MicroBiology MCQs with Answer and Explnation | Chapter 20

Answer: Tolerance

Tolerance refers to the ability of the immune system to recognize and tolerate self-antigens, preventing immune responses against the body’s own tissues. It involves mechanisms that prevent the immune system from attacking normal cells and tissues while remaining responsive to foreign or non-self-antigens.

The other options are incorrect:

• Specific Immunity: Specific immunity, also known as adaptive or acquired immunity, involves the recognition of specific pathogens or antigens by immune cells. It includes both humoral and cell-mediated immune responses.
• Humoral Immunity: Humoral immunity involves the production of antibodies by B cells to neutralize or eliminate pathogens. While important in the immune response, it is not specifically focused on the recognition of self-antigens.
• Cell-Mediated Immunity: Cell-mediated immunity involves the activation of T cells to directly attack and destroy infected or abnormal cells. Like humoral immunity, it is part of specific immunity but does not specifically address the recognition of self-antigens.

Answer: other staphylococci

Staphylococcus aureus is the only Staphylococcus species that is coagulase-positive, meaning it produces the coagulase enzyme which converts fibrinogen in blood plasma to fibrin, causing a clot to form. All other staphylococcus species are coagulase-negative and will not form a clot in the test. Therefore, the coagulase test is a reliable and easy way to differentiate S. aureus from other staphylococci.

The other options are incorrect:

• Streptococci: These are Gram-positive bacteria but belong to a different genus than Staphylococcus and are not included in the coagulase test.
• Micrococci: These are also Gram-positive cocci, but they are not closely related to Staphylococcus and do not produce coagulase.
• Enterococci: These are Gram-positive cocci belonging to the genus Enterococcus, distinct from Staphylococcus and not included in the coagulase test.

Answer: Precipitation

Precipitation is the formation of an insoluble antigen-antibody complex, which settles out of solution. This occurs when the antigen is multivalent (has multiple antigenic determinants) and the antibody is bivalent (has two antigen binding sites). Precipitation is not an antigen-antibody interaction that occurs inside a living host. It primarily happens in vitro during laboratory tests.

The other options are incorrect:

• Neutralization: This is the process by which antibodies bind to toxins or viruses, preventing them from causing damage to the host.
• Opsonization: This is the process by which antibodies coat antigens, making them more easily recognized and phagocytized by immune cells.
• Agglutination: This is the process by which antibodies bind to multiple antigens, causing them to clump together.

Answer: Monocytes

Monocytes are a type of leukocyte categorized as agranulocytes. Agranulocytes do not have visible granules in their cytoplasm, unlike granulocytes (neutrophils, basophils, and eosinophils). After migrating from the bloodstream into tissues, monocytes mature into macrophages and dendritic cells, playing crucial roles in the immune system.

The other options are incorrect:

• Neutrophils: These are granulocytes with visible cytoplasmic granules and are the most abundant type of leukocytes in the body, primarily involved in phagocytizing bacteria.
• Basophils: These are granulocytes known for releasing histamine and other inflammatory mediators, involved in allergic reactions and immune response modulation.
• Eosinophils: These are granulocytes with specific roles in allergic reactions and defense against parasitic infections.

Answer: Necrosis

Necrosis is not a protective mechanism of the body; instead, it is a form of cell death that occurs due to factors such as injury, toxins, or infection. Protective mechanisms are processes or responses that the body employs to defend itself against harmful stimuli.

The other options are incorrect:

• Fever: Fever is a protective response where the body increases its temperature to help combat infections by enhancing immune functions and inhibiting the growth of some pathogens.
• Phagocytosis: Phagocytosis is a protective mechanism involving the engulfment and digestion of foreign particles, such as bacteria or dead cells, by immune cells like macrophages and neutrophils.
• Inflammation: Inflammation is a protective response characterized by redness, heat, swelling, and pain. It is a crucial part of the immune system’s reaction to injury or infection, aiming to eliminate the cause of cell injury, clear out damaged cells and tissues, and initiate tissue repair.

Answer: Both Pathogenicity and Spread

Bioterrorism microbial agents are classified based on both pathogenicity (the ability to cause disease) and spread (how easily the agent can be disseminated from person to person or through the environment). This classification helps assess the potential impact and threat posed by these agents in terms of their ability to cause disease and the ease with which they can be transmitted.

The other options are incorrect:

• Pathogenicity: This refers to the ability of a microorganism to cause disease. While pathogenicity is an important factor in classifying bioterrorism agents, it’s not the sole criterion.
• Spread: The spread of a microbial agent is indeed a crucial aspect in its classification. However, considering spread alone may not provide a comprehensive understanding of the threat; pathogenicity is also essential to assess the potential impact.
• Availability: While the availability of a microbial agent is a concern, it is not the primary basis for classifying bioterrorism agents. Pathogenicity and spread are more directly related to the potential harm and threat posed by these agents.

