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Quizzes > Science

Microbiology Final Exam Practice Test

Quick, free microbiology exam practice quiz with instant feedback.

Editorial: Review CompletedCreated By: Adam HansenUpdated Aug 26, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art microbes lab tools pathogens around final exam quiz title on teal background.

Use this microbiology final exam practice test to check your grasp of microbes, lab methods, and pathogens with instant feedback. Strengthen weak spots and, if you want more targeted review, try our microbiology exam 1 practice test, explore the clinical microbiology quiz, or drill cell basics with a prokaryotic cell quiz.

Which of the following is a prokaryotic organism?
Aspergillus niger
Escherichia coli
Saccharomyces cerevisiae
Plasmodium falciparum
Prokaryotic organisms lack a nucleus and membrane-bound organelles, which is characteristic of bacteria like Escherichia coli. Yeasts such as Saccharomyces cerevisiae are eukaryotes. Plasmodium falciparum is a protozoan parasite (eukaryotic) and Aspergillus niger is a fungus (eukaryotic). .
Gram-negative bacteria have which of the following molecules in their outer membrane?
Lipopolysaccharide
Teichoic acid
Mycolic acid
Peptidoglycan
The outer membrane of Gram-negative bacteria contains lipopolysaccharide (LPS), which is absent in Gram-positive bacteria. Teichoic acids are found in the thick peptidoglycan layer of Gram-positive cells. Mycolic acids are unique to acid-fast bacteria. Peptidoglycan is present in both but not part of the outer membrane. .
Which microscope is typically used to view the ultrastructure of cells at high resolution?
Transmission electron microscope
Phase-contrast microscope
Scanning acoustic microscope
Light microscope
Transmission electron microscopes use electron beams to achieve resolutions below 1 nm, allowing visualization of ultrastructural details. Light microscopes are limited by light wavelength (~200 nm). Scanning acoustic and phase-contrast microscopes do not reach electron microscope resolution. .
What is the primary purpose of aseptic technique in microbiology labs?
To enhance microbial growth rate
To stain cells for microscopy
To measure pH of culture medium
To prevent contamination by unwanted microbes
Aseptic technique involves practices to prevent unwanted microbial contamination of cultures and the environment. It does not inherently affect microbial growth rate or stains cells. Measuring pH is a separate procedure. .
The catalase test in microbiology is used to identify organisms that produce which enzyme?
Catalase
Oxidase
Urease
Coagulase
The catalase test detects the enzyme catalase, which decomposes hydrogen peroxide into water and oxygen, evidenced by bubbling. Oxidase, urease, and coagulase tests detect different enzymes and reactions. .
MacConkey agar is selective for which group of bacteria?
Gram-positive cocci
Anaerobic bacteria
Gram-negative enteric bacteria
Acid-fast bacteria
MacConkey agar contains bile salts and crystal violet to inhibit Gram-positive bacteria, selecting for Gram-negative enterics. It also differentiates lactose fermenters. It does not select for acid-fast or anaerobic organisms. .
What shape describes bacilli?
Spiral
Comma-shaped
Spherical
Rod-shaped
Bacilli are rod-shaped bacteria. Spherical bacteria are cocci, spiral bacteria are spirilla or spirochetes, and comma-shaped are vibrios. .
Bacterial binary fission is a form of which process?
Budding
Sexual reproduction
Spore formation
Asexual reproduction
Binary fission is an asexual reproduction method where one cell divides into two genetically identical daughter cells. Sexual reproduction involves recombination of genetic material, spore formation is a survival strategy, and budding is a different asexual method. .
Which medium is used to cultivate viruses in the lab?
Cell culture
MacConkey agar
Nutrient agar
Blood agar
Viruses require living host cells, and cell culture provides the necessary environment for viral replication. Blood agar, MacConkey agar, and nutrient agar are designed for bacteria, not viruses. .
Endospore formation is characteristic of which bacterial genera?
Staphylococcus and Streptococcus
Escherichia and Salmonella
Mycobacterium and Nocardia
Bacillus and Clostridium
Only certain Gram-positive rods, notably Bacillus and Clostridium, form highly resistant endospores. Staphylococcus, Streptococcus, Mycobacterium, Nocardia, Escherichia, and Salmonella do not produce endospores. .
Why is agar used as a solidifying agent in microbiological media?
It selectively inhibits Gram-positive bacteria
It remains solid at incubation temperatures
It provides nutrients for growth
It stains cells for microscopy
Agar is a polysaccharide that melts at 100°C and solidifies at around 45°C, maintaining solidity at typical incubation temperatures (25 - 37°C). It is inert nutritionally and does not selectively inhibit specific bacteria. .
In the Gram staining process, which reagent is the primary stain?
Gram's iodine
Decolorizer
Safranin
Crystal violet
