Which of the following is an example of a pathogen?

A pathogen is an organism that can cause disease in its host, typically by invading the body and interfering with normal biological functions. In this context, Streptococcus bacteria are classified as a pathogen because they can lead to infections in humans, such as strep throat, pneumonia, and other illnesses. These bacteria possess the ability to reproduce and spread, which is a key characteristic of pathogens.

On the other hand, insulin is a hormone that regulates glucose levels in the blood and does not have the ability to cause disease. Hemoglobin is a protein in red blood cells that carries oxygen and does not have pathogenic properties. Glucose is a simple sugar that serves as a primary energy source for cells and is not capable of causing disease. Thus, among the options, Streptococcus bacteria is clearly the example of a pathogen, as it is responsible for various infectious diseases.