Chapter 3 with our Microbiology MCQs and explanations! Test your knowledge and understanding of key concepts with our complete set of multiple choice questions with detailed explanations for each answer. Increase your confidence and understanding of the fascinating world of microorganisms!
Microbiology MCQs 101 to 150
Anaphylaxia was first observed by?
- a) Portier & Richet
- b) Gell
- c) Coombs
- d) None of these
Explanation:
Anaphylaxis was first discovered and named by Charles Richet and Paul Portier in 1902 during their research on the toxins of sea anemones. Richet received the Nobel Prize in 1913 for this work.
Why other options are incorrect:
Why other options are incorrect:
- • Gell & Coombs: These two scientists (Philip Gell and Robin Coombs) are famous for creating the classification system for hypersensitivity reactions in 1963, but they did not first observe anaphylaxis.
- • None of these: This is incorrect because the discovery is historically documented and attributed to Portier and Richet.
E.coli was first isolated by?
- a) Louis Pasteur
- b) Shiga
- c) Robert Koch
- d) Escherich
Explanation:
Theodor Escherich isolated E. coli (originally named Bacterium coli commune) in 1885 from the feces of healthy infants. The genus was later renamed Escherichia in his honor.
Why other options are incorrect:
Why other options are incorrect:
- • Louis Pasteur: Famous for the principles of vaccination, microbial fermentation, and pasteurization, but did not isolate E. coli.
- • Shiga: Kiyoshi Shiga is credited with the discovery of Shigella dysenteriae, the cause of bacterial dysentery.
- • Robert Koch: Known for identifying the specific causative agents of tuberculosis, cholera, and anthrax.
The functions of plasmid are?
- a) Cell wall synthesis
- b) Protein synthesis
- c) DNA replication
- d) None of the above
Explanation:
Plasmids are extrachromosomal DNA molecules that usually carry accessory genes (such as antibiotic resistance, toxin production, or fertility factors). They are not responsible for the cell’s primary “housekeeping” functions.
Why other options are incorrect:
Why other options are incorrect:
- • Cell wall synthesis: This is governed by chromosomal genes and enzymatic processes in the cytoplasm and membrane.
- • Protein synthesis: This is the primary function of ribosomes and the translation of mRNA derived from chromosomal DNA.
- • DNA replication: While plasmids replicate themselves, the primary DNA replication of the bacterial genome is a function of the chromosomal machinery, not the plasmid.
Enhancement of virulence is known as?
- a) Exaltation
- b) Attenuation
- c) Both Exaltation and Attenuation
- d) None of these
Explanation:
Exaltation is the process of increasing the virulence (the degree of pathogenicity) of a microorganism, often achieved by repeatedly passing the pathogen through a susceptible host.
Why other options are incorrect:
Why other options are incorrect:
- • Attenuation: This is the exact opposite of exaltation. It refers to the process of weakening or reducing the virulence of a pathogen (commonly used to create live-attenuated vaccines).
- • Both Exaltation and Attenuation: These terms describe opposite effects on virulence, so they cannot both mean “enhancement.”
- • None of these: This is incorrect because Exaltation is the standard microbiological term for this process.
What disease the Nesser will produce? (Identifying Microbes by Action)
- a) Toxigenic microbes
- b) Lipolytic organisms
- c) Saccharolytic microbes
- d) Proteolytic organisms
Explanation:
This question refers to the classification of microbes based on their biochemical activity. Proteolytic organisms are those that decompose proteins, often leading to putrefaction and the production of foul-smelling compounds.
Definitions of classifications:
Definitions of classifications:
- • Proteolytic: Microbes that break down proteins into amino acids (e.g., Clostridium).
- • Saccharolytic: Microbes that break down complex carbohydrates or sugars.
- • Lipolytic: Microbes that break down lipids (fats).
- • Toxigenic: Microbes that produce specific toxins (exotoxins or endotoxins) that cause disease symptoms.
If a person can be infected by direct contact with infected tissue of another person, it is termed as?
- a) Direct contact transmission
- b) Indirect contact transmission
- c) Attachment
- d) None of these
Explanation:
Direct contact transmission occurs when there is physical contact between an infected person and a susceptible person. This includes touching, kissing, sexual contact, or contact with infected oral secretions and body lesions.
Why other options are incorrect:
Why other options are incorrect:
- • Indirect contact transmission: This occurs when a person is infected via a contaminated intermediary object (fomite), such as a doorknob, medical instrument, or clothing.
- • Attachment: This refers to the specific stage where a pathogen adheres to host cells using surface molecules (adhesins); it is a mechanism of infection, not a mode of transmission.
- • None of these: This is incorrect as “Direct contact transmission” accurately describes the scenario provided.
Phagocytic theory was proposed by?
- a) Elie Metchnikoff
- b) Behring
- c) Louis Pasteur
- d) Widal
Explanation:
The Phagocytic theory was proposed by Elie Metchnikoff in the 1880s. He discovered that certain white blood cells (phagocytes) could engulf and destroy invading microorganisms, establishing the basis for cellular immunity. He was awarded the Nobel Prize in 1908 for this work.
