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8: Photosynthesis

  • Page ID
    104323
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    The processes in all organisms—from bacteria to humans—require energy. To get this energy, many organisms access stored energy by eating, that is, by ingesting other organisms. But where does the stored energy in food originate? All of this energy can be traced back to photosynthesis.

    • 2.5.1: Introduction
      Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities (energy transformation).
    • 2.5.2: Overview of Photosynthesis
      Photosynthesis is essential to all life on earth; both plants and animals depend on it. It is the only biological process that can capture energy that originates in outer space (sunlight) and convert it into chemical compounds (carbohydrates) that every organism uses to power its metabolism. In brief, the energy of sunlight is captured and used to energize electrons, which are then stored in the covalent bonds of sugar molecules.
    • 2.5.3: The Light-Dependent Reactions of Photosynthesis
      Like all other forms of kinetic energy, light can travel, change form, and be harnessed to do work. In the case of photosynthesis, light energy is converted into chemical energy, which photoautotrophs use to build carbohydrate molecules. However, autotrophs only use a few specific components of sunlight.
    • 2.5.4: Using Light Energy to Make Organic Molecules
      The products of the light-dependent reactions, ATP and NADPH, have lifespans in the range of millionths of seconds, whereas the products of the light-independent reactions (carbohydrates and other forms of reduced carbon) can survive for hundreds of millions of years. The carbohydrate molecules made will have a backbone of carbon atoms. Where does the carbon come from? It comes from carbon dioxide, the gas that is a waste product of respiration in microbes, fungi, plants, and animals.
    • 2.5.5: Key Terms
    • 2.5.6: Chapter Summary
    • 2.5.7: Visual Connection Questions
    • 2.5.8: Review Questions
    • 2.5.9: Critical Thinking Questions

    Thumbnail: Plant cells (bounded by purple walls) filled with chloroplasts (green), which are the site of photosynthesis. (CC BY-SA 3.0; Kristian Peters).​​​​​


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