Complex sentence: Free radicals play an important role in a number of biological processes, some of them necessary for life, such as the intracellular killing of bacteria by phagocytic cells such as granulocytes and macrophages.
Split into simpler sentences: Free radicals play an important role in a number of biological processes. Some of these are necessary for life, such as the intracellular killing of bacteria by phagocytic cells such as granulocytes and macrophages.