Microbiology: Classification of Microorganisms – Guided Study Notes

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Q1. Define taxonomy, taxon, and phylogeny. Of what value are taxonomy and systematics?

Background

Topic: Microbial Classification and Systematics

This question tests your understanding of the basic terminology and importance of classifying microorganisms, as well as the evolutionary relationships among them.

Key Terms

Taxonomy: The science of classifying organisms.
Taxon: A group or level of organization into which organisms are classified.
Phylogeny: The evolutionary history and relationships among organisms.
Systematics: The study of the diversity of organisms and their evolutionary relationships.

Step-by-Step Guidance

Start by defining each term in your own words, using textbook definitions as a guide.
Explain how taxonomy helps organize biological diversity and why it is important in microbiology.
Describe what a taxon is and give an example (e.g., genus, species).
Discuss the concept of phylogeny and how it relates to evolutionary relationships.
Consider the value of taxonomy and systematics in identifying, naming, and understanding relationships among microorganisms.

Try answering these definitions and explanations before checking the answer!

Q2. Discuss the limitations of a two-kingdom classification system. Why shouldn’t bacteria be placed in the plant kingdom?

Background

Topic: Evolution of Classification Systems

This question examines your understanding of historical classification systems and why they were revised as scientific knowledge advanced.

Key Concepts

Two-kingdom system: Early classification divided life into Plantae and Animalia.
Bacteria: Prokaryotic organisms, fundamentally different from plants.

Step-by-Step Guidance

Recall the characteristics of the two-kingdom system and what types of organisms were included in each.
Identify the main differences between bacteria and plants (e.g., cell structure, mode of nutrition, presence of nucleus).
Explain why these differences make it inappropriate to classify bacteria as plants.
Discuss how the discovery of prokaryotes led to the development of new classification systems.

Try to list at least two major differences before moving on!

Q3. Identify the contributions of Linnaeus, von Nägeli, Chatton, Whittaker, and Woese.

Background

Topic: History of Microbial Classification

This question asks you to connect key scientists to their contributions in taxonomy and classification.

Key Figures

Linnaeus: Developed binomial nomenclature and the hierarchical system of classification.
von Nägeli: Proposed bacteria and fungi be placed in the plant kingdom.
Chatton: Distinguished between prokaryotic and eukaryotic cells.
Whittaker: Proposed the five-kingdom system.
Woese: Introduced the three-domain system based on rRNA sequencing.

Step-by-Step Guidance

Match each scientist to their major contribution in the field of classification.
Briefly describe the impact of each contribution on how we classify microorganisms today.
Consider how advances in technology (e.g., molecular biology) influenced these changes.

Try to write a one-sentence summary for each scientist before checking the answer!

Q4. Discuss the advantages of the three-domain system. What evidence supports classifying organisms into three domains?

Background

Topic: Modern Classification Systems

This question focuses on the rationale and evidence for the three-domain system (Bacteria, Archaea, Eukarya).

Key Concepts

Three-domain system: Classification based on differences in ribosomal RNA (rRNA) sequences.
Domains: Bacteria, Archaea, Eukarya.

Step-by-Step Guidance

List the three domains and the types of organisms found in each.
Explain the molecular evidence (such as rRNA sequencing) that led to this classification.
Discuss the advantages of this system over previous ones (e.g., better reflects evolutionary relationships).
Consider how this system helps clarify the differences between prokaryotes and eukaryotes.

Try to identify at least one piece of molecular evidence before proceeding!

Q5. List the characteristics of the Bacteria, Archaea, and Eukarya domains. Compare archaea and bacteria; bacteria and eukarya; and archaea and eukarya.

Background

Topic: Domains of Life

This question tests your ability to distinguish between the three domains based on cellular and molecular characteristics.

Key Terms

Bacteria: Prokaryotic, peptidoglycan cell walls, diverse metabolism.
Archaea: Prokaryotic, unique cell wall composition, often extremophiles.
Eukarya: Eukaryotic, membrane-bound organelles, includes plants, animals, fungi, protists.

Step-by-Step Guidance

List the defining features of each domain (cell type, cell wall, membrane lipids, genetic material).
Compare and contrast archaea and bacteria (e.g., cell wall composition, habitat, genetic sequences).
Compare bacteria and eukarya (e.g., presence of nucleus, organelles, reproduction).
Compare archaea and eukarya (e.g., similarities in some genetic processes, differences in cell structure).

Try making a comparison table before checking the answer!

Q6. Explain why scientific names are used. Using Escherichia coli and Entamoeba coli as examples, explain why the genus name must always be written out for the first use. Why is binomial nomenclature preferable to the use of common names?

Background

Topic: Scientific Nomenclature

This question explores the importance of standardized naming in microbiology and the rules for writing scientific names.

