Final answer:
About 30-40% of transferrin molecules are normally bound by iron.
Step-by-step explanation:
Transferrin is a protein that binds to iron in the plasma. Normally, transferrin molecules are only partially saturated with iron. The percentage of transferrin molecules that are bound by iron can vary depending on the individual. However, in general, it is estimated that about 30-40% of transferrin molecules are normally bound by iron.