Chapter 4 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 151 to 200
Parasitic form must contain?
- a) Endospores
- b) Flagella
- c) Capsule
- d) Cell-wall
Explanation:
The Capsule is a vital structure for many parasitic or pathogenic bacteria. It provides a protective layer that helps the organism evade the host’s immune system, specifically by preventing phagocytosis (being eaten by white blood cells).
Why other options are incorrect:
Why other options are incorrect:
- • Endospores: These are highly resistant, dormant structures meant for survival in extreme environments, not specifically for parasitism.
- • Flagella: These are organs of locomotion. While some parasites have them to move, they are not a “must-have” requirement for a parasitic lifestyle.
- • Cell-wall: Most bacteria (both free-living and parasitic) possess a cell wall; therefore, it is not a defining characteristic exclusive to the parasitic form.
Cytoplasmic streaming is present in?
- a) Prokaryotes
- b) Animals
- c) Eukaryotes
- d) Both Prokaryotes and Animals
Explanation:
Cytoplasmic streaming, also known as cyclosis, is the movement of the fluid substance (cytoplasm) within a cell. This process is a characteristic feature of Eukaryotic cells and is driven by the cytoskeleton.
Why other options are incorrect:
Why other options are incorrect:
- • Prokaryotes: These cells lack a complex cytoskeleton and membrane-bound organelles, so they do not exhibit organized cytoplasmic streaming.
- • Animals: While it does occur in animal cells, animal cells are a subset of Eukaryotes. The most scientifically accurate choice covering all such cells (plants, animals, fungi) is ‘Eukaryotes’.
- • Both Prokaryotes and Animals: This is incorrect because prokaryotes definitely do not show this movement.
Cytochromes are?
- a) ATP acceptors
- b) Oxygen acceptors
- c) Electron acceptors
- d) Protein acceptors
Explanation:
Cytochromes are redox-active proteins containing a heme group. They function as electron acceptors and donors (carriers) in the electron transport chain during cellular respiration and photosynthesis.
Why other options are incorrect:
Why other options are incorrect:
- • ATP acceptors: Cytochromes are involved in the process of creating the proton gradient for ATP synthesis, but they do not “accept” ATP.
- • Oxygen acceptors: While cytochromes pass electrons toward oxygen (specifically cytochrome c oxidase), oxygen itself is the final electron acceptor, not the cytochromes.
- • Protein acceptors: Cytochromes are proteins themselves; they interact with other proteins but their primary functional role is the transport of electrons.
Histones are found in?
- a) Eukaryotes
- b) Prokaryotes
- c) Viruses
- d) None of these
Explanation:
Histones are highly alkaline proteins found in eukaryotic cell nuclei. They package and order the DNA into structural units called nucleosomes, playing a critical role in gene regulation and DNA compaction.
Why other options are incorrect:
Why other options are incorrect:
- • Prokaryotes: Most prokaryotes (bacteria) do not have histones; they use other types of proteins, often called “histone-like” or nucleoid-associated proteins, to organize their DNA.
- • Viruses: Viruses package their genetic material within a protein shell called a capsid, but they generally do not utilize histones for DNA organization.
- • None of these: Since eukaryotes is the scientifically established answer for the presence of true histones, this option is incorrect.
Viral genome can become integrated into the bacterial genomes are known as?
- a) Metaphage
- b) Prophage
- c) Temperate phage
- d) Bacteriophage
Explanation:
A Prophage is the specific term for the viral DNA when it is integrated into the circular bacterial chromosome. During this stage, the viral genes are replicated along with the host DNA without destroying the cell.
Why other options are incorrect:
Why other options are incorrect:
- • Metaphage: This is not a standard biological term used to describe integrated viral genomes.
- • Temperate phage: This refers to the type of virus that is capable of undergoing the lysogenic cycle, but the integrated genome itself is called the prophage.
- • Bacteriophage: This is the general name for any virus that infects bacteria, regardless of whether it is integrated or currently in a lytic (infectious) phase.
Following Cocci are non-motile except?
- a) Rhodococcus agilis
- b) Staphylococcus
- c) Gonococcus
- d) Meningococcus
Explanation:
As a general rule, almost all cocci (spherical bacteria) are non-motile because they lack flagella. However, Rhodococcus agilis (also known as Planococcus agilis) is a rare exception that possesses flagella and is motile.
Why other options are incorrect:
Why other options are incorrect:
- • Staphylococcus: These are classic non-motile gram-positive cocci that grow in clusters.
- • Gonococcus: (Neisseria gonorrhoeae) is a non-motile gram-negative diplococcus.
- • Meningococcus: (Neisseria meningitidis) is also a non-motile gram-negative diplococcus.
Mesosomes are also known as?
- a) Chloroplasts
- b) Chondroids
- c) Mitochondria
- d) Golgi complex
Explanation:
Mesosomes are folded invaginations of the plasma membrane in bacteria. Historically, they were referred to as Chondroids because scientists believed they functioned similarly to mitochondria in eukaryotic cells (carrying out respiration and secretion).