Answer: Ig G

Immunoglobulin G (IgG) is the only immunoglobulin that can cross the placenta from the mother to the fetus during pregnancy. This transfer of IgG provides passive immunity to the newborn, offering protection against certain infections.

Incorrect Options:

• IgM: IgM is a large immunoglobulin that does not cross the placental barrier efficiently. It is primarily found in the bloodstream and is the first antibody produced in response to an infection.
• IgA: IgA is mainly found in mucosal secretions and does not cross the placenta. It plays a crucial role in mucosal immunity, providing protection at mucosal surfaces.
• IgD: IgD is primarily found on the surface of B cells and has a role in the activation of the immune response. It does not cross the placenta.

Answer: Vascular smooth muscle cells

Hematopoietic stem cells are precursor cells that give rise to various blood cells, including lymphocytes, monocytes, and erythrocytes. However, they are not the precursors for vascular smooth muscle cells, which arise from a different lineage of stem cells and play a role in the structure and function of blood vessels.

The other options are incorrect:

• Lymphocytes: Hematopoietic stem cells give rise to lymphocytes, which are key components of the immune system.
• Monocytes: Hematopoietic stem cells differentiate into monocytes, which are a type of white blood cell involved in immune responses.
• Erythrocytes: Hematopoietic stem cells are the precursors for erythrocytes, also known as red blood cells, which are responsible for oxygen transport.

Answer: Kupffer cells

Macrophages present in the liver are called Kupffer cells. Kupffer cells are specialized macrophages located in the liver sinusoids, and they play a crucial role in the immune system by phagocytosing pathogens, foreign particles, and old or damaged red blood cells.

The other options are incorrect:

• Microglial cells: Microglial cells are macrophages found in the central nervous system, particularly in the brain and spinal cord.
• Alveolar macrophages: Alveolar macrophages are found in the lungs and are involved in the defense against inhaled pathogens and particles.
• Wondering macrophages: This term does not correspond to a specific type of macrophage. It might be a typo, and the correct term is “wandering macrophages,” which refers to macrophages that move freely in tissues and play a role in immune surveillance.

Answer: Fleming

Antibiotic penicillin was introduced by Sir Alexander Fleming. He discovered penicillin in 1928 when he observed that the mold Penicillium notatum produced a substance that killed a wide variety of bacteria. This discovery marked the beginning of the era of antibiotics, revolutionizing medicine and significantly improving the treatment of bacterial infections.

The other options are incorrect:

• Pasteur: Louis Pasteur was a French microbiologist and chemist known for his contributions to the understanding of microbial fermentation and the development of the pasteurization process. However, he did not discover penicillin.
• Jenner: Edward Jenner was an English physician who developed the smallpox vaccine, introducing the concept of vaccination. His work laid the foundation for immunology, but he was not associated with the discovery of penicillin.
• Lister: Joseph Lister was a British surgeon who pioneered antiseptic surgical techniques, promoting the use of carbolic acid to prevent infection during surgery. While his contributions significantly improved surgical outcomes, he was not the discoverer of penicillin.

Answer: Mitochondria

Prokaryotic cells lack mitochondria. Prokaryotes, which include bacteria and archaea, are characterized by the absence of membrane-bound organelles, including mitochondria. Instead, prokaryotic cells have a simpler structure with a single, circular DNA molecule, ribosomes, and a cell membrane.

The other options are incorrect:

• DNA: Prokaryotic cells do have DNA, but it is not organized within a membrane-bound nucleus. The genetic material in prokaryotes is typically found in a single, circular DNA molecule in the nucleoid region of the cell.
• Ribosomes: Prokaryotic cells have ribosomes, which are involved in protein synthesis. However, they differ slightly in structure from the ribosomes found in eukaryotic cells.
• Plasma membrane: Prokaryotic cells have a plasma membrane that encloses the cell and regulates the entry and exit of substances. This membrane is simpler in structure compared to the complex membrane systems found in eukaryotic cells.

Answer: passive naturally acquired

Immunity against yellow fever in newborns acquired through the transfer of maternal antibodies is an example of passive naturally acquired immunity. This type of immunity occurs when antibodies are passed from the mother to the infant naturally, such as through the placenta during pregnancy or through breast milk after birth.

The other options are incorrect:

• Active naturally acquired: This type of immunity results from natural exposure to an infectious agent, leading to the production of antibodies by the individual’s own immune system. It is not applicable to the transfer of antibodies from mother to newborn.
• Passive artificially acquired: This type of immunity involves the administration of pre-formed antibodies, often through injection of immune serum or immunoglobulins. It is not a natural process but rather an artificial intervention.
• Artificial immunity: This term refers to immunity acquired through deliberate interventions, such as vaccination. It does not specifically describe the transfer of antibodies from mother to newborn.

