Metals corrosion and biological respiration: Similarities and disparities: An overview

Both metallic corrosion and biological respiration involve oxidation - reduction reactions, taking place upon electron transfer between the participating entities. Metals corrode as a consequence of their tendency to return to the oxide state prevailing in the original ores. Corrosion occurs by reduction of dissolved oxygen in neutral pH solutions, or by reduction of H ⁺ ions in acidic solutions. The involvement of oxygen and redox reactions is also essential for sustaining life in biological systems. Biological respiration in humans relies on the oxidation of carbohydrates, fats and amino acids as a part of the vital network of metabolic processes that generate the energy necessary to maintain normal body function and temperature. In plant systems the biological 'respiration' process of photosynthesis, which involves chlorophyll, is a major source of oxygen on the planet. For example, in human biological systems, unlike corrosion processes in metals, oxygen transport by blood is carried out by haemoglobin as the essential process of human respiration. Haemoglobin is a tetrameric protein located in the red blood cells, containing porphyrin-bound Fe ²⁺. Haemoglobin picks up oxygen in the lungs, carries it to the tissues and releases it there, where it is actually used. On its way back, haemoglobin picks up the metabolic CO ₂ produced in the tissues and releases it into the lungs. In photosynthesis the chlorophyll molecule is the inverse analog to haemoglobin; both molecules are porphyrins with the difference of central metal atoms being Fe in haemoglobin and Mg in chlorophyll. In this report similarities and disparities between metallic corrosion and biological respiration are presented, taking into account the respective reactants, products and catalysts. This comparative study allows for the interaction between teachers and students, in order to explain the similarities and diversities of the fundamentals of natural processes such as metallic corrosion and biological respiration. This paper covers elements from the mineral, animal and vegetable kingdom, with a comparative approach.