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ACTIVIT Y OVERVIEW
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Who’s Who?
V EST IGA
SUMMARY
Cards with images of the major groups of disease-causing microbes (protists, bacteria,
and viruses) are presented. Students classify these cards into six classes according to
their characteristics.
KEY CONCEPTS AND PROCESS SKILLS
1.
All living things are composed of microscopic units called cells. Protists and
bacteria are single-celled microbes.
2.
Most infectious diseases are caused by microbes.
3. The category of “microbes” includes microorganisms, such as bacteria and
protists, and also viruses, which are not considered to be alive.
4. Characteristics that distinguish microbes include size, shape, and structure.
Differences between protists, bacteria, and viruses include whether they are
cells, the presence or absence of a nucleus, and relative size.
KEY VOCABULARY
bacteria
microbe
cell
nucleus
cell membrane
protist
cytoplasm
virus
magnify/magnification
Teacher’s Guide
C-193
Activity 44 • Who’s Who
MATERIALS
For the teacher
Transparency 44.1, “Key to Microbe Identities”
*
1
overhead projector
For the class
8
sets of Classification Cards
For each group of four students
1
set of Micro-Life Cards
*Not supplied in kit
TEACHING SUMMARY
Getting Started
1.
Review students’ observations of microbes in Activity 43, “Microbes Under
View.”
Doing the Activity
2.
Student groups work together to classify Micro-Life Cards according to the
five-kingdom classification scheme.
3.
The class discusses the classification of the microbes on the Micro-Life Cards.
Follow-Up
4.
The class discusses criteria used to classify microbes.
BACKGROUND INFORMATION
Disease-Causing Microbes
There are many disease-causing agents, including animals, fungi, bacteria, protists,
and viruses. Microbial species of fungi cause athlete’s foot and yeast infections such
as thrush. Animals such as tapeworms also can infect humans. However, this activity
focuses on three groups of disease-causing agents: protists, bacteria, and viruses.
Protists are single-celled microorganisms that contain a nucleus (and other cell compartments). Trypanosoma lewisi is a protist that causes disease in rats. It belongs to the
same genus as Trypanosoma brucei, the protist that causes African sleeping sickness in
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Science and Life Issues
Who’s Who • Activity 44
humans. Both trypanosomes have a flagellum, a tail-like structure used for locomotion. Different species of Paramecium live in freshwater and saltwater environments,
where they feed on bacteria, algae, and other protists. Paramecia move by beating their
cilia, small structures that look like tiny hairs on the outside of the cell. Amoeba proteus is another protist. Like Paramecia, Amoebae eat other microorganisms found in
water and also in soil. Some Amoebae do cause disease: Entamoeba histolytica causes
dysentery. Amoebae move by extending portions of their body (known as pseudopodia, or “false feet”).
Bacteria are single-celled microorganisms that lack a nucleus (as well as other membrane-bound organelles). Escherichia coli (E. coli) is one bacterial species that is familiar to most people. Some strains of E. coli are common residents of the human digestive system and are harmless. However, other strains of E.coli can cause disease,
including some well-known recent outbreaks of an especially virulent strain that can
be transmitted by food, animals, and in swimming pools.
Viruses are not classified as organisms because they are not free-living cells. Instead,
they have a core of genetic material surrounded by a protein coat. Viral diseases
include colds, flu, chickenpox, hepatitis, and AIDS. Viruses introduce their genetic
material into the host cell. The host cell then reproduces the virus, and new viruses
are released to continue the infection.
Classification Systems
The approach to classifying organisms continues to develop based on new evidence.
In this activity, students use the five-kingdom approach to classifying organisms. In
the next activity, they learn the latest approach to the classification of microbes.
Teacher’s Guide
C-195
Who’s Who • Activity 44
TEACHING SUGGESTIONS
GETTING STARTED
1.
Each group of students should receive a complete
set of the 9 Micro-Life Cards. Students have an
opportunity to view and classify pictures of actual
disease-causing agents as well as other organisms.
Review students’ observations of microbes
Have them turn to the Procedure in the Student
in Activity 43, “Microbes Under View.”
Book and follow the directions.
n Teacher’s Note: You may wish to assess students
Students are asked to first observe the cards. Do not
on either element (“Task Management” or “Shared
tell the students how to classify; allow them to make
Opportunity”) of the G ROUP I NTERACTION (GI) vari-
their own observations and decisions about what cri-
able during this activity. If your students do not
teria to use for classification. The cards illustrate the
have much experience with classification, you may
shape and external structure as observed through an
want to prepare them for this activity by having
electron microscope as well as a sketch of the inter-
them classify coins. They will realize that coins can
nal structure of each microbe. The size of each
be classified by different criteria (size, color, picture,
microbe in microns is provided on the card. One
etc.) and that different criteria can lead to different
micron is one thousandth of a millimeter (0.001
classification schemes.
mm), or one millionth of a meter (0.000001 m), also
expressed as 10-6 meters. Each card also states
Tell students that they will have an opportunity to
get a closer look at microbes and to develop a system for classifying them. Ask, What kinds of differences have you observed so far in your observations of microbes? Their answers are likely to
whether the agent is a single cell or not a cell. (This
activity does not include any multicellular organism
cards. They will be added to the classification scheme
in Unit E, “Ecology,” in Science and Life Issues.)
include differences in size, shape, and whether they
Students should work together to group the various
could observe any internal details, such as the pres-
cards and record the groups that were formed. Most
ence of a nucleus. Ask, If you were unable to see a
importantly, students should record the character-
nucleus, can you be certain that none was present?
istics used to form each of the groups. If students
Help students realize that they cannot be sure; dif-
are having problems, make suggestions to get them
ferent stains or higher magnification might reveal
started, but allow them to work as independently as
more detail. Explain that they will use photos and
possible. Allow students to view the work of other
drawings obtained at higher magnification to help
groups, either by having them circulate around the
them refine their classification of the microbes.
room or by having a few groups present their classification systems.
