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MICROBIOLOGY MIDTERM EXAM JERSEY COLLEGE VERSION 1 QUESTIONS AND CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES 2025
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1. Which structure do prokaryotic cells lack? A. Cytoplasm B. Ribosomes C. Nucleus D. Plasma membrane Prokaryotes do not have a membrane-bound nucleus; their DNA is located in the nucleoid region. 2. What type of bond holds together the two strands of DNA? A. Ionic bonds B. Covalent bonds C. Hydrogen bonds D. Peptide bonds
Hydrogen bonds form between the nitrogenous bases of DNA, stabilizing the double helix.
3. Which of the following is NOT a characteristic of viruses? A. Acellular B. Require a host to replicate C. Capable of independent metabolism D. Contain either DNA or RNA Viruses cannot perform metabolic functions on their own; they rely entirely on a host cell. 4. Which type of microorganism is classified as a eukaryote? A. Bacteria B. Archaea C. Fungi D. Viruses Fungi are eukaryotic, meaning they have a true nucleus and organelles. 5. The Gram stain differentiates bacteria based on what? A. Shape B. Cell wall composition C. Presence of capsule D. Metabolic enzymes Gram-positive and Gram-negative bacteria differ in their peptidoglycan layer thickness in the cell wall.
B. Protection from phagocytosis C. Protein synthesis D. Energy production Capsules help bacteria evade the host immune system by preventing engulfment by phagocytes.
10. Which stain is used to detect Mycobacterium tuberculosis? A. Gram stain B. Endospore stain C. Acid-fast stain D. Capsule stain The acid-fast stain targets the waxy mycolic acid in the cell wall of Mycobacterium species. 11. The term "pathogen" refers to a microorganism that: A. Lives in harmony with the host B. Enhances the host’s health C. Causes disease D. Is always present in the body Pathogens are disease-causing microorganisms. 12. What is the role of enzymes in microbial metabolism? A. Destroy cell walls B. Maintain osmotic balance C. Lower activation energy
D. Form DNA strands Enzymes speed up biochemical reactions by reducing the activation energy.
13. Which of the following structures helps bacteria exchange genetic material? A. Flagella B. Capsule C. Pilus D. Ribosome Pili (specifically sex pili) facilitate conjugation, a method of horizontal gene transfer. 14. Which of the following statements about endospores is correct? A. They are involved in reproduction B. They are present in all bacteria C. They allow survival in harsh conditions D. They cause disease directly Endospores are dormant structures that help bacteria survive extreme environmental stress. 15. Which phase of bacterial growth curve involves active division? A. Lag phase B. Log (exponential) phase C. Stationary phase D. Death phase
19. What makes fungi different from bacteria? A. Lack of cell wall B. Smaller size C. Presence of a nucleus D. Use of photosynthesis Fungi are eukaryotic and contain a nucleus, while bacteria are prokaryotic. 20. Which bacterial shape is described as spherical? A. Bacillus B. Coccus C. Spirillum D. Vibrio Cocci are round or spherical in shape. 21. What does the term "obligate aerobe" mean? A. Can survive without oxygen B. Prefers anaerobic environments C. Requires oxygen to survive D. Grows best in acidic conditions Obligate aerobes rely on oxygen for cellular respiration. 22. Plasmids are best described as: A. Energy-producing organelles B. Components of the ribosome C. Extrachromosomal DNA
D. Viral particles Plasmids are small, circular DNA molecules that exist independently of the bacterial chromosome.
23. The main difference between Gram-positive and Gram-negative bacteria is: A. DNA content B. Cell wall thickness C. Ribosome size D. Presence of flagella Gram-positive bacteria have thick peptidoglycan layers, unlike Gram- negative bacteria. 24. The process by which bacteria reproduce is: A. Mitosis B. Binary fission C. Budding D. Conjugation Binary fission is an asexual method of reproduction where the bacterial cell divides into two. 25. Which of the following is a sterilization method? A. Hand washing B. Alcohol swab C. Autoclaving D. Using antibiotics
29. In the Gram stain, crystal violet is: A. Counterstain B. Primary stain C. Decolorizer D. Mordant Crystal violet is the first dye used to stain all cells before differentiation. 30. Which of the following destroys bacterial endospores? A. Boiling water B. Alcohol C. Autoclave D. Freezing Autoclaving is one of the few methods effective against highly resistant endospores. 31. Which of the following is a method of horizontal gene transfer in bacteria? A. Binary fission B. Conjugation C. Mitosis D. Sporulation Conjugation involves direct cell-to-cell contact and transfer of plasmid DNA via a pilus.
