MicroBiology MCQs with Answer and Explnation | Chapter 23

Answer: High MW and chemical complexity

For a molecule (protein) to be considered an antigen, it generally needs to have both high molecular weight (MW) and chemical complexity. Antigens are substances that can induce an immune response, and high MW and chemical complexity contribute to the ability of an antigen to be recognized by the immune system. The immune system recognizes specific epitopes on antigens, and the size and complexity of the molecule can enhance its immunogenicity.

The other options are incorrect:

• High molecular weight: This option is partially correct. While high molecular weight contributes to antigenicity, chemical complexity is also important for the molecule to be considered a true antigen.
• Chemical complexity: This option is partially correct. Chemical complexity is important for antigenicity, but high molecular weight is also a significant factor.
• Nucleic acid: Nucleic acids (DNA and RNA) can be immunogenic, but they are generally not considered antigens in the traditional sense. Antigens are often proteins or large molecules with complex structures.

Answer: Artificial active immunity

Artificial active immunity refers to the process of acquiring immunity through the deliberate introduction of a weakened or inactive form of a pathogen, such as a vaccine. This stimulates the body’s immune system to produce its own antibodies and memory cells, providing long-term protection against the disease.

The other options are incorrect:

• Passive immunity: Passive immunity involves the transfer of ready-made antibodies from another individual. This provides temporary protection but does not induce long-term immune memory.
• Natural active immunity: Natural active immunity is acquired through exposure to the actual disease-causing organism. This results in the development of natural immunity through the activation of the immune system.
• Local immunity: Local immunity refers to the immune response specifically at the site of infection. It is not directly related to the type of immunity acquired.

Answer: Serum

The fluid extruded from clotted blood is known as serum. When blood clots, it forms a solid component (clot) and a liquid component. The liquid portion, which is devoid of clotting factors and fibrinogen, is serum. Serum retains many of the blood’s components, such as antibodies, electrolytes, and proteins, but lacks the clotting factors that are present in plasma.

The other options are incorrect:

• Plasma: Plasma is the liquid component of blood before clotting occurs. It contains clotting factors, fibrinogen, and other components that contribute to blood clotting.
• Buffy coat: The buffy coat is a thin, whitish layer that forms between the red blood cells and plasma during centrifugation. It consists of white blood cells and platelets.
• Lymph: Lymph is a clear fluid that circulates in the lymphatic system. It is not directly derived from clotted blood but rather from interstitial fluid and lymphatic vessels.

Answer: Toll-like receptors

Toll-like receptors (TLRs) are a family of pattern recognition receptors (PRRs) that recognize distinct molecular structures, known as pathogen-associated molecular patterns (PAMPs), which are abundant on many cells, especially pathogens. Humans have ten different TLRs, each recognizing a specific range of PAMPs.

The other options are incorrect:

• Nod-like receptors (NLRs): NLRs are another family of PRRs that recognize intracellular PAMPs and damage-associated molecular patterns (DAMPs). However, they do not share the characteristics of being abundant on many cells and existing in ten distinct forms in humans.
• RIG-like receptors (RLRs): RLRs are cytosolic PRRs that recognize viral RNA. While they are important in the innate immune response, they do not recognize distinct molecular structures present on many cells or exist in ten different forms in humans.
• PAMP of neutrophils: PAMPs are not specific to neutrophils but are instead recognized by various immune cells, including neutrophils, through specific PRRs like TLRs.

Answer: PAMP

PAMP stands for Pathogen-Associated Molecular Pattern. These are molecules commonly found on the surface of microbes and are recognized by phagocytes, which are immune cells that engulf and destroy foreign invaders. PAMPs provide a signal to phagocytes that the microbe is a threat and needs to be eliminated.

The other options are incorrect:

• Complement: Complement is a protein system in the immune system that participates in several immune responses, including phagocytosis. However, it is not a signaling molecule released directly by microbes.
• Pyrogen: Pyrogens are substances that cause fever. While some microbes can produce pyrogens, they are not the only source, and pyrogen recognition is not a specific function of phagocytes.
• Lectin: Lectins are carbohydrate-binding proteins involved in various biological processes, including immune responses. However, they are not specific to microbes and are not the primary signaling molecules recognized by phagocytes for microbial identification.

Answer: Bradykinin

Bradykinin is not produced by phagocytes. Bradykinin is a peptide that plays a role in inflammation and vasodilation, but it is primarily generated in the plasma and tissues during the activation of the kinin system, which is part of the inflammatory response. Phagocytes, such as neutrophils and macrophages, are known for producing reactive oxygen species (ROS) like hydroxyl radicals, superoxide anions, and hydrogen peroxide as part of their antimicrobial activity.

The other options are incorrect:

• Hydroxyl radical: Hydroxyl radicals are produced by phagocytes as part of the respiratory burst during the oxidative burst mechanism, contributing to the destruction of engulfed microbes.
• Superoxide anion: Superoxide anions are generated by phagocytes as a part of the respiratory burst. They are involved in the oxidative killing of engulfed pathogens.
• Hydrogen peroxide: Hydrogen peroxide is produced by phagocytes and serves as a reactive oxygen species (ROS) during the respiratory burst. It plays a role in the destruction of engulfed microbes.

