BIO 260 — Microbiology

Question 1: Which structural feature distinguishes Gram-positive bacteria from Gram-negative bacteria?

•          Presence of a nucleus

•          A thick peptidoglycan cell wall

•          Presence of flagella

•          Ability to form spores

Explanation: Gram-positive bacteria have a thick peptidoglycan layer that retains crystal violet stain during Gram staining, appearing purple, whereas Gram-negative bacteria have a thinner peptidoglycan layer surrounded by an outer membrane and stain pink.

Question 2: Viruses are considered living organisms because they can reproduce independently.

•          True

•          False

Explanation: Viruses cannot reproduce on their own; they lack the cellular machinery for independent metabolism and replication, requiring a host cell's ribosomes and enzymes to synthesize new viral particles.

Question 3: Which process do bacteria use to reproduce asexually?

•          Mitosis

•          Binary fission

•          Meiosis

•          Budding only

Explanation: Bacteria typically reproduce through binary fission, in which a single cell replicates its DNA and divides into two genetically identical daughter cells.

Question 4: What is the primary function of antibiotics?

•          To kill or inhibit the growth of bacteria

•          To kill viruses

•          To boost the human immune system directly

•          To neutralize fungal toxins

Explanation: Antibiotics target structures or processes unique to bacterial cells, such as cell wall synthesis or ribosomal function, to kill bacteria or inhibit their growth; they are not effective against viruses.

Question 5: Endospores allow certain bacteria to survive extreme environmental conditions.

•          True

•          False

Explanation: Endospores are dormant, highly resistant structures produced by certain bacteria, such as Bacillus and Clostridium species, allowing them to survive heat, desiccation, radiation, and chemical exposure until conditions favor growth again.

Question 6: Which component of a virus contains its genetic material?

•          Capsid

•          Envelope

•          Core

•          Spike protein

Explanation: The core of a virus houses its genetic material, which can be either DNA or RNA, encoding the instructions necessary to hijack a host cell's machinery and produce new viral particles.

Question 7: What term describes microorganisms that require oxygen to survive?

•          Anaerobes

•          Aerobes

•          Facultative anaerobes

•          Extremophiles

Explanation: Aerobes, also called obligate aerobes, require oxygen to carry out cellular respiration efficiently and cannot survive or grow in its absence.

Question 8: Fungi are classified as prokaryotic organisms.

•          True

•          False

Explanation: Fungi are eukaryotic organisms, possessing membrane-bound nuclei and organelles, distinguishing them from prokaryotic bacteria and archaea despite some superficial similarities in habitat and lifestyle.

Question 9: What is the primary mode of nutrient acquisition in fungi?

•          Photosynthesis

•          Absorption of nutrients after extracellular digestion

•          Ingestion of solid food

•          Chemosynthesis

Explanation: Fungi secrete digestive enzymes into their surroundings to break down complex organic matter, then absorb the resulting simpler molecules through their cell walls and membranes.

Question 10: Which type of immunity involves the production of specific antibodies in response to a pathogen?

•          Innate immunity

•          Adaptive immunity

•          Passive immunity only

•          Physical barrier defense

Explanation: Adaptive immunity is a highly specific immune response in which B and T lymphocytes recognize particular antigens and generate targeted antibodies and memory cells for long-term protection.

Question 11: Bacteriophages are viruses that specifically infect bacterial cells.

•          True

•          False

Explanation: Bacteriophages, often called phages, are viruses that target and infect bacteria, injecting their genetic material into the bacterial cell to hijack its replication machinery and produce new phage particles.

Question 12: Which of the following best describes horizontal gene transfer in bacteria?

•          Passing genes from parent to offspring during division

•          Transfer of genetic material between organisms in the same generation

•          Random spontaneous mutation

•          Loss of genetic material during replication

Explanation: Horizontal gene transfer allows bacteria to acquire genetic material, such as antibiotic resistance genes, from other bacteria through mechanisms like conjugation, transformation, or transduction, rather than through direct inheritance.

Question 13: Protozoa are best classified as which type of organism?

•          Multicellular eukaryotes

•          Unicellular eukaryotes

•          Prokaryotes

•          Acellular organisms

Explanation: Protozoa are single-celled eukaryotic organisms that display diverse modes of locomotion and nutrition, including free-living and parasitic forms, and possess membrane-bound organelles like a nucleus.