Crystal violet is applied first to stain all cells purple. Gram's iodine acts as a mordant, the decolorizer removes the stain from Gram-negative cells, and safranin counterstains them pink. .
The term colony morphology refers to what characteristic?
Genetic variation among colonies
Metabolic by-products
Microscopic cell structure
Appearance of microbial colonies on solid media
Colony morphology describes observable features such as shape, margin, elevation, color, and texture of microbial colonies on agar plates. It does not refer to genetic variation, microscopic cell structures, or metabolic by-products. .
Which cellular structure contains the bacterial chromosome?
Nucleoid
Nucleus
Endoplasmic reticulum
Mitochondrion
Bacteria lack a membrane-bound nucleus; their DNA is located in a region called the nucleoid. Nucleus, mitochondria, and endoplasmic reticulum are eukaryotic organelles. .
Phenol red is commonly used in microbiology to detect production of which compound?
Gas
Alcohol
Acid
Oxygen
Phenol red is a pH indicator that changes color from red to yellow under acidic conditions, indicating acid production in fermentation tests. It does not directly detect gas, alcohol, or oxygen. .
Escherichia coli is a normal resident of which part of the human body?
Intestines
Oral cavity
Lungs
Skin
Escherichia coli is part of the normal gut microbiota in the human intestines. It is not a common resident of skin, lungs, or oral cavity, though it may transiently appear. .
What is the primary function of bacterial capsules?
Synthesize ATP
Protect against phagocytosis
Aid in DNA replication
Produce toxins
Capsules are polysaccharide layers outside the cell wall that prevent recognition and ingestion by phagocytes, aiding in immune evasion. They do not directly aid DNA replication, toxin production, or ATP synthesis. .
Polymerase chain reaction (PCR) is used to:
Sequence proteins
Amplify DNA sequences
Stain nucleic acids
Lyse bacterial cells
PCR uses primers and a thermostable DNA polymerase to exponentially amplify specific DNA sequences. It does not sequence proteins, lyse cells, or stain nucleic acids. .
DNA absorbs UV light maximally at what wavelength?
260 nm
230 nm
300 nm
280 nm
Nucleic acids have peak absorbance at 260 nm due to aromatic bases, whereas proteins peak at 280 nm. 230 nm is associated with some contaminants. .
Which technique separates proteins based on their size and charge?
PCR
SDS-PAGE
ELISA
Western blot
SDS-PAGE denatures proteins and applies an electric field to separate them primarily by molecular weight. ELISA and Western blot detect proteins but Western blot uses SDS-PAGE first. PCR amplifies DNA, not proteins. .
Selective toxicity of antibiotics refers to:
Enhancing immune response
Killing microbes without harming host cells
Promoting microbial growth
Neutralizing toxins
Selective toxicity is the ability of an antibiotic to target microbial structures or functions absent or significantly different in host cells, reducing harm to the host. It does not enhance immunity or promote growth. .
Endotoxins are found in which part of Gram-negative bacteria?
Outer membrane
Cytoplasm
Cell wall peptidoglycan
Nucleoid
Endotoxins are lipopolysaccharides (LPS) located in the outer leaflet of the outer membrane of Gram-negative bacteria. They are not in the cytoplasm, peptidoglycan, or nucleoid. .
ELISA is commonly used to detect:
Antigens or antibodies
Lipids
RNA
Carbohydrates
Enzyme-linked immunosorbent assays (ELISAs) use antibodies to detect the presence of specific antigens or antibodies in a sample. They are not designed to detect lipids, carbohydrates, or RNA directly. .
A plaque assay measures:
Parasite load
Bacterial motility
Viral infectivity
Fungal spore count
A plaque assay quantifies infectious viral particles by counting clear zones (plaques) formed on a cell monolayer. It does not measure bacterial motility or fungal and parasite counts. .
What is the difference between lytic and lysogenic bacteriophage cycles?
Lytic integrates genome; lysogenic destroys
Both integrate genome
Lytic destroys host immediately; lysogenic integrates genome
Both destroy immediately
In the lytic cycle, phages replicate and lyse the host cell. In the lysogenic cycle, phage DNA integrates into the host genome as a prophage without immediate lysis. .
Antigenic shift in influenza viruses involves:
Reassortment of genome segments
Increased replication rate
Point mutations
Formation of syncytia
Antigenic shift occurs when two different influenza strains infect a cell and exchange genomic segments, creating a novel strain. Point mutations cause antigenic drift. .
Quorum sensing in bacteria refers to:
Cell-to-cell chemical communication
Protein synthesis
Genetic mutation rate
Cell division
Quorum sensing is a mechanism where bacteria produce and detect small signaling molecules called autoinducers to coordinate gene expression based on population density. It does not refer to mutation rates or basic cellular processes. .
Minimum inhibitory concentration (MIC) is defined as:
Highest that kills all cells
