MicroBiology MCQs with Answer and Explnation | Chapter 26

Answer: Mannose receptor

The mannose receptor is an example of a pattern recognition receptor (PRR). Pattern recognition receptors play a crucial role in the innate immune system by recognizing conserved molecular patterns associated with pathogens, known as pathogen-associated molecular patterns (PAMPs). The mannose receptor specifically recognizes carbohydrates, including mannose, on the surface of pathogens.

The other options are incorrect:

• BCR (B-cell receptor): BCR is part of the adaptive immune system and is responsible for recognizing specific antigens. It does not function as a pattern recognition receptor for general pathogen-associated molecular patterns.
• Interleukin-1 receptor: Interleukin-1 receptor is involved in the recognition of the cytokine interleukin-1, but it is not a pattern recognition receptor for pathogen-associated molecular patterns.
• Fc receptor: Fc receptors bind to the Fc region of antibodies and are involved in antibody-mediated immune responses. While they play a role in immune recognition, they are not classified as pattern recognition receptors.

Answer: Hapten

A molecule that reacts with specific antibodies but lacks the ability to trigger an immune response by itself is called a hapten. They are small molecules that can bind to antibodies due to their specific chemical structure, but they lack the necessary features to activate B cells and initiate antibody production.

The other options are incorrect:

• Carrier: This refers to a large molecule (protein, polysaccharide) that can be conjugated to a hapten. The carrier provides the immunogenicity that the hapten lacks. When the combined molecule is introduced to the body, the immune system recognizes the carrier and mounts an immune response, resulting in antibody production against both the carrier and the hapten.
• Antigen: Any substance that can be recognized by the immune system and trigger an immune response is considered an antigen. This includes haptens when they are conjugated to carriers, but also larger molecules like proteins and polysaccharides that can directly activate B cells and induce antibody production.
• Immunogen: This specifically refers to an antigen that can both induce and be recognized by the immune system. Haptens lack the ability to induce an immune response, so they are not considered immunogens.

Answer: It is an example of a subunit vaccine

Influenza vaccines are typically subunit vaccines. These vaccines contain purified components of the influenza virus, such as specific surface proteins (hemagglutinin and neuraminidase), but not the whole live virus. This allows the vaccine to trigger an immune response against the virus without the risk of causing illness.

The other options are incorrect:

• Live attenuated vaccine: These vaccines contain a weakened or inactive form of the virus, which can still replicate to a limited extent. While some live attenuated vaccines exist, they are not commonly used for influenza due to the potential for side effects and the risk of transmission to immunocompromised individuals.
• Passive immunization: This involves providing pre-made antibodies against the virus, offering immediate protection but not long-term immunity. Influenza vaccines, on the other hand, stimulate the recipient’s own immune system to produce antibodies over time.
• Recombinant vaccine: These vaccines are produced using recombinant DNA technology, allowing for the targeted expression of specific viral proteins. While some research is ongoing on recombinant influenza vaccines, the most common type currently used are subunit vaccines.

Answer: C1q

C1q is the initial complement component bound by complement-fixing antibodies. These antibodies, primarily IgM and IgG2, recognize specific protein structures on the surface of pathogens or immune complexes. When they bind to these structures, the C1q component of the complement system, which exists as a six-armed protein, gets attached through its binding sites. This C1q-antibody complex initiates the classical pathway of complement activation, leading to a cascade of reactions that ultimately result in opsonization, inflammation, and cell lysis.

The other options are incorrect:

• C1s: This is another component of the C1 complex, but it doesn’t directly bind to antibodies. C1s is an enzyme that gets activated by the C1q-antibody complex and subsequently cleaves other complement components in the cascade.
• C3b: This is a breakdown product of complement component C3, generated later in the cascade. It can covalently bind to pathogens and immune complexes, serving as a tag for phagocytosis by immune cells. However, it’s not directly involved in the initial binding by complement-fixing antibodies.
• C5a: This is another complement component with different functions, including chemotaxis (attracting immune cells) and increased vascular permeability. It’s not involved in the initial binding by complement-fixing antibodies.