Answer: Spores

Spores are not external to the cell wall; instead, they are structures formed by certain bacteria as a means of survival under unfavorable conditions. Spores are often produced within the bacterial cell and are resistant to harsh environmental conditions.

The other options are incorrect:

• Glycocalyx: Glycocalyx is an external structure that surrounds the cell wall of some bacteria. It can be in the form of a capsule or slime layer, contributing to protection and adherence.
• Flagella: Flagella are whip-like structures extending from the cell surface that are involved in bacterial motility. They are external to the cell wall and enable bacteria to move in liquid environments.
• Pili: Pili (or fimbriae) are hair-like appendages that protrude from the bacterial cell surface. They are involved in adherence to surfaces and other cells, promoting interactions. Pili are external to the cell wall.

Answer: 1/1000

A typical bacterial cell has only about 1/1000 the volume of a typical eukaryotic cell. Bacterial cells are generally much smaller and simpler in structure compared to eukaryotic cells, which have membrane-bound organelles and a more complex internal organization.

The other options are incorrect:

• 1/10: This ratio overestimates the size of a bacterial cell compared to a eukaryotic cell. Bacterial cells are smaller than eukaryotic cells.
• 1/100: This ratio is closer but still overestimates the size of a bacterial cell compared to a eukaryotic cell.
• 1/10000: This ratio underestimates the size of a bacterial cell compared to a eukaryotic cell. Bacterial cells are larger than this value suggests.

Answer: DNA ligase

The polymerase chain reaction (PCR) is a molecular biology technique used to amplify DNA. It involves the use of a DNA template, DNA polymerase, and four deoxyribonucleotide triphosphates (dNTPs) to synthesize new DNA strands. DNA ligase is not typically included in a standard PCR reaction. DNA ligase is an enzyme involved in the joining of DNA fragments and is more commonly used in DNA cloning or genetic engineering processes.

The other options are incorrect:

• DNA polymerase: DNA polymerase is a crucial component of PCR, responsible for synthesizing new DNA strands complementary to the template strands during the amplification process.
• Four dNTPs: The four deoxyribonucleotide triphosphates (dATP, dTTP, dCTP, and dGTP) are essential components of PCR, providing the building blocks for the synthesis of new DNA strands.
• DNA template: A DNA template, which contains the target DNA sequence to be amplified, is a necessary component of PCR. The primers designed to flank the target sequence bind to the template to initiate DNA synthesis.

Answer: A specific DNA sequence

Southern hybridization is a molecular biology technique used to identify and characterize specific DNA sequences. The method involves the hybridization of a labeled DNA probe with complementary sequences within a sample of DNA that has been separated by gel electrophoresis. This technique is named after the scientist Edwin Southern, who developed it.

The other options are incorrect:

• A specific protein: Southern hybridization is not used to identify specific proteins. Other techniques, such as Western blotting, are more suitable for protein detection.
• A specific RNA seq: Southern hybridization is not designed for the identification of RNA sequences. Techniques like Northern blotting are used for the analysis of specific RNA molecules.
• Both A specific protein and A specific RNA seq: Southern hybridization is specific to DNA sequences and does not apply to the identification of proteins or RNA sequences.

Answer: Staphylococcus

Staphylococcus is not a member of the family Enterobacteriaceae. Staphylococcus belongs to a different bacterial family, Staphylococcaceae. The other three bacteria—Escherichia coli (E. coli), Shigella, and Salmonella—are all members of the Enterobacteriaceae family.

The other options are incorrect:

• E. coli: Escherichia coli is a member of the family Enterobacteriaceae. It is a common and important bacterium, with various strains that can be both commensal in the human gut and pathogenic.
• Shigella: Shigella is a genus of bacteria within the family Enterobacteriaceae. It includes species that can cause gastrointestinal infections and diseases.
• Salmonella: Salmonella is also a member of the family Enterobacteriaceae. Various Salmonella species can cause foodborne illnesses and other infections in humans and animals.

Answer: Restriction endonucleases

A library of DNA fragments is created through the use of restriction endonucleases. These enzymes recognize specific DNA sequences and cleave the DNA at or near those recognition sites. The resulting DNA fragments can be used to construct a library that represents the entire genome or specific segments of it.

The other options are incorrect:

• Viruses: Viruses are infectious agents that can insert their genetic material into a host organism’s DNA, but they are not typically involved in the creation of DNA fragment libraries.
• DNA ligases: DNA ligases are enzymes that join DNA fragments together. While important in various molecular biology techniques, they are not used to create libraries of DNA fragments.
• Plasmids: Plasmids are circular DNA molecules that are often used as vectors to carry and replicate foreign DNA fragments, but they are not directly involved in the generation of DNA fragment libraries.

Answer: Proteus

Swarming growth, characterized by the rapid and coordinated movement of bacterial populations over solid surfaces, is a distinctive feature of Gram-negative bacteria, specifically the genus Proteus. Proteus species are known for their ability to swarm, often forming concentric rings on agar surfaces.