32. Which component of the cell wall is unique to Gram-negative bacteria? A. Peptidoglycan B. Lipopolysaccharide (LPS) C. Teichoic acid D. Mycolic acid LPS is found in the outer membrane of Gram-negative bacteria and contributes to toxicity. 33. The term "antiseptic" refers to: A. Agent that kills spores B. Used to clean instruments C. Applied to living tissue D. Sterilizing agent Antiseptics are safe for use on skin to reduce microbial load. 34. A bacteriophage infects: A. Fungi B. Bacteria C. Animals D. Algae Bacteriophages are viruses that specifically infect bacterial cells. 35. Which phase of the bacterial growth curve shows equal rates of cell division and death? A. Lag phase B. Log phase
D. Base The diaphragm controls light intensity to improve contrast.
39. Which structure helps bacteria adhere to surfaces? A. Ribosome B. Fimbriae C. Capsule D. Endospore Fimbriae are hair-like appendages used for attachment to surfaces or host cells. 40. What is a biofilm? A. Pure culture of viruses B. Isolated colony C. Community of microbes in a matrix D. Free-floating bacteria Biofilms are structured microbial communities encased in a protective matrix. 41. Which of the following statements is true about prions? A. They contain DNA B. They can be killed with antibiotics C. They are infectious proteins D. They are a type of virus
Prions are misfolded proteins that can induce abnormal folding in other proteins.
42. The bacterial shape classified as spiral is called: A. Coccus B. Bacillus C. Spirillum D. Vibrio Spirillum bacteria have a helical or spiral shape. 43. What is the best definition of selective media? A. Shows hemolysis B. Inhibits some microbes and allows others C. Distinguishes between two types of microbes D. Contains all nutrients Selective media suppress growth of unwanted organisms and promote the growth of the desired microbe. 44. Which of the following is an example of a vector? A. Contaminated water B. Mosquito C. Infected surface D. Dirty needle Vectors are living organisms that transmit pathogens, like mosquitoes transmitting malaria.
C. Artificial active D. Artificial passive Vaccination induces artificial active immunity by stimulating antibody production.
49. Which of the following is a DNA virus? A. HIV B. Influenza C. Herpes simplex D. Ebola Herpes simplex is a DNA virus; the rest are RNA viruses. 50. Which enzyme helps bacteria break down hydrogen peroxide? A. Amylase B. Oxidase C. Catalase D. Ligase Catalase breaks down hydrogen peroxide into water and oxygen. 51. Which microscope provides the highest resolution of internal cell structures? A. Compound light B. Phase-contrast C. Transmission electron D. Scanning electron
Transmission electron microscopes provide detailed images of internal ultrastructure.
52. Which term describes an organism that thrives in high salt environments? A. Thermophile B. Halophile C. Acidophile D. Mesophile Halophiles are adapted to live in environments with high salt concentrations. 53. A microbe that grows only at the bottom of a thioglycollate broth tube is: A. Obligate aerobe B. Obligate anaerobe C. Facultative anaerobe D. Microaerophile Obligate anaerobes cannot tolerate oxygen and grow only where oxygen is absent. 54. What structure allows bacterial cells to survive antibiotic treatment? A. Capsule B. Pilus C. Endospore
58. The transfer of DNA via a virus is known as: A. Conjugation B. Transformation C. Transduction D. Mutation Transduction is the process of DNA transfer from one bacterium to another via bacteriophages. 59. Which bacterial structure is most important in antibiotic resistance? A. Ribosomes B. Endospores C. Plasmids D. Nucleoid Plasmids often carry genes for antibiotic resistance and can be transferred between bacteria. 60. What is the best method to sterilize heat-sensitive solutions? A. Boiling B. Filtration C. Autoclaving D. Dry heat Filtration removes microbes without applying heat, ideal for heat-sensitive liquids.
61. Which of the following is an acid-fast bacterium? A. Escherichia coli B. Mycobacterium tuberculosis C. Staphylococcus aureus D. Streptococcus pyogenes Mycobacterium tuberculosis has a waxy cell wall that retains acid-fast stain. 62. The area of inhibition in an antibiotic sensitivity test indicates: A. Growth B. Resistance C. Susceptibility D. Inflammation A clear zone around the antibiotic disk shows the bacteria are susceptible to the drug. 63. Which organism is considered an obligate intracellular parasite? A. Yeast B. Virus C. Bacteria D. Protozoa Viruses require a host cell to replicate; they cannot live independently. 64. Which of the following is a component of peptidoglycan? A. Lipid A B. Teichoic acid