Answer: Lymphocytes

Acquired/adaptive immune cells are specialized white blood cells that are responsible for the specific and long-lasting immune response. They are able to recognize and target specific antigens, providing protection against infections and other foreign substances.

The other options are incorrect:

• Eosinophils: Eosinophils are innate immune cells involved in allergic reactions and parasitic infections. They are not part of the adaptive immune system.
• Basophils: Basophils are also innate immune cells involved in allergic reactions and inflammation. They are not considered adaptive immune cells.
• Neutrophils: Neutrophils are the most abundant type of white blood cell and are the first line of defense against bacterial infections. They are part of the innate immune system and not involved in the adaptive response.

Answer: Binary Fission

Reproduction in bacteria occurs by binary fission. Binary fission is a simple form of asexual reproduction in which a single bacterial cell divides into two daughter cells. The process involves DNA replication, elongation of the cell, and division of the cell into two genetically identical daughter cells. Binary fission is the primary mode of reproduction in bacteria and allows for rapid population growth.

The other options are incorrect:

• Budding: Budding is a form of asexual reproduction in which a new organism develops as an outgrowth or “bud” from the parent organism. This method is not characteristic of bacterial reproduction.
• Bursting: Bursting refers to the lytic cycle in bacteriophages, where the host bacterial cell is lysed (burst open) to release newly replicated phage particles. It is not a method of bacterial reproduction.
• Fragmentation: Fragmentation involves the breaking of an organism into fragments, and each fragment can grow into a new organism. This process is not typical of bacterial reproduction but is more characteristic of some eukaryotic organisms.

Answer: Bacteriophages

Bacteriophages, often shortened to phages, are viruses that specifically infect and destroy bacteria. They are the most abundant biological entities on Earth and play a crucial role in regulating bacterial populations and preventing harmful bacterial infections.

The other options are incorrect:

• Phagocytes: These are immune cells that engulf and destroy foreign invaders, including bacteria. While they play a similar role to bacteriophages in controlling bacterial populations, they are distinct entities.
• Viricides: These are substances that kill viruses, not bacteria. Bacteriophages are specific to bacteria and do not affect viruses.
• Prophages: These are bacteriophages that have integrated their genetic material into the bacterial chromosome. They are not active viruses but can reactivate under certain conditions.

Answer: Staphylococcus

Staphylococcus is a Gram-positive bacterium. This means that in the Gram staining procedure, it retains the crystal violet stain, appearing purple or blue under the microscope. This is due to the thick layer of peptidoglycan in the cell wall, which traps the stain.

The other options are incorrect:

• E. coli: E. coli is a Gram-negative bacterium. It does not retain the crystal violet stain during Gram staining and appears red or pink under the microscope.
• Salmonella: Salmonella is also a Gram-negative bacterium with the same staining characteristics as E. coli.
• Pseudomonas: Pseudomonas is another Gram-negative bacterium with a thin peptidoglycan layer and negative Gram staining results.

Answer: potassium acetate

In plasmid DNA isolation, potassium acetate solution is used to neutralize the lysis buffer, which contains sodium hydroxide (NaOH) and SDS (sodium dodecyl sulfate). The neutralization step is crucial for enabling the renaturation of plasmid DNA, which involves the reformation of its double-stranded structure.

The other options are incorrect:

• NaCl: Although sodium chloride (NaCl) is commonly used in biological buffers, it does not neutralize the high pH of the lysis buffer and is not specific to plasmid DNA isolation procedures.
• Acetic acid: Acetic acid can be used to neutralize certain buffers, but it is not commonly used in plasmid DNA isolation and may damage the DNA if used incorrectly.

Answer: proteinase K

In genomic DNA isolation, the disruption of nucleoproteins and degradation of proteins is carried out by the enzyme proteinase K. Proteinase K is a broad-spectrum serine protease that is able to digest a wide range of proteins, including nucleases and nucleoproteins, which are associated with DNA. This enzyme is commonly used in DNA extraction protocols to remove proteins and other contaminants, allowing for the isolation of purified genomic DNA.

The other options are incorrect:

• SDS (Sodium dodecyl sulfate): SDS is a detergent that is often used to solubilize and denature proteins, but it is not specifically involved in the degradation of proteins during genomic DNA isolation.
• Isopropanol: Isopropanol is typically used for DNA precipitation but does not play a role in the disruption of nucleoproteins or the degradation of proteins during the initial steps of genomic DNA isolation.
• Alcohol: “Alcohol” is a broad term and does not specify a particular reagent used for the disruption of nucleoproteins or degradation of proteins during genomic DNA isolation. Proteinase K is a more specific enzyme used for this purpose.

Answer: Yeast

Cryptococcus is transmitted in the form of yeast. Cryptococcus species, such as Cryptococcus neoformans, are encapsulated yeast-like fungi. The infectious form of Cryptococcus is the yeast, and it is commonly associated with respiratory infections, particularly in immunocompromised individuals. The encapsulated yeast cells are capable of causing cryptococcosis, a fungal infection that can affect the lungs and other organs.