Concentration for half inhibition
Concentration causing resistance
Lowest antibiotic concentration that inhibits visible growth
MIC is the minimum concentration of an antimicrobial agent needed to prevent visible growth of a microorganism after incubation. It is not the highest lethal dose, half-maximal inhibitory concentration, or resistance threshold. .
Biofilms are problematic because they:
Are easier to sterilize
Grow faster than planktonic cells
Produce more toxins
Resist antibiotics and host defenses
Biofilms are structured microbial communities encased in extracellular polymeric substances, which hinder antibiotic penetration and immune clearance. They do not necessarily grow faster or produce inherently more toxins, and are harder to sterilize. .
Sterilization differs from disinfection in that it:
Selectively kills fungi
Reduces pathogens to safe level
Destroys all forms of microbial life
Only removes dirt
Sterilization is a process that eliminates or kills all forms of microbial life, including spores. Disinfection reduces microbial load but may not eliminate all spores. .
Which plasmid-mediated mechanism can confer antibiotic resistance?
Changing ribosome type
Enhancing spore formation
Altering host DNA replication
Producing enzyme that degrades antibiotic
Many resistance plasmids carry genes encoding enzymes like beta-lactamases that degrade antibiotics. Altering DNA replication, spore formation, or ribosome type are not typical plasmid-mediated mechanisms. .
How do oxidase tests identify cytochrome c oxidase activity?
pH change
Color change due to reduced reagent
Fluorescence under UV
Gas production
The oxidase test uses tetramethyl-p-phenylenediamine that turns purple when reduced by cytochrome c oxidase. Gas production and pH changes are not involved, nor does it rely on UV fluorescence. .
Beta-lactam antibiotics inhibit bacterial growth by targeting:
Protein synthesis
Peptidoglycan cross-linking
DNA gyrase
Folate synthesis
Beta-lactam antibiotics bind to penicillin-binding proteins and inhibit the transpeptidation step in peptidoglycan synthesis, leading to cell lysis. They do not directly affect protein synthesis, DNA gyrase, or folate pathways. .
Bacterial conjugation differs from transformation in that it:
Occurs only in presence of phage
Uses naked DNA uptake
Transfers DNA via direct cell contact
Involves viral vectors
Conjugation requires donor and recipient cells to establish a sex pilus for DNA transfer, whereas transformation involves uptake of free DNA from the environment. Transduction uses viral vectors. .
The lac operon is repressed when:
RNA polymerase binds promoter
cAMP levels are high
Repressor binds operator in absence of lactose
Lactose is present
In the absence of lactose, the lac repressor binds the operator, preventing transcription. When lactose (or allolactose) is present, it binds the repressor, causing it to release from the operator. High cAMP levels signal glucose scarcity, enhancing transcription when not repressed. .
Sigma factors in bacteria are responsible for:
Cell wall synthesis
Directing RNA polymerase to specific promoters
Protein folding
DNA replication initiation
Sigma factors associate with RNA polymerase to recognize promoter sequences and initiate transcription. They do not fold proteins, start DNA replication, or synthesize cell walls. .
Acid-fast bacteria resist decolorization by acid-alcohol because their cell walls contain:
Teichoic acids
Chitin
Lipopolysaccharides
Mycolic acids
Acid-fast bacteria have high concentrations of mycolic acids (long-chain fatty acids) in their cell walls, making them waxy and resistant to decolorization by acid-alcohol during staining. Teichoic acids are in Gram-positive, lipopolysaccharides are in Gram-negative, and chitin is in fungi. .
Specialized transduction differs from generalized transduction by:
Requiring conjugation pili
Occurring in all bacterial species
Transferring only specific genes near prophage insertion site
Randomly packaging host DNA into phage heads
Specialized transduction occurs when a lysogenic phage excises incorrectly and takes specific adjacent host genes, whereas generalized transduction randomly packages host DNA from lysed cells. It does not require pili. .
Which antibiotic class targets the 30S ribosomal subunit causing mRNA misreading?
Aminoglycosides
Oxazolidinones
Macrolides
Tetracyclines
Aminoglycosides bind the 30S subunit, causing misreading of mRNA and polypeptide synthesis errors. Macrolides target the 50S subunit, tetracyclines block tRNA binding, and oxazolidinones inhibit initiation. .
Two-component regulatory systems in bacteria generally consist of:
Sensor kinase and response regulator
Peptidoglycan synthase and autolysin
DNA polymerase and helicase
Ribosome and tRNA
Two-component systems comprise a membrane-bound sensor histidine kinase that autophosphorylates in response to stimuli and a cytoplasmic response regulator that modulates gene expression. The others are unrelated protein pairs. .
Which autoclave condition is standard for sterilizing laboratory media?
