False-colour scanning transmission electron micro- graph (STEM) of a crystal of the enzyme catalase. Magnified 176, 500 times at 35mm size, the micro- graph shows the regular crystalline lattice of individual molecules forming the enzyme. Catalase is crucial to the metabolism of plants & animals, including humans, because it breaks down hydrogen peroxide, a poison formed during the metabolic process, to water & oxygen. 1 molecule of catalase can break down 1 million molecules of hydrogen peroxide per minute. It depends for its action on an atom of iron; 1 milligram of iron in catalase is as effective in decomposing hydrogen peroxide as 10 tons of ordinary inorganic iron.