The other options are incorrect:

• Endospores: Endospores are a specialized, resistant form of bacteria (e.g., Bacillus and Clostridium species), not fungi like Cryptococcus.
• Conidia: Conidia are asexual reproductive structures produced by certain fungi, particularly molds, and are not associated with Cryptococcus.
• Spores: While the term “spores” is generic and can refer to various reproductive structures, it does not specifically describe the infectious form of Cryptococcus. Cryptococcus is transmitted in the yeast form.

Answer: Lowenstein–Jensen (LJ) medium

Lowenstein–Jensen (LJ) medium is the most commonly used selective media for the isolation of Mycobacterium tuberculosis, the causative agent of tuberculosis (TB). This medium is enriched with glycerol and asparagine, which support the growth of TB bacilli while inhibiting the growth of most other bacteria. Additionally, LJ medium contains various inhibitors, such as malachite green and brilliant green, which further suppress the growth of competing bacteria.

The other options are incorrect:

• NNN media: This medium is not commonly used for TB diagnosis. It is primarily used for the isolation of Nocardia species, a different type of bacteria.
• Mannitol Salt Agar (MSA): MSA is a selective medium for the isolation of Staphylococcus aureus. While it can inhibit the growth of some other bacteria, it is not suitable for isolating TB bacilli.
• MacConkey media: This medium is used to differentiate between lactose-fermenting and non-lactose-fermenting bacteria. It is not selective for TB bacilli.

Answer: Typhoid fever

The Widal test is used for the diagnosis of typhoid fever, an infectious disease caused by the bacterium Salmonella enterica serotype Typhi. The test detects antibodies produced in response to infection with Salmonella Typhi. The Widal test involves the agglutination of bacterial antigens (O and H antigens) with patient serum, and the presence of specific antibodies is indicative of a recent or current infection with Salmonella Typhi.

The other options are incorrect:

• Salmonella: While the Widal test is used to detect antibodies against Salmonella Typhi, it is specifically designed for the diagnosis of typhoid fever caused by Salmonella Typhi.
• Brucellosis: The Widal test is not used for the diagnosis of brucellosis. Brucellosis is caused by bacteria of the genus Brucella, and different serological tests, such as the Rose Bengal test or the standard tube agglutination test, are used for the diagnosis of brucellosis.

Answer: Chitin

The cell wall of fungi is primarily composed of chitin. Chitin is a complex polysaccharide that provides strength and rigidity to the fungal cell wall.

The other options are incorrect:

• Peptidoglycan: Peptidoglycan is a component of bacterial cell walls, not fungal cell walls.
• Murine: “Murine” refers to things related to mice or rats and is not a component of fungal cell walls.
• Cellulose: Cellulose is a polysaccharide found in the cell walls of plants, not fungi. Fungal cell walls contain chitin instead.

Answer: Anthrax

Ascoli’s test is used to confirm the laboratory diagnosis of anthrax. It is a serological test that detects antibodies against the protective antigen of Bacillus anthracis, the bacterium that causes anthrax.

The other options are incorrect:

• Tetanus: Ascoli’s test is not relevant to tetanus. Tetanus is caused by the bacterium Clostridium tetani.
• Typhoid: Ascoli’s test is not used for the diagnosis of typhoid fever. Typhoid fever is caused by the bacterium Salmonella Typhi.
• Cholera: Ascoli’s test is not applicable to cholera. Cholera is caused by the bacterium Vibrio cholerae.

Answer: eukaryotic

Transfection refers to the process of introducing foreign DNA into eukaryotic cells. This can be done for various purposes, such as studying gene function, producing proteins, or developing gene therapies. Bacteria have a different mechanism for DNA uptake called transformation, which does not involve transfection methods.

The other options are incorrect:

• Bacterial: While bacteria can take up foreign DNA through transformation, this process is distinct from transfection. Transfection specifically refers to the introduction of DNA into eukaryotic cells.
• Viruses: Viruses deliver their own genetic material into host cells, but this is not considered transfection. Transfection refers to the introduction of non-viral DNA into cells.
• Both bacterial and eukaryotic: This is incorrect because transfection is specific to eukaryotic cells.

Answer: Color and density

In agarose gel electrophoresis, loading buffer serves the purpose of providing color to the sample for easy visualization and density to the sample to ensure it sinks into the wells during loading. The color helps in tracking the movement of the sample through the gel during electrophoresis.

The other options are incorrect:

• Color: While color is provided by the loading buffer, it is not the only function. Density is also crucial for proper sample loading.
• Density: Density is indeed a crucial function of the loading buffer, but it also provides color. This option is partially correct but incomplete.
• Shade: “Shade” is not a specific function of the loading buffer in agarose gel electrophoresis. The loading buffer primarily provides color and density to the sample.

Answer: Neurotoxin

The virulence factor of botulism is a neurotoxin produced by the bacterium Clostridium botulinum. This neurotoxin blocks the release of acetylcholine at neuromuscular junctions, leading to muscle paralysis and the characteristic symptoms of botulism.