Why other options are incorrect:
Why other options are incorrect:
- • Behring: Emil von Behring is known as the “father of humoral immunity” for his work on antitoxins (antibodies) rather than cellular phagocytosis.
- • Louis Pasteur: While he developed the germ theory and several vaccines, he did not discover the mechanism of phagocytosis.
- • Widal: Georges-Fernand Widal is famous for developing the “Widal test,” a serological test used to diagnose typhoid fever.
The apparatus used to maintain a continuous culture?
- a) Autostat
- b) Chemostat
- c) Thermostat
- d) Both Chemostat and Thermostat
Explanation:
A Chemostat is a bioreactor to which fresh medium is continuously added, while culture liquid containing metabolic end products and microorganisms are continuously removed at the same rate. This keeps the culture volume constant and the microorganisms in a steady state of exponential growth.
Why other options are incorrect:
Why other options are incorrect:
- • Thermostat: This is a device used to maintain a constant temperature, not to manage the flow of nutrients or the growth of a culture.
- • Autostat: This is not a standard term used in microbiology for continuous culture systems (the term “Auxostat” exists, which controls the flow based on pH or other parameters, but Chemostat is the primary answer).
- • Both Chemostat and Thermostat: Incorrect because a thermostat only regulates heat, while a chemostat specifically manages the continuous replenishment of media.
Diphtheria is caused by?
- a) Staphylococcus
- b) Streptococcus
- c) Corynebacterium
- d) None of these
Explanation:
Diphtheria is a serious infection caused by strains of bacteria called Corynebacterium diphtheriae that make toxin. It typically causes a thick gray coating in the nose or throat, along with fever and swollen glands.
Why other options are incorrect:
Why other options are incorrect:
- • Staphylococcus: These bacteria are common causes of skin infections (like boils), pneumonia, and food poisoning, but not diphtheria.
- • Streptococcus: While some species cause “Strep throat” or scarlet fever, they do not produce the specific diphtheria toxin.
- • None of these: This is incorrect because Corynebacterium is the well-established causative agent.
Arthus reaction was discovered by?
- a) Richet
- b) Von Perquit
- c) Porter
- d) Marrice Arthus
Explanation:
The Arthus reaction was named after Maurice Arthus, who discovered it in 1903. It is a local type III hypersensitivity reaction that occurs when an antigen is injected into the skin of an individual who already has high levels of circulating antibody (IgG) against that antigen.
Why other options are incorrect:
Why other options are incorrect:
- • Richet & Porter: Charles Richet and Paul Portier are famous for their discovery of systemic anaphylaxis (Type I hypersensitivity), not the localized Arthus reaction.
- • Von Perquit (Pirquet): Clemens von Pirquet was a pediatrician who coined the term “allergy” and discovered serum sickness.
Primary mediators in anaphylaxis?
- a) Serotonin
- b) Histamine
- c) Heparin
- d) All of these
Explanation:
Primary mediators are substances stored in the granules of mast cells and basophils that are released immediately during degranulation in a Type I hypersensitivity (anaphylactic) reaction. Histamine, Serotonin, and Heparin are all key components released during this process.
Roles of these mediators:
Roles of these mediators:
- • Histamine: Causes vasodilation, increased capillary permeability, and smooth muscle contraction.
- • Serotonin: Similar to histamine, it increases vascular permeability and causes smooth muscle contraction (particularly significant in certain animal species).
- • Heparin: An anticoagulant that helps maintain the fluidity of the blood and may modulate the activity of other mediators.
In most of purple bacteria, the light harvesting centers are?
- a) B 850 & Fe-S
- b) B 845 & B 875
- c) B 850 & B 830
- d) B 850 & B 875
Explanation:
Purple photosynthetic bacteria typically possess two types of light-harvesting complexes: LH1 (B875) and LH2 (B800-850). These complexes contain bacteriochlorophyll molecules that absorb light at specific wavelengths (850nm and 875nm) and channel the energy toward the reaction center.
Key Details:
Key Details:
- • B 875 (LH1): This complex surrounds the reaction center directly and is found in all purple bacteria.
- • B 850 (LH2): This is a peripheral complex that captures light and transfers the energy to LH1.
- • Fe-S: Iron-sulfur centers are involved in electron transport chains but are not the primary light-harvesting pigment complexes.
Staphylococcus aureus was isolated by?
- a) Passet
- b) Louis Pasteur
- c) Rosenbach
- d) Sir Alexander Ogston
Explanation:
Sir Alexander Ogston, a Scottish surgeon, discovered and isolated Staphylococcus in 1880 from pus in surgical abscesses. He also coined the name “Staphylococcus” (from the Greek ‘staphyle’ meaning a bunch of grapes).
Why other options are incorrect:
Why other options are incorrect:
- • Rosenbach: Friedrich Julius Rosenbach later differentiated the genus into two species based on the color of their colonies: S. aureus (gold) and S. albus (white).
- • Passet: In 1885, Passet isolated Staphylococcus citreus, which produces lemon-yellow colonies.