Answer: Adaptive; Lymphocytes; Innate; Phagocytes

The adaptive immune system uses lymphocytes (T cells and B cells) as well as antigen recognition molecules (such as antibodies). Lymphocytes play a key role in the adaptive immune response by recognizing specific antigens and generating immune responses tailored to those antigens.

The other options are incorrect:

• Adaptive; Phagocytes; Innate; Lymphocytes: The sequence of “Adaptive; Phagocytes” is incorrect. Phagocytes are primarily associated with the innate immune system.
• Innate; Lymphocytes; Adaptive; Phagocytes: The sequence of “Innate; Lymphocytes” is incorrect. Lymphocytes, which include T cells and B cells, are characteristic of the adaptive immune system.Innate;
• Phagocytes; Adaptive; Lymphocytes: The sequence of “Innate; Phagocytes” is correct for the innate immune system, but the subsequent sequence of “Adaptive; Lymphocytes” is incorrect. Lymphocytes are part of the adaptive immune system.

Answer: B-lymphocyte

B-lymphocytes, also known as B cells, are the only immune cells that use antibodies as membrane-bound receptors. These receptors, called B cell receptors (BCRs), are composed of two heavy chains and two light chains, all linked together and anchored to the B cell membrane. Each BCR has a unique antigen-binding site that can specifically recognize and bind to a particular antigen (foreign molecule).

The other options are incorrect:

• T-helper cell: These cells do not express BCRs and instead use T cell receptors (TCRs) to recognize antigen presented by other cells.
• Cytotoxic T-cell: Similar to T-helper cells, cytotoxic T cells recognize antigens via TCRs and do not have BCRs.
• Macrophage: These are phagocytic cells and antigen presenters but lack BCRs. They interact with pathogens through other receptors like complement receptors and mannose receptors.

Answer: Alternate pathway

The alternative pathway of the complement system is the first to be activated among the various pathways. It is a rapid and innate immune response that can be triggered independently of antibody involvement. The alternative pathway is initiated by the spontaneous hydrolysis of C3 (complement component 3) in the blood, leading to the formation of C3b and the activation of downstream complement components.

The other options are incorrect:

• Classical pathway: The classical pathway is typically activated by the binding of antibodies to antigens. It is an important component of the adaptive immune response and is activated later than the alternative pathway.
• Lectin pathway: The lectin pathway is initiated when mannose-binding lectin (MBL) binds to microbial surfaces. It is also part of the innate immune response but is generally activated after the alternative pathway.
• All act simultaneously: The complement pathways do not all act simultaneously. While they can converge at the level of C3 activation, the alternative pathway is the first to be initiated, followed by the lectin and classical pathways.

Answer: Thyroid gland

While the other options are all forms of lymphoid tissue, the thyroid gland is an endocrine gland primarily responsible for producing thyroid hormones that regulate metabolism, growth, and development. It lacks the characteristic features of lymphoid tissue, such as the presence of lymphocytes and organized structures for immune cell interaction and antigen presentation.

The other options are incorrect:

• Spleen: A large, soft organ rich in immune cells like B and T lymphocytes, macrophages, and dendritic cells. It filters blood, removes pathogens, and serves as a site for antibody production and immune cell activation.
• Lymph node: Clusters of lymphatic vessels containing lymphocytes, dendritic cells, and macrophages. They filter lymph fluid, trap pathogens, and initiate immune responses.
• GALT (Gut-associated lymphoid tissue): This term encompasses various lymphoid structures associated with the digestive tract, including Peyer’s patches, tonsils, and appendix. These structures provide immune surveillance and protection against pathogens entering through the GI tract.

Answer: phagocytes that recognize foreign molecules

Toll-like receptors (TLRs) are crucial protein receptors found on the surface of phagocytes, primarily macrophages and dendritic cells. These cells play a vital role in the innate immune system, acting as the first line of defense against pathogens. TLRs have the ability to recognize pathogen-associated molecular patterns (PAMPs), which are molecules specific to microorganisms and absent in human cells. This recognition triggers the innate immune response, leading to phagocytosis of the pathogen, inflammation, and the initiation of the adaptive immune response.

