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How organisms obtain energy for life processes is being tested. Some make their own energy-rich molecules from inorganic sources using light or chemical energy—these are autotrophs. Others must obtain energy by consuming other organisms and depend on preformed organic compounds from those organisms; these are heterotrophs. Saprotrophs are a subset that feed on decaying matter by secreting enzymes, but the general term for organisms that must rely on others for energy is heterotrophic. Chemotrophic describes energy derived from chemical reactions rather than the mode of obtaining carbon, so while some heterotrophs are chemotrophs, chemotrophy alone doesn’t define this lifestyle.