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1.E: An Invisible World (Exercises)

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    1.1: What Our Ancestors Knew

    Microorganisms (or microbes) are living organisms that are generally too small to be seen without a microscope. Throughout history, humans have used microbes to make fermented foods such as beer, bread, cheese, and wine. Long before the invention of the microscope, some people theorized that infection and disease were spread by living things that were too small to be seen. They also correctly intuited certain principles regarding the spread of disease and immunity.

    Multiple Choice

    Which of the following foods is NOT made by fermentation?

    1. beer
    2. bread
    3. cheese
    4. orange juice


    Who is considered the “father of Western medicine”?

    1. Marcus Terentius Varro
    2. Thucydides
    3. Antonie van Leeuwenhoek
    4. Hippocrates


    Who was the first to observe “animalcules” under the microscope?

    1. Antonie van Leeuwenhoek
    2. Ötzi the Iceman
    3. Marcus Terentius Varro
    4. Robert Koch


    Who proposed that swamps might harbor tiny, disease-causing animals too small to see?

    1. Thucydides
    2. Marcus Terentius Varro
    3. Hippocrates
    4. Louis Pasteur


    Fill in the Blank

    Thucydides is known as the father of _______________.


    scientific history

    Researchers think that Ötzi the Iceman may have been infected with _____ disease.



    The process by which microbes turn grape juice into wine is called _______________.



    Short Answer

    What did Thucydides learn by observing the Athenian plague?

    Why was the invention of the microscope important for microbiology?

    What are some ways people use microbes?

    Critical Thinking

    Explain how the discovery of fermented foods likely benefited our ancestors.

    What evidence would you use to support this statement: Ancient people thought that disease was transmitted by things they could not see.

    1.2: A Systematic Approach

    Carolus Linnaeus developed a taxonomic system for categorizing organisms into related groups. Binomial nomenclature assigns organisms Latinized scientific names with a genus and species designation. A phylogenetic tree is a way of showing how different organisms are thought to be related to one another from an evolutionary standpoint. The first phylogenetic tree contained kingdoms for plants and animals; Ernst Haeckel proposed adding a kingdom for protists.

    Multiple Choice

    Which of the following was NOT a kingdom in Linnaeus’s taxonomy?

    1. animal
    2. mineral
    3. protist
    4. plant


    Which of the following is a correct usage of binomial nomenclature?

    1. Homo Sapiens
    2. homo sapiens
    3. Homo sapiens
    4. Homo Sapiens


    Which scientist proposed adding a kingdom for protists?

    1. Carolus Linnaeus
    2. Carl Woese
    3. Robert Whittaker
    4. Ernst Haeckel


    Which of the following is NOT a domain in Woese and Fox’s phylogenetic tree?

    1. Plantae
    2. Bacteria
    3. Archaea
    4. Eukarya


    Which of the following is the standard resource for identifying bacteria?

    1. Systema Naturae
    2. Bergey’s Manual of Determinative Bacteriology
    3. Woese and Fox’s phylogenetic tree
    4. Haeckel’s General Morphology of Organisms


    Short Answer

    What is a phylogenetic tree?

    Which of the five kingdoms in Whittaker’s phylogenetic tree are prokaryotic, and which are eukaryotic?

    What molecule did Woese and Fox use to construct their phylogenetic tree?

    Name some techniques that can be used to identify and differentiate species of bacteria.

    Critical Thinking

    Why is using binomial nomenclature more useful than using common names?

    Label the three Domains found on modern phylogenetic trees.

    The phylogenetic Tree of Life. A drawing of branching lines. The central line at the bottom branches into two main branches. On the left branch is a purple branch that contains the following sub-branches: Green filamentous bacteria, Gram positives, Cyanobacteria, Proteobacteria, and Spirocheres. The branch to the right subdivides into a red and a brown branch. The brown branch contains the following sub-branches: Smile molds, Plants, Fungi and Animals. The red branch contains the following sub-branches: Thermoproteus, Methanococcus, Methanobacterium, and Halophiles.

    1.3: Types of Microorganisms

    Microorganisms are very diverse and are found in all three domains of life: Archaea, Bacteria, and Eukarya. Archaea and bacteria are classified as prokaryotes because they lack a cellular nucleus. Archaea differ from bacteria in evolutionary history, genetics, metabolic pathways, and cell wall and membrane composition. Archaea inhabit nearly every environment on earth, but no archaea have been identified as human pathogens.

    Multiple Choice

    Which of the following types of microorganisms is photosynthetic?

    1. yeast
    2. virus
    3. helminth
    4. alga


    Which of the following is a prokaryotic microorganism?

    1. helminth
    2. protozoan
    3. cyanobacterium
    4. mold


    Which of the following is acellular?

    1. virus
    2. bacterium
    3. fungus
    4. protozoan


    Which of the following is a type of fungal microorganism?

    1. bacterium
    2. protozoan
    3. alga
    4. yeast


    Which of the following is not a subfield of microbiology?

    1. bacteriology
    2. botany
    3. clinical microbiology
    4. virology


    Fill in the Blank

    A ________ is a disease-causing microorganism.



    Multicellular parasitic worms studied by microbiologists are called ___________.



    The study of viruses is ___________.



    The cells of prokaryotic organisms lack a _______.



    Short Answer

    Describe the differences between bacteria and archaea.

    Name three structures that various protozoa use for locomotion.

    Describe the actual and relative sizes of a virus, a bacterium, and a plant or animal cell.

    Critical Thinking

    Contrast the behavior of a virus outside versus inside a cell.

    Where would a virus, bacterium, animal cell, and a prion belong on this chart?

    A bar along the bottom indicates size of various objects. At the far right is a from egg at approximately 1 mm. To the left are a human egg and a pollen grain at approximately 0.1 mm. Next is a red blood cell at just under 10 µm. Next is a mitochondrion at approximately 1 µm. Next are proteins which range from 5-10 nm. Next are lipids which range from 2-5 nm. Next is C60 (fullerene molecule) which is approximately 1 nm. Finally, atoms are approximately 0.1 nm.

    1.E: An Invisible World (Exercises) is shared under a CC BY license and was authored, remixed, and/or curated by LibreTexts.

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