What is the primary function of the immune system?

The primary function of the immune system is to defend the body against pathogens and diseases. This system is made up of various cells, tissues, and organs that work together to identify and eliminate harmful invaders such as bacteria, viruses, parasites, and fungi. By recognizing these threats, the immune system initiates an immune response that can involve inflammation, the production of antibodies, and the activation of immune cells to destroy the pathogens. This protective role is vital for maintaining health and preventing infections.

The other options do not pertain to the immune system's fundamental role. Regulating body temperature is a function of the body's thermoregulatory mechanisms. Transporting oxygen in the blood is primarily the role of red blood cells and the circulatory system, while digestion is handled by the gastrointestinal system. Thus, the immune system's specific focus on defending against diseases makes it distinct and critical for overall health.