The other options are incorrect:

• Clostridium: Clostridium is a genus of Gram-positive bacteria known for its ability to form endospores. Swarming growth is not a characteristic of Clostridium species.
• Pasteurella: Pasteurella species are Gram-negative bacteria, but they are not typically associated with swarming growth. They are often found as commensals or pathogens in various animals.
• Pseudomonas: Pseudomonas is a Gram-negative genus known for its diverse characteristics, but swarming growth is more commonly associated with Proteus species.

Answer: 16oC

Mesophilic bacteria are organisms that thrive in moderate temperature ranges. The term “mesophilic” typically refers to bacteria with an optimum growth temperature between 20°C and 45°C. Therefore, mesophilic bacteria cannot grow at temperatures as low as 16°C.

The other options are incorrect:

• 25oC: Mesophilic bacteria can grow at this temperature because it falls within the mesophilic range.
• 35oC: This temperature is within the mesophilic range, and mesophilic bacteria can grow well at 35°C.
• 38oC: Again, this temperature is within the mesophilic range, and mesophilic bacteria can grow at 38°C.

Answer: O² and also CO²

Facultative anaerobic bacteria can grow in the presence of both oxygen (O²) and in anaerobic conditions. Additionally, they can utilize carbon dioxide (CO²) for growth. These bacteria have metabolic flexibility and can switch between aerobic and anaerobic respiration based on the availability of oxygen.

The other options are incorrect:

• Only O²: This option does not accurately describe facultative anaerobic bacteria. They can grow in the presence of oxygen but can also adapt to anaerobic conditions.
• Only CO²: While carbon dioxide is utilized by some bacteria for growth, facultative anaerobes do not exclusively grow in the presence of CO² alone. They are adaptable to a range of environmental conditions.
• N²: Nitrogen (N²) is an essential component of bacterial growth, but it is not the primary factor distinguishing facultative anaerobic bacteria. These bacteria are more notably characterized by their ability to thrive in both aerobic and anaerobic conditions.

Answer: Both Selective medium and Differential medium

Mannitol salt agar (MSA) is a commonly used microbiological medium that serves both selective and differential purposes.

Selective: It contains high salt concentration (7.5%) that inhibits the growth of most bacteria, except for those that tolerate high salt levels like Staphylococci, Enterococci, and some Micrococcaceae. This makes it selective for these specific groups of bacteria.
Differential: It contains mannitol, a sugar that can be fermented by some bacteria. When fermented, mannitol produces an acidic product that changes the color of the medium from red (phenol red indicator) to yellow. This allows for the differentiation between mannitol-fermenting (yellow colonies) and non-fermenting (red colonies) bacteria.

The other options are incorrect:

• Selective medium: While MSA is selective, it also provides information about the metabolic capabilities of bacteria, making it more than just a selective medium.
• Differential medium: While MSA differentiates between bacteria based on their ability to ferment mannitol, it also selects for specific bacteria that tolerate high salt concentrations, making it more than just a differential medium.
• Enrichment medium: Enrichment media are designed to encourage the growth of specific bacteria, often in low numbers, from a mixed sample. MSA, while selective for some bacteria, does not specifically enrich for any particular organism.

Answer: Cytoplasm

Translation, the process of synthesizing proteins from mRNA, occurs in the cytoplasm of the cell. In eukaryotic cells, transcription (formation of mRNA from DNA) takes place in the nucleus, and the mRNA then exits the nucleus to be translated by ribosomes in the cytoplasm.

The other options are incorrect:

• Nucleus: While transcription occurs in the nucleus, translation specifically takes place in the cytoplasm. The mRNA, synthesized in the nucleus, carries the genetic information to the cytoplasm for translation.
• Ribosomes: Ribosomes are cellular structures that play a crucial role in translation. However, translation itself occurs in the cytoplasm, where ribosomes read the mRNA code and synthesize proteins.
• Both Nucleus and Cytoplasm: This option is partially correct in the context of the entire process of gene expression. Transcription occurs in the nucleus, but translation occurs in the cytoplasm. The two processes are distinct and take place in different cellular compartments.

Answer: DNA

An intron is a non-coding sequence found in the DNA of genes. Introns are transcribed into pre-mRNA along with exons (coding sequences). During RNA processing (splicing), introns are removed, and the remaining exons are ligated together to form mature mRNA, which is then translated into a protein.

The other options are incorrect:

• RNA: In general, RNA molecules do not contain introns. Introns are specific to the DNA sequences of genes.
• mRNA: While mRNA undergoes splicing to remove introns, introns themselves are not found in mature mRNA. They are initially present in the pre-mRNA and are removed during RNA processing.
• tRNA: Transfer RNA (tRNA) molecules do not contain introns. Introns are primarily a feature of eukaryotic protein-coding genes, and tRNA is a type of RNA involved in protein synthesis.

