Viruses are at the border of the living and non-living. They depend on the cellular components and metabolites of the hosts where they multiply, which is why they are called obligatory intracellular parasites. Viruses are the smallest microorganisms (15 to 300 nanometers) and have a protein structure, the capside, containing DNA and RNA, and sometimes, an envelope.
Viruses are at the border of the living and non-living. They depend on the cellular components and metabolites of the hosts where they multiply, which is why they are called obligatory intracellular parasites. Viruses are the smallest microorganisms (15 to 300 nanometers) and have a protein structure, the capside, containing DNA and RNA, and sometimes, an envelope.

© Armand-Frappier Museum, 2008. All rights reserved.

Influenza virus

Photo : Robert Alain

© Robert Alain, SME, INRS-Institut Armand-Frappier


Bacteria are primitive cells that have no nuclear membrane or organised intracellular organelles. They can be observed when magnified 1000 times. Bacteria have large surface areas compared to their volume, allowing nutrients to enter quickly. This explains the metabolism and rapid growth of bacteria: some bacteria undergo cellular division every 20 minutes!
Bacteria are primitive cells that have no nuclear membrane or organised intracellular organelles. They can be observed when magnified 1000 times. Bacteria have large surface areas compared to their volume, allowing nutrients to enter quickly. This explains the metabolism and rapid growth of bacteria: some bacteria undergo cellular division every 20 minutes!

© Armand-Frappier Museum, 2008. All rights reserved.

The bacterium Staphylococcus aureus

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Molds are microscopic pluricellular fungi possessing spore-generating filamentous structures called hyphae. These structures are called mycelia when they become numerous and visible to the naked eye. Molds have rigid cell walls and feed by absorbing nutrients dissolved in the environment.
Molds are microscopic pluricellular fungi possessing spore-generating filamentous structures called hyphae. These structures are called mycelia when they become numerous and visible to the naked eye. Molds have rigid cell walls and feed by absorbing nutrients dissolved in the environment.

© Armand-Frappier Museum, 2008. All rights reserved.

The fungus Aspergillus ustus

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Yeasts are unicellular organisms from 1 to 30 µm that exist in various forms: from spheric to oval and ellipsoidal to filamentous. Yeasts have rigid cell walls, mutliply by budding, and feed by absorbing nutrients dissolved in the environment.
Yeasts are unicellular organisms from 1 to 30 µm that exist in various forms: from spheric to oval and ellipsoidal to filamentous. Yeasts have rigid cell walls, mutliply by budding, and feed by absorbing nutrients dissolved in the environment.

© Armand-Frappier Museum, 2008. All rights reserved.

The yeast Saccharomyces cerevisiae

Lallemand

© Lallemand


Like plants, algae contain chlorophyll and other photosynthetic pigments. They can be unicellular and microscopic or pluricelllular and reach several meters in length. The various species of algae cover a wide range of size and shape; some are even mobile.
Like plants, algae contain chlorophyll and other photosynthetic pigments. They can be unicellular and microscopic or pluricelllular and reach several meters in length. The various species of algae cover a wide range of size and shape; some are even mobile.

© Armand-Frappier Museum, 2008. All rights reserved.

The algae Spirogyra

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Protozoa are unicellular and can be oval-shaped, spheric, or elongated. They range in diameter from 1 to 2000 µm (2 mm, thus visible to the naked eye). Some are mobile, thanks to their cillia, which are small accessories resembling hair or flagella with whip-like structures. Their movements are quick and noticeable when a water sample is observed under the microscope.
Protozoa are unicellular and can be oval-shaped, spheric, or elongated. They range in diameter from 1 to 2000 µm (2 mm, thus visible to the naked eye). Some are mobile, thanks to their cillia, which are small accessories resembling hair or flagella with whip-like structures. Their movements are quick and noticeable when a water sample is observed under the microscope.

© Armand-Frappier Museum, 2008. All rights reserved.

The paramacium Paramecium multimicronucleatum

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Learning Objectives

The learner will:
  • familiarize himself with the vocabulary used in microbiology;
  • explain the relationship between developments in imaging technology and the current understanding of the cell;
  • identify which microorganisms are infectious, how the immune system fights against them, and the reinforcements of modern medicine;
  • describe the benefits of microorganisms .

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