Why other options are incorrect:
Why other options are incorrect:
- • Chloroplasts: These are membrane-bound organelles found in plants and algae for photosynthesis, which are absent in prokaryotes.
- • Mitochondria: While mesosomes are often compared to mitochondria due to respiratory enzymes, prokaryotes do not possess true membrane-bound mitochondria.
- • Golgi complex: This is an organelle involved in protein packaging and transport found only in eukaryotic cells.
Enterotoxin responsible for food poisoning is secreted by?
- a) Staphylococci
- b) Entamoeba histolytica
- c) Enterobacteriaceae
- d) Enterococci
Explanation:
Certain species of Staphylococci, most notably Staphylococcus aureus, secrete heat-stable enterotoxins into food. When ingested, these toxins act on the gastrointestinal tract, causing rapid-onset symptoms like vomiting and abdominal cramps.
Why other options are incorrect:
Why other options are incorrect:
- • Entamoeba histolytica: This is a protozoan parasite that causes amoebic dysentery through tissue invasion, not through the secretion of classical bacterial enterotoxins.
- • Enterobacteriaceae: While this family includes pathogens like E. coli and Salmonella, the specific “enterotoxin” food poisoning referred to in rapid-onset clinical cases is classically linked to Staphylococci.
- • Enterococci: These are bacteria usually found in the gut that can cause UTIs or endocarditis, but they are not the primary producers of the toxins responsible for common food poisoning.
Thickness of cell wall ranges from?
- a) 9-10 nm
- b) 10-25 nm
- c) 30-40 nm
- d) 12-13 nm
Explanation:
The thickness of the bacterial cell wall typically ranges from 10 to 25 nm. This thickness varies between Gram-positive bacteria (which have a thicker peptidoglycan layer, sometimes up to 80nm) and Gram-negative bacteria (which have a much thinner layer).
Why other options are incorrect:
Why other options are incorrect:
- • 9-10 nm: This range is generally considered too thin for a standard bacterial cell wall, though it may approximate the thickness of the plasma membrane alone.
- • 30-40 nm: While Gram-positive cell walls can be this thick, the standard range provided in most microbiology textbooks for a general “cell wall” question is 10-25 nm.
- • 12-13 nm: This is too narrow a range and does not account for the biological variation found across different bacterial species.
Cell wall of gram negative bacteria is?
- a) Teichoic acids are absent
- b) Thick
- c) Lipids are present
- d) None of these
Explanation:
One of the primary chemical differences between the two types of bacterial cell walls is that teichoic acids are absent in Gram-negative bacteria. Teichoic acids are polyalcohol phosphates found specifically in the thick peptidoglycan layer of Gram-positive bacteria.
Why other options are incorrect:
Why other options are incorrect:
- • Thick: Gram-negative cell walls are actually thin (8–12 nm) compared to the much thicker (20–80 nm) Gram-positive walls.
- • Lipids are present: While Gram-negative bacteria do have an outer membrane containing Lipopolysaccharides (LPS), the absence of teichoic acids is a more fundamental structural differentiator often used in comparative biology.
- • None of these: Since option (a) is a scientifically accurate defining characteristic of Gram-negative bacteria, this option is incorrect.
Bacterial capsule is chemically composed of?
- a) Polysaccharides
- b) Polypeptide
- c) Polypeptides or polysaccharides
- d) Polynucleotides
Explanation:
The bacterial capsule is a very large structure of many bacteria. Chemically, most capsules consist of polysaccharides (complex sugars), but in some species, they are made of polypeptides (such as the D-glutamic acid capsule of Bacillus anthracis).
Why other options are incorrect:
Why other options are incorrect:
- • Polysaccharides: While this is the most common material, choosing only this option ignores bacteria that have protein-based (polypeptide) capsules.
- • Polypeptide: This is only true for specific bacteria like Bacillus anthracis; it is not the universal composition.
- • Polynucleotides: These are nucleic acids (DNA and RNA) which carry genetic information and are not structural components of the external bacterial capsule.
Teichoic acids and Teichuronic acids are found in?
- a) Gram negative bacteria
- b) Gram positive bacteria
- c) Fungi
- d) None of these
Explanation:
Teichoic acids and teichuronic acids are water-soluble polymers found in the cell walls of Gram-positive bacteria. They are covalently linked to the thick peptidoglycan layer and play roles in cell wall elasticity, surface charge, and division.
Why other options are incorrect:
Why other options are incorrect:
- • Gram negative bacteria: These bacteria have a much thinner peptidoglycan layer and an outer membrane; they do not possess teichoic or teichuronic acids.
- • Fungi: Fungal cell walls are primarily composed of chitin, glucans, and glycoproteins, not the acidic phosphate polymers found in bacteria.
- • None of these: Since option (b) is the correct biological classification for these molecules, this option is incorrect.
The most infectious food borne disease is?
