Immunity

How does our immune system protect us from disease?

Why?

One way in which organisms maintain homeostasis is by detecting foreign cells and particles like
pathogens and cancer cells. Once the pathogen is detected and identified, other systems in the
organism’s body can attack the invader, thus keeping the organism healthier. Cells of the human
immune system are finely tuned to recognize and respond quickly to disease-causing organisms.

Model 1 – Cell Mediated Response

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Th Th
Th

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1. In Model 1 a pathogen (virus, bacteria, foreign protein, parasite) has entered the
bloodstream of an individual. Draw the symbol that represents the pathogen.I can’t edit any
drawings

I can’t edit any drawings.

2. One response of the human immune system is endocytosis of a pathogen by a phagocyte (a

type of white blood cell). Refer to Model 1.
a. Which diagram in the cell mediated response illustration shows this process?

Diagram 1

b. Draw the symbol that represents the phagocyte.

I can’t edit any drawings

3. Another type of white blood cell that is involved in the cell mediated response is a helper T-
cell.

a. Draw the symbol that represents the helper T-cell in Model 1.

2 POGIL™ Activities for AP* Biology

 I can’t edit any drawings

b. In your drawing above, circle the specialized surface proteins on the helper T-cell.
I can’t edit any drawings. The specializd surface proteins are above the helper T-cell.

4. According to Model 1, are all helper T-cells the same? Justify your answer with specifi c
evidence from Model 1.

No, some helper T-cells have thicker arms than others.

Immunity 3
4 POGIL™ Activities for AP* Biology
5. The following statements are labels for the cell mediated process in Model 1.
• __2__ A piece of the pathogen is presented on the surface of the phagocyte.
• ___4_ The helper T-cell disperses a chemical signal to activate other immune response
systems.
• __3__ The helper T-cell binds to the piece of pathogen presented on the phagocyte.
• __1__ Pathogen is broken apart by chemicals in the phagocyte.
a. Determine the order of the statements by referring to Model 1.
b. With your group, decide where each statement belongs in the diagram and label Model
1 appropriately. Note that more than one statement may match a diagram and some
diagrams may not match any statement.
6. According to Model 1, do the helper T-cells interact with the free pathogens in the blood?

Read This!

The pieces of pathogen that are presented on the surface of a cell are called antigens. Cells that
present antigens on their surface, such as the phagocyte in Model 1, are called antigen-presenting
cells (APC). They activate helper T-cells. After being activated by an antigen, the helper T-cell will
begin a phase of rapid cell division. The resulting daughter cells may be effector Th cells or memory
Th cells. The memory Th cells will stay in the body for several years, ready to respond to the pathogen
if it should ever infiltrate the body again.

7. Do all types of helper T-cells bind to all antigens? Justify your answer with specific evidence
from Model 1.
No. Some helper T-cells have different arms to other T-cells.

8. Add labels to Model 1 for the “antigen” and “antigen-presenting cell.”

Model 2 – Humoral Response

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9. B-cells are a third type of white blood cell that is involved in immunity.

a. What is the name of the immune system response that involves B-cells?
Humoral Response

10. According to Model 2, are all B-cells the same? Justify your answer with specific evidence
from Model 2.
No, some B-cells have thicker arms than others.

11. In diagram 2 of Model 2, binding occurs between an antigen and a B-cell. How is this
interaction different from the binding that occurs between antigens and helper T-cells?
T-cells will only activate on an antigen presenting cell.

6 POGIL™ Activities for AP* Biology

 12. Consider diagrams 3–5 in Model 2. Write descriptions similar to those in Question 5 for each
of these steps in the humoral response.
The B cell binds to a pathogen and spreads to create an immune response.

13. Is a B-cell an antigen-presenting cell? Justify your reasoning.

It is an antigen-presenting cell it has an antigen on its surface.

14. According to Model 2, do B-cells ever interact with pathogens that have infected a cell?
Justify your reasoning with specific evidence from Model 2.
No, since they onlyi nteract with pathogens in body fluid.

15. Predict what would happen if a B-cell like the one shown in diagram 5 of Model 2 were to
run into a helper T-cell like the ones in Model 1.
The t cell would bind to the b cell.

Model 3 – Adaptive Immunity

16. Label the following items in Model 3.

Pathogen B-Cell Helper T-cell
17. Describe the interaction between the B-cell and the helper T-cell in Model 3.

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 The t cell is binding to the b cell.

