Final answer:
The immature Blood-brain barrier in young infants allows chemicals and drugs to more easily affect their central nervous system, due to its not fully developed protective function.
Step-by-step explanation:
The correct answer to the question 'Due to an immature __________, drugs and other chemicals may more easily affect the CNS in young infants' is C) Blood-brain barrier. The blood-brain barrier (BBB) is a physiological structure that restricts the passage of substances from the bloodstream into the central nervous system (CNS), providing protection against toxic substances and pathogens. In young infants, the BBB is not yet fully developed, making their CNS more susceptible to the effects of chemicals and drugs. Compounds that might be blocked by a mature BBB can more easily pass into the CNS of infants, potentially causing greater harm. This is significant considering the delicate and critical developmental stage of an infant's brain and nervous system. Although the liver, kidney, and respiratory system do play roles in metabolizing and excreting chemicals, it is the immaturity of the blood-brain barrier that is directly related to the increase in CNS susceptibility in infants.