Introduction to Microbiology

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Questions and Answers

Why are bacteria considered essential for the existence of life on Earth?

  • They produce human hormones such as insulin.
  • They directly provide food for humans.
  • They control insect populations.
  • They decompose organic material and recycle elements. (correct)

A researcher studying the production of human proteins by bacteria would best fit into which field of microbiology?

  • Immunology
  • Microbial ecology
  • Biotechnology (correct)
  • Microbial physiology

A scientist who studies the fungus Candida albicans would best fit into which field?

  • Molecular biology
  • Virology
  • Microbial genetics
  • Mycology (correct)

In the Gram-staining procedure, what is the primary stain that is used?

<p>Crystal violet (A)</p> Signup and view all the answers

What is the function of the decolorizer in the Gram-staining procedure?

<p>To remove the primary stain from gram-negative bacteria. (C)</p> Signup and view all the answers

In the Gram-staining procedure, what is the purpose of the counterstain?

<p>To stain gram-negative bacteria. (B)</p> Signup and view all the answers

What is the role of iodine in the Gram-staining procedure?

<p>Mordant (A)</p> Signup and view all the answers

What color are gram-positive and gram-negative organisms, respectively, after the primary stain is applied but before the decolorizer?

<p>purple; purple (D)</p> Signup and view all the answers

Which characteristic most distinctly differentiates the field of microbiology from other biological disciplines?

<p>An integrated consideration of both organism size and the investigative techniques employed. (B)</p> Signup and view all the answers

Which of the following is NOT considered a beneficial application of microorganisms?

<p>Exclusive application in industrial processes without ecological benefits. (C)</p> Signup and view all the answers

Which of the following pairings is INCORRECT?

<p>Fungi: Cell wall made of cellulose; photosynthetic (B)</p> Signup and view all the answers

Acid-fast bacteria, such as Mycobacterium tuberculosis, exhibit resistance to decolorization due to a high concentration of which substance in their cell walls?

<p>Lipids (A)</p> Signup and view all the answers

Which of the following is NOT a universal characteristic of all bacteria?

<p>Identical cellular morphology across all species (C)</p> Signup and view all the answers

Considering the structural components of microorganisms, which of the following statements is accurate?

<p>Certain bacteria lack a peptidoglycan cell wall. (A)</p> Signup and view all the answers

When comparing prokaryotic and eukaryotic cells, which of the following characteristics is exclusively found in eukaryotes and not in prokaryotes?

<p>A defined nucleus bounded by a nuclear membrane. (A)</p> Signup and view all the answers

If a newly discovered microorganism is found to thrive in extremely acidic conditions (pH 1-2), which classification would be most appropriate?

<p>Acidophile (A)</p> Signup and view all the answers

What would be the observed staining result if the decolorizer step is skipped during Gram staining?

<p>Both Gram-positive and Gram-negative bacteria would appear purple. (C)</p> Signup and view all the answers

Why is the Gram stain considered a differential staining procedure?

<p>It distinguishes bacteria based on differences in their cell wall structure. (B)</p> Signup and view all the answers

What is the expected outcome when a Gram-positive bacterium is placed in distilled water containing penicillin?

<p>The bacterium will likely lyse due to the combined effects of osmotic pressure and penicillin inhibiting cell wall synthesis. (B)</p> Signup and view all the answers

What is the expected outcome when a Gram-positive bacterium is placed in an aqueous solution of lysozyme and 10% sucrose?

<p>The bacterium will form a protoplast due to lysozyme removing the cell wall, but the sucrose prevents lysis by balancing osmotic pressure. (B)</p> Signup and view all the answers

After the decolorizer has been added during Gram staining, what colors are gram-positive and gram-negative organisms, respectively?

<p>Purple; Colorless (A)</p> Signup and view all the answers

Following the addition of the secondary stain (safranin) in the Gram staining procedure, what colors are gram-positive and gram-negative organisms, respectively?

<p>Purple; Pink (D)</p> Signup and view all the answers

If the decolorizer is left on for an extended period during Gram staining, what colors would gram-positive and gram-negative organisms likely appear as, respectively?

<p>Pink; Pink (A)</p> Signup and view all the answers

Which of the following is NOT a distinguishing characteristic of prokaryotic cells?

<p>They lack a plasma membrane. (D)</p> Signup and view all the answers

Match the microorganisms in column A to their descriptions in column B: Column A a. Archaea b. Algae c. Bacteria

<p>a-Neither Eukaryotic nor Prokaryotic, b-Photosynthetic Eukaryotes, c-Prokaryotes with peptidoglycan (B)</p> Signup and view all the answers

Why does penicillin have no effect on most gram-negative cells?

<p>Penicillin cannot penetrate the outer membrane of gram-negative cells to reach the peptidoglycan layer. (B)</p> Signup and view all the answers

A bacterial cell is placed in a solution with a high concentration of sucrose. Which of the following outcomes is most likely?

<p>Water will move out of the cell. (D)</p> Signup and view all the answers

Which one is an accurate pairing?:

<p>Archaea- cell wall lacks peptidoglycan (B)</p> Signup and view all the answers

Flashcards

Microbiology

The study of microorganisms, focusing on their size and the techniques used to study them.

Beneficial activities of microorganisms

Microorganisms can be used as food, consume carbon dioxide, provide nitrogen for plants, and assist in sewage treatment.

Fungi

Eukaryotic organisms with cell walls made of chitin; includes molds and yeasts.