The other options are incorrect:

• Endotoxin: Botulism is not associated with endotoxins. Endotoxins are typically associated with the outer membrane of Gram-negative bacteria.
• Enterotoxin: Botulism is not caused by an enterotoxin. Enterotoxins typically affect the intestines and cause symptoms like diarrhea and vomiting.
• Hemolysin enzyme: Botulism is not characterized by a hemolysin enzyme. Hemolysins are enzymes that can cause the lysis of red blood cells, and they are not the primary virulence factor in botulism.

Answer: Treponema

Treponema is a genus of spiral-shaped bacteria belonging to the phylum Spirochaetes. These bacteria are known for their distinctive helical morphology and are responsible for various diseases, including syphilis, yaws, and pinta.

The other options are incorrect:

• Gonococci: Gonococci are gram-negative diplococci belonging to the genus Neisseria. They are the causative agents of gonorrhea, a sexually transmitted infection.
• Staphylococcus: Staphylococci are gram-positive cocci that grow in clusters resembling grapes. They are common inhabitants of the skin and mucous membranes and can cause various infections, including skin infections, pneumonia, and sepsis.
• Streptococcus: Streptococci are gram-positive cocci that can grow in chains or pairs. They are also common inhabitants of the skin and mucous membranes and can cause various illnesses, including strep throat, scarlet fever, and pneumonia.

Answer: Phagolysosome

Once the phagosome, which is a vacuole formed during phagocytosis, fuses with a lysosome, the resulting structure is called a phagolysosome. This fusion allows the enzymes from the lysosome to mix with the engulfed material in the phagosome, facilitating digestion and degradation of the internalized particles.

The other options are incorrect:

• Lysophagosome: This term is not commonly used in cell biology. The correct term for the fusion of a phagosome with a lysosome is a phagolysosome.
• Macrophage: A macrophage is a type of immune cell that can engulf and digest foreign particles, but it is not the term used for the structure formed by the fusion of a phagosome and a lysosome.
• Membrane attack complex: The membrane attack complex is a part of the immune system, but it is not formed by the fusion of a phagosome and lysosome. It is involved in the complement system and the destruction of target cells.

Answer: Thymus

T-lymphocytes, also known as T cells, are essential components of the immune system responsible for cell-mediated immunity. They mature in the thymus, a gland located behind the breastbone. In the thymus, T cells undergo a rigorous selection process where they develop the ability to recognize and destroy foreign invaders while avoiding attacking the body’s own tissues.

The other options are incorrect:

• Thyroid: The thyroid gland is located in the neck and produces hormones essential for metabolism and growth. It has no role in T cell development.
• Bone marrow: Bone marrow is the primary site of blood cell production, including B lymphocytes (another type of immune cell). However, while T cells originate in the bone marrow, they mature solely in the thymus.
• Tonsils: Tonsils are small masses of lymphatic tissue located at the back of the throat. They play a role in the immune response by trapping and filtering foreign particles, but they do not participate in T cell development.

Answer: Lysozyme

Lysozyme is an enzyme found in tears, saliva, serum, and mucus that helps protect against bacterial infections. It specifically breaks down the peptidoglycan, a major component of the cell wall in Gram-positive bacteria, leading to cell lysis and death.

The other options are incorrect:

• Amylase: Amylase is an enzyme that breaks down starch into sugars. While important for digestion, it does not affect bacteria.
• Keratinase: Keratinase is an enzyme that breaks down keratin, a protein found in hair, nails, and skin. It has no role in bacterial defense.
• Peptidase: Peptidases are a broad category of enzymes that break down proteins. Lysozyme is a specific type of peptidase that targets peptidoglycan in bacterial cell walls.

Answer: Phagosome

When a pathogen is internalized via endocytosis, it is engulfed by the host cell and enclosed within a membrane-bound vesicle called a phagosome. The phagosome is responsible for transporting the pathogen into the cell’s interior for further processing.

Incorrect Options:

• Lipid bilayer: While endocytosis involves the formation of a vesicle with a lipid bilayer, the specific term for the membrane vacuole containing an internalized pathogen is a phagosome.
• Lysosome: Lysosomes are cellular organelles that contain enzymes for digestion. They may fuse with the phagosome to form a phagolysosome, but initially, the pathogen is enclosed in a phagosome.
• Phagolysosome: A phagolysosome is formed when a phagosome containing a pathogen fuses with a lysosome. However, the initial vacuole enclosing the pathogen is called a phagosome.

Answer: S. typhi

Salmonella typhi (S. typhi) is primarily a human pathogenic bacterium and is responsible for causing typhoid fever. It is transmitted through contaminated food and water and can cause systemic infections in humans.

The other options are incorrect:

• E. coli: Escherichia coli (E. coli) is a diverse bacterium, and while some strains can be pathogenic, many strains are harmless and part of the normal gut microbiota. Pathogenic strains can cause gastrointestinal infections.
• S. aureus: Staphylococcus aureus (S. aureus) is a bacterium that can cause a range of infections in humans. While it is an important pathogen, it is not primarily associated with systemic infections like S. typhi.
• Mycobacterium: Mycobacterium includes species such as Mycobacterium tuberculosis, which causes tuberculosis. While Mycobacterium species can be pathogenic to humans, they are not primarily known for causing gastrointestinal infections like S. typhi.

