Skip to Main Content

Challenge 1: What are “pathogens” and how does our immune system deal with them?

Learning Targets:

  • I can define “pathogen”.
  • I can compare and contrast 4 main pathogens based on their structure and how they cause infection.
  • I can develop a model (diagram) to explain how the immune system works.
  • I can describe how B-cells and T-cells function

Estimated Time: 60 minutes

Activity 1 - Understanding Pathogens


Write & Discuss

  • What is a pathogen?
  • What are some of the features of pathogens?
  • How do pathogens infect us?
  • How are viruses different from other pathogens?

Activity 2: How the Immune System works


Immune System



  • How is a chaperone like our immune system”?

Imagine you are hosting a large party and have invited all of your friends and many of you classmates. Unfortunately, you hear a rumor that a few uninvited kids plan to crash the party and cause a disruption. You don’t know the identity of the uninvited kids but to protect the party from them you hire a few chaperones.

Because the chaperones don’t know the identities of the potential party crashers, they circulate through the party and look for anyone who is misbehaving. At one point, they see a couple of kids pouring fish oil into the punch. The chaperones confront the beverage polluters and escort them from the party. Before letting them go, the chaperones take a picture of the party crashers so they can easily recognize them amongst the other guests if they return to the party. Our immune system works similar to the chaperones and shares three important features. First, the chaperones have to circulate through the party and be alert to signs of trouble or disruption.

Our immune system contains several different types of cells whose job is to monitor conditions throughout the body and respond to signs of damage. Second, the chaperones have to eliminate the cause of the disruption (the party crashers). Our immune system has cells that eliminate pathogens or produce proteins that eliminate pathogens. Third, the chaperones can remember the identities of the party crashers which allows them to more easily find the party crashers if they return. After removing a pathogen, our immune system can remember the identity of the pathogen so that if it returns, our immune system can remove the pathogen before it makes us sick.

  • Antibodies from B-cells
  • Cytotoxic T-lymphocytes (CD8+)
  • Helper T-cells (CD4+) to stimulate and regulate B-cells and CTL

Answer & Discuss

  • How does the immune system eliminate pathogens from our bodies?
  • How does the immune system recognize pathogens and other foreign organisms?

Review the following:

  • Receptors on B-cells and T-cells bind to specific peptides and other small macromolecules.
  • Each B-cell and T-cell expresses a receptor on its surface that binds to a unique biological molecule which is usually a peptide from a protein but can be nucleic acid or carbohydrate.
  • Specific cells in our bodies engulf pathogens, digest those pathogens and present small pieces of those pathogens on their cell membrane.
  • Specific receptors on T-cells and B-cells can bind to those small pieces.

Answer & Discuss

  • How does the immune system remember pathogens that have infected us?
  • How does the immune system’s memory protect us from future infection?