- • Louis Pasteur: While he studied many bacteria and fermentation, he is not the primary figure credited with the specific isolation of S. aureus.
T. pallidum was discovered by?
- a) Schaudinn and Hoffman
- c) Edward Jenner
- d) Louis Pasteur
Explanation:
Fritz Schaudinn (a zoologist) and Erich Hoffmann (a dermatologist) discovered Treponema pallidum, the causative agent of syphilis, in 1905. They identified the spiral-shaped bacteria (spirochetes) using a Giemsa stain.
Why other options are incorrect:
Why other options are incorrect:
- • Robert Koch: Famous for discovering the bacteria causing anthrax, cholera, and tuberculosis, but not syphilis.
- • Edward Jenner: Known as the “father of immunology” for developing the smallpox vaccine.
- • Louis Pasteur: Renowned for his work on pasteurization, fermentation, and the development of vaccines for rabies and anthrax.
The test used to detect the deamination of the amino acids by bacteria?
- a) Lactose test
- b) Proteolytic test
- c) Nessler’s reagent test
- d) Indole Test
Explanation:
Nessler’s reagent test is used to detect the presence of ammonia. During the process of deamination, bacteria remove the amino group ($NH_2$) from an amino acid, which is then released as ammonia ($NH_3$). Nessler’s reagent reacts with this ammonia to produce a yellow-to-brown color change.
Why other options are incorrect:
Why other options are incorrect:
- • Lactose test: This measures the ability of an organism to ferment lactose (a sugar) into acid and gas, not amino acid deamination.
- • Proteolytic test: This is a general term for tests that observe the breakdown of proteins (like gelatin or casein) into smaller peptides, but it isn’t the specific chemical test for deamination products.
- • Indole Test: While this involves the breakdown of the amino acid tryptophan, it specifically detects the production of “indole” rather than general deamination.
In Streptococcus fecalis, the conjugation takes place at?
- a) Pili
- b) Cell wall
- c) Flagella
- d) Cell membrane
Explanation:
In Streptococcus faecalis (now Enterococcus faecalis), which is a Gram-positive bacterium, conjugation does not involve sex pili. Instead, it involves the production of “aggregation substances” on the cell wall in response to sex pheromones. This causes the cells to adhere to one another so DNA can be transferred.
Why other options are incorrect:
Why other options are incorrect:
- • Pili: While sex pili are essential for conjugation in Gram-negative bacteria (like E. coli), Gram-positive bacteria like S. fecalis generally lack these structures for gene transfer.
- • Flagella: These are hair-like appendages used primarily for motility (movement), not for the exchange of genetic material.
- • Cell membrane: While the DNA eventually passes through the membranes, the actual site of attachment and the mechanism that facilitates conjugation is located on the surface of the cell wall.
Protein particles which can infect are called?
- a) Prions
- b) Virons
- c) Nucleoida
- d) None of these
Explanation:
Prions (Proteinaceous Infectious Particles) are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein. They are unique because they do not contain any nucleic acids (DNA or RNA) and cause fatal neurodegenerative diseases like Mad Cow Disease and Creutzfeldt-Jakob disease.
Why other options are incorrect:
Why other options are incorrect:
- • Virons (Virions): These are complete, infectious virus particles that consist of an outer protein shell (capsid) and an inner core of nucleic acid (DNA or RNA).
- • Nucleoida (Nucleoids): This is the region within a prokaryotic cell (like bacteria) where the genetic material is concentrated; it is not an infectious particle.
- • None of these: This is incorrect as “Prions” is the specific term for infectious protein particles.
Mycobacterium tuberculosis was first discovered by?
- a) Louis Pasteur
- b) Edward Jenner
- c) Robert Koch
- d) None of these
Explanation:
Robert Koch discovered Mycobacterium tuberculosis, the bacterium that causes tuberculosis (TB), in 1882. For this discovery, and his work on TB, he received the Nobel Prize in Physiology or Medicine in 1905.
Why other options are incorrect:
Why other options are incorrect:
- • Louis Pasteur: While he proved the germ theory of disease and created the rabies vaccine, he did not isolate the TB bacillus.
- • Edward Jenner: He is known for developing the first successful vaccine (for smallpox) in 1796, nearly a century before the discovery of the TB bacterium.
- • None of these: This is incorrect because Robert Koch is the historically recognized scientist for this achievement.
Treponema pallidum was discovered by?
- a) Louis Pasteur
- b) Laennec
- c) Burgey
- d) Schaudinn and Hoffman
Explanation:
Fritz Schaudinn and Erich Hoffmann discovered Treponema pallidum, the causative agent of syphilis, in 1905. They identified the thin, corkscrew-shaped spirochete using specialized staining techniques.
Why other options are incorrect:
Why other options are incorrect:
- • Louis Pasteur: Famous for germ theory and rabies/anthrax vaccines, but he did not discover the cause of syphilis.
- • Laennec: René Laennec was the French physician who invented the stethoscope.
- • Burgey: David Hendricks Bergey is best known for “Bergey’s Manual of Determinative Bacteriology,” a primary resource for bacterial classification.