Answer: Selenite F broth

Selenite F broth is an enrichment medium used for the isolation of Salmonella species from clinical and environmental samples. It contains selenite, which inhibits the growth of other bacteria and enriches for the growth of Salmonella.

The other options are incorrect:

• Alkaline peptone water: Alkaline peptone water is used for the pre-enrichment of Vibrio species, not specifically for Salmonella.
• MacConkey broth: MacConkey broth is a selective medium for Gram-negative bacteria, but it is not commonly used as an enrichment medium for Salmonella.
• Nutrient broth: Nutrient broth is a general-purpose medium and does not selectively enrich for Salmonella. It is used for routine cultivation of a variety of microorganisms.

Answer: Both “Maintain pH” and “Block endonucleases”

TE buffer (Tris-EDTA buffer) serves the dual function of maintaining a stable pH and inhibiting the activity of endonucleases. Tris helps in maintaining a constant pH, while EDTA chelates divalent cations, such as Mg²⁺, which are cofactors for many endonucleases, preventing their activity.

The other options are incorrect:

• Maintain pH: This option is correct. TE buffer is designed to maintain a stable pH.
• Block endonucleases: This option is correct. The EDTA in TE buffer chelates divalent cations, inhibiting the activity of endonucleases.
• Denature proteins: TE buffer is not specifically designed to denature proteins. Its primary functions are pH maintenance and inhibition of endonuclease activity. It is not a denaturing buffer commonly used for proteins.

Answer: Size

Agarose gel electrophoresis separates molecules based on their size. The gel matrix acts as a sieve, and when an electric current is applied, smaller molecules move more easily through the pores of the gel, while larger molecules move more slowly.

The other options are incorrect:

• Electrical charge: Agarose gel electrophoresis primarily separates molecules based on size, not electrical charge. The movement is influenced by the size of the molecules and their interaction with the gel matrix.
• Shape: Agarose gel electrophoresis is not designed to separate molecules based on their shape. It primarily focuses on size-based separation.
• All of these: The correct factor for separation in agarose gel electrophoresis is size. While electrical charge does play a role, and shape to some extent, the primary basis is size. The “All of these” option is not accurate as it implies an equal emphasis on electrical charge and shape, which is not the case

Answer: All of these

Accidental exposure to Brucella in a laboratory setting can occur through various routes, including working with Brucella on an open bench, direct contact with abraded skin, and ingestion. Brucella is a bacterium that can cause brucellosis, and laboratory personnel must follow appropriate safety protocols to minimize the risk of exposure.

The other options are incorrect:

• Working with Brucella on an open bench: This is a correct statement. Accidental exposure can occur when working with Brucella on an open bench if proper safety precautions are not followed.
• Direct contact with abraded skin: This is a correct statement. Brucella can enter the body through abraded skin, leading to accidental exposure.
• Ingestion: This is a correct statement. Ingestion of Brucella, such as through accidental ingestion of contaminated materials, can lead to exposure and infection.

Answer: Large, small

Lower percentage agarose gels, such as a 0.7% gel, are suitable for resolving larger DNA fragments, as they have larger pores in the gel matrix, allowing for easier movement of larger molecules. On the other hand, higher percentage agarose gels, like a 2% gel, are used for resolving smaller DNA fragments, as they provide a denser matrix, slowing down larger molecules and allowing separation of smaller ones.

The other options are incorrect:

• Small, large: This option is incorrect. Lower percentage agarose gels provide good resolution for larger DNA fragments, while higher percentage gels are suitable for smaller DNA fragments.
• Both Large, small & small, large: The correct answer is “Large, small.” This option is incorrect as it suggests both combinations, but only “Large, small” is accurate for 0.7% and 2% agarose gels, respectively.
• None of these: The correct answer is “Large, small.” This option is incorrect as it suggests that neither combination is accurate, but the statement about 0.7% and 2% agarose gels is accurate.

Answer: Antibody production

Innate immunity is the body’s first line of defense against pathogens and includes mechanisms like anatomical barriers, phagocytosis, and inflammatory responses. However, antibody production is a part of the adaptive immune system, which is not considered innate. Adaptive immunity develops more slowly and specifically targets pathogens based on previous exposure.

The other options are incorrect:

• Anatomical barriers: Innate immunity includes anatomical barriers such as the skin and mucous membranes that act as physical barriers to prevent pathogens from entering the body.
• Phagocytosis: Phagocytosis is a key component of innate immunity, involving the engulfment and destruction of pathogens by specialized cells such as macrophages and neutrophils.
• Inflammatory mechanisms: Inflammatory responses, characterized by redness, swelling, heat, and pain, are part of innate immunity and help recruit immune cells to the site of infection or tissue damage.

Answer: The physical barrier produced by hairs.