Key Terms

Binomial nomenclature: Two-part scientific naming system (genus and species).
Genus: The first part of the name, always capitalized.
Species: The second part, not capitalized.

Step-by-Step Guidance

Explain the purpose of scientific names in avoiding confusion.
Describe the rules for writing scientific names (italicized or underlined, genus capitalized, species lowercase).
Use the examples given to show why the genus name is important for clarity.
Discuss why common names can be misleading or ambiguous.

Try writing out the full scientific names and abbreviations before moving on!

Q7. List the major taxa. Find the gram-positive bacteria Staphylococcus in Appendix F. To which bacteria is this genus more closely related: Bacillus or Streptococcus?

Background

Topic: Taxonomic Hierarchy and Relationships

This question asks you to recall the order of taxonomic ranks and apply your knowledge to determine relationships among bacteria.

Key Terms

Taxa: Levels of classification (Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species).
Gram-positive bacteria: Bacteria with thick peptidoglycan cell walls that retain crystal violet stain.

Step-by-Step Guidance

List the major taxonomic ranks in order from broadest to most specific.
Identify the family and order to which Staphylococcus, Bacillus, and Streptococcus belong.
Compare their classification to determine which is more closely related to Staphylococcus.
Use a reference (such as Appendix F or a phylogenetic tree) to support your answer.

Try to find the taxonomic hierarchy for each genus before checking the answer!

Q8. Differentiate culture, clone, and strain. Use the terms species, culture, clone, and strain in one sentence to describe growing methicillin-resistant Staphylococcus aureus (MRSA).

Background

Topic: Microbial Terminology

This question tests your understanding of terms used to describe groups of microorganisms in laboratory and clinical contexts.

Key Terms

Culture: Microorganisms grown in a controlled environment.
Clone: A population of cells derived from a single parent cell.
Strain: Genetic variant or subtype of a microorganism.
Species: The basic unit of classification.

Step-by-Step Guidance

Define each term clearly and concisely.
Think about how these terms relate to each other in the context of laboratory work.
Construct a sentence that uses all four terms to describe MRSA.

Try writing your own sentence before checking the answer!

Q9. List the major characteristics used to differentiate the three kingdoms of multicellular Eukarya. Assume you discovered a new organism: it is multicellular, is nucleated, is heterotrophic, and has cell walls. To what kingdom does it belong?

Background

Topic: Eukaryotic Kingdoms

This question asks you to recall the distinguishing features of the kingdoms within Eukarya and apply them to classify a new organism.

Key Terms

Kingdoms of Eukarya: Plantae, Animalia, Fungi.
Heterotrophic: Obtains food by consuming other organisms.
Cell wall: Structural layer outside the cell membrane.

Step-by-Step Guidance

List the main characteristics of each eukaryotic kingdom (nutrition, cell wall, motility, etc.).
Analyze the features of the new organism described in the question.
Match these features to the appropriate kingdom.

Try to match the organism's features to a kingdom before checking the answer!

Q10. Define protist. Write your own definition of protist.

Background

Topic: Protists

This question encourages you to synthesize information about protists and express it in your own words.

Key Terms

Protist: A diverse group of mostly unicellular eukaryotic organisms.

Step-by-Step Guidance

Review the characteristics that define protists (cell type, nutrition, habitat).
Write a concise definition in your own words.

Try to write your own definition before checking the answer!

Q11. Differentiate eukaryotic, prokaryotic, and viral species. Why wouldn’t the definition of a viral species work for a bacterial species?

Background

Topic: Species Concepts in Microbiology

This question asks you to compare how species are defined for different types of organisms and why these definitions differ.

Key Terms

Eukaryotic species: Group of organisms that can interbreed and produce fertile offspring.
Prokaryotic species: Population of cells with similar characteristics.
Viral species: Population of viruses with similar characteristics that occupies a particular ecological niche.

Step-by-Step Guidance

Define species for eukaryotes, prokaryotes, and viruses.
Explain why the viral species concept (ecological niche, similar characteristics) does not apply to bacteria.
Discuss the challenges in defining species for asexual organisms like bacteria.

Try to explain the difference in your own words before checking the answer!

Q12. Compare and contrast classification and identification. Is a cladogram used for identification or classification?

Background

Topic: Methods in Microbial Taxonomy

This question tests your understanding of the goals and tools of classification versus identification.

Key Terms

Classification: Arranging organisms into groups based on similarities.
Identification: Determining the identity of an unknown organism.
Cladogram: Diagram showing evolutionary relationships.

Step-by-Step Guidance

Define classification and identification, noting their different purposes.
Describe what a cladogram is and how it is used.
Decide whether a cladogram is more useful for classification or identification, and explain why.