121°C for 5 minutes
80°C for 30 minutes
121°C for 15 minutes
100°C for 60 minutes
Standard autoclaving uses 121°C at 15 psi for at least 15 minutes to achieve sterilization. Boiling at 100°C or shorter times at 121°C are insufficient for spores. .
Horizontal gene transfer by transduction is mediated by:
Integrons
Transposons
Plasmids
Bacteriophages
Transduction involves bacteriophages transferring host DNA between bacteria. Plasmids transfer via conjugation, transposons jump within genomes, and integrons capture gene cassettes. .
Persister cells in bacterial populations are characterized by:
Temporary antibiotic tolerance without genetic resistance
Increased growth rate
Phase variation
Permanent antibiotic resistance via mutation
Persister cells are dormant variants that survive antibiotic treatment due to low metabolic activity, not genetic resistance. They are not faster growing and differ from phase variation by reversible gene expression. .
The generation time of a bacterial population is:
Time to form biofilm
Time for single cell to divide only once
Time required for the population to double
Time to produce endospores
Generation time is the interval for a bacterial population to double under defined conditions. It does not refer to sporulation, biofilm formation, or a single cell's division in isolation. .
ELISPOT assay differs from ELISA by detecting:
DNA fragments
Total protein concentration
Bacterial counts
Cytokine secretion at single-cell level
ELISPOT captures secreted cytokines or antibodies at the single-cell level, forming spot counts. ELISA measures total antigen or antibody concentration in bulk. It does not detect DNA or bacterial load. .
Lipid A is the toxic component of:
Lipoteichoic acid
Mycolic acid
Phosphatidylcholine
Lipopolysaccharide
Lipid A is the lipid anchor of lipopolysaccharide (LPS) in Gram-negative bacteria and is responsible for its endotoxic effects. Lipoteichoic acid is in Gram-positive, phosphatidylcholine is a membrane phospholipid, and mycolic acid is in acid-fast bacteria. .
Glycolysis in bacteria occurs in:
Ribosomes
Cytoplasm
Mitochondria
Periplasmic space
Prokaryotes lack membrane-bound organelles; glycolysis takes place in the cytoplasm. Mitochondria are eukaryotic, and periplasmic space and ribosomes are not glycolytic compartments. .
R plasmids in bacteria are primarily associated with:
Antibiotic resistance
Photosynthesis
Sporulation
Nitrogen fixation
R (resistance) plasmids carry genes that confer resistance to antibiotics. They are not linked to photosynthesis, nitrogen fixation, or sporulation, which involve different plasmids or chromosomal genes. .
Multi-drug efflux pumps in Pseudomonas aeruginosa are part of which family?
ABC transporter family
RND family (Resistance-Nodulation-Cell Division)
Sec protein family
Symporter family
Pseudomonas aeruginosa expresses RND family efflux pumps (e.g., MexAB-OprM) that export a broad range of antibiotics and toxins. ABC transporters use ATP hydrolysis, symporters use ion gradients, and Sec proteins mediate secretion. .
Quorum sensing in Vibrio fischeri involves which autoinducer molecule?
N-acyl homoserine lactone
Peptidoglycan monomer
Cyclic di-GMP
Lipoteichoic acid
Vibrio fischeri uses N-acyl homoserine lactone (AHL) as its quorum sensing signal to regulate bioluminescence gene expression. Peptidoglycan and lipoteichoic acid are cell wall components, and cyclic di-GMP is a secondary messenger for biofilm formation. .
In bacterial mismatch repair, the MutH protein's role is to:
Recognize hemimethylated DNA and nick unmethylated strand
Ligate Okazaki fragments
Unwind the DNA helix
Add methyl groups to adenines
MutH identifies the newly synthesized, unmethylated DNA strand at hemimethylated GATC sites and introduces a nick to initiate repair. It does not ligate or unwind DNA or methylate bases. .
Persister cell formation is regulated by which toxin-antitoxin system?
CRISPR-Cas
MazEF
LacI-LacZ
Trp operon
The MazEF toxin-antitoxin system in E. coli can trigger a dormant state in a subpopulation, leading to persister cell formation. LacI-LacZ and the trp operon regulate metabolism, and CRISPR-Cas provides adaptive immunity. .
Metagenomics allows for:
Analysis of genetic material from environmental samples without culturing
Sequencing only viral genomes
Analyzing protein structure
Measuring metabolic flux
Metagenomics bypasses culture by directly extracting and sequencing DNA from environmental or clinical samples to profile microbial communities. It is not limited to viruses or protein structures and does not measure metabolic flux. .
The CRISPR-Cas9 system provides bacteria with:
Adaptive immunity against phages
Increased cell motility
Enhanced spore formation
Resistance to antibiotics
CRISPR-Cas9 captures sequences from invading phages or plasmids into the CRISPR array, enabling sequence-specific targeting and cleavage of foreign DNA upon reinfection. It does not confer antibiotic resistance, sporulation enhancement, or motility changes. .
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Study Outcomes

