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:
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
Standard C– Life
• 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
• 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.
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
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).
are also other ways that we classify things in the world
around us. Often we consider things
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.