Which one of the following was Gram-negative, chemolithotrophic bacteria?
- a) Mycoplasms
- b) E.coli
- c) Spirellum
- d) Siderococcus
Explanation:
Siderococcus is an iron-oxidizing bacterium. It is classified as a chemolithotroph because it obtains energy by oxidizing inorganic substances (in this case, ferrous iron). Most iron-oxidizing bacteria of this type are Gram-negative.
Why other options are incorrect:
Why other options are incorrect:
- • Mycoplasms: These are unique bacteria that lack a cell wall entirely and are chemoorganotrophs (obtaining energy from organic compounds).
- • E.coli: While it is Gram-negative, it is a chemoorganotroph, as it uses organic compounds like glucose for energy and carbon.
- • Spirellum (Spirillum): These are Gram-negative, motile bacteria, but they are generally chemoorganotrophic, not lithotrophic.
The etiologic agent of botulism is a?
- a) Neurotoxin
- b) Enterotoxin
- c) Endotoxin
- d) All of the above
Explanation:
The bacterium Clostridium botulinum produces a potent neurotoxin. This toxin blocks the release of the neurotransmitter acetylcholine from nerve endings at the neuromuscular junction, leading to flaccid paralysis.
Why other options are incorrect:
Why other options are incorrect:
- • Enterotoxin: These are toxins that specifically affect the gastrointestinal tract (causing vomiting/diarrhea). While botulism is often foodborne, the toxin’s action is on the nervous system, not the intestinal lining.
- • Endotoxin: Endotoxins are lipopolysaccharides found in the outer membrane of Gram-negative bacteria. C. botulinum is a Gram-positive bacterium and produces an exotoxin.
Neisseria gonorrhoeae was first described by?
- a) Neisser in 1879
- b) Pasteur in 1878
- c) Robert Koch
- d) None of these
Explanation:
Albert Neisser discovered and described the causative agent of gonorrhea (Neisseria gonorrhoeae) in 1879. He identified the characteristic “diplococcus” (bacteria occurring in pairs) in pus samples from patients. The genus Neisseria was later named in his honor.
Why other options are incorrect:
Why other options are incorrect:
- • Pasteur in 1878: While Louis Pasteur was active during this time proving the germ theory, he was primarily working on fowl cholera and anthrax, not gonorrhea.
- • Robert Koch: Koch was famous for his postulates and the discovery of the TB and Cholera bacilli, but he was not the one who first described the Gonococcus.
- • None of these: This is incorrect because Neisser’s discovery is the established historical fact.
Cold like symptoms are caused by which bacteria?
- a) Haemophilus influenza
- b) Haemophilus streptococcus
- c) Pseudomonas
- d) E.coli
Explanation:
Haemophilus influenzae was originally (and incorrectly) thought to cause the flu. While the common cold is usually viral, H. influenzae is a major bacterial cause of respiratory infections, including sinusitis and bronchitis, which present with cold-like symptoms such as a runny nose, cough, and congestion.
Why other options are incorrect:
Why other options are incorrect:
- • Haemophilus streptococcus: This is not a scientifically valid species name; it appears to be a combination of two different genera (Haemophilus and Streptococcus).
- • Pseudomonas: While it can cause lung infections (especially in cystic fibrosis patients), it is not a common cause of typical cold-like symptoms in healthy individuals.
- • E.coli: This bacterium is primarily associated with urinary tract infections (UTIs) and gastrointestinal illnesses (diarrhea), not respiratory “cold” symptoms.
Disease that effects many people at different countries is termed as?
- a) Endemic
- b) Pandemic
- c) Epidemic
- d) Sporadic
Explanation:
A Pandemic is an epidemic that has spread over several countries or continents, usually affecting a large number of people. It represents the highest level of disease spread in terms of geography and population.
Terminology Definitions:
Terminology Definitions:
- • Endemic: A disease that is consistently present in a specific population or region (e.g., the common cold).
- • Epidemic: A sudden increase in the number of cases of a disease above what is normally expected in a specific area.
- • Sporadic: A disease that occurs infrequently and irregularly without a consistent pattern.
The infected mad dogs may contain?
- a) Niagri bodies
- b) Negri bodies
- c) Neisser bodies
- d) Nergi bodies
Explanation:
Negri bodies are eosinophilic, intracytoplasmic inclusion bodies found in the nerve cells (neurons) of animals or humans infected with the Rabies virus. They are specifically found in the cytoplasm of neurons in the brain, such as the Purkinje cells of the cerebellum.
Key Details:
Key Details:
- • Discovery: They were discovered by the Italian pathologist Adelchi Negri in 1903.
- • Diagnostic Value: Historically, the presence of these bodies was the primary way to confirm a rabies diagnosis during a post-mortem examination.
- • Distractors: Options like “Niagri,” “Nergi,” and “Neisser” are either misspellings or refer to different scientists (like Albert Neisser) and are not associated with rabies pathology.
The bacterium that is most commonly used in genetic engineering is?
