Final answer:
The transfer of antibodies from mother to fetus through the placenta is an example of natural passive immunity, primarily involving the IgG antibody and providing immediate, though temporary, protection to the newborn.
Step-by-step explanation:
The transfer of antibodies through the placenta from mother to fetus is an example of natural passive immunity. This type of immunity occurs when maternal antibodies are transported across the placenta, imparting a temporary defense to the infant. The primary antibody involved is IgG, which can cross the placenta and provide protective immunity to the newborn for the first few months of life. In contrast, active immunity involves the production of antibodies by the individual's own immune system, either in response to infection or vaccination. Hence, options A, B, and D relating to active immunity or innate immunity are incorrect.
Natural passive immunity is beneficial as it provides immediate protection to the newborn against pathogens. However, unlike active immunity, it does not contribute to the development of long-term immunological memory in the infant. It's also worth noting that secretory IgA is transferred from mother to infant through breast milk, contributing to natural passive immunity after birth.