Routes of Entry
Author: Sarah Kenyon and Rachel Hughes

Time: 3 days
Preparation Time: 30 minutes photocopying
Materials: Teacher guide 1
Disease overhead

Students classify diseases as having pathogenic or non-pathogenic routes. They explore the differences between different pathogenic agents and identify causal agents for a variety of diseases. Students explore and explain one disease and its causal pathogen in detail and present to class.

Students will be able:

1. Explain the difference between diseases with pathogenic and non-pathogenic causes and classify diseases in this manner on a chart.
2. Name four different types of disease-causing pathogens and related diseases on a chart.
3. Summarize commonalities between some diseases of a specific pathogen.

National Science Education Standard:
Living organisms have the capacity to produce populations of infinite size, but environments and resources are finite. This fundamental tension has profound effects on the interactions between organisms.
CONTENT STANDARD F: Science in Personal and Social Perspectives
The severity of disease symptoms is dependent on many factors, such as human resistance and the virulence of the disease-producing organism. Many diseases can be prevented, controlled, or cured. Some diseases, such as cancer, result from specific body dysfunctions and cannot be transmitted.



1.Ask students to think back to the diseases that they have been introduced to over the past few weeks (if you are doing this lesson out of order ask students to identify some diseases that are of interest.) How are these diseases spread from person to person? Have students list the diseases on index cards. During this time, discuss the difference between an infection, the action of a disease-causing pathogen entering the body, and a disease, when the body is not able to immediately fend off the pathogen and the pathogen is able to cause damage to the body.

2. Reviewing the diseases that students named can they identify what type of pathogen has caused the disease? Is this a virus, a bacterium, fungi, protozoa, or a parasitic worm? Previously students have been briefly introduced to different types of pathogens; this is an opportunity to revisit the classifications of these pathogens. Concentrate on making sure students note that not all microorganisms are of the same type and that they know the difference between a virus and bacteria.

Viruses consist of a small amount of nucleic acid (DNA or RNA) enveloped by a protective coat of protein, or protein and lipid. Viruses are smaller than a cell and only reproduce by invading eukaryotic cells and then making use of the invaded cells’ reproductive structures which viruses lack. Viruses are not considered to be living. Viruses are considered obligate intracellular parasites. (Particles of a similar type that invade prokaryotes are known as bacteriophages.) Examples of diseases caused by a virus infection include the common cold, smallpox and HIV/AIDS.
Unlike viruses, bacteria are considered living organisms. Prokaryotic cells and bacteria are typically unicellular and don’t have the membrane bound organelles that are found in eukaryotic cells. Bacteria are able to reproduce asexually through binary fission.

3. If students are able to identify the type of pathogen associated with a disease they should note that on the disease index card. Review the different diseases and pathogens as a class. Are some more virulent than others? Do some diseases seem to pass through a population more quickly than others? As a class make a chart (see Overhead # 1) that includes the disease’s name and whether it has a pathogen or non-pathogenic cause. If pathogenic, what type of pathogen causes the disease, is it a virus, a bacteria, a fungi, or a parasitic worm? How is it passed from one host to another? Use the Teacher Guide #1 to help students provide examples of a variety of pathogenic and non-pathogenic causes.

4. Student groups are each given a disease caused by a pathogen (human or veterinary) and asked to answer a number of questions. Students should be encouraged to provide graphical as well as written responses to some of these questions:

i. What cell type? What pathogen type?
ii. How does it invade the host? What is its’ host?
iii. What is the immune response to it? Are there any natural, evolutionary responses to it (i.e. with malaria and sickle cell anemia?)
iv. Where is it when it is outside of the organism (if it ever is)? (Describe its’ life cycle)
v. How is it passed from one host to another?
vi. Are there artificial means that have been used to combat this?
vii. Will antibiotics or vaccinations work with this disease why? Why not?
viii. What are the ramifications of infection/invasion?
ix. Does it affect all people equally?

5. Students should present their information to class and fill in a class table addressing these questions.

6. Review the class table. Are there patterns that you can see among viruses, bacteria, fungi etc? In how they infect and cause disease? As a class, come up with a summary for each type of pathogen. How does the structure of the pathogen play a role in the infection and in the disease?


Students will need to spend some time researching their disease, answering the questions and preparing to present it to the class.

Homework - Major Project

Remind students that the Public Health Reflection II Homework sheet is to be turned in at the start of class tomorrow, before beginning the “Describe the perfect pathogen” lesson.

Embedded Assessment

1. Class discussion and the charts allow for assessment of students’ ability to define a pathogen versus non-pathogen cause to a disease.

2. Student presentation and subsequent chart allows for assessment of the ability to identify four different types of pathogens.

3. Student summary provides an opportunity for assessment of students to articulate any commonalities/patterns between diseases and infections of a specific type of pathogen.



PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

1996-2007, The University of Arizona
Last update: November 10, 2009
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