Question 14: The overuse of antibiotics has contributed to the rise of antibiotic-resistant bacteria.

•          True

•          False

Explanation: Overuse and misuse of antibiotics apply strong selective pressure that favors the survival and reproduction of bacteria carrying resistance genes, accelerating the spread of antibiotic-resistant strains within populations.

Question 15: What is the term for a substance produced by microorganisms that stimulates an immune response?

•          Antibody

•          Antigen

•          Enzyme

•          Toxin only

Explanation: An antigen is any molecule, often found on the surface of a pathogen, that the immune system recognizes as foreign and responds to by producing specific antibodies or activating immune cells.

Question 16: Which laboratory technique is commonly used to grow and isolate bacterial colonies?

•          PCR

•          Streak plate method on agar media

•          Electrophoresis

•          Centrifugation

Explanation: The streak plate method involves spreading a bacterial sample across the surface of a nutrient agar plate in a pattern that dilutes the sample, allowing individual cells to grow into separate, isolated colonies for study.

Question 17: Archaea share more genetic and biochemical similarities with eukaryotes than bacteria do, despite structural similarities to bacteria.

•          True

•          False

Explanation: Although archaea resemble bacteria structurally, being unicellular and lacking a nucleus, their genetic transcription and translation machinery share more similarities with eukaryotes, supporting their classification as a distinct domain of life.

Question 18: Which of the following best describes a pathogen?

•          Any microorganism

•          A microorganism capable of causing disease

•          A beneficial microorganism

•          A microorganism found only in soil

Explanation: A pathogen is any microorganism, such as certain bacteria, viruses, fungi, or protozoa, capable of causing disease in a host organism by damaging tissues or disrupting normal physiological function.

Question 19: What role do decomposer microorganisms play in an ecosystem?

•          They cause disease exclusively

•          They break down organic matter and recycle nutrients

•          They produce oxygen through photosynthesis only

•          They have no ecological role

Explanation: Decomposer bacteria and fungi break down dead organisms and organic waste into simpler inorganic compounds, returning essential nutrients like nitrogen and carbon to the soil and atmosphere for reuse by other organisms.

Question 20: Vaccines work by exposing the immune system to a harmless version or component of a pathogen.

•          True

•          False

Explanation: Vaccines contain weakened, inactivated, or partial forms of a pathogen, or genetic instructions to produce a harmless piece of it, allowing the immune system to develop memory cells and antibodies without causing full disease.

Question 21: Which of the following microorganisms is generally used in the fermentation process to produce bread and beer?

•          Escherichia coli

•          Saccharomyces cerevisiae (yeast)

•          Streptococcus pyogenes

•          Plasmodium falciparum

Explanation: Saccharomyces cerevisiae, commonly known as baker's or brewer's yeast, ferments sugars into carbon dioxide and ethanol, processes that are essential to bread leavening and alcoholic beverage production.

Question 22: What is the primary distinction between exotoxins and endotoxins?

•          Exotoxins are secreted by living bacteria, while endotoxins are components of the bacterial cell wall released upon cell death

•          Endotoxins are secreted proteins, while exotoxins are part of the cell membrane

•          There is no meaningful distinction

•          Exotoxins only affect plants

Explanation: Exotoxins are proteins actively secreted by living bacteria, often highly potent and specific in their targets, whereas endotoxins are lipopolysaccharide components of Gram-negative bacterial cell walls that are released when the cell lyses or dies.

Question 23: Biofilms are communities of microorganisms that adhere to surfaces and are encased in a protective matrix.

•          True

•          False

Explanation: Biofilms form when microorganisms attach to a surface and secrete a protective extracellular matrix, allowing them to resist environmental stresses, antibiotics, and immune defenses more effectively than free-floating cells.

Question 24: Which type of microscope uses electron beams rather than light to achieve much higher magnification?

•          Compound light microscope

•          Electron microscope

•          Stereo microscope

•          Phase-contrast microscope

Explanation: Electron microscopes use focused beams of electrons instead of visible light, achieving far greater resolution and magnification than light microscopes, making them essential for visualizing viruses and fine cellular structures.

Question 25: Which term describes an organism that lives on or inside another organism and benefits at that host's expense?

•          Commensal

•          Parasite

•          Mutualist

•          Saprophyte

Explanation: A parasite obtains nutrients or other benefits from a host organism while causing harm to it, as exemplified by protozoan parasites such as Plasmodium, which causes malaria.