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Biology LibreTexts

8.3C: The Carbon Cycle

  • Page ID
    13212
  • All organisms need energy to perform life functions, and energy that is released is reused in other ways.

    LEARNING OBJECTIVES

    Describe the importance of the carbon cycle

    KEY TAKEAWAYS

    Key Points

    • Every single atom of energy is conserved by changing form or moving from one type of energy to another, so waste does not exist in nature.
    • Photosynthesis absorbs light energy to build carbohydrates, and aerobic cellular respiration releases energy by using oxygen to metabolize carbohydrates.
    • Photosynthesis consumes carbon dioxide and produces oxygen, and aerobic respiration consumes oxygen and produces carbon dioxide.
    • Both photosynthesis and cellular respiration use electron transport chains to capture the energy necessary to drive other reactions.

    Key Terms

    • heterotroph: an organism that requires an external supply of energy in the form of food, as it cannot synthesize its own
    • cellular respiration: the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP)
    • aerobic: living or occurring only in the presence of oxygen

    The Carbon Cycle

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    Photosynthesis and Aerobic Respiration: Photosynthesis consumes carbon dioxide and produces oxygen. Aerobic respiration consumes oxygen and produces carbon dioxide. These two processes play an important role in the carbon cycle.

    Whether the organism is a bacterium, plant, or animal, all living things access energy by breaking down carbohydrate molecules. But if plants make carbohydrate molecules, why would they need to break them down, especially when it has been shown that the gas organisms release as a “waste product” (CO2) acts as a substrate for the formation of more food in photosynthesis? Living things need energy to perform life functions. In addition, an organism can either make its own food or eat another organism; either way, the food still needs to be broken down. Finally, in the process of breaking down food, called cellular respiration, heterotrophs release needed energy and produce “waste” in the form of CO2 gas.

    In nature, there is no such thing as waste. Every single atom of matter and energy is conserved, recycling over and over, infinitely. Substances change form or move from one type of molecule to another, but their constituent atoms never disappear.

    CO2 is no more a form of waste than oxygen is wasteful to photosynthesis. Both are byproducts of reactions that move on to other reactions. Photosynthesis absorbs light energy to build carbohydrates in chloroplasts, and aerobic cellular respiration releases energy by using oxygen to metabolize carbohydrates in the cytoplasm and mitochondria. Photosynthesis consumes carbon dioxide and produces oxygen. Aerobic respiration consumes oxygen and produces carbon dioxide. Both processes use electron transport chains to capture the energy necessary to drive other reactions. These two powerhouse processes, photosynthesis and cellular respiration, function in biological, cyclical harmony to allow organisms to access life-sustaining energy that originates millions of miles away in the sun.

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