Answer: Terminator

The signal responsible for the end of transcription is the terminator sequence. The terminator is a specific DNA sequence that signals to RNA polymerase that it has reached the end of the gene or transcription unit. This prompts the release of the RNA transcript, terminating the transcription process.

The other options are incorrect:

• Stop codon: Stop codons are signals in mRNA that indicate the end of translation (protein synthesis) during the process of protein synthesis on ribosomes. They are not involved in transcription.
• RNA polymerase run out: Transcription does not typically end because RNA polymerase “runs out.” Instead, it terminates at a specific terminator sequence.
• End of DNA chain: While the end of the DNA chain is a concept related to the linear nature of DNA, transcription termination is specifically signaled by the terminator sequence, not simply the end of the DNA chain.

Answer: Transformation

Plasmids are inserted into bacterial cells through a process called transformation. Transformation involves the uptake of external DNA, such as plasmids, by the bacterial cell. The foreign DNA is then incorporated into the bacterial genome, and the cell may express the genes carried by the plasmid.

The other options are incorrect:

• DNA ligase: DNA ligase is an enzyme that catalyzes the joining of DNA fragments. While important in various molecular biology techniques, DNA ligase is not the process by which plasmids are inserted into bacterial cells.
• Transfection: Transfection refers to the introduction of foreign DNA into eukaryotic cells. It is not the correct term for the insertion of plasmids into bacterial cells.
• Transduction: Transduction involves the transfer of genetic material from one bacterial cell to another by bacteriophages (viruses that infect bacteria). It is not the mechanism by which plasmids are introduced from the environment into bacterial cells.

Answer: Meninges

The meninges, which are protective membranes surrounding the brain and spinal cord, could NOT be a portal of entry for pathogens. The meninges provide a barrier that is not easily penetrated by microorganisms, making it a relatively secure and protected area.

The other options are incorrect:

• Skin: The skin is a potential portal of entry for pathogens, especially if there are cuts, abrasions, or other breaches in its protective barrier. Skin is a common route of entry for various microorganisms.
• Placenta: The placenta can serve as a portal of entry for pathogens during pregnancy, allowing them to be transmitted from the mother to the developing fetus. Some microorganisms can cross the placental barrier and cause infections.
• Small intestine: The small intestine can be a portal of entry for pathogens, particularly through ingestion of contaminated food or water. Pathogens may enter the body through the mucosal lining of the gastrointestinal tract.

Answer: Contagious

A highly communicable pathogen, especially one that spreads easily via direct contact, is referred to as “contagious.” Contagious diseases are those that can be transmitted from person to person through various means such as respiratory droplets, skin-to-skin contact, or contact with contaminated objects.

The other options are incorrect:

• Zoonotic: Zoonotic diseases are those that can be transmitted from animals to humans or vice versa. While some zoonotic diseases can be communicable, the term “zoonotic” specifically refers to the origin of the pathogen.
• Nosocomial: Nosocomial infections are acquired in a hospital or healthcare setting. These infections are not necessarily highly communicable via direct contact; instead, they are often associated with healthcare procedures.
• Communicable: While “communicable” is a broader term referring to the ability of a disease to be transmitted from one person to another, it does not specifically emphasize the high communicability associated with direct contact. “Contagious” is a more precise term in this context.

Answer: Both Hanging drop method and Soft agar method

111

Hanging drop method: This method involves placing a drop of bacterial culture on a coverslip and inverting it over a depression slide. The bacteria at the edge of the drop are observed under a microscope to assess their motility.
Soft agar method: This method involves embedding the bacterial culture in a semi-solid agar medium. Motile bacteria will spread outwards through the agar, forming a visible zone of growth.

The other options are incorrect:

• Pour plate method: This method involves pouring a mixture of bacterial culture and melted agar into a petri dish. After solidification, colonies of bacteria are visible, but their motility cannot be directly observed.

Answer: E. coli

O157:H7 refers to a pathogenic strain of Escherichia coli, specifically E. coli O157:H7. This strain is associated with foodborne illness and can cause severe gastrointestinal symptoms, including bloody diarrhea and, in some cases, kidney damage.

The other options are incorrect:

• Salmonella typhi: Salmonella typhi is the bacterium responsible for causing typhoid fever. It is not associated with the O157:H7 designation, and typhoid fever presents with different symptoms.
• S. aureus: Staphylococcus aureus is a different bacterium that can cause various infections, but it is not associated with the O157:H7 designation. Staphylococcus aureus infections are often characterized by skin and soft tissue infections, among others.
• Streptococcus: Streptococcus is a genus of bacteria that includes various species, some of which can cause infections. However, the O157:H7 designation is not related to streptococci.