Algae

Has a cell wall made of cellulose and is photosynthetic.

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Protozoa

Unicellular organisms with a complex cell structure but lacking a cell wall.

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Archaea

Prokaryotes without peptidoglycan in their cell walls.

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Acid-fast organisms

High concentration of lipids in their cell walls prevents decolorization by acid-alcohol.

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Characteristics of bacteria

Bacteria are prokaryotic, have peptidoglycan cell walls, grow by binary fission, and have the ability to move.

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Why are bacteria essential?

Bacteria decompose organic material and recycle elements, which is essential for life on Earth.

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What is microbial ecology?

Microbial ecology studies the biodegradation and interaction of microbes in the environment.

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What does Virology study?

Virology is the study of viruses, including their structure, function, and role in disease.

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What is Biotechnology?

Biotechnology uses biological systems, organisms, or derivatives to make or modify products or processes.

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What is Candida albicans?

Candida albicans is a fungus studied in mycology.

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Primary stain in Gram stain?

Crystal violet is the primary stain used in the Gram-staining procedure.

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Decolorizer in Gram stain?

Alcohol is used as the decolorizer in the Gram-staining procedure.

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Counterstain in Gram stain?

Safranin is used as the counterstain in the Gram-staining procedure.

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Differential Staining

A staining technique that differentiates bacteria based on cell wall structure.

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Gram-positive stain color

Gram-positive bacteria retain the crystal violet stain, appearing purple after Gram staining.

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Gram-negative stain color

Gram-negative bacteria appear pink after Gram staining due to the safranin counterstain.

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Gram stain: Insufficient decolorization

Gram-positive will be purple; gram-negative will be colorless.

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Penicillin and Gram-positive

Penicillin inhibits cell wall synthesis, and distilled water causes water to rush inside the cell. This is how gram positive bacterium are affected.

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Bacteria

Prokaryotic, cell walls contain peptidoglycan.

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Gram stain after decolorizer

Gram-positive: purple; Gram-negative: colorless.

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Gram stain after secondary stain

Gram-positive: purple; Gram-negative: pink.

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Gram stain if decolorizer is left on too long

Gram-positive: pink; Gram-negative: pink.

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Prokaryotic cell distinguishers

Eukaryotic cells possess a plasma membrane; prokaryotes do not lack them.

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Effect of hypotonic solution on cell

Water will move into the cell.

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Study Notes

  • Microbiology is distinguished from other fields of biology by the size of the organisms studied and the techniques employed in their study.
  • Microorganisms are used as food, consume carbon dioxide, provide nitrogen for plant growth, and are used in sewage treatment processes.
  • Bacteria decompose organic material and recycle elements, which is essential for life on Earth.

Matching Researchers to Microbiology Fields

  • Studies biodegradation of toxic wastes: Biotechnology
  • Studies the causative agent of Ebola virus disease: Virology
  • Studies the production of human proteins by bacteria: Microbial physiology
  • Studies the symptoms of AIDS: Immunology
  • Studies the production of toxin by E. coli: Molecular biology
  • Studies biodegradation of pollutants: Microbial ecology
  • Develops gene therapy for a disease: Microbial genetics
  • Studies the fungus Candida albicans: Mycology

Matching Microorganisms to Descriptions

  • Archaea: Prokaryote without peptidoglycan cell wall
  • Algae: Cell wall of cellulose, photosynthetic
  • Bacteria: Cell wall made of peptidoglycan
  • Fungi: Cell wall of chitin
  • Helminths: Multicellular animals
  • Protozoa: Unicellular, complex cell structure lacking a cell wall
  • Viruses: Not composed of cells

Acid-Fast Organisms

  • Acid-fast organisms, like Mycobacterium tuberculosis, resist decolorization due to the high concentration of lipids in their cell walls.

Characteristics of Bacteria

  • Bacteria are prokaryotic, have peptidoglycan cell walls, grow by binary fission, move and have the same shape.

Gram-Staining Procedure

  • Primary stain: Crystal violet
  • Decolorizer: Alcohol
  • Counterstain: Safranin
  • Mordant: Iodine

Gram Stain Results

  • After the primary stain but before decolorization: Gram-positive and gram-negative organisms stain purple.
  • After decolorization: Gram-positive organisms are purple, gram-negative organisms are colorless.
  • After the secondary stain: Gram-positive organisms are purple, gram-negative organisms are pink.
  • Over-decolorization: Gram-positive organisms stain purple, gram-negative stain pink.
  • Insufficient decolorization: Gram-positive and gram-negative organisms stain purple.

Differential Staining

  • Gram stain and Acid-fast stain are differential staining procedures.

Bacterial Cell Walls

  • Gram-positive bacterium contains teichoic acid and peptidoglycan in the cell wall.
  • Gram-negative bacterium contains lipopolysaccharide, phospholipid and lipoprotein in the cell wall.
  • Penicillin is not effective against most gram-negative cells.
  • Essential molecules enter cells through each wall.
  • Only one cell wall is toxic to humans.

Prokaryotic Cells

  • Prokaryotic cells have a single, circular chromosome, 70S ribosomes, and peptidoglycan cell walls but lack a plasma membrane.
  • DNA is not associated with histones.

Solutions

  • Gram-positive bacterium in distilled water and penicillin will undergo osmotic lysis.
  • Gram-negative bacterium in distilled water and penicillin: Water will move into the cell.
  • Gram-positive bacterium in lysozyme and 10% sucrose: Water will move out of the cell

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