  1. Recall Fundamental Microbial Structures -

    Describe the major components of bacterial, viral, and fungal cells to solidify your understanding for the microbiology final exam.

  2. Differentiate Microbial Taxonomy -

    Classify bacteria, archaea, and eukaryotic microorganisms based on phenotypic and genetic characteristics to master final exam microbiology concepts.

  3. Apply Core Lab Techniques -

    Demonstrate proper use of aseptic methods, staining protocols, and culture techniques to replicate real-world lab scenarios.

  4. Analyze Microscopy and Staining Results -

    Interpret Gram stains, acid-fast tests, and microscopy images to accurately identify microbial specimens.

  5. Evaluate Pathogen-Host Interactions -

    Explain mechanisms of microbial virulence and host defense to understand how pathogens cause disease.

  6. Solve Exam-Style Questions -

    Utilize strategies for answering multiple-choice and practical questions to boost your confidence for the final exam microbiology quiz.

Cheat Sheet

  1. Bacterial Cell Envelope Structure -

    Review the key distinctions between Gram-positive and Gram-negative bacteria: a thick peptidoglycan layer vs. a thin layer plus an outer membrane. Mnemonic: "Purple positives, red negatives" helps you recall crystal violet retention and safranin counterstain. (Sources: CDC, Brock Biology of Microorganisms)

  2. Microbial Growth Curve Phases -

    Memorize the four stages - lag, log, stationary, and death - with the mnemonic "Let's Grow Some Dead." Understand what happens in each phase, such as exponential cell division during log phase. (Sources: University of California, Berkeley Microbiology Lecture Notes)

  3. Enzyme Tests & Biochemical IDs -

    Practice catalase, oxidase, and coagulase assays to distinguish common pathogens (e.g., Staphylococcus aureus is catalase- and coagulase-positive). Remember "CATs OX Combine" to cue catalase before oxidase. (Sources: American Society for Microbiology)

  4. Sterilization & Disinfection Methods -

    Compare autoclaving (121 °C, 15 psi, 15 min), pasteurization (63 °C, 30 min), and membrane filtration (0.22 µm). A handy phrase: "Heat Destroys, Filters Remove" clarifies method selection. (Sources: World Health Organization Guidelines)

  5. Lab Techniques & Exam Practice -

    Familiarize yourself with PCR, ELISA, and microscopy protocols, then test your recall by reviewing a final exam microbiology questions and answers pdf from university repositories. Regular self-quizzing on past questions builds confidence for the microbiology final exam. (Sources: University of Michigan OpenCourseWare)

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