Answer: Clostridium

Clostridium is a genus of bacteria that includes spore-forming species. While many bacteria, including Escherichia coli, Streptococcus, and Leptospira, are non-spore forming, Clostridium species have the ability to form endospores under certain conditions.

The other options are incorrect:

• E. coli: Escherichia coli is a non-spore forming bacterium. It does not produce endospores and is commonly found in the intestines of humans and animals.
• Streptococcus: Streptococcus bacteria are generally non-spore forming. They are known for causing various infections, including strep throat and pneumonia, but they do not produce endospores.
• Leptospira: Leptospira bacteria are non-spore forming spirochetes. They are responsible for causing the disease leptospirosis and do not possess the ability to form endospores.

Answer: Resolving power

The ability of a microscope to distinguish between two separate objects and show them as distinct entities is known as resolving power or resolution. It is a measure of the microscope’s ability to reveal fine details and separate closely spaced objects.

The other options are incorrect:

• Magnification power: Magnification refers to the degree of enlargement of an object when viewed through a microscope. While magnification is important, it does not specifically address the ability to distinguish separate objects.
• Wavelength: Wavelength is a characteristic of light and other forms of electromagnetic radiation. It is not a direct measure of a microscope’s ability to distinguish between two objects.

Answer: Epidemic

An epidemic refers to a sudden outbreak of a disease that affects a higher-than-expected number of individuals within a specific population or geographic area. It indicates a rapid and widespread increase in the incidence of a particular disease during a defined period.

The other options are incorrect:

• Endemic: Endemic refers to the constant presence of a disease within a particular geographic area or population at a relatively steady level. It does not imply a sudden increase in cases.
• Sporadic: Sporadic refers to the occurrence of isolated cases of a disease that occur irregularly and without a specific pattern. It does not involve a sudden and widespread increase in cases.
• Pandemic: A pandemic is a global outbreak of a disease that affects people over a large geographic area, often multiple continents. While a pandemic involves a widespread increase in cases, it differs from an epidemic in terms of its geographic scope.

Answer: Clotted

Serum is collected from clotted blood. When blood is allowed to clot, the clot retracts, and the liquid remaining is serum, which is essentially blood plasma without the clotting factors. Serum can be used for various laboratory tests and analyses.

The other options are incorrect:

• Heparinized: Heparinized blood refers to blood that has been treated with heparin, an anticoagulant. Heparin prevents blood clotting, and therefore, serum cannot be collected from heparinized blood.
• Unclotted: Unclotted blood is synonymous with whole blood or blood that has not undergone the process of clotting. Serum is specifically obtained from clotted blood, not unclotted blood.
• All of these: This option is incorrect because serum is not collected from heparinized or unclotted blood. It is collected specifically from clotted blood.

Answer: Sheep

Amboceptors are antibodies raised against red blood cells (RBCs) of sheep. These antibodies can react with antigens on the surface of sheep RBCs and play a role in immune responses, such as those involved in certain blood typing procedures.

The other options are incorrect:

• Cow: Amboceptors are not raised against the RBCs of cows. Each species typically has specific antibodies against its own RBCs.
• Goat: Amboceptors are not raised against the RBCs of goats. Like cows, goats have their own specific antibodies.
• Horse: Amboceptors are not raised against the RBCs of horses. Antibodies raised against horse RBCs would be specific to horses.

Answer: All of these

GET buffer, used in plasmid isolation from bacteria, typically contains Glucose, EDTA (Ethylenediaminetetraacetic acid), and Tris (Tris(hydroxymethyl)aminomethane). These components serve specific purposes in the isolation process, such as providing an energy source (glucose), chelating divalent cations to prevent DNA degradation (EDTA), and maintaining a stable pH (Tris).

Answer: Protein

The majority of antigens, which are substances that can elicit an immune response, are proteins. Proteins are highly diverse molecules with a wide range of structures, and they often serve as antigens recognized by the immune system.

The other options are incorrect:

• Nucleic acid: While nucleic acids can be immunogenic, the majority of antigens are proteins. Nucleic acids are more commonly associated with genetic information.
• Lipids: Lipids can also act as antigens, but they are generally less immunogenic than proteins. Many antigens involved in immune responses, such as those on the surface of pathogens, are proteins.
• Carbohydrates: Carbohydrates can function as antigens, particularly on the surfaces of some bacteria and viruses. However, proteins remain the predominant type of antigen.

Answer: RNA interference

“RNAi” stands for “RNA interference.” RNA interference is a biological process in which RNA molecules inhibit the expression of specific genes. It involves the introduction of double-stranded RNA (dsRNA) into a cell, leading to the degradation of target messenger RNA (mRNA) molecules and, consequently, the suppression of gene expression.

