Final answer:
Ferritin binds and stores intracellular iron, preventing the formation of free radicals. It oxidizes Fe²+ to Fe³+ and stores it in its central cavity. When needed, the Fe³+ is reduced back to Fe²+.
Step-by-step explanation:
Stored intracellular iron is bound to ferritin, which prevents iron from forming free radicals via the Fenton reaction. Ferritin uses oxygen to oxidize Fe²+ to Fe³+ and stores it in its central cavity. When iron is needed by a cell, the Fe³+ is reduced to the more soluble Fe²+ by a reductant such as ascorbic acid.