Metabolism refers to the sum of chemical processes that occur in living organisms. Organisms convert chemical substances into intermediates (metabolites) and end products. These biochemical processes maintain and build the body substance (anabolism), supply energy (energy metabolism/catabolism) and thus maintain bodily functions. Enzymes that speed up and drive (catalyze) chemical reactions are crucial for the metabolism. If the body metabolizes foreign substances that have been absorbed from outside, this is also called foreign matter (xenobiotic metabolism). The transformation of organism-foreign substances into organism material is called assimilation. The opposite is dissimilation. It refers to the degradation of an organism’s own substances. Metabolism also includes the conversion of harmful substances into substances that can be excreted (biotransformation). Plants, algae, some bacteria and archaea perform photosynthesis. They use light energy to convert carbon dioxide, water and other starting substances into their own cell material. This serves either directly to build and grow the organism, or as a storage substance, e.g. carbohydrates. The reserve substances can later be processed in the anabolism or energy metabolism. Secondary plant compounds are chemical compounds that are produced by plants but are neither required either in the anabolism nor in the energy metabolism.