide (CO2) and water (H2O) into carbohydrates (sugar).
• Photosynthesis creates oxygen.
• 2 Parts of Photosynthesis

  1. Light-dependent
  2. Light-independent or Calvin Cycle
• Photosynthesis occurs in the chloroplast.
• The chloroplast is a plastid that carries out photosynthesis.
• Thylakoid Membrane


  Highly folded into stacks of interconnected thylakoids [Light-dependent reactions].
• Stroma


  Cytoplasm-like fluid inside the chloroplast [Light-independent reactions].
• Pigment


  Organic molecule that selectively absorbs certain wavelengths of light.
• Chlorophyll a is the most common pigment in plants
• Chlorophyll a absorbs violet, red, and orange light, but reflects green.
• PHASE 1: Light Reaction

  1. Light hits a leaf

  2. Electron in chlorophyll enters an excited state (higher energy level) within the chloroplast's thylakoid membrane

  3. Excited electron leaves the chlorophyll

  4. Enzyme splits a water molecule to replace the electron lost by the chlorophyll

  5. Released electron goes through electron transport chain

  6. Electron is bounced between proteins in the thylakoid membrane

  7. Electron is eventually passed to another chlorophyll molecule

  8. Electron is passed to the final electron acceptor (ferredoxin NADP reductase)

  9. Ferredoxin NADP+ reductase gives the electron to an electron carrier NADP which turns it into NADPH

  10. NADPH carriers the electron to the next phase
• Phase 1: Light Reaction

  Total byproducts:  ATP (Used in LIR), NADPH (Used in LIR), O2 (Exits plant)
• Phase 2: Dark Reaction (Light-Independent) is also called the Calvin-Benson Cycle.
• Phase 2: Dark Reaction (Light-Independent)

  Carbon dioxide, ATP and NADPH are used to make sugar (glucose) in the stroma.
• Phase 2: Dark Reaction (Light-Independent)


  1. RUBISCO takes carbon dioxide and connects it to RuBP to form PGA

  2. Enzymes use ATP and NADPH to rearrange PGA into G3P

  3. Some G3P sent to cytoplasm to make glucose

  4. Some G3P used to make RuBP to restart dark reactions

  5. ADP and NADP sent back to light reactions to get recharged
• RUBISCO


  Enzyme in the stroma that takes carbon dioxide and connects it to RuBP to form PGA
• RuBP


  Molecule that RUBISCO connects carbon dioxide to, forming PGA
• PGA


  3 carbon molecule formed when RUBISCO connects carbon dioxide to RuBP
• G3P


  Molecules formed when enzymes use ATP and NADPH to rearrange PGA
• ADP


  Molecule formed when ATP is used as energy in the dark reactions
• NADP


  Molecule formed when NADPH is used as energy in the dark reactions
• Chemosynthesis


  The synthesis of organic compounds by bacteria or other living organisms using energy from reactions involving inorganic chemicals, typically in the absence of sunlight.
• Chemosynthesis


  They use chemicals instead of water as an electron donor before the electron transport chain.
• The Calvin–Benson cycle


  Builds sugars in the stroma of chloroplasts.