- a) Botulism
- b) Tetanus
- c) Gas gangrene
- d) Dysentery
Explanation:
Botulism is a severe and potentially fatal food-borne disease caused by a toxin produced by the bacterium Clostridium botulinum. It is often highlighted in microbiology as the most significant food-borne “intoxication” because the botulinum toxin is one of the most lethal substances known.
Why other options are incorrect:
Why other options are incorrect:
- • Tetanus: Caused by Clostridium tetani, this disease is usually contracted through deep puncture wounds or cuts, not through the ingestion of food.
- • Gas gangrene: Caused by Clostridium perfringens, this is primarily a necrotic infection of muscle tissue resulting from wound contamination, though the bacteria can cause a milder form of food poisoning.
- • Dysentery: While highly infectious and spread via contaminated food/water (e.g., Shigella), it is generally considered less lethal and “severe” in a clinical/toxicological context compared to Botulism.
In bacteria, pigment bearing structures are?
- a) Protoplast
- b) Chloroplast
- c) Chromatophores
- d) Sphaeroplast
Explanation:
In photosynthetic bacteria, pigments are located in internal membrane systems called Chromatophores. These are extensions of the plasma membrane that contain the necessary compounds for capturing light energy.
Why other options are incorrect:
Why other options are incorrect:
- • Protoplast: This refers to a bacterial cell that has had its cell wall entirely removed by enzymatic treatment; it is not a pigment structure.
- • Chloroplast: While these contain pigments, they are membrane-bound organelles found only in eukaryotic organisms like plants and algae. Bacteria lack these organelles.
- • Sphaeroplast: Similar to a protoplast, this is a bacterium with a partially removed cell wall, typically derived from Gram-negative bacteria.
Pigment bearing structure of bacteria are?
- a) Mitochondria
- b) Plasmids
- c) Mesosomes
- d) Chromophores
Explanation:
In photosynthetic bacteria, the light-harvesting pigments are located in specialized membrane-bound structures or regions known as Chromophores (or Chromatophores). Because bacteria lack chloroplasts, they use these membrane extensions to perform photosynthesis.
Why other options are incorrect:
Why other options are incorrect:
- • Mitochondria: These are eukaryotic organelles responsible for ATP production; bacteria do not possess mitochondria.
- • Plasmids: These are small, circular, extrachromosomal DNA molecules that carry accessory genes (like antibiotic resistance) but do not contain pigments.
- • Mesosomes: These are invaginations of the plasma membrane primarily involved in respiration, cell wall synthesis, and DNA replication, rather than pigment storage.
Rancidity of stored foods is due to the activity of?
- a) Proteolytic microbes
- b) Toxigenic microbes
- c) Lipolytic microbes
- d) Saccharolytic microbes
Explanation:
Rancidity is the spoilage of fats and oils. It is primarily caused by Lipolytic microbes, which produce lipase enzymes that break down lipids (fats) into free fatty acids and glycerol, resulting in unpleasant odors and flavors.
Why other options are incorrect:
Why other options are incorrect:
- • Proteolytic microbes: These break down proteins, a process known as putrefaction, which usually results in a “rotten” smell rather than oily rancidity.
- • Toxigenic microbes: These produce toxins that cause food poisoning (like botulism), but they may not necessarily change the physical appearance or smell of the food.
- • Saccharolytic microbes: These break down carbohydrates/sugars, usually leading to fermentation and the production of acids, gases, or alcohols.
The test used for detection of typhoid fever?
- a) ELISA
- b) Westernblotting
- c) WIDAL test
- d) Rosewaller test
Explanation:
The WIDAL test is a classic serological test used to diagnose enteric fever (typhoid and paratyphoid fever). It works by detecting agglutinating antibodies against the H (flagellar) and O (somatic) antigens of Salmonella typhi in a patient’s serum.
Why other options are incorrect:
Why other options are incorrect:
- • ELISA: (Enzyme-Linked Immunosorbent Assay) is a broad technique used to detect various antibodies or antigens, commonly used for HIV screening or pregnancy tests, but is not the specific “classic” test named for typhoid.
- • Westernblotting: This is a confirmatory test used to detect specific proteins, most famously used as the second-step confirmation for an HIV diagnosis.
- • Rosewaller test: This test (Rose-Waaler) is used to detect the Rheumatoid Factor (RF) in the blood, helping in the diagnosis of Rheumatoid Arthritis.
The viruses that attack bacteria are?
- a) Bacteriophages
- b) Various
- c) Bacterial viruses
- d) Bacterial pathogens
Explanation:
Viruses that specifically infect and replicate within bacteria are called Bacteriophages (often shortened to “phages”). They were discovered independently by Frederick Twort and Félix d’Hérelle.
Why other options are incorrect:
Why other options are incorrect:
- • Various: This is a vague term and not a scientific classification for a biological entity.
- • Bacterial viruses: While descriptively correct, “Bacteriophage” is the universally accepted scientific name for these viruses.
- • Bacterial pathogens: This term usually refers to the bacteria themselves that cause disease in humans, animals, or plants, rather than the viruses that kill bacteria.
Acridine dyes are more effective against?
