Unit 1: Microbes
Microbes are microscopic; thus, we cannot see them by the naked eye. Antoni van Leeuwenhoek crafted the first microscope lenses that magnified over 200 times, and he turned his lenses towards everything. He saw blood cells, sperm, hatching ants, and every cellular microbe groups that we know of today. About 150 years later, Louis Pasteur's meticulously designed swan-necked flask experiments were instrumental in putting off the spontaneous generation hypothesis for microbes. Pasteur showed that microbes arise from microbes, and they are not generated spontaneously from non-living matter. Before any microbe has ever been linked to a disease, the independent death rate analyses of Semmelweis and Nightingale led to the introduction of procedures that we call antiseptic today. Koch was the first to photograph a pathogen in infected tissue; he also laid down guidelines on how to link a microorganism to a disease. These guidelines are Koch's postulates. Only a few microbes cause disease; most microbes are harmless. Microbes are present in all three domains of life: Bacteria, Archaea, and Eukaryota.
Completing this unit should take you approximately 15 hours.
Upon successful completion of this unit, you will be able to:
- explain what microbes are;
- recognize and distinguish micrographs taken by light, phase contrast, and electron microscopes;
- predict microbial growth in experiments similar to Pasteur's experiment;
- employ Koch's postulates for the identification of a pathogen; identify the limits of Koch's postulates in the real world;
- design ways to control microbial growth;
- compare and contrast microbes of the three domains of life; and
- compare and contrast cells and viruses.
1.1: Microscopic Life
1.1.1: Magnification Is the Key: Leeuwenhoek Discovers Animalcules
Read this article. Leeuwenhoek crafted superior lenses, which allowed him to observe live microbes, and he also well-documented his observations.
Watch these videos.
Read this article.
Read this page. Leeuwenhoek described representatives of all cellular microbes, including prokaryotes, protists, and fungi. The magnification and resolution of Leeuwenhoek's lenses were not sufficient to describe infectious non-living particles, such viruses, viroids, and prions.
1.1.2: The Modern Microscopes
Read this page, and click on the links "From Thrilling Toy to Important Tool," "Microscopy Time Line," and "Resolving Power Line" to read these pages as well. You can always return to the starter page by hitting the "Back" button on the top right corner of the window. From the main page, click on the links "Phase Contrast Microscopes," "Fluorescence Microscopes," "Transmission Electron Microscopes," and "Scanning Tunneling Microscopes," and study these pages to learn about modern microscope techniques.
1.2: Spontaneous Generation vs. Biogenesis
Read this page. The origin of life has always been fascinating, and the discovery of microbes was also followed by a debate on their origins. Prominent scientists of the time performed experiments to prove or disprove the spontaneous generation of microbes from non-living matter. The debate was going on for about 200 years, when finally Pasteur put off the spontaneous generation theory with a set of smartly designed and carefully performed experiments.
Read this page. Louis Pasteur was a meticulous experimenter, who believed that hard work should bring results. As Pasteur stated, "Chance favors only the prepared mind."
Read this review of Pasteur's experimental design for testing spontaneous generation. Pasteur's steps of observing, asking a question, making a hypothesis, conducting an experiment, and then accepting (or rejecting) his hypothesis later became codified as the scientific method.
1.3: The Germ Theory
Read this page. Note the significance and limits of Koch's postulates in the identification of the causative agent. Koch took the first photomicrograph of bacteria and the first photomicrograph of bacteria in diseased tissue.
1.4: Antiseptic Procedures
Read this page. Today, native Hungarians regard Semmelweis as "the savior of mothers"; however, during his life, many rejected his chlorine hand-wash antiseptic procedure. The childbed fever death rates dropped from 18% to 2% when he was in charge in the clinics and increased 10-fold when he was removed. The web media below connects you to a graph that was generated based on Semmelweis' data on childbed fever mortality. The Semmelweis' reflex term is used to describe the irrational rejection of the very obvious.
Study this graph, which was generated from the data published by Semmelweis in 1861. In the Wien maternity clinic, pathological anatomy was permitted; thus, physicians and medical students could carry pathogens from cadavers to patients. The Dublin maternity hospital had no medical pathology. Note the death rate drop after the introduction of the chlorine handwash. Wikimedia Commons user Power.corrupts constructed this graph using Semmelweis' data.
Read this page. Nightingale generated the polar-area diagram; she was very successful in communicating her findings with these graphs.
1.5: General Antimicrobial Methods
Read this chapter to review the methods and techniques used to control the growth of microorganisms. Make sure to click on the "Chapter Continued" link at the bottom of each page to read all 6 pages of the chapter.
1.6: Classification System
1.6.1: Three Domains of Life
Read this page to review the three domains of life. Microscopic forms of life can be found in all three domains.
Read this page. Genetic data indicate DNA transfer between species to some extent.
1.6.2: Prokaryotes and Eukaryotes
- Read this page to review the prokaryotic and eukaryotic cell structure.
- View Receive a grade
Complete this brief ungraded assessment. Remember that there are microbes among prokaryotes and eukaryotes as well.
Read this page. Archaea adapt to diverse environments. Many archaea are extremophile, meaning they live in an environment that seems very hostile to the human eye.
Read this page. Note the molecular differences between the bacterial and archaea cell membrane and cell wall.
Read this page. Some archaea traits are similar to eukaryotes, while other traits are similar to prokaryotes.
Read this chapter to learn about the structure and function of bacterial cells. Make sure to click on the "Chapter Continued" link at the bottom of each page to move on to subsequent pages.
1.6.5: Eukaryotic Cells
Navigate your way through these slides on organelles by pressing "Next," located at the bottom of the slide frame. There are a total of 13 slides. There are eukaryotic microorganisms among fungi and protists.
Read this page. The cell is the smallest unit of life, because it can support its own life including reproduction. Viruses cannot support their own life, but they can hijack the metabolism of specific host cells. Without a specific host cell, a virus cannot grow, change, develop, or multiply.