- a) Klebsiella
- b) Escherichia
- c) Serratia
- d) Proteus
Explanation:
Escherichia coli (E. coli) is the most widely used host organism in genetic engineering because it is easy to grow, its genome is well-understood, and it can easily take up foreign DNA (plasmids).
Why other options are incorrect:
Why other options are incorrect:
- • Klebsiella: While used in specific industrial and nitrogen-fixation research, it is not the standard model organism for general cloning.
- • Serratia: Known for producing a red pigment, it is used in certain biological studies but lacks the extensive genetic toolkits available for E. coli.
- • Proteus: Mostly known for its “swarming” motility and clinical significance in UTIs, rather than being a tool for routine genetic manipulation.
Endotoxin produced by gram-negative bacteria is present in?
- a) Lipopolysaccharide
- b) Teichoic acid
- c) Peptidoglycan
- d) Inner membrane
Explanation:
Endotoxins are specifically part of the Lipopolysaccharide (LPS) complex located in the outer membrane of Gram-negative bacteria. The toxic component of LPS is specifically known as Lipid A.
Why other options are incorrect:
Why other options are incorrect:
- • Teichoic acid: These are found in the cell walls of Gram-positive bacteria, not Gram-negative bacteria.
- • Peptidoglycan: This is a structural layer found in both Gram-positive and Gram-negative bacteria, but it does not function as an endotoxin.
- • Inner membrane: While Gram-negative bacteria have an inner membrane, the endotoxin (LPS) is uniquely located on the outer leaflet of the outer membrane.
The most important virulence factors are?
- a) Adhesins
- b) Invasiveness
- c) Enzymes
- d) Toxigenicity
- e) All of the above
Explanation:
Virulence factors are the molecules produced by bacteria, viruses, fungi, and protozoa that add to their effectiveness and enable them to colonize a host. Since colonization, entry, and damage are all parts of pathogenesis, all the listed factors are essential.
Breakdown of Factors:
Breakdown of Factors:
- • Adhesins: Allow the pathogen to attach to host cells/tissues to avoid being washed away.
- • Invasiveness: The ability of a pathogen to enter into host cells or spread through the body.
- • Enzymes: Many bacteria secrete enzymes (like hyaluronidase or collagenase) that break down host tissue.
- • Toxigenicity: The capacity to produce toxins (exotoxins or endotoxins) that cause systemic or localized damage to the host.
The lethal dose required to kill 50% of the lab animals tested under standard conditions is called?
- a) ID50
- b) LD50
- c) MLD
- d) ID
Explanation:
LD50 (Lethal Dose, 50%) is a standardized measure used in toxicology to determine the virulence or toxicity of a substance. It represents the specific dose required to kill half the members of a tested population after a specified test duration.
Why other options are incorrect:
Why other options are incorrect:
- • ID50: This stands for Infectious Dose 50%, which is the dose required to cause an infection (but not necessarily death) in 50% of the test subjects.
- • MLD: This stands for Minimum Lethal Dose. It is the smallest dose observed to kill an individual experimental animal, but it is not a statistical measure like the LD50.
- • ID: This is a generic abbreviation for Infectious Dose and does not specify a quantitative percentage of the population.
The transfer of genetic material during transformation is proved basing on Griffith’s experiment by?
- a) Zinder & Lederberg
- b) Watson & Crick
- c) Avery Macleod & Mc.Carthy
- d) Lederberg & Tatum
Explanation:
While Frederick Griffith discovered the “transforming principle” in 1928, it was Oswald Avery, Colin MacLeod, and Maclyn McCarty in 1944 who provided the definitive proof that DNA was the chemical substance causing the transformation.
Why other options are incorrect:
Why other options are incorrect:
- • Zinder & Lederberg: They are famous for discovering transduction (the transfer of bacterial DNA via viruses/bacteriophages).
- • Watson & Crick: They are credited with discovering the double-helix structure of DNA in 1953, not the mechanism of transformation.
- • Lederberg & Tatum: They discovered conjugation, which is the transfer of genetic material through direct cell-to-cell contact.
If the vectors transmit the infection mechanically they are called?
- a) Mechanical vectors
- b) Biological reservoir
- c) Biological vectors
- d) Both Biological vectors and Biological reservoir
Explanation:
Mechanical vectors transport pathogens from one host to another without being infected themselves. The pathogen does not undergo any part of its life cycle or multiplication inside the vector’s body (e.g., a housefly carrying bacteria on its legs from waste to food).
Why other options are incorrect:
Why other options are incorrect:
- • Biological reservoir: A reservoir is the natural habitat (human, animal, or environment) where an infectious agent normally lives and multiplies. It is not the mode of transmission itself.
- • Biological vectors: In these vectors, the pathogen must complete part of its life cycle or multiply within the vector’s body before becoming infective (e.g., the Malaria parasite in a mosquito).
- • Option d: Since mechanical transmission is distinct from biological processes and reservoirs, this combination is incorrect.
Mycorrhiza was first observed by?
- a) Frank
- b) Crick
- c) Fisher
- d) Funk
Explanation:
The term Mycorrhiza (meaning “fungus-root”) was first introduced and described by the German botanist Albert Bernhard Frank in 1885. He observed the symbiotic relationship between fungal mycelia and the roots of trees.