- a) Gram negative
- b) Gram positive
- c) Rickettsia
- d) Mycoplasma
Explanation:
Acridine dyes (such as proflavine and acriflavine) are basic dyes that interfere with DNA synthesis. They are generally much more effective against Gram-positive bacteria because these bacteria lack the protective outer membrane found in Gram-negative species.
Why other options are incorrect:
Why other options are incorrect:
- • Gram negative: These bacteria have an outer lipopolysaccharide membrane that acts as a permeability barrier, making them more resistant to many dyes and antibiotics.
- • Rickettsia: These are obligate intracellular bacteria. Because they live inside host cells, they are not easily targeted by dyes in the same way free-living bacteria are.
- • Mycoplasma: These bacteria lack a cell wall entirely. While they are unique, acridine dyes are classically categorized by their differential effectiveness between Gram-positive and Gram-negative cell wall structures.
Bacillus is an example of?
- a) Virus
- b) Viroid
- c) Gram negative bacteria
- d) Gram positive bacteria
Explanation:
The genus Bacillus consists of rod-shaped, Gram-positive bacteria that are members of the phylum Bacillota. They are characterized by their ability to produce endospores under stressful environmental conditions.
Why other options are incorrect:
Why other options are incorrect:
- • Virus: Viruses are non-cellular infectious agents that require a host cell to replicate; Bacillus is a living, single-celled prokaryotic organism.
- • Viroid: Viroids are the smallest infectious pathogens known, consisting solely of a short strand of circular, single-stranded RNA without a protein coat.
- • Gram negative bacteria: Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane; Bacillus species possess the thick peptidoglycan layer that retains the crystal violet stain in Gram staining.
Aspergillus fumigatus can infect?
- a) Animals
- b) Birds
- c) Man
- d) All of above
Explanation:
Aspergillus fumigatus is a widespread opportunistic fungal pathogen. It is responsible for a group of diseases called aspergillosis, which can affect a wide variety of hosts including humans, various mammals, and especially birds.
How it affects these groups:
How it affects these groups:
- • Animals: It causes infections in many mammals; for example, it can cause mycotic abortion in cattle or nasal infections in dogs and horses.
- • Birds: It is extremely common in poultry and wild birds, causing a fatal respiratory disease known as “brooder pneumonia.”
- • Man: In humans, it can lead to allergic bronchopulmonary aspergillosis, fungal balls in the lungs (aspergilloma), or systemic infections in immunocompromised individuals.
Intermediate group of pathogen between bacteria and viruses which are intracellular parasites are called?
- a) Virusoides
- b) Mycoplasmas
- c) Rickettsias
- d) Prions
Explanation:
Rickettsias are considered an intermediate group because they share characteristics of both bacteria and viruses. Like bacteria, they have a cell wall and metabolic enzymes, but like viruses, they are obligate intracellular parasites, meaning they can only grow and reproduce inside living host cells.
Why other options are incorrect:
Why other options are incorrect:
- • Virusoides: These are small, circular, single-stranded RNA molecules that require a “helper virus” to infect a cell. They are not cellular organisms.
- • Mycoplasmas: These are the smallest free-living bacteria. While they are very small, they do not have a cell wall and most species are not obligate intracellular parasites.
- • Prions: These are infectious protein particles that do not contain any DNA or RNA at all.
The stain used to demonstrate fungus?
- a) Albert
- b) Nigerosin
- c) Lactophenol cotton blue
- d) None of these
Explanation:
Lactophenol cotton blue (LPCB) is the most common stain used for the microscopic examination of fungi. It contains three key components: Phenol (to kill the organism), Lactic acid (to preserve fungal structures), and Cotton blue (to stain the chitin in the fungal cell walls).
Why other options are incorrect:
Why other options are incorrect:
- • Albert: This stain is specifically used to demonstrate metachromatic granules in Corynebacterium diphtheriae.
- • Nigerosin: This is an acidic dye used for “negative staining” to visualize bacterial capsules or the morphology of organisms against a dark background.
- • None of these: Since option (c) is the gold-standard stain for fungi, this option is incorrect.
Koplik spots observed in the mucous membrane is characteristic feature of the disease?
- a) Measles
- b) Mumps
- c) Influenza
- d) Rubella
Explanation:
Koplik spots are a diagnostic indicator for Measles (rubeola). They appear as small, white spots (often described as “grains of salt on a red background”) on the buccal mucosa (inside of the cheeks) 2 to 3 days before the measles rash itself appears.
Why other options are incorrect:
Why other options are incorrect:
- • Mumps: This viral infection is primarily characterized by the painful swelling of the parotid (salivary) glands.
- • Influenza: This is a respiratory illness characterized by fever, chills, and muscle aches; it does not produce specific oral lesions like Koplik spots.
- • Rubella: Also known as German Measles, it causes a rash and fever, but lacks the specific Koplik spots found in “true” Measles.
The cells having F plasmid in the chromosomes were termed as?
