The ________ defends against disease by identifying and killing pathogens and tumor cells.

A) circulatory system
B) endocrine system
C) nervous system
D) immune system

Immune System

The complex network of cells, tissues, and organs that work together to defend the body against attacks by foreign invaders such as bacteria, viruses, and other pathogens.

Pathogens

Microorganisms or agents that are capable of causing disease or illness in their hosts.

Tumor Cells

Abnormal cells that grow and divide uncontrollably, forming a tumor, and may invade nearby tissues or spread to other parts of the body.