The other options are incorrect:

• Skin cells that provide barriers to infection: While skin cells do form a physical barrier against pathogens, they don’t typically express significant amounts of TLRs.
• Viruses that stimulate immune reactions: Viruses themselves are pathogens recognized by the immune system, not the ones expressing TLRs.
• Lymphocytes that damage parasitic worms: Lymphocytes are another major immune cell type, but they primarily rely on T cell receptors (TCRs) for antigen recognition, not TLRs.

Answer: bradykinin

Bradykinin is not produced by phagocytes. Bradykinin is a peptide that plays a role in inflammation, vasodilation, and pain sensation. It is produced through the activation of the kinin-kallikrein system, which is distinct from the mechanisms involved in reactive oxygen species (ROS) production by phagocytes.

The other options are incorrect:

• Hydroxyl radical: Hydroxyl radicals are produced by phagocytes during the respiratory burst, a process that generates reactive oxygen species (ROS) as a part of the immune response against pathogens.
• Superoxide anion: Superoxide anions are also generated by phagocytes during the respiratory burst. They contribute to the antimicrobial activity of phagocytes against engulfed microorganisms.
• Hydrogen peroxide: Hydrogen peroxide is produced by phagocytes as a byproduct of the respiratory burst. It has antimicrobial properties and participates in the oxidative killing of engulfed pathogens.

Answer: Prostaglandin

Prostaglandins increase chemotaxis, phagocytosis, and blood coagulation, and they also serve as endogenous pyrogens, meaning they can induce fever. These functions contribute to the inflammatory response and the immune system’s defense against infection and injury.

The other options are incorrect:

• Interferon gamma: Interferon gamma is a cytokine that plays a role in the activation of immune cells, particularly macrophages, and is involved in antiviral and immune regulatory functions. However, it is not primarily associated with chemotaxis, phagocytosis, blood coagulation, or serving as an endogenous pyrogen.
• Histamine: Histamine is released during allergic reactions and inflammation. While it contributes to vasodilation and increased vascular permeability, it is not directly involved in blood coagulation, and its role in chemotaxis and phagocytosis is limited.
• Tumor Necrosis Factor (TNF): TNF is a cytokine involved in inflammation and immune regulation. It plays a role in various immune responses, including promoting the recruitment of immune cells. However, it is not primarily associated with blood coagulation and does not serve as an endogenous pyrogen.

Answer: IgG

The major immunoglobulin (Ig) present in human serum is IgG (Immunoglobulin G). IgG constitutes the majority of circulating antibodies in the blood and is involved in various immune functions, including neutralizing toxins, opsonizing pathogens for phagocytosis, and providing passive immunity to the fetus during pregnancy.

The other options are incorrect:

• IgA: IgA is primarily found in mucosal secretions, such as saliva and breast milk. While it is important for mucosal immunity, it is not the major immunoglobulin in human serum.
• IgE: IgE is involved in allergic responses and defense against parasitic infections. It is present in low concentrations in the serum and is not the major immunoglobulin in the bloodstream.
• IgM: IgM is often the first antibody produced during an initial immune response. It is large and pentameric, playing a role in early defense against pathogens. However, IgG surpasses IgM in terms of abundance in human serum.

Answer: Interferon Gamma

Interferon Gamma (IFN-γ) is an immune regulator that plays a crucial role in the activation and regulation of macrophages, B cells, and T cells. It is produced by activated T cells, particularly T helper 1 (Th1) cells, and it enhances the antimicrobial activity of macrophages, stimulates B cells to produce antibodies, and modulates the activity of T cells.