- a) Hfr
- b) F–
- c) Hbr
- d) C+
Explanation:
When the F (fertility) plasmid integrates into the bacterial chromosome, the cell is called an Hfr cell (High Frequency of Recombination). Unlike F+ cells (where the plasmid is free-floating), Hfr cells can transfer chromosomal genes to a recipient cell during conjugation.
Why other options are incorrect:
Why other options are incorrect:
- • F–: These are recipient cells that completely lack the F plasmid and cannot act as donors.
- • Hbr: This is not a recognized biological term in bacterial genetics.
- • C+: This notation is not used to describe the presence or location of the F plasmid.
The cell wall deficient form of bacteria is?
- a) Protoplast
- b) Spheroplast
- c) Mycoplasma
- d) ‘L’ form
Explanation:
‘L’ forms (named after the Lister Institute) are strains of bacteria that lack cell walls but are still capable of growth and division. They can develop from both Gram-positive and Gram-negative bacteria, often under the influence of antibiotics like penicillin.
Why other options are incorrect:
Why other options are incorrect:
- • Protoplast: This refers to a bacterium (usually Gram-positive) where the cell wall has been entirely removed, but it is typically unstable.
- • Spheroplast: This refers to a bacterium (usually Gram-negative) where the cell wall is only partially removed.
- • Mycoplasma: These are a genus of bacteria that naturally lack a cell wall; they are not considered a “form” of a normally walled bacteria.
Rod shaped bacteria are known as?
- a) Cocci
- b) Pleomorphic forms
- c) Bacilli
- d) Comma forms
Explanation:
Bacilli (singular: Bacillus) are bacteria that are shaped like rods or cylinders. Examples include Escherichia coli and Bacillus anthracis.
Why other options are incorrect:
Why other options are incorrect:
- • Cocci: These are bacteria with a spherical, ovoid, or generally round shape.
- • Pleomorphic forms: These are bacteria that lack a single characteristic shape and can vary their morphology depending on environmental conditions (e.g., Mycoplasma).
- • Comma forms: These are known as Vibrios. They are curved rods that look like a comma (e.g., Vibrio cholerae).
Exotoxins are?
- a) Part of cell wall
- b) Polymerized complexes
- c) Heat labile
- d) Heat stable
Explanation:
Exotoxins are proteins secreted by living bacteria. Because they are proteinaceous in nature, they are generally heat-labile, meaning they are inactivated or denatured by heat (usually above 60°C).
Why other options are incorrect:
Why other options are incorrect:
- • Part of cell wall: This describes Endotoxins (Lipopolysaccharides), which are integral parts of the Gram-negative bacterial cell wall.
- • Polymerized complexes: Exotoxins are typically soluble monomeric or multimeric proteins, not described as polymerized complexes in this context.
- • Heat stable: This is a characteristic of Endotoxins, which can withstand high temperatures (even autoclaving) without being destroyed.
Which of the following is a Spirochete?
- a) Gonococci
- b) Treponema pallidum
- c) Streptococci
- d) Staphylococci
Explanation:
Treponema pallidum is a classic example of a spirochete. These are thin, spiral-shaped (corkscrew), motile bacteria that are the causative agents of syphilis.
Why other options are incorrect:
Why other options are incorrect:
- • Gonococci: These are Gram-negative diplococci (spherical shape) responsible for gonorrhea.
- • Streptococci: These are Gram-positive cocci (spherical) that typically grow in chains.
- • Staphylococci: These are Gram-positive cocci (spherical) that typically grow in grape-like clusters.
The procedure of differential staining of bacteria was developed by?
- a) H.C. Gram
- b) H.A. Gram
- c) A.H. Gram
- d) N.C. Gram
Explanation:
The Gram stain was developed in 1884 by the Danish bacteriologist Hans Christian Gram (H.C. Gram). It is the most important differential staining technique in microbiology, used to classify bacteria into Gram-positive and Gram-negative groups.
Quick Facts:
Quick Facts:
- • Full Name: Hans Christian Joachim Gram.
- • Discovery: He discovered the technique while working in a morgue in Berlin, trying to visualize bacteria in lung tissue of pneumonia victims.
- • Mechanism: The stain differentiates bacteria based on the chemical and physical properties of their cell walls (specifically the peptidoglycan layer).
A bacterium containing prophage is called as?
- a) Lysogen
- b) Lytic
- c) Lytogen
- d) None of these
Explanation:
A Lysogen (or lysogenic bacterium) is a bacterial cell that carries a prophage—which is viral DNA integrated into the bacterial chromosome. In this state, the phage remains dormant and replicates whenever the bacterium divides.
Why other options are incorrect:
Why other options are incorrect:
- • Lytic: This refers to the “Lytic Cycle,” where the virus actively replicates and eventually bursts (lyses) the host cell to release new virions.
- • Lytogen: This is a non-existent or incorrect term in microbiology used as a distractor.
- • None of these: Incorrect because “Lysogen” is the scientifically accepted term for this condition.
The bacterial cell multiplication is usually by?
