Anatomy and Physiology II Practice Test 2025 - Free Anatomy Practice Questions and Study Guide

Complement fixation is a crucial biological mechanism in the immune system that enables certain immune cells to kill invading pathogens, such as bacteria and viruses. This process involves a series of proteins known as complement proteins that work together to create a pore-like structure in the plasma membrane of the target cell. Once this membrane is disrupted, it can lead to cell lysis, which is the breaking down of the cell's membrane and ultimately the death of the invading organism.

The complement system not only helps to directly kill pathogens but also enhances other immune responses by marking pathogens for destruction and promoting inflammation. In contrast, phagocytosis involves the engulfing of pathogens by immune cells, apoptotic mechanisms lead to programmed cell death without disrupting nearby cells, and endocytosis generally describes the process of taking substances into the cell, rather than killing invading cells. Thus, the mechanism of complement fixation specifically targets the disruption of plasma membranes to eliminate threats.