Compost is Part of the Carbon Cycle You will often hear the carbon cycle analogized to breathing; the analogy is not perfect, but it can help simplify a complex pathway. Plant leaves take up carbon dioxide (CO2) and release oxygen (O2) through the process of photosynthesis that uses light energy to transform carbon dioxide and other elements into structural and energy molecules called carbohydrates (sugars). Plant tissues also release carbon dioxide into the air as they break apart carbon compounds (including carbohydrates) to give their cells energy through the process of respiration. Worms, cows, and humans all breathe in oxygen and breathe out carbon dioxide, again because they are breaking apart carbon compounds in their food to drive their cells’ activities. Many microbes also take up oxygen and release carbon dioxide. Some microbes do very different “breathing” when there is no available oxygen in the environment, such as in soil saturated with water or deep in a landfill that has compressed material; they might take up solid things like metals found in rocks or gases and release methane, metals, or other gases.
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