- a) Conjugation
- b) Binary-fission
- c) Meiosis
- d) Mitosis
Explanation:
Bacteria primarily reproduce asexually through Binary fission. In this process, a single cell duplicates its genetic material (DNA) and then divides into two identical daughter cells.
Why other options are incorrect:
Why other options are incorrect:
- • Conjugation: This is a method of horizontal gene transfer (often called “bacterial mating”) where DNA is transferred between cells, but it is not the primary way bacteria multiply in number.
- • Meiosis: This is a specialized cell division that occurs only in eukaryotes to produce gametes (sex cells).
- • Mitosis: This is the process of nuclear division in eukaryotic cells. Since bacteria lack a true nucleus, they do not undergo mitosis.
Bacteriophage capable of only lytic growth is called?
- a) Temperate
- b) Virulent
- c) Avirulent
- d) None of these
Explanation:
A Virulent phage is one that always causes the lytic cycle upon infecting a host cell. It replicates immediately and eventually lyses (destroys) the host cell to release new phage particles.
Why other options are incorrect:
Why other options are incorrect:
- • Temperate: These phages are capable of both lytic growth and lysogeny (where they integrate their DNA into the host genome without killing it immediately).
- • Avirulent: This term generally describes a microorganism that does not cause disease; while related, it is not the standard classification for phages based on their growth cycle.
- • None of these: Incorrect because “Virulent” is the specific term for phages that only perform the lytic cycle.
An example for common air borne epidemic disease?
- a) Typhoid
- b) Malaria
- c) Influenza
- d) Encephalitis
Explanation:
Influenza (the flu) is a classic example of an air-borne epidemic disease. It spreads rapidly through respiratory droplets and aerosols produced when an infected person coughs, sneezes, or talks.
Why other options are incorrect:
Why other options are incorrect:
- • Typhoid: This is a water-borne and food-borne disease caused by Salmonella Typhi, spread via the fecal-oral route.
- • Malaria: This is a vector-borne disease spread by the bite of infected female Anopheles mosquitoes.
- • Encephalitis: Most common forms (like Japanese Encephalitis) are vector-borne, usually transmitted by mosquitoes or ticks, rather than through the air.
Virulence of the microorganisms can be reduced by?
- a) A virulence
- b) Freezing
- c) Attenuation
- d) Inactivation
Explanation:
Attenuation is the process of reducing the virulence (the ability to cause disease) of a pathogen while still keeping it viable (alive). This is the fundamental principle used to create live-attenuated vaccines (e.g., BCG, MMR, Polio Sabin).
Why other options are incorrect:
Why other options are incorrect:
- • A virulence: This is a state where a microbe is “avirulent” (unable to cause disease), rather than the process used to reduce its strength.
- • Freezing: This is primarily a preservation technique. While it may kill some individual cells, the remaining survivors usually maintain their original virulence once thawed.
- • Inactivation: This involves killing the pathogen entirely (usually via heat or chemicals) so it can no longer replicate at all, rather than just weakening its disease-producing power.
Virion means?
- a) Non-infectious particles
- b) Defective virus particles
- c) Incomplete particles
- d) Infectious virus particles
Explanation:
A Virion is a complete, fully functional, and infectious virus particle existing outside of a host cell. It consists of the genetic material (DNA or RNA) wrapped in a protein shell called a capsid, and in some cases, an outer envelope.
Why other options are incorrect:
Why other options are incorrect:
- • Non-infectious particles: While some viral particles may be degraded or non-infectious, the term “virion” specifically refers to the mature, infectious form.
- • Defective virus particles: These are viruses that lack a complete genome and cannot replicate without the help of another virus (a “helper virus”).
- • Incomplete particles: These are often “empty” capsids that do not contain the viral genome, making them unable to cause an infection.
Amoebic dysentery in humans is caused by?
- a) Paramecium
- b) Entamoeba histolytica
- c) Yeast
- d) Plasmodium
Explanation:
Amoebic dysentery (amoebiasis) is caused by the protozoan parasite Entamoeba histolytica. It is typically transmitted through the ingestion of contaminated food or water containing the cyst stage of the parasite.
Why other options are incorrect:
Why other options are incorrect:
- • Paramecium: This is a free-living, non-parasitic ciliate found in freshwater and does not cause disease in humans.
- • Yeast: These are unicellular fungi. While some (like Candida) can cause infections, they are not responsible for amoebic dysentery.
- • Plasmodium: This is the protozoan parasite responsible for causing Malaria, which is transmitted by mosquitoes, not through the intestinal route.
Diphtheria bacillus is otherwise known as?
- a) Kleb’s – lofflers bacillus
- b) Koch’s bacillus
- c) Frchs bacillus
- d) Fried-Landers bacillus
Explanation:
Corynebacterium diphtheriae, the causative agent of diphtheria, is commonly known as the Klebs-Löffler bacillus. It was identified in 1884 by German bacteriologists Edwin Klebs and Friedrich Löffler.