Why other options are incorrect:
Why other options are incorrect:
- • Crick: Francis Crick is famous for his work on the double-helix structure of DNA, not plant-fungal symbiosis.
- • Fisher: Ronald Fisher was a statistician and evolutionary biologist known as the father of modern statistics.
- • Funk: Casimir Funk was a biochemist who is credited with first formulating the concept of vitamins in 1912.
Which of the following genera is most likely to contain organisms capable of surviving high temperature?
- a) Torula
- b) Coxiella
- c) Vibrio
- d) Pseudomonas
Explanation:
Coxiella (specifically Coxiella burnetii, the agent of Q fever) is highly resistant to environmental stresses, including high temperatures. It forms spore-like structures that allow it to survive pasteurization, which is why milk pasteurization temperatures are specifically calculated to ensure its destruction.
Why other options are incorrect:
Why other options are incorrect:
- • Torula: This is a genus of yeasts which are generally sensitive to heat and are easily killed at temperatures well below boiling.
- • Vibrio: These are typically aquatic bacteria that prefer moderate temperatures; they are quite sensitive to heat and drying.
- • Pseudomonas: While these bacteria are very hardy and can grow in diverse environments (some even in refrigerators), they do not produce spores and are easily killed by high heat.
Mycobacterium leprae was discovered by?
- a) Hansen
- b) Edward Jenner
- c) Louis Pasteur
- d) Robert Koch
Explanation:
Gerhard Armauer Hansen, a Norwegian physician, discovered Mycobacterium leprae in 1873. It was the first bacterium to be identified as a causative agent of a human disease (Leprosy), which is why Leprosy is also known as “Hansen’s Disease.”
Why other options are incorrect:
Why other options are incorrect:
- • Edward Jenner: Known as the father of immunology, he developed the first vaccine (for smallpox).
- • Louis Pasteur: Famous for the germ theory of disease, pasteurization, and vaccines for rabies and anthrax.
- • Robert Koch: Discovered the causative agents of tuberculosis (M. tuberculosis) and cholera (V. cholerae), and formulated Koch’s postulates.
Streptococcus pneumoniae was isolated by?
- a) Louis Pasteur
- b) Edward Jenner
- c) Robert Koch
- d) Antony von Leeuwenhoek
Explanation:
Louis Pasteur independently isolated Streptococcus pneumoniae (alongside George Sternberg) in 1881. He isolated the bacterium from the saliva of a child suffering from rabies, though it was later identified as the primary cause of bacterial pneumonia.
Why other options are incorrect:
Why other options are incorrect:
- • Edward Jenner: He is famous for developing the smallpox vaccine in the late 18th century, long before the isolation of specific bacteria like Pneumococcus.
- • Robert Koch: While a giant in microbiology, Koch is best known for isolating the bacteria that cause anthrax, cholera, and tuberculosis.
- • Antony von Leeuwenhoek: Known as the “Father of Microbiology,” he was the first to observe “animalcules” (microorganisms) using his handcrafted microscopes, but he did not isolate specific pathogenic species in a laboratory sense.
Fluorescent substances used in fluorescent microscopy are?
- a) Quinine sulphate
- b) Auramine
- c) None of these
- d) All of these
Explanation:
Fluorescent substances (fluorochromes) absorb light at one wavelength and emit it at another. Both Quinine sulphate and Auramine are known for their fluorescent properties. Auramine (specifically Auramine O) is widely used in microbiology to stain acid-fast bacteria like M. tuberculosis.
Details on the substances:
Details on the substances:
- • Quinine sulphate: One of the earliest observed fluorescent substances; it is often used as a standard for measuring fluorescence quantum yield.
- • Auramine: A common fluorochrome used in the Auramine-Rhodamine stain to detect organisms that have waxy cell walls.
- • Note: Other common fluorochromes include Fluorescein isothiocyanate (FITC) and Acridine Orange.
The major role of minor elements inside living organisms is to act as?
- a) Constituents of hormones
- b) Co-factors of enzymes
- c) Binder of cell structure
- d) Building blocks of important amino acids
Explanation:
Minor elements (also known as trace elements like Zinc, Copper, Manganese, and Molybdenum) primarily function as co-factors for enzymes. They are essential for the catalytic activity of many enzymes, either by helping to fold the enzyme into its active shape or by participating directly in the chemical reaction.
Why other options are incorrect:
Why other options are incorrect:
- • Constituents of hormones: While some elements (like Iodine) are parts of specific hormones, this is a specialized role rather than the major role for most minor elements.
- • Binder of cell structure: Structural integrity is usually maintained by macro-elements (like Calcium in bones or cell walls) and organic polymers.
- • Building blocks of amino acids: Amino acids are primarily composed of major elements: Carbon, Hydrogen, Oxygen, Nitrogen, and sometimes Sulfur.
Pseudomonas aeruginosa was first named/described by?
