What is the main function of the immune system?

The immune system's primary role is to protect the body from pathogens, which include bacteria, viruses, fungi, and parasites. It achieves this through a complex network of cells, tissues, and organs that work together to identify and eliminate these harmful invaders. When the body encounters a pathogen, the immune system responds by activating various defenses, including white blood cells, antibodies, and signaling molecules. This response not only helps to fight off infections but also provides the body with memory, allowing it to respond more effectively to future exposures to the same pathogens.

The other options refer to essential bodily functions that are regulated by different systems. Regulating body temperature is primarily the role of the integumentary system and the endocrine system. Producing energy is mainly a function of the metabolic processes that occur throughout various systems, particularly the digestive and cellular processes. Controlling movement is the responsibility of the muscular and nervous systems, which work together to facilitate voluntary and involuntary movements in the body.