The physical barrier produced by hairs. Sneezing in response to dust is an example of a mechanical or physical barrier provided by tiny hair-like structures (cilia) in the nasal passages. These hairs trap dust particles and help to expel them through sneezing, protecting the respiratory system.

The other options are incorrect:

• The low pH of the environment: Low pH is not a mechanism involved in sneezing. It is more related to acidic environments, which can be a defense mechanism in the stomach against ingested pathogens.
• Phagocytosis by macrophages: Phagocytosis by macrophages is a cellular process where immune cells engulf and digest pathogens. It is not directly related to the act of sneezing in response to dust.
• Mucus joint with movement of cilia of lining cells: While mucus and cilia play a role in the respiratory system’s defense, the specific mechanism described in the question is the physical barrier produced by hairs, not the joint action of mucus and cilia. The latter is more associated with the mucociliary escalator, which helps in removing particles from the respiratory tract.

Answer: Antigenic specificity in only one system.

“Antigenic specificity in only one system.” The key distinction between the innate and adaptive immune systems is the presence of antigenic specificity in the adaptive immune system. The adaptive immune system can recognize and respond to specific antigens, which are molecules on the surface of pathogens. This specificity allows the adaptive immune system to mount targeted and tailored responses to particular pathogens.

The other options are incorrect:

• Only one system to produce cytokines: Both the innate and adaptive immune systems can produce cytokines. Cytokines are signaling molecules that play crucial roles in regulating immune responses, and they are produced by various cells in both immune systems.
• Only one system to recognize virally infected cells: Both the innate and adaptive immune systems can recognize and respond to virally infected cells. The innate system uses general mechanisms, while the adaptive system employs specific recognition through antigen receptors.
• Only one system to mediate cell cytotoxicity: Both the innate and adaptive immune systems can mediate cell cytotoxicity. Natural killer (NK) cells, a component of the innate immune system, are known for their cytotoxic activity, while cytotoxic T cells in the adaptive immune system also play a role in killing infected or abnormal cells.

Answer: Secreting HCl

“Secreting HCl.” The stomach clears out pathogens primarily by secreting hydrochloric acid (HCl). The low pH created by HCl is highly acidic and serves as a strong antimicrobial barrier, killing many pathogens that enter the stomach with ingested food.

The other options are incorrect:

• Normal microflora: Normal microflora refers to the beneficial microorganisms that naturally inhabit certain parts of the body, such as the gut. While these microorganisms play a role in preventing the overgrowth of harmful pathogens, they are not the primary mechanism by which the stomach clears out pathogens.
• Phagocytosis: Phagocytosis is a cellular process where immune cells engulf and digest pathogens. This mechanism is more characteristic of the immune responses occurring in tissues rather than the stomach’s direct action in clearing pathogens.
• All of these: While the stomach does secrete HCl to clear pathogens, normal microflora and phagocytosis are not direct actions of the stomach. Normal microflora is more associated with the gut, and phagocytosis is a cellular process carried out by immune cells in other parts of the body.

Answer: Liver

Kupffer cells are macrophages found in the liver. They are specialized tissue-resident macrophages that reside in the liver sinusoids, the blood-filled spaces within the liver. Kupffer cells play a crucial role in immune surveillance within the liver, where they engulf and remove pathogens, cellular debris, and foreign particles from the blood.

The other options are incorrect:

• Lung: Macrophages in the lung are often referred to as alveolar macrophages. They play a role in immune defense within the respiratory system.
• Bone: Macrophages in bone are known as osteoclasts, and they are involved in bone remodeling rather than immune defense.
• Kidney: Macrophages in the kidney are part of the renal tissue’s immune surveillance, but they are not specifically called Kupffer cells. Kupffer cells are unique to the liver.

Answer: Thermogens

Thermogens.” Thermogens are substances or chemicals that induce or promote an increase in body temperature. This increase in temperature can be a result of metabolic processes or other mechanisms that generate heat.

The other options are incorrect:

• Pyrogens: Pyrogens are substances that can induce fever by raising the body’s temperature. While pyrogens can lead to an increase in temperature, the term “temperature rising chemicals” is more accurately described by thermogens.
• Pyogenic: Pyogenic refers to substances or organisms that can induce the formation of pus, typically associated with infection. It does not specifically relate to the concept of temperature elevation.
• All of these: While pyrogens can contribute to an increase in body temperature, and pyogenic substances may be associated with infections, the term “temperature rising chemicals” is most accurately represented by thermogens, which encompass a broader range of substances contributing to temperature elevation.

Answer: Skin and the mucosal membranes.

Skin and the mucosal membranes.” These are considered physical barriers of the immune system. The skin acts as a protective barrier that prevents pathogens from entering the body, and mucosal membranes, such as those lining the respiratory and digestive tracts, provide additional protection by producing mucus and other substances that trap and eliminate pathogens.