DOING THE ACTIVIT Y
2.
After groups have completed their classifications,
Student groups work together to classify
provide them with a set of the 6 Classification
Micro-Life Cards according to the five-
Cards. Have them complete Step 7 of the Procedure
kingdom classification scheme.
and record in their notebooks what kinds of
changes in classification they had to make.
Teacher’s Guide
C-197
Activity 44 • Who’s Who
n Teacher’s Note: Students will find that the Classi-
parency 44.1, “Key to Microbe Identities.” You can
fication Cards include cards for animals, plants, and
use this information to review which microbes are
fungi. However, none of their Micro-Life Cards
protists, bacteria, or viruses. The disease examples
include examples from these categories of organ-
given are sometimes for the exact microbe depicted
isms. Explain to students that they will have a
on the card, and sometimes for a microbe with a
chance to classify more organisms and use these cat-
very similar appearance and internal structure. You
egories in Unit E, “Ecology,” of Science and Life Issues.
may wish to mention that other groups of organisms, namely fungi and animals, can cause diseases.
3.
The class discusses the classification of the
microbes on the Micro-Life Cards.
Discuss students’ final classification schemes. Explain
that they are based on a system widely adopted in
1969. Before then, all organisms were classified as
either animals or plants. Point out that though the
Classification Cards include five kingdoms plus the
non-living viruses, there are other possible classification schemes. Classification schemes can be modified based on additional information and should be
evaluated based on usefulness.
Discuss the benefits of a classification scheme. At
Some examples are the fungi that cause athletes
foot, the mites that cause scabies, and parasitic
worms, such as roundworms and tapeworms.
Treatments for these diseases depend on the biology
of the disease-causing organism. In some cases, treatment is very difficult. For example, worm parasites
are much more closely related to humans than bacteria and viruses. For this reason, it is very difficult to
get rid of these parasitic infections without causing
side effects for the human host. Drug therapy for
worm infestations often requires hospitalization,
making prevention a much better option.
the most basic level, it allows scientists all over the
FOLLOW–UP
world to communicate regarding organisms. Classification schemes first arose as a way to create an
orderly system of categories of organisms that could
4.
The class discusses criteria used to classify
microbes.
be grouped for study. As new evidence about similarities and differences among organisms is discov-
Use this investigation to reinforce some of the key
ered, the classification systems are modified. Most
parts of cells, such as the cell membrane, nucleus,
scientists now favor a new system, to be discussed in
cytoplasm, and cell wall. Some of the other struc-
Activity 45, “The World of Microbes.” However, the
tures, such as the cilia and flagella used for locomo-
five-kingdom system is helpful for students in
tion by some protists and bacteria, can also be men-
thinking about the diversity of organisms.
tioned briefly, but are not a major focus of this
activity. In the case of viruses, the absence of a cellu-
As a class, review how microbes are classified. A key
to the disease-causing agents is provided in Trans-
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Science and Life Issues
lar structure is one key criterion that leads to its classification as a non-living microbe.
Who’s Who • Activity 44
1.
SUGGESTED ANSWERS
Students may have used various features, such
TO ANALYSIS QUESTIONS
as internal structures, external structures,
and/or size, to classify the organisms. These
How could knowing the structure and clas-
may or may not correspond to the convention-
sification of disease-causing microbes help
al five-kingdom system.
scientists fight a disease?
Students may suggest that treatments such as
shots or drugs may work against different
groups of microbes. You may wish to expand on
this and explain that if scientists know the
structure of a microbe, they can search for
chemicals (or other methods) to attack specific
structures of the microbe. For example, some
antibiotics attack the membranes of bacteria,
while others attack internal structures and prevent the bacteria from reproducing. Ask students what would happen if scientists decided
to try to attack a part of a microbe that was very
similar to a structure in human cells. The
human cells might be damaged by the drug that
was supposed to be killing the microbe. This is
one reason why many drugs have side effects.
Scientists try to find drugs that target unique
features of the disease-causing microbe that
humans do not share. That way, the drug will
attack only the microbe.
2.
How did your system of classification compare
to the Classification Cards?
3.
Look back at the generalized animal cell in Figure 1
in Activity 42, “A Closer Look” on page C-59.
Explain how this drawing of a cell is similar to or
different from the structure of each of the following
groups of microbes:
a. protists
Like the drawing, protists are made up of a single cell containing a nucleus, cytoplasm, and a
cell membrane.
b. bacteria
Like the drawing, bacteria are made up of a single cell with a cell membrane and cytoplasm.
However, they lack the nucleus shown in the
figure.
c. viruses
Viruses are not made of cells, so there is less
basis for comparison between the drawing and
viruses. However, viruses do have an external
coat, which acts like the cell membrane, to
define the boundary of the virus.
Teacher’s Guide
C-199
Type of
Microbe
bacterium
bacterium
protist
virus
virus
protist
virus
bacterium
protist
Card
Number
1
2
3
4
5
6
7
8
9
©2006 The Regents of the University of California
Science and Life Issues Transparency 44.1
Trypanosoma
spirillum
influenza virus
Amoeba
adenovirus
tobacco mosaic virus
Paramecium
bacillus (rods)
coccus (round)
Genus (or type)
sleeping sickness
rat-bite fever, meningitis
flu
amoebic dysentery
colds
plant diseases
none
tuberculosis
strep throat
Disease(s) It Can Cause
Key to Microbe Identities
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