- a) Edward Jenner
- b) Schroeter and Gessard
- c) Louis Pasteur
- d) Robert Koch
Explanation:
The bacterium was first discovered by Carle Gessard in 1882, who identified it by the blue-green pigment it produced (pyocyanin). The genus Pseudomonas was characterized by Schroeter.
Why other options are incorrect:
Why other options are incorrect:
- • Edward Jenner: Focused on immunology and the smallpox vaccine.
- • Louis Pasteur: Primarily known for his work on fermentation, pasteurization, and vaccines for rabies and anthrax.
- • Robert Koch: Famous for his work on B. anthracis, M. tuberculosis, and V. cholerae, but not specifically the naming of P. aeruginosa.
The ability of a pathogen to spread in the host tissues after establishing the infection is known as?
- a) Adhesion
- b) Toxigenicity
- c) Invasiveness
- d) None of these
Explanation:
Invasiveness is the ability of a microorganism to overcome host defense mechanisms, enter the body, and spread through various tissues. It often involves the production of enzymes (like hyaluronidase) that break down tissue barriers.
Why other options are incorrect:
Why other options are incorrect:
- • Adhesion: This refers to the initial step of infection where the pathogen attaches or “sticks” to the host cell surface using pili or fimbriae.
- • Toxigenicity: This is the capacity of a pathogen to produce toxins (chemical substances) that damage host cells or disrupt physiological processes.
- • None of these: This is incorrect because “Invasiveness” is the standard scientific term for the ability to spread through tissues.
Reduction of virulence is known as?
- a) Attenuation
- b) Exaltation
- c) Both Exaltation and Attenuation
- d) None of these
Explanation:
Attenuation is the process of reducing the virulence or pathogenicity of a microorganism (like a bacterium or virus) while keeping it viable (alive). This is a fundamental technique used in the development of “live-attenuated” vaccines.
Why other options are incorrect:
Why other options are incorrect:
- • Exaltation: This is the exact opposite of attenuation. It refers to the increase in virulence of a pathogen, often achieved through repeated passage in a susceptible host.
- • Both: This is incorrect because the two terms describe opposite biological processes.
- • None of these: This is incorrect because “Attenuation” is the standard scientific term for this process.
Mycoplasmas are bacterial cells that?
- a) Are resistant to penicillin
- b) Stain well with Gram’s stain
- c) Have a rigid cell wall
- d) Fail to reproduce on artificial media
Explanation:
Mycoplasmas are unique because they naturally lack a cell wall. Since Penicillin and other beta-lactam antibiotics work by inhibiting cell wall synthesis (specifically peptidoglycan), Mycoplasmas are inherently resistant to them.
Why other options are incorrect:
Why other options are incorrect:
- • Stain well with Gram’s stain: Gram staining relies on the presence of a thick or thin peptidoglycan cell wall. Because Mycoplasmas lack this wall, they do not stain well or consistently with the Gram method.
- • Have a rigid cell wall: This is factually incorrect; Mycoplasmas are pleomorphic (they can change shape) precisely because they lack a rigid cell wall.
- • Fail to reproduce on artificial media: While they are “fastidious” (meaning they need complex nutrients like sterols), most Mycoplasmas can be grown on specialized artificial media, typically forming “fried egg” shaped colonies.
Rh factor of the blood was discovered by scientist?
- a) Landsteiner and Weiner
- b) Moss
- c) Janskey
- d) Louis Pasteur
- e) None of these
Explanation:
The Rh (Rhesus) factor was discovered in 1937/1940 by Karl Landsteiner and Alexander S. Wiener. They identified this antigen while experimenting with the blood of Rhesus monkeys and later found it to be a crucial factor in human blood transfusions and pregnancy.
Why other options are incorrect:
Why other options are incorrect:
- • Moss and Janskey: Both William Moss and Jan Janský are known for their early, independent classification systems for the primary ABO blood groups, but not the Rh factor.
- • Louis Pasteur: A pioneer in microbiology and immunology, known for pasteurization and vaccines, but he was not involved in blood group research.
The bacterial cells are at their metabolic peak during?
- a) Lag phase
- b) Decline
- c) Log
- d) Stationary
Explanation:
The Log phase (also called the Exponential phase) is the period when bacterial cells are dividing most rapidly. During this phase, metabolic activity is at its maximum as the cells are actively synthesizing new DNA, RNA, proteins, and cell wall components.
Why other options are incorrect:
Why other options are incorrect:
- • Lag phase: This is a period of adaptation. While cells are metabolically active (making enzymes), they are not yet dividing at their maximum rate.
- • Stationary phase: Growth slows down as nutrients are depleted and waste products accumulate. The rate of cell death equals the rate of new cell production.
- • Decline phase: Also known as the death phase, where the number of dying cells exceeds the number of new cells due to toxic conditions and lack of food.
Hybridoma technique was developed by?
- a) Niel’s Jerne
- b) Kochler & Milston
- c) All of Above
- d) None of these
Explanation:
The Hybridoma technique is used to produce monoclonal antibodies. It was pioneered in 1975 by Georges Köhler and César Milstein.
Breakdown of Contributors:
Breakdown of Contributors:
- • Köhler & Milstein: Performed the actual laboratory work of fusing B-cells with myeloma cells to create “immortal” antibody-producing cells.
