MMBS111 Unit 1 Microbiology Study Guide – Step-by-Step Guidance

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Q1. What are the key microbes? Give a description of each including which ones are prokaryotes, which are eukaryotes, which are non-cellular. Include any other important distinguishing features.

Background

Topic: Classification and Characteristics of Microbes

This question tests your understanding of the main groups of microbes, their cellular organization (prokaryote, eukaryote, non-cellular), and their distinguishing features.

Key Terms:

Prokaryote: Organisms without a nucleus (e.g., Bacteria, Archaea)
Eukaryote: Organisms with a nucleus (e.g., Fungi, Protozoa, Helminths)
Non-cellular: Entities not composed of cells (e.g., Viruses, Prions)

Step-by-Step Guidance

List each major group of microbes: Bacteria, Archaea, Fungi, Protozoa, Helminths, Viruses, Prions.
For each group, determine if it is prokaryotic, eukaryotic, or non-cellular.
Write a brief description of each group, including key characteristics (e.g., cell wall composition, reproduction, unique features).
Provide an example microbe or disease for each group.
Organize your information in a table for clarity.

Try solving on your own before revealing the answer!

Final Answer:

Microbe	Type	Key Characteristics	Example
Bacteria	Prokaryote	Unicellular, peptidoglycan cell wall, binary fission	Escherichia coli (E. coli)
Archaea	Prokaryote	Unicellular, no peptidoglycan, extremophiles	Halobacterium
Fungi	Eukaryote	Uni/multicellular, chitin cell wall, sexual/asexual reproduction	Yeast (Saccharomyces cerevisiae)
Protozoa	Eukaryote	Unicellular, no cell wall, motile	Amoeba
Helminths	Eukaryote	Multicellular, parasitic worms	Schistosoma
Viruses	Non-cellular	DNA/RNA genome, protein coat, require host	Influenza virus
Prions	Non-cellular	Infectious proteins, no nucleic acids	Prion causing Creutzfeldt-Jakob disease

Each group is classified based on cellular structure and unique features. For example, bacteria are prokaryotes with peptidoglycan cell walls, while viruses are non-cellular and require a host to replicate.

Q2. Would describing a microbe as a microscopic, living organism be a good definition of a microbe? Why or why not?

Background

Topic: Definition of Microbes

This question asks you to critically evaluate the definition of a microbe and consider exceptions.

Key Terms:

Microbe: A microscopic organism or infectious agent
Living organism: Capable of metabolism, growth, reproduction, response to stimuli

Step-by-Step Guidance

Consider whether all microbes are living (think about viruses and prions).
Think about whether all microbes are microscopic (are there exceptions?).
Reflect on the characteristics that define life and whether all microbes meet these criteria.
Formulate your reasoning for why the definition may or may not be sufficient.

Try solving on your own before revealing the answer!

Final Answer:

Describing a microbe as a microscopic, living organism is not entirely accurate. Some microbes, such as viruses and prions, are not considered living because they lack cellular structure and cannot reproduce independently. Additionally, some microbes (e.g., certain helminths) can be seen without a microscope. Therefore, a more precise definition would be: "Microbes are microscopic organisms and infectious agents, including bacteria, archaea, fungi, protozoa, viruses, and prions."

Q3. What are the differences between prokaryotes and eukaryotes?

Background

Topic: Cell Structure and Classification

This question tests your understanding of the fundamental differences between prokaryotic and eukaryotic cells.

Key Terms:

Prokaryote: Cell without a nucleus or membrane-bound organelles
Eukaryote: Cell with a nucleus and membrane-bound organelles

Step-by-Step Guidance

List structural features unique to prokaryotes (e.g., nucleoid, 70S ribosomes).
List structural features unique to eukaryotes (e.g., nucleus, 80S ribosomes, organelles).
Compare cell division methods (binary fission vs. mitosis/meiosis).
Note differences in cell wall composition and presence.
Summarize the main differences in a table or bullet points.

Try solving on your own before revealing the answer!

Final Answer:

Prokaryotes lack a nucleus and membrane-bound organelles; their DNA is in a nucleoid region, and they have 70S ribosomes. Cell division is by binary fission.
Eukaryotes have a true nucleus, membrane-bound organelles (e.g., mitochondria), and 80S ribosomes. Cell division is by mitosis or meiosis.
Prokaryotic cell walls often contain peptidoglycan (bacteria), while eukaryotic cell walls (if present) are made of cellulose (plants) or chitin (fungi).

Q4. How are microbes named according to the binomial naming system? Provide and explain examples.

Background

Topic: Microbial Nomenclature

This question tests your understanding of the scientific naming system for organisms.

Key Terms:

Binomial nomenclature: Two-part scientific naming system (Genus species)
Genus: Capitalized, italicized or underlined
Species: Lowercase, italicized or underlined

Step-by-Step Guidance

Recall the rules for writing scientific names (Genus species format).
Give an example, such as Escherichia coli, and explain the formatting.
Describe why this system is used (universal identification).
Explain what each part of the name represents.

Try solving on your own before revealing the answer!

Final Answer:

Microbes are named using binomial nomenclature: the first part is the genus (capitalized), and the second is the species (lowercase). Both are italicized or underlined. For example, Staphylococcus aureus refers to the genus Staphylococcus and the species aureus. This system allows for consistent and universal identification of organisms.

Q5. What are the two primary methods used to classify microbes? Explain how each of these methods are conducted.

Background

Topic: Microbial Classification Methods

This question tests your knowledge of how scientists classify microbes.

Key Terms:

Phenotypic methods: Based on observable traits (morphology, staining, metabolism)
Genotypic methods: Based on genetic information (DNA/RNA sequencing)

Step-by-Step Guidance

Identify the two main classification methods: phenotypic and genotypic.
Describe how phenotypic classification is performed (e.g., Gram stain, shape, metabolic tests).
Describe how genotypic classification is performed (e.g., sequencing 16S rRNA genes).
Explain the advantages and limitations of each method.

Try solving on your own before revealing the answer!

Final Answer:

Phenotypic methods involve observing physical and metabolic traits, such as cell shape, Gram staining, and biochemical tests.
Genotypic methods involve analyzing genetic material, such as sequencing the 16S rRNA gene, to determine evolutionary relationships.
Both methods are used together for accurate classification.

Q6. What are some complications of using a 97% sequence similarity cut-off when identifying a microbe? Provide an example.

Background

Topic: Microbial Identification and Genetic Similarity

This question tests your understanding of the limitations of using genetic similarity thresholds for microbial identification.

Key Terms:

Sequence similarity: Percentage of identical nucleotides in a gene sequence
Operational Taxonomic Unit (OTU): Grouping based on sequence similarity

Step-by-Step Guidance

Explain what the 97% sequence similarity cut-off means in microbial taxonomy.
Discuss why this threshold might not accurately reflect species boundaries (e.g., different species can have >97% similarity).
Provide an example where two distinct species share high sequence similarity.
Consider the impact on microbial identification and classification.

Try solving on your own before revealing the answer!

Final Answer:

Using a 97% sequence similarity cut-off can group distinct species together or split a single species into multiple groups. For example, Escherichia coli and Shigella species have over 97% 16S rRNA gene similarity but are different species. This can complicate accurate identification and classification.