The other options are incorrect:

• RNA inducer: This term is not associated with “RNAi.” RNAi is specifically related to the interference or inhibition of gene expression, not induction.
• RNA insertion: This term does not represent the meaning of “RNAi.” RNA interference involves the degradation of specific RNA molecules rather than their insertion.
• RNA intron: “RNAi” does not stand for “RNA intron.” An intron is a non-coding region within a gene that is transcribed into RNA but is typically removed during RNA processing. RNA interference is a different process related to the post-transcriptional regulation of gene expression.

Answer: A neurotoxin

Botulism intoxication occurs due to a neurotoxin produced by the bacterium Clostridium botulinum. The neurotoxin, known as botulinum toxin, affects the nervous system by blocking the release of acetylcholine, a neurotransmitter, leading to muscle paralysis.

The other options are incorrect:

• An enterotoxin: Botulism is not caused by an enterotoxin. Enterotoxins typically affect the intestines and are associated with food poisoning caused by certain bacteria.
• A mycotoxin: Botulism is not caused by a mycotoxin. Mycotoxins are toxins produced by fungi and are generally not associated with Clostridium botulinum or botulism.
• All of these: This option is incorrect because botulism is specifically caused by a neurotoxin produced by Clostridium botulinum. It is not associated with enterotoxins, mycotoxins, or a combination of these toxin types.

Answer: Mechanical carrier

A mechanical carrier is an animal that only acts as a short-term transmitter of pathogens. These carriers mechanically transfer the pathogens from one host to another without being actively involved in the pathogen’s life cycle or undergoing any developmental changes. Mechanical carriers may carry pathogens on their bodies or appendages.

The other options are incorrect:

• Passive carrier: A passive carrier is typically an individual who has recovered from a disease and can inadvertently transmit the pathogen without showing symptoms. It does not refer to an animal that mechanically transmits pathogens.
• Biological carrier: A biological carrier is an organism that plays an active role in the life cycle of a pathogen, serving as a host for the pathogen to reproduce or develop. It is not synonymous with a short-term transmitter.
• Asymptomatic carrier: An asymptomatic carrier is an individual who carries a pathogen but does not show symptoms of the disease. It is not specific to animals and does not necessarily imply short-term transmission.

Answer: Purines

Adenine and guanine are examples of purines, a class of nitrogenous bases found in nucleotides. Purines are characterized by a double-ring structure, distinguishing them from pyrimidines, which have a single-ring structure. Adenine and guanine are two of the four nitrogenous bases that make up the genetic code in DNA and RNA.

The other options are incorrect:

• Large: This term does not specifically describe adenine and guanine as nitrogenous bases. While purines are relatively larger compared to pyrimidines, the term “large” is not commonly used to categorize nitrogenous bases.
• Pyrimidines: This is incorrect because adenine and guanine are purines, not pyrimidines. Pyrimidines include cytosine, thymine (in DNA), and uracil (in RNA).
• Small: While purines are relatively larger than pyrimidines, the term “small” is not commonly used to describe nitrogenous bases. It is not a specific term related to the classification of adenine and guanine.

Answer: Motility

The capsule of bacteria primarily serves functions such as attachment to surfaces, protection from the host’s immune system, and participation in biofilm formation. However, capsules are not involved in motility. Motility in bacteria is often associated with structures like flagella or pili, which enable movement.

The other options are incorrect:

• Attachment: Capsules are involved in attachment. They help bacteria adhere to surfaces, including host tissues or medical devices.
• Biofilm: Capsules contribute to the formation and stability of biofilms. Biofilms are communities of microorganisms embedded in a self-produced matrix.
• Used as nutrition: Capsules are not used as nutrition. They are protective structures that help bacteria evade host defenses.

Answer: Trichomonas

The Whiff test is used for the diagnosis of Trichomonas vaginalis infection. Trichomoniasis is a sexually transmitted infection caused by the protozoan parasite Trichomonas vaginalis. The Whiff test involves adding a few drops of potassium hydroxide (KOH) to a sample from the vagina. A characteristic fishy odor, known as a positive Whiff test, can be indicative of Trichomonas infection.

The other options are incorrect:

• Entamoeba: The Whiff test is not used for the diagnosis of Entamoeba infections. Entamoeba histolytica is a protozoan parasite that causes amoebiasis.
• Giardia: The Whiff test is not used for the diagnosis of Giardia lamblia infections. Giardiasis is caused by a different protozoan parasite and is diagnosed using other methods such as microscopy or antigen detection.
• E. coli: The Whiff test is not used for the diagnosis of E. coli infections. E. coli is a bacterium commonly found in the intestines and can cause various infections, but the Whiff test is specific to Trichomonas vaginalis.

Answer: Bacillus

Bacillus is a Gram-positive rod-shaped bacterium that is known for its ability to form endospores. The spore formation is a characteristic feature of certain bacteria in the Bacillus genus. These endospores are highly resistant structures that allow the bacterium to survive harsh environmental conditions.