Try to reason out the main purpose of a cladogram before checking the answer!

Q13. Explain the purpose of Bergey’s Manual. What is in Bergey’s Manual?

Background

Topic: Bacterial Identification

This question focuses on a key reference used in microbiology labs for identifying bacteria.

Key Terms

Bergey’s Manual: Standard reference for bacterial classification and identification.

Step-by-Step Guidance

State the main purpose of Bergey’s Manual in microbiology.
Describe the types of information it contains (e.g., descriptions, identification keys, classification schemes).

Try to list at least two uses of Bergey’s Manual before checking the answer!

Q14. Describe how staining and biochemical tests are used to identify bacteria. Design a rapid test for a Staphylococcus aureus.

Background

Topic: Laboratory Identification Methods

This question asks you to explain common lab techniques for bacterial identification and apply them to a specific case.

Key Terms

Staining: Using dyes to visualize and differentiate bacteria (e.g., Gram stain).
Biochemical tests: Tests that detect metabolic or enzymatic activities.

Step-by-Step Guidance

Explain how staining (such as Gram staining) helps distinguish bacterial groups.
Describe how biochemical tests (e.g., catalase, coagulase) are used to identify bacteria.
Propose a rapid test for S. aureus, considering its unique characteristics (e.g., positive for coagulase test).

Try to outline a test procedure before checking the answer!

Q15. Differentiate Western blotting from Southern blotting. What is tested in Western blotting and Southern blotting?

Background

Topic: Molecular Identification Techniques

This question asks you to distinguish between two important laboratory techniques used to detect specific molecules.

Key Terms

Western blotting: Detects specific proteins using antibodies.
Southern blotting: Detects specific DNA sequences using labeled probes.

Step-by-Step Guidance

Define each technique and what it detects (protein vs. DNA).
Describe the general steps involved in each method.
Explain the applications of each technique in microbiology.

Try to summarize the main difference before checking the answer!

Q16. Explain how serological tests and phage typing can be used to identify an unknown bacterium. What is identified by phage typing?

Background

Topic: Bacterial Identification Methods

This question focuses on two methods for distinguishing bacterial strains and species.

Key Terms

Serological tests: Use antibodies to detect specific antigens on bacteria.
Phage typing: Uses bacteriophages to identify bacterial strains based on susceptibility.

Step-by-Step Guidance

Describe how serological tests work and what they detect.
Explain the principle of phage typing and what it reveals about bacterial strains.
Discuss how these methods can be used to identify unknown bacteria in the lab.

Try to explain the principle of each method before checking the answer!

Q17. Describe how a newly discovered microbe can be classified by DNA base composition, DNA fingerprinting, and PCR. Why does PCR identify a microbe?

Background

Topic: Molecular Classification Techniques

This question explores how molecular methods are used to classify and identify microorganisms.

Key Terms

DNA base composition: The proportion of G+C content in DNA.
DNA fingerprinting: Analysis of DNA fragment patterns.
PCR (Polymerase Chain Reaction): Amplifies specific DNA sequences.

Step-by-Step Guidance

Explain how DNA base composition can be used to compare organisms.
Describe the process of DNA fingerprinting and what information it provides.
Outline how PCR can be used to detect and identify microbes based on unique DNA sequences.
Discuss why PCR is a powerful tool for microbial identification.

Try to describe the role of each technique before checking the answer!

Q18. Describe how microorganisms can be identified by nucleic acid hybridization, Southern blotting, DNA chips, ribotyping, and FISH. Which techniques involve nucleic acid hybridization?

Background

Topic: Nucleic Acid-Based Identification

This question asks you to explain several molecular techniques and identify which rely on nucleic acid hybridization.

Key Terms

Nucleic acid hybridization: Formation of double-stranded molecules between complementary DNA or RNA strands.
Southern blotting, DNA chips, ribotyping, FISH: Techniques that use hybridization to detect specific sequences.

Step-by-Step Guidance

Briefly describe each technique and its purpose.
Identify which methods use nucleic acid hybridization as a key step.
Explain how hybridization helps in identifying microorganisms.

Try to match each technique to its use of hybridization before checking the answer!

Q19. Differentiate a dichotomous key from a cladogram. Is a cladogram used for identification or classification?

Background

Topic: Tools for Classification and Identification

This question asks you to compare two common tools used in taxonomy and explain their purposes.

Key Terms

Dichotomous key: A tool that allows the identification of organisms through a series of choices.
Cladogram: A diagram showing evolutionary relationships.

Step-by-Step Guidance

Define each tool and its main function.
Explain how a dichotomous key is used in identification.
Describe the purpose of a cladogram in classification.
Decide which tool is used for which purpose and justify your reasoning.