Biological Systems MCAT Practice Exam

Which component of the immune system is responsible for nonspecific protection against invaders?

1. Antibodies

2. Complement system

3. Memory cells

4. Macrophages

The correct answer is: Complement system

The complement system plays a vital role in the immune system by providing nonspecific protection against pathogens. It consists of a series of proteins found in the bloodstream and tissues that, when activated, work together to enhance the effectiveness of antibodies and phagocytic cells in clearing microbes and damaged cells. One of the key functions of the complement system is to mark pathogens for destruction, a process known as opsonization, which makes them more recognizable and easier for cells like macrophages to engulf. Additionally, it can directly kill pathogens through the formation of membrane attack complexes that penetrate the cell membranes of bacteria. In contrast, antibodies are specific proteins produced by B cells that target particular antigens. Memory cells are a part of the adaptive immune system, created after an initial infection, that help mount a faster response to previously encountered pathogens. Macrophages are immune cells that engulf and digest cellular debris and pathogens, but they play a more active role in the specific adaptive immune response alongside other immune functions. While all these components contribute to immune defense, the complement system is specifically known for its rapid and broad-spectrum response to a wide variety of invaders, embodying the concept of nonspecific immunity.