Introduction to Microorganisms
Copyright ©2009by Gary Fromert
PETRI Project, Northampton Community College
After completing this exercise, you should be able to:
1.
2.
3.
4.
Explain what is meant by a microorganism.
Demonstrate an understanding of the types and classifications of microorganisms.
Demonstrate an understanding for the usage of a light microscope.
Demonstrate an understanding of microbial size and morphology.
Microbiology is the study of organisms that are of microscopic dimensions and thus
cannot be seen except with the aid of a microscope. Hence, these microscopic organisms
are called microorganisms. Microbiologists are scientists who study microorganisms. The
microorganisms they study generally include bacteria, fungi, protozoa, algae, and viruses.
These tiny organisms make up a large and diverse group of free-living (except the
viruses) forms that exist either as single cells, cell bunches or clusters.
Microorganisms can be found in abundance almost anywhere on earth. The vast majority
of microorganisms are not harmful. Many microorganisms, or microbes, occur as single
cells (unicellular); others are multicellular; and still others, viruses, do not have a true
cellular appearance. Because microorganisms exist as single cells or cell bunches, they
are unique and distinct from cells of animals and plants, which are not able to live as freeliving cells but can only exist as part of a multicellular organism.
There are three main classifications of microorganisms; eukaryotic, prokaryotic or
acaryotic.
Classification
Cellular Form
General Class
Eucaryotic
Multicellular
Fungi, Algae
Unicellular
Micro-fungi,
Protozoa, Microalgae
Bacteria,
Cyanobacteria
Viruses
Procaryotic
Unicellular
Acaryotic
Noncellular
Relative Size
Range
Macroscopic
Microscopic
Microscopic
Ultra-microscopic
Microorganisms can be studied in terms of there size and shape, or morphology. The
relative size of microorganisms range from macroscopic, 10-3 meter to ultra-microscopic,
10-8 meter (Figure 1). The shape or morphology of the microorganisms varies widely.
The following figures represent the relative morphology of the microscopic bacteria,
algae, protozoa, and fungi (Figures 2, 3, 4, and 5). The viruses will be covered in
Laboratory 5.
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Figure 1. Relative Size of Microorganisms. (http://www.slic2.wsu.edu)
Figure 2. Relative Bacterial Morphologies. (http://www.emc.maricopa.edu)
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Figure 3. Relative Algal Morphologies. (http://universe-review.ca)
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Figure 4. Relative Protozoal Morphologies. (http://www.tulane.edu)
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Figure 5. Relative Fungal Morphologies. (http://kentsimmons.uwinnipeg.ca)
There are certain identifying characteristics associated with the different classes of
microorganism. Size and shape being the most obvious, other characteristics are: nucleus
or lack of nucleus (nucleoid), certain cellular features and organelles (Figures 6 and 7),
color: when viewed under the microscope algae tend to be green or bluish-green or brown,
bacteria and protozoa tend to be colorless, fungi may exhibit a variety of colors. When
viewing prepared slides of certain microorganisms, mainly the bacteria and sometimes
protozoa and fungi, they will exhibit the color of a stain which may be used for better
viewing and to bring out certain features and characteristics. The color of the stain should
not be directly associated as an identifying characteristic of that or any other class of
microorganism. Another feature may be the presence of flagella, typically used for
motility and sometimes adhesion (Figure 6 and 7). Though there are many differentiating
characteristics, there are still many characteristics that are common among the classes of
microorganisms (Figure 8).
In this laboratory you will become familiar with the features and use of the light
microscope. You will also be viewing prepared slides of microorganisms representing the
four classes of microorganisms discussed above: bacteria, algae, protozoa, and fungi.
You will make observations based on size (magnification), and the other identifying
characteristics as discussed above. You will also make a basic sketch of your microscopic
observations.
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Figure 6. Typical Bacterial Cell. (http://www.steve.gb.com)
Figure 7. Eucaryotic Features and Organelles. (http://water.me.vccs.edu)
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Figure 8. Comparison of an Algal Cell and Bacterial Cell
(http://www.scienceclarified.com)
Materials (per student)
1 Light Microscope
Supplemental Handouts of Microorganism
Procedure 1
Introduction to the microscope. Follow the laboratory entitled Introduction to the
Microscope.
Procedure 2
Viewing prepared slides of microorganisms. Using the light microscope, view prepared
slides from each of four classes of representative microorganisms, sketch and record your
observations in the following table.
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Observations and Interpretations
Fill in the chart for each of the four classes of microbes that you observe.
Organism
Write down name
from slide
Sketch
Magnification
Identifying
Characteristics
List only those you
observe
Bacteria
Algae
Protozoa
Fungi
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Laboratory Review
1. Based on your observations, is size (magnification) alone a good characteristic in
which to definitively classify microorganisms?
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2. Would you be able to classify microorganisms with out the use of a light microscope?
Explain your answer.
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3. What identifying characteristics did you find most useful in classifying the
microorganisms? Why?
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4. In your own words, define and describe what a microorganism is:
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