Question

The complement system is a group of in the blood that detect pathogens that have entered the body.

Answer 1

The complement system that detects pathogens entering the body is the immune system. It is considered as a "network of cells, tissues, and organs" that detects and defend the body against pathogens and microbes attempting to enter our body. These microbes could either be microscopic organisms like bacteria and fungi.

Answer 2

Answer;

Proteins

The complement system is a group of proteins in the blood that detect pathogens that have entered the body.

Explanation;

• The complement system is a group of proteins in the blood that attack pathogens that enter the body and kill them.
• The complement system is activated when an infection occurs, leading to a sequence of events on the surface of a pathogen that helps destroy pathogens and eliminate the infection.
• It is consist of 25 known serum proteins, and is part of the innate immunity. Twelve of these proteins are directly involved in the mechanisms of elimination of pathogens, the others  regulate the activity of the former to avoid an autoimmune reaction.