Why other options are incorrect:
Why other options are incorrect:
- • Koch’s bacillus: This is the name given to Mycobacterium tuberculosis, the bacterium that causes tuberculosis, discovered by Robert Koch.
- • Frchs bacillus: (Likely referring to Frisch bacillus) This usually refers to Klebsiella rhinoscleromatis.
- • Fried-Landers bacillus: This is the common name for Klebsiella pneumoniae, which causes a severe form of bacterial pneumonia.
Mordant used in grams staining is?
- a) Saffranin
- b) Iodine
- c) Crystal violet
- d) All of above
Explanation:
In Gram staining, Iodine (specifically Gram’s Iodine) acts as the mordant. A mordant is a substance that “fixes” a dye in or on a cell. The iodine combines with the crystal violet to form a large CV-I complex that gets trapped within the thick peptidoglycan layer of Gram-positive bacteria.
Why other options are incorrect:
Why other options are incorrect:
- • Saffranin: This is the counterstain used at the end of the procedure to color Gram-negative bacteria pink/red.
- • Crystal violet: This is the primary stain used to color all bacterial cells purple initially.
- • All of above: Incorrect because each chemical has a very specific, different role in the differential staining process.
The size of virus particle may range?
- a) 0.1–100 μm
- b) 0.02–0.2 μm
- c) 0.5–10 μm
- d) 0.015–0.2 μm
Explanation:
Viruses are significantly smaller than bacteria. Most viruses range in size from about 20 nanometers (0.02 μm) to 200–300 nanometers (0.2–0.3 μm). Because of this extremely small size, they cannot be seen with a standard light microscope and require an electron microscope for visualization.
Size Comparisons:
Size Comparisons:
- • 0.02–0.2 μm: The standard range for most human and animal viruses (e.g., Poliovirus is ~30nm, Poxvirus is ~250nm).
- • 0.5–10 μm: This range typically describes the size of bacteria (e.g., E. coli is about 1-2 μm).
- • 10–100 μm: This range describes eukaryotic cells like human red blood cells (~7 μm) or large protozoa.
Viral genome that can become integrated into bacterial genome is called?
- a) Bacteriophage
- b) Temperate phage
- c) Metaphage
- d) Prophage
Explanation:
A Prophage is the specific term for the latent form of a bacteriophage, in which the viral genes are incorporated into the bacterial chromosome without causing disruption of the bacterial cell.
Why other options are incorrect:
Why other options are incorrect:
- • Bacteriophage: This is the general name for any virus that infects bacteria, whether it integrates or stays in the lytic cycle.
- • Temperate phage: This is the type of virus that is capable of integration, but the integrated genome itself is called the prophage.
- • Metaphage: This is not a standard scientific term used to describe integrated viral DNA in microbiology.
The characteristic shape of the bacteria is maintained because of?
- a) Slime layer
- b) Capsule
- c) Cell wall
- d) Cell membrane
Explanation:
The Cell wall is a rigid outer layer that provides structural support and protection. It is primarily responsible for maintaining the specific shape of the bacterium (such as coccus, bacillus, or spirillum) and preventing the cell from bursting due to osmotic pressure.
Why other options are incorrect:
Why other options are incorrect:
- • Slime layer: This is a thin, disorganized extra-cellular layer mainly used for adherence and protection against dehydration, but it lacks the rigidity to define shape.
- • Capsule: While it is a protective outer layer, its primary functions are protection from phagocytosis and attachment; the underlying cell wall is what actually dictates the shape.
- • Cell membrane: The plasma membrane is a flexible, fluid lipid bilayer. Without the cell wall, the membrane would not be able to maintain a fixed shape against internal pressure.
Mesosomes are?
- a) Kind of ribosomes
- b) Part of cell wall
- c) Formed during cell division
- d) Principal sites of respiratory enzymes
Explanation:
Mesosomes are invaginations (infoldings) of the plasma membrane in bacteria. They are considered the functional equivalent of mitochondria in eukaryotes because they are the principal sites of respiratory enzymes (the electron transport chain).
Functions of Mesosomes:
Functions of Mesosomes:
- • Respiration: They increase the surface area of the plasma membrane to carry out cellular respiration.
- • Cell Division: They play a role in the formation of the cross-wall (septum) during binary fission and help in the distribution of receptors/DNA to daughter cells.
- • Secretion: They help in the secretion of various enzymes and cell wall components.
Which of the following is a motile bacterium?
- a) Shigella
- b) B. anthracis
- c) S. typhi
- d) K. pneumoniae
Explanation:
Salmonella Typhi (S. typhi) is a motile bacterium. It moves using peritrichous flagella (flagella projecting in all directions from the cell surface).
Why other options are incorrect:
Why other options are incorrect:
- • Shigella: All species of Shigella are characteristically non-motile.
- • B. anthracis: While many species in the Bacillus genus are motile, Bacillus anthracis is a notable exception and is non-motile.
- • K. pneumoniae: Klebsiella species are non-motile and possess a thick polysaccharide capsule.
The percentage of O2 tolerated/required by a moderate anaerobe is?