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Immunity 9
 disperse antibodies.

a. According to Model 3, what does the antibody do to pathogens?

Antibodies bind to pathogens to destroy them.

19. How might the interaction between the antibody and pathogens affect the pathogen’s
ability to infect its host?

The pathogens won't be able to function.

Read This!

After the B-cell is activated by the helper T-cell, the B-cell enters a phase of rapid cell division. Some
of the daughter cells become plasma cells that make even more antibody molecules, some reaching
a rate of 2,000 molecules per second. The other daughter cells become memory B-cells that will stay
in the body for several years, ready to respond to the pathogen if it should ever enter the body
again.

Model 4 – Immune Response to a Pathogen

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 90

80

Amount of the Antibody Present

70

60

50

40

30

20 First Encounter
with the
10 Pathogen

!"0
Time Second Encounter
with the Same Pathogen

20. What does the y-axis of the graph in Model 4 represent?

The amount of antibodies.

21. How many times did the organism in Model 4 encounter the same pathogen?

2 times

22. Using Model 4, compare the amount of the antibody generated by the B-cells after the fi rst
encounter with the antigen to the amount of the antibody generated in the second
encounter with the antigen.

More antibody was generated the second time.

23. Refer to Model 4.

a. Compare the time needed to reach the peak amount of antibody production for the fi rst
and second encounters.

The time was much less the second time. The second time it was about half the forest
time.

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 b. How does your answer to part a explain the fact that we get sick the fi rst time we
encounter a virus, but we do not get sick the second time we encounter the same virus?
The t cells remember the pathogen and the immune response is faster and stronger.
24. People who are allergic to bee stings are actually having a response to the antibodies
produced by their immune system when they are stung. This is called anaphylaxis. Most
people who end up having a bee sting allergy did not have anaphylaxis the fi rst time they
were stung. It is only upon the second sting, or subsequent stings that they have an allergic
response. Use what you have learned in this activity to explain this phenomenon.

Due to the fact that more antibodies are created in the second bee sting, the reaction would
be much more major the second time.

12 POGIL™ Activities for AP* Biology

Immunity 13
 immune response. Which cells are responsible for the response to the second pathogen
exposure illustrated in Model 4? Justify your reasoning.

Memory t cells help te body remember the pathogen. Same with helper b cells.

26. Consider Models 1 and 2, and the interaction that helper T-cells and B-cells have with the
pathogen.
a. Why is the process in Model 1 called a “cell mediated” response?

It is cell mdediated beccause hte antigen has to be presented.

b. Why is the process in Model 2 called a “humoral” response? Note: Blood was once
referred to as one of the humors of the body.

It is not humoral because it doesent bind to all pathogens in blood.

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Extension Questions
27. Consider the life cycle of a cell. When the memory cells of the immune system are not
activated or responding to a pathogen exposure, what phase of the cell cycle are they likely
in? Justify your reasoning.

Read This!

Edward Jenner, an English country doctor, is credited with giving the first relatively safe vaccine. He
noticed that girls who milked cows developed sores on their hands that were similar to the sores of
smallpox victims. These sores were called cowpox, but the girls did not seem to be sick and they did
not become ill with the dreaded human disease, smallpox. Legend states that Jenner purposely
infected a young boy with scrapings from cowpox sores and then exposed the boy to smallpox. The
boy did not become ill, and the practice of vaccinations moved rapidly into mainstream medicine.
The word vaccination comes from the Latin word for cow, vacca. Today, thanks to intensive
vaccination practices in the last half of the 20th century, smallpox is no longer a dreaded human
disease. Since then, vaccines for other diseases like polio and measles have been developed, and we
no longer have widespread deaths from these diseases.

28. Use what you learned in this activity to explain why the girls observed by Jenner did not get
sick from smallpox.

29. Using the information from this activity and the Read This! box, write a definition for the
term vaccine, using the terms antigen, antibody, and memory B-cells.

30. The common cold is a viral disease. So is AIDS, which is caused by the Human
Immunodeficiency Virus, or HIV. Effective vaccines against these viral diseases have not
been developed despite years of research and work by dedicated scientists. One reason for
this is the rapid mutation rate of these viruses, leading to new surface proteins in a very
short time. Return to Model 2 to speculate about how this rapid change in the cold virus
and HIV make vaccinations difficult to develop.

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 31. Propose a reason why you must get vaccine “booster” shots every few years.

16 POGIL™ Activities for AP* Biology