The other options are incorrect:

• Skin, body temperature, and mucosal membranes: While skin and mucosal membranes are physical barriers, body temperature is more related to the physiological response of fever, which is a part of the immune response, rather than a physical barrier.
• Skin, inflammation, and the mucosal membranes: Inflammation is a dynamic response of tissues to injury or infection and is not a physical barrier. Skin and mucosal membranes are physical barriers, but inflammation is a part of the immune response that occurs after a breach in these barriers.
• The bones and the mucosal membranes: Bones are not typically considered physical barriers of the immune system. Physical barriers are structures that prevent the entry of pathogens, and bones do not directly contribute to this function.

Answer: Tears, breast milk, sweat, saliva, stomach acid.

Chemical barriers are a component of the immune system that involves the production of various substances with antimicrobial properties. The correct answer includes tears, breast milk, sweat, saliva, and stomach acid, all of which contain compounds that can help inhibit the growth and activity of pathogens.

The other options are incorrect:

• Tears, sweat, saliva, stomach acid and feces: While tears, sweat, saliva, and stomach acid are indeed chemical barriers, feces is not typically considered a chemical barrier. Feces are more associated with the elimination of waste from the digestive system.
• Hair, breast milk, sweat, saliva, stomach acid: Hair is not a chemical barrier; it is a physical barrier. Chemical barriers involve substances with antimicrobial properties, and hair does not possess such properties.
• Tears and urine: While tears are a chemical barrier, urine is not typically considered a chemical barrier of the immune system. Urine primarily serves to eliminate waste products from the body and maintain fluid balance.

Answer: Healthy host cells

Interferons are signaling proteins released by infected cells to warn neighboring healthy cells of the presence of a virus. These healthy cells then activate a series of antiviral mechanisms to prevent further viral replication and spread. Therefore, interferons primarily protect healthy host cells from viral infection.

The other options are incorrect:

• Only viral infected cells: While interferons are triggered by viral infection, they primarily act on uninfected surrounding cells, offering them a temporary antiviral defense.
• Only bacterial infected cells: Interferons are not specific to viral infections. They can also be produced in response to bacterial infections, but their antiviral effects are more prominent.
• Blood cells: While some blood cells, like lymphocytes, play a crucial role in the immune response, interferons do not specifically target them. Their primary function is to protect various healthy tissues and cells from viral invasion.

Answer: Uracil

RNA (ribonucleic acid) contains the nitrogenous base uracil. In RNA, uracil replaces thymine, which is found in DNA. The four nitrogenous bases in RNA are adenine (A), cytosine (C), guanine (G), and uracil (U).

The other options are incorrect:

• Alanine: Alanine is an amino acid, not a component of RNA. Amino acids are the building blocks of proteins.
• Thymidine: Thymidine is a nitrogenous base found in DNA, not in RNA. RNA uses uracil instead of thymine.
• Arginine: Arginine is an amino acid and is not a component of RNA. It is involved in protein synthesis but is not part of the genetic code in nucleic acids.

Answer: Generation time

“Generation time.” Generation time refers to the time it takes for a bacterial population to double through binary fission, the process by which a single bacterial cell divides into two identical daughter cells. It is a measure of the rate of bacterial reproduction.

The other options are incorrect:

• Incubation time: Incubation time generally refers to the period between exposure to a pathogen and the appearance of symptoms. It is not specifically related to the time taken for bacterial multiplication from 1 to 2.
• Growth rate: While growth rate is related to the increase in the number of bacterial cells, the specific time taken for one bacterium to divide into two is better represented by the concept of generation time.
• Both “Growth rate” and “Generation time”: While growth rate and generation time are related, they are not the same. Growth rate is a broader term, while generation time specifically measures the time for bacterial population doubling.

Answer: Plasmids

Plasmids are self-replicating, small circular DNA molecules that exist independently of the bacterial chromosomal DNA. They are commonly found in bacterial cells and can carry genes that provide additional functionalities, such as antibiotic resistance or the ability to metabolize certain substances.

The other options are incorrect:

• Cosmids: Cosmids are hybrid molecules that combine the features of plasmids and bacteriophages. They are used as cloning vectors in genetic engineering.
• Plasmomeros: “Plasmomeros” is not a recognized term. It may be a made-up or misspelled term. There is no specific cellular structure or component known as plasmomeros.
• Plastids: Plastids are organelles found in plant cells and some algae. They are involved in processes such as photosynthesis and are not related to self-replicating circular DNA molecules in bacterial cells.

Answer: Mucus joint with movement of cilia of lining cells

Mucus joint with movement of cilia of lining cells.” In the respiratory tract, mucus is produced to trap dust particles and other pathogens. The coordinated movement of cilia on the lining cells helps move the mucus along with the trapped particles out of the respiratory tract. This mechanism is known as the mucociliary escalator and plays a crucial role in preventing the entry of particles into the alveoli.

