Essential and trace elements in biological systems; biological importance of relative abundance, adaptation to natural abundances; problems in biological systems: agriculture, air pollution, acid rain, particulate air pollution and mining problems; metalloporphyrin, chlorophyll, photosynthesis and respiration; simulated photosynthetic processes, synthetic leaf and ‘antenna’ molecules.  Cytochromes; bioredox agents and mechanisms; enzymes and synthetic enzyme model; their action, inhibition and poisoning. Models for hemoglobin, nitrogenase and vitamin B12 complexes.