Final answer:
Iron oxidizing bacteria use large amounts of iron because it's a critical energy source for their metabolism. They secrete siderophores that solubilize Fe(III), enabling its uptake and use in energy-producing reactions. The correct option is B.
Step-by-step explanation:
Iron oxidizing bacteria use large amounts of iron because iron is a crucial energy source for their metabolism. In the environment, iron often exists in the Fe(III) state, which is insoluble under neutral pH conditions. These bacteria secrete organic compounds known as siderophores, which have a high affinity for Fe(III), effectively solubilizing and mobilizing the metal to increase its availability.
Siderophores, like enterobactin produced by bacteria, bind iron in an octahedral arrangement with a strong formation constant, enabling the dissolution of otherwise insoluble Fe(III) compounds. This iron complex can then be transported into the bacterial cell, where iron is reduced to the more biologically useful Fe(II).
Thus, the process provides an essential supply of iron for the bacteria's metabolic functions, including energy production through oxidation reactions.