Which system in the body is responsible for recognizing and attacking foreign substances?

The immune system is the body's primary defense mechanism against foreign substances such as pathogens, including bacteria, viruses, and fungi. It is composed of a network of cells, tissues, and organs that work together to identify and eliminate these harmful invaders. The immune system employs various types of white blood cells, antibodies, and other components to recognize specific antigens (substances that provoke an immune response) and mount a targeted attack against them.

One of the key features of the immune system is its ability to remember previous encounters with pathogens, which allows for a more rapid and efficient response upon subsequent exposures. This memory function is the basis of how vaccinations work, as they prepare the immune system to recognize and respond to specific diseases.

In contrast, the endocrine system regulates physiological processes using hormones, the nervous system coordinates bodily functions and responses to stimuli, and the circulatory system transports blood, nutrients, and gases throughout the body. While these systems play crucial roles in maintaining health and homeostasis, they do not primarily focus on recognizing and attacking foreign substances.