The other options are incorrect:

• Released granular contents of your granulocytes: Granulocytes release granular contents as part of immune responses, such as during inflammation, but their primary role is in the immune defense rather than the physical removal of dust particles from the respiratory tract.
• The low pH of the environment: The low pH of the environment, as seen in the stomach, is effective against pathogens in the digestive system. However, it is not a mechanism for eliminating dust particles in the respiratory tract.
• The physical barrier produced by hairs: The physical barrier produced by hairs, such as in the nasal passages, can prevent larger particles from entering the respiratory tract, but it is not directly involved in the elimination of particles that have already entered further down the

Answer: Translation

Translation is the process in which the information encoded in messenger RNA (mRNA) is used to build a corresponding protein. This occurs in the ribosomes, cellular structures where transfer RNA (tRNA) molecules bring amino acids to the mRNA template, and the ribosome catalyzes the formation of a polypeptide chain.

The other options are incorrect:

• Central dogma: The central dogma of molecular biology describes the flow of genetic information, stating that DNA is transcribed into mRNA, and then mRNA is translated into proteins. While translation is part of the central dogma, the term “Central dogma” alone does not specifically refer to the formation of proteins.
• Transcription: Transcription is the process of synthesizing mRNA from a DNA template. It occurs in the nucleus and precedes translation. Transcription produces the mRNA that carries the genetic information from the DNA to the ribosomes where translation takes place.
• Both Central dogma and Translation: While translation is indeed part of the central dogma, the term “Both Central dogma and Translation” is redundant. The central dogma encompasses both transcription and translation as sequential processes in the flow of genetic information.

Answer: Capnophiles

Capnophiles are bacteria that require more carbon dioxide (CO2) than the atmospheric concentration (0.04%) for their optimal growth. They typically thrive in environments with CO2 levels ranging from 5% to 10%, such as soil, the digestive tracts of animals, and certain fermentation processes.

The other options are incorrect:

• Halophiles: Halophiles are bacteria that require high salt concentrations for their growth. They are typically found in environments like salt lakes and oceans.
• Acidophiles: Acidophiles are bacteria that can grow in acidic environments with low pH values. They are commonly found in acidic soils, volcanic hot springs, and fermented foods.
• Hyperthermophiles: Hyperthermophiles are bacteria that thrive at extremely high temperatures, often exceeding 80°C. They are found in geothermal vents, deep-sea hydrothermal vents, and hot springs.

Answer: Passive natural acquired immunity

Passive natural acquired immunity occurs when antibodies are transferred from one individual to another through natural means, without the recipient having to actively develop their own immune response. This is the case with breast milk, where the mother’s antibodies pass to the baby through milk and provide temporary protection against various infections.

The other options are incorrect:

• Active natural acquired immunity: This occurs when an individual develops their own immune response to an antigen after being exposed to it. For example, recovering from a natural infection or exposure to a live attenuated vaccine.
• Passive artificial acquired immunity: This occurs when antibodies are transferred from one individual to another through artificial means, such as receiving an injection of antibodies (immunoglobulins).
• Active artificial acquired immunity: This occurs when an individual develops their own immune response to an antigen after receiving a vaccine containing a weakened or inactive form of the antigen.

Answer: A fungus

Penicillin is an antibiotic obtained from the fungus Penicillium notatum or Penicillium chrysogenum. These fungi produce penicillin as a natural defense mechanism against other bacteria. After its discovery by Alexander Fleming in 1928, penicillin revolutionized the field of medicine by becoming the first widely used antibiotic to effectively treat bacterial infections.

The other options are incorrect:

• A capsular bacterium: While some bacteria have capsules made of polysaccharides that offer protection against phagocytosis, penicillin is not derived from any bacterial species.
• A yeast: Yeasts are single-celled fungi different from the filamentous Penicillium species that produce penicillin.
• An alga: Algae are photosynthetic organisms that are not related to fungi and do not produce penicillin.

Answer: bacteriophages

Viruses that infect bacteria are known as bacteriophages. Bacteriophages are viruses that specifically target and infect bacterial cells. They have a complex structure and can inject their genetic material into bacterial cells, leading to the replication of new viral particles within the host bacterium.

The other options are incorrect:

• Virons: “Virons” is a general term for complete virus particles, including the genetic material and protein coat. While bacteriophages are a type of viron, the term “virons” is more inclusive and not specific to viruses that infect bacteria.
• Bacteroids: “Bacteroids” is not a term commonly used to describe viruses. It may be confused with structures in certain bacteria or other biological entities, but it is not the term for viruses that infect bacteria.
• Retroviruses: Retroviruses are a different type of virus that infects eukaryotic cells, including animals. They are characterized by the reverse transcription of their RNA genome into DNA within the host cell. Retroviruses do not infect bacteria.

Answer: Fungi

The Kingdom of recyclers refers to the Fungi. They play a vital role in decomposition, breaking down dead organic matter into simpler components that can be reused by other organisms. This process is crucial for nutrient cycling and ecosystem balance.

The other options are incorrect:

• Algae: While some algae can contribute to decomposition, their primary role is photosynthesis, not recycling organic matter.
• Bacteria: While bacteria also play a significant role in decomposition, they are not the only or the primary decomposers. Fungi are particularly well-suited for breaking down complex organic matter that bacteria cannot handle.
• Embryophata: This term is not widely used and doesn’t directly relate to the ecological role of recycling. It might refer to the plant kingdom, which includes Embryophyta, but plants are not primarily decomposers.