Catch a Bug

By: Sarah Kenyon

Time: 1class period
Preparation Time: 15 minutes (photocopy overhead/handout for in-class assignment)

Diversity pie chart
Public Health Reflection II Homework sheet

Students consider the multiple meanings of the word “bug” and use it to describe both the diversity of organisms and the connection between organisms and diseases. Students should be able to consider the biological origins of disease.

Students will be able to:

1. create a classification scheme for brainstormed “bugs”
2. explore and place anecdotal accounts of organisms into their classifications
3. identify the four major classes of microorganisms by using diseases as a springboard
4. describe different classification schemes and describe what each one is used for

National Science Education Standard:
Content Standard C– Life Science

• The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms.
• The millions of different species of plants, animals, and microorganisms that live on earth today are related by descent from common ancestors.
• Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.

Teacher Background
Ordinarily, the diversity of life is introduced to students via charismatic mega fauna. In this lesson, VERY non-charismatic micro fauna are used instead. Increasingly, from the first glimmer of understanding into the biological basis of infectious disease, humans have realized that there is a vast community of microbial life living (literally) right underneath their noses. Through history, the exact nature of these organisms has been uncovered to a greater and greater degree. In this lesson students will be presented with anecdotal accounts that explore the invisible diversity that surrounds us. They will be challenged to make classification decisions, and then discuss the basis of these classifications.

Classification: General biological units have involved using morphological characters to reach the current trend that considers different organisms in light of their similar DNA sequences. Both are important and have their own difficulties. In both genetic and morphological evidence for classification and relatedness of species and taxa, scientists have to deal with homologous and analogous characters- homologous characters are those that have biological and evolutionary relevance (like the bones in a whale’s flipper and those in a human arm), while analogous characters are those which have evolved through convergent evolution-such as tackling a common problem (like bat wings and insect wings).

There are also other ways that we classify things in the world around us. Often we consider things in relationship to their importance to us as humans. In the case of pathogenic organisms, we do this. We split them in the KPCOFGS (Kingdom, Phylum Class, Order…) system as well, but we talk of them as “biohazard levels” – an example being biohazard 4 which are clean rooms with scientists in space suits working with Ebola-type organisms that are highly infectious, very devastating, and difficult or impossible to control. Both types of classification schemes are equally useful and appropriate.

It is important for students to consider what each type of classification scheme can tell us, and to consider its source. Each is subject to different types of bias and what is good for one is seldom good for another.

Related and Resource Websites
Microbes from http://www.niaid.nih.gov/publications/pdf/microbesbook.pdf - (copyright 2001)
This book goes over the four main types of microbes and their importance in our lives.



Ask students what the word “bug” means. Ask them to brainstorm different ways that the term is used. A student may read the dictionary definition for bug and then segue into describing different kinds of insects and diseases.

• First: Bug as an ‘insect’- diversity of organisms
Ask students to come up with as many examples of bugs as ‘insects’ as they can. Ask if there are any general patterns/groupings (classifications) of these insects that they have heard of or that make sense to them. Have students try to figure out why organisms might be classified in one way versus another. At the end of this section of the lesson put up the following pie chart showing the diversity of organisms and let the students make observations and discuss their responses to the chart.

Insect diversity by Daly (1978)

Once students have looked at the chart and compared it to the lists they have generated, talk about diversity. What is it? Are they surprised that insect species diversity is so huge compared with other things? Why do they think this is? This could be a good group activity – to come up with reasons why the diversity of insects is so much larger and how valid they think those reasons are.

• Bugs as Diseases:
Have students come up with examples of bugs as ‘diseases’. Can they separate them into general patterns or classifications? What is the reasoning behind any groupings they identify? At first they will probably come up with different types of diseases/afflictions- but push them to consider the origin of each one they come up with. Is this caused by an organism? What kind? Do they have names/classes of organisms that they know are associated with diseases? Are there other kinds of these types of organisms that do not have negative effects? Can they find the names for these on the chart that they looked at earlier? The primary lesson that students need to come away with from this section of the lesson is that there are four major categories that can cause disease as we know it – fungi, bacteria, protests (single–celled organisms), and viruses (prions can also cause disease, but less so in the diversity context). One important thing to consider is whether infection and disease are synonymous. They aren’t, but they are connected.

Challenge students to think about how diseases caused by these different agents are different. (There is a big difference between a eukaryotic organism like a fungus or protest, a prokaryotic organism like bacteria and viruses in how they affect us and how we deal with them.) How are they different? What might be some important differences?

Challenge students to consider why we call them diseases. What is it that they do (i.e. What constitutes a disease?) Where do these organisms live? What sort of diversity do we expect to find within them? How can and do we fight them? Students will, hopefully, immediately think of the immune system, but also antibiotics, vaccines, topical applications ex. athlete’s foot treatment, rest, etc.

Have students identify the four main categories of pathogenic organisms and define pathogenic versus beneficial. Have students discern between infection and disease. Give them a picture of a natural scene and identify all the different types of living organisms in it and classify them into groups.

Homework-Major project
At this time, give students the Public Health Reflection II Homework sheet to be turned in at the start of the “Describe the perfect pathogen” lesson. This homework asks students to take the Public Health issue that they identified in week 3 and find both a website and a person appropriate to help them learn more about their topic. Remind them at the end of “Routes of Entry” to bring in their homework the next day, and there will be a short discussion at the start of “Describe the perfect pathogen”

Embedded Assessment

1. Students’ ability to create a classification scheme for brainstormed “bugs” can be assessed through this task orientated procedure.
2. In-class discussions students hold can be assessed for the ability to identify the four major classes of microorganism by using diseases as a springboard.
3. Are students able to describe different classification schemes and describe what each one is used for? During the class discussions, students can be assessed for their ability to describe different classification schemes.


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

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