Wonders of Life: Exploring the Most Extraordinary Phenomenon in the Universe (Wonders Series)

by Brian Cox

The Oxygen Evolving Complex is an odd structure: more mineral than biological. It consists of four manganese atoms and a single calcium atom, held together in a lattice of oxygen. Manganese is locked away in vast mineral deposits on the ocean floor today, but in the early history of our oceans it would have been available in seawater for organisms to use. Bacteria use manganese to protect them from UV light, in much the same way as we use melanin – manganese is easily ‘photo-oxidised’, absorbing the potentially harmful UV photon and releasing an electron in the process. This may have been one of the ways in which electrons made their way into the primitive photosystem II in early bacteria. So manganese, at least, was already an important component of living things from the earliest of times. Today, manganese performs a different task. It sits at the heart of the Oxygen Evolving Complex, whose job is to grab water molecules and hold them ready for electrons to be ripped off and used as input into photosystem II. As a result, water molecules are split apart and, just as in the electrolysis of water so beloved of Mr Bell (see here), oxygen is released as a gas.