- a) 2 – 8%
- b) 0%
- c) < 0.5%
- d) 5 – 10%
Explanation:
Moderate anaerobes (such as Bacteroides fragilis) are capable of growing in the presence of 2% to 8% oxygen. While they do not use oxygen for metabolism, they possess enzymes like superoxide dismutase to protect themselves from oxygen toxicity for a limited time.
Comparison of Oxygen Requirements:
Comparison of Oxygen Requirements:
- • < 0.5% (Strict Anaerobes): These are killed by even very small amounts of oxygen because they lack protective enzymes.
- • 5 – 10% (Microaerophiles): These organisms actually require oxygen for growth, but at lower concentrations than the atmospheric level (which is 21%).
- • 0%: This is the ideal condition for all obligate anaerobes, but “moderate” ones specifically have a higher tolerance threshold than strict ones.
Interferon is formed by?
- a) Lymphocytes
- b) Fibroblasts
- c) Lymphoblasts
- d) All of these
Explanation:
Interferons (IFNs) are a group of signaling proteins (cytokines) made and released by host cells in response to the presence of several viruses. Different types of interferons are produced by different cell types: IFN-α is primarily produced by leukocytes (lymphocytes), IFN-β by fibroblasts, and IFN-γ by T-lymphocytes and NK cells.
Types of Interferons and their Sources:
Types of Interferons and their Sources:
- • Lymphocytes: These white blood cells produce Alpha-interferon (IFN-α) and Gamma-interferon (IFN-γ).
- • Fibroblasts: These connective tissue cells are the primary source of Beta-interferon (IFN-β).
- • Lymphoblasts: These are immature lymphocytes that also retain the capability of producing interferons during viral induction.
Gram staining is an example for?
- a) Simple staining
- b) Negative staining
- c) Differential staining
- d) None of these
Explanation:
Differential staining is a procedure that uses more than one dye to distinguish between different types of microorganisms or different parts of a single organism. Gram staining is the most famous example, as it differentiates bacteria into two large groups (Gram-positive and Gram-negative) based on their cell wall structure.
Why other options are incorrect:
Why other options are incorrect:
- • Simple staining: This technique uses only a single basic dye (like Methylene Blue) to color the entire cell, making it easier to see the basic shape and size but not distinguishing between types.
- • Negative staining: This method stains the background instead of the cells (using dyes like India Ink or Nigrosin), making the cells appear as clear spots against a dark background.
- • None of these: Incorrect, as “Differential staining” is the scientifically accurate classification for the Gram stain.
Autolysis is done by?
- a) Peroxisomes
- b) Golgi bodies
- c) Lysosomes
- d) Mitochondria
Explanation:
Lysosomes are responsible for autolysis (self-digestion). They contain powerful hydrolytic enzymes that break down cellular waste. If a cell is severely damaged or dies, lysosomes can burst, releasing these enzymes into the cytoplasm to digest the entire cell, which is why they are often called “suicide bags.”
Why other options are incorrect:
Why other options are incorrect:
- • Peroxisomes: These organelles are involved in lipid metabolism and chemical detoxification, specifically neutralizing reactive oxygen species like hydrogen peroxide.
- • Golgi bodies: These act as the “packaging center” of the cell, modifying and sorting proteins for secretion or delivery to other organelles.
- • Mitochondria: Known as the “powerhouse” of the cell, their primary role is the production of energy (ATP) through aerobic respiration.
A facultative anaerobe is?
- a) Only grow in the presence of O2
- b) Only grow anaerobically
- c) Ordinarily an anaerobe but can grow with O2
- d) Ordinarily an aerobe but can grow in absence of O2
Explanation:
Facultative anaerobes are versatile organisms. They ordinarily use oxygen (aerobic respiration) because it produces more energy (ATP), but they have the metabolic “faculty” to switch to fermentation or anaerobic respiration when oxygen is not available.
Why other options are incorrect:
Why other options are incorrect:
- • Only grow in the presence of O2: This describes Obligate Aerobes (e.g., Mycobacterium tuberculosis).
- • Only grow anaerobically: This describes Obligate Anaerobes (e.g., Clostridium species), which may even be killed by oxygen.
- • Ordinarily an anaerobe but can grow with O2: While similar, this is more accurately the definition of Aerotolerant Anaerobes, which do not use oxygen for growth but are not harmed by it.
Recombination process occurring through the mediation of phages is?
- a) Transfection
- b) Conjunction
- c) Transformation
- d) Transduction
Explanation:
Transduction is the process by which DNA is transferred from one bacterium to another by a virus (a bacteriophage). It was first discovered by Norton Zinder and Joshua Lederberg in 1952.
Why other options are incorrect:
Why other options are incorrect:
- • Transfection: This is the process of deliberately introducing naked or purified nucleic acids into eukaryotic cells, or specifically viral DNA into bacterial cells.
- • Conjunction (Conjugation): This is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection (pilus).
- • Transformation: This is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous (naked) DNA from its surroundings.
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