The other options are incorrect:

• Pseudomonas: Pseudomonas is a Gram-negative bacterium. It is not Gram-positive and does not form endospores.
• Staphylococcus: Staphylococcus is a Gram-positive bacterium, but it is not spore-forming. It does not produce endospores.
• Salmonella: Salmonella is a Gram-negative bacterium. It does not belong to the Gram-positive group and does not form endospores.

Answer: Tetanus

The vaccine recommended for pregnant women is the Tetanus Toxoid vaccine. Tetanus is a serious and potentially life-threatening bacterial infection, and the vaccine provides immunity against the toxins produced by the bacterium Clostridium tetani.

The other options are incorrect:

• Tuberculosis: The tuberculosis (TB) vaccine (BCG) is not routinely recommended for pregnant women. BCG vaccination is often given in areas with a high prevalence of tuberculosis, but it is not a routine vaccination during pregnancy.
• AIDS: There is no vaccine specifically for AIDS (caused by the human immunodeficiency virus, HIV). Prevention and management of HIV during pregnancy involve antiretroviral therapy, but there is no vaccine for general use.
• Poliomyelitis: While polio vaccination is important for overall population health, it is not specifically recommended as a routine vaccine for pregnant women. The inactivated polio vaccine (IPV) may be administered during pregnancy if there is a specific risk of exposure.

Answer: Streptococcus

Natural competence, the ability of a bacterium to take up DNA from its environment and incorporate it into its own genome, was first described by Frederick Griffith in 1928. He observed this phenomenon in Streptococcus pneumoniae, demonstrating the transfer of a virulence factor between strains.
The other options are incorrect:

• E. coli: Although naturally competent strains of E. coli exist, the phenomenon was not first observed in this species.
• Staphylococcus: While some Staphylococcus species are naturally competent, the initial description of the phenomenon did not involve this genus.
• Bacillus: Natural competence is well-studied in Bacillus species, but its discovery predates the observations in this genus.

Answer: Both Block endonucleases and Maintain pH

In genomic DNA isolation, TE buffer (Tris-EDTA buffer) serves two main functions. It helps to maintain a stable pH, as Tris acts as a buffering agent, preventing large fluctuations in pH. Additionally, EDTA in the buffer chelates divalent cations, such as Mg2+, and helps to inhibit the activity of endonucleases, thereby blocking their action on DNA.

The other options are incorrect:

• Block endonucleases: This is part of the correct answer. TE buffer helps to block endonucleases by chelating divalent cations required for their activity.
• Maintain pH: This is part of the correct answer. TE buffer is used to maintain a stable pH during DNA isolation procedures.
• Denature protein: TE buffer is not primarily designed to

Answer: Tetanus

An example of a non-communicable disease is Tetanus. Tetanus is caused by the bacterium Clostridium tetani and is not spread directly from person to person. Instead, it typically occurs through the introduction of bacterial spores into wounds or cuts.

The other options are incorrect:

• Measles: Measles is a communicable disease caused by the measles virus. It spreads through respiratory droplets and is highly contagious.
• Tuberculosis: Tuberculosis (TB) is a communicable disease caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs and can spread through the air when an infected person coughs or sneezes.
• Leprosy: Leprosy, or Hansen’s disease, is a communicable disease caused by the bacterium Mycobacterium leprae. It mainly spreads through respiratory droplets.

Answer: Shiga toxin

Escherichia coli (E. coli) O157:H7 is known for producing Shiga toxin. This toxin is associated with severe foodborne illnesses caused by certain strains of E. coli. Shiga toxin can cause damage to the lining of the intestine and lead to symptoms such as bloody diarrhea and, in severe cases, hemolytic uremic syndrome (HUS).

The other options are incorrect:

• Colon toxin: There is no specific term “colon toxin” associated with E. coli O157:H7. The primary toxin produced by this strain is Shiga toxin.
• Neurotoxin: E. coli O157:H7 is not known for producing neurotoxins. Neurotoxins typically affect the nervous system, and the symptoms associated with E. coli O157:H7 are primarily related to the gastrointestinal system.
• Exotoxin: While Shiga toxin is a type of exotoxin, the term “exotoxin” is broad and not specific to E. coli O157:H7. Shiga toxin is a more specific term for the toxin produced by this bacterium.

Answer: CaCl2

Treatment with calcium chloride (CaCl²) is used to induce competence in bacterial cells, a state where the cells can take up foreign DNA from their environment. This process is often referred to as calcium chloride transformation, and it is commonly used in laboratory settings for genetic engineering experiments.

The other options are incorrect:

• NaCl: Sodium chloride (NaCl) is a common salt, but it is not used to induce competence in bacterial cells. Competence is typically induced using calcium chloride.
• HgCl: Mercury chloride (HgCl) is not used to induce competence in bacterial cells. It is not associated with the process of transformation.
• NaHCO³: Sodium bicarbonate (NaHCO³) is not used to induce competence in bacterial cells. Competence is commonly induced using calcium chloride.