Which immune system responds to broad categories of pathogens and does not change throughout an organism's life?

The innate immune system is designed to provide immediate, non-specific defense against a wide variety of pathogens, such as bacteria, viruses, fungi, and parasites. This system does not adapt or change in response to different infections or exposures over an organism's lifetime. Instead, it relies on physical barriers (like the skin and mucous membranes), cellular responses (such as phagocytosis by macrophages and neutrophils), and various biochemical mechanisms (including the action of cytokines and complement proteins) to swiftly respond to and eliminate threats.

In contrast, the adaptive immune system evolves over time, developing specific responses to pathogens that the organism has encountered previously. This system includes lymphocytes, such as B cells and T cells, which remember past infections and can provide long-term immunity. The acquired or specific immune system is synonymous with the adaptive immune system and also changes and matures as the organism encounters different antigens during its life.

Thus, the innate immune system's characteristics of being non-specific, immediate, and stable throughout life clarify why this option is the correct answer.