- • Niels Jerne: Developed the “Natural Selection Theory” of antibody formation, which laid the conceptual foundation for understanding how specific antibodies are produced.
The electrons passed out from the specimen (emitted from the surface) are called?
- a) Secondary electrons
- b) Tertiary electrons
- c) Primary electrons
- d) None of these
Explanation:
In Scanning Electron Microscopy (SEM), Secondary electrons are those emitted from the atoms of the specimen after being excited by the primary electron beam. These low-energy electrons are primarily responsible for showing the morphology and topography of the sample.
Why other options are incorrect:
Why other options are incorrect:
- • Primary electrons: These are the high-energy electrons that originate from the electron gun and make up the initial beam that hits the specimen.
- • Tertiary electrons: This is not a standard term used to describe the basic imaging signals in electron microscopy.
- • Note: Another common signal is “Backscattered electrons,” which are primary electrons that are reflected back after hitting the sample.
The virulence of a pathogen is usually measured by?
- a) LD
- b) MLD
- c) ID
- d) All of the above
Explanation:
Virulence is the quantitative measure of the degree of pathogenicity. It is expressed as the number of microorganisms or micrograms of toxin necessary to kill or infect a host. Therefore, all these statistical measures are used to quantify it.
Breakdown of Measures:
Breakdown of Measures:
- • LD (Lethal Dose): Specifically LD50, the dose required to kill 50% of the test population.
- • MLD (Minimum Lethal Dose): The smallest dose that causes death in a specific experimental animal.
- • ID (Infectious Dose): Specifically ID50, the dose required to cause a detectable infection in 50% of the test population.
Serum sickness reaction was discovered by?
- a) Von Pirquet
- b) Richet
- c) Porter
- d) Maurice Arthus
Explanation:
Clemens von Pirquet (along with Béla Schick) first described serum sickness in 1905. They observed that patients receiving large amounts of horse serum (used for diphtheria antitoxin) developed fever, skin rashes, and joint pain. Von Pirquet also coined the term “allergy.”
Why other options are incorrect:
Why other options are incorrect:
- • Richet: Charles Richet is famous for discovering anaphylaxis, for which he received the Nobel Prize.
- • Porter: Rodney Porter is known for his work on the chemical structure of antibodies (IgG).
- • Maurice Arthus: He discovered the Arthus reaction, which is a localized Type III hypersensitivity reaction, whereas serum sickness is a systemic Type III reaction.
The mode of reproduction which occurs in mycoplasma is?
- a) Binary fusion
- b) Bursting
- c) Binary fission
- d) Budding
Explanation:
The primary mode of reproduction in Mycoplasma is Binary fission. Since they are prokaryotic organisms, they replicate their DNA and divide into two daughter cells, although their lack of a cell wall can sometimes make this process appear irregular compared to other bacteria.
Why other options are incorrect:
Why other options are incorrect:
- • Binary fusion: This is a common distractor term; “fusion” implies joining together, which is the opposite of reproduction (division).
- • Bursting: This is not a reproductive method; it usually refers to cell lysis (death), often seen when viruses exit a host cell.
- • Budding: While some species of Mycoplasma can occasionally show budding-like processes or fragmentation due to their pleomorphic nature, binary fission remains the fundamental reproductive mechanism.
B. anthracis was isolated by?
- a) Leeuwenhoek
- b) Robert Koch
- c) Louis Pasteur
- d) None of these
Explanation:
Robert Koch was the first to isolate Bacillus anthracis in pure culture in 1876. He demonstrated that the bacterium formed spores and proved, through his famous Koch’s Postulates, that it was the specific cause of Anthrax.
Why other options are incorrect:
Why other options are incorrect:
- • Leeuwenhoek: While he was the first to see bacteria under a microscope, he did not isolate or identify specific pathogenic species like B. anthracis.
- • Louis Pasteur: While Pasteur did significant work on Anthrax and developed the first vaccine for it, he was not the one who first isolated the bacterium in pure culture.
- • None of these: This is incorrect because Robert Koch is the established scientist credited with this milestone.
Which of the following enzymes acts as a spreading factor?
- a) DNase
- b) Hyaluronidase
- c) Catalase
- d) Coagulase
Explanation:
Hyaluronidase is known as the “spreading factor” because it hydrolyzes hyaluronic acid, a polysaccharide that binds cells together in the extracellular matrix. By breaking down this “intercellular cement,” the enzyme allows pathogens to spread more easily through host tissues.
Why other options are incorrect:
Why other options are incorrect:
- • DNase: This enzyme breaks down DNA. In an infection, it helps reduce the viscosity of pus (caused by dead host DNA), but it is not the primary “spreading factor.”
- • Catalase: This enzyme breaks down hydrogen peroxide into water and oxygen, protecting the bacterium from oxidative stress caused by white blood cells.
- • Coagulase: This enzyme actually does the opposite of a spreading factor; it causes fibrinogen to clot, which helps wall off the bacteria from the host’s immune system, localizing the infection.
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