The other options are incorrect:

• Interferon Alpha: Interferon Alpha (IFN-α) is primarily involved in antiviral responses and is produced by various cells, including leukocytes. While it has immune regulatory functions, it is not as specifically associated with macrophages, B cells, and T cells as IFN-γ.
• Interferon Beta: Interferon Beta (IFN-β) is another type of interferon involved in antiviral responses. Like IFN-α, it has immune regulatory functions but is not as specifically associated with macrophages, B cells, and T cells as IFN-γ.
• All of these: While all three types of interferons (Alpha, Beta, and Gamma) have immune regulatory functions, Interferon Gamma is the primary interferon associated with the activation and regulation of macrophages, B cells, and T cells.

Answer: TCRs cannot interact with free antigen

T-cell antigen receptors (TCRs) are distinguished from antibodies by the fact that TCRs cannot interact with free, soluble antigen. Unlike antibodies that can recognize and bind free antigens in the extracellular fluid, TCRs are designed to recognize antigens only when presented on the surface of host cells in the context of major histocompatibility complex (MHC) molecules.

The other options are incorrect:

• TCRs are glycosylated: Both TCRs and antibodies can be glycosylated, so glycosylation is not a distinguishing feature between the two.
• T-Cell receptors bind various cytokines: TCRs do not directly bind cytokines. Cytokine receptors on T cells interact with cytokines, and this interaction influences T cell behavior, but it is distinct from the antigen recognition function of TCRs.
• T-Cell receptors bind complement to lyse cells: TCRs do not interact with complement to lyse cells. The complement system is primarily activated through the classical pathway, involving antibodies, not TCRs.

Answer: Antibodies

Cell-mediated immunity is a branch of the adaptive immune response that relies primarily on T-lymphocytes and their various functions, such as direct killing of infected cells, activation of macrophages, and immune regulation. It does not heavily involve antibodies, which are the key players in humoral immunity.

The other options are incorrect:

• Macrophages: These phagocytic cells can present antigens to T cells, activate other immune cells, and directly kill pathogens through phagocytosis and the release of reactive oxygen species.
• Eosinophils: These granulocytes play a role in parasite defense and can contribute to tissue damage during allergic reactions. Although not as central as T cells, they participate in some cell-mediated responses.
• T-lymphocytes: As mentioned, T cells are the driving force behind cell-mediated immunity. They come in various forms, including cytotoxic T cells that directly kill infected cells, helper T cells that activate other immune cells, and regulatory T cells that control immune responses.

Answer: IgG

IgG (Immunoglobulin G) can provide naturally acquired passive immunity for the newborn. During pregnancy, IgG antibodies are transported across the placenta from the mother to the fetus, offering temporary protection to the newborn during the early months of life. This transfer of maternal antibodies provides the infant with immunity to various infections until the baby’s immune system becomes more developed.

The other options are incorrect:

• IgA: IgA is primarily found in mucosal secretions, such as breast milk, saliva, and colostrum. While it provides protection in mucosal areas, it does not cross the placenta to confer passive immunity to the newborn.
• IgE: IgE is associated with allergic responses and immune reactions against parasites. It is not typically involved in providing passive immunity to newborns.
• IgM: IgM is the first antibody produced during an initial immune response, and it is relatively large. While it plays a role in the immune response, IgM does not cross the placenta as effectively as IgG and is not a major contributor to naturally acquired passive immunity for the newborn.

Answer: MHC molecule

The major molecules responsible for the rejection of transplants are MHC molecules (Major Histocompatibility Complex). MHC molecules, also known as human leukocyte antigens (HLAs) in humans, play a crucial role in immune recognition. The immune system recognizes foreign MHC molecules on transplanted tissues as non-self, leading to an immune response against the graft, known as graft rejection.

The other options are incorrect:

• Cytokine: Cytokines are signaling molecules that play various roles in immune responses, including communication between immune cells. While cytokines are involved in the immune response to transplants, they are not the primary molecules responsible for rejection.
• Interferon: Interferons are signaling proteins involved in antiviral responses and immune regulation. While they may be produced during immune responses, they are not the primary molecules responsible for transplant rejection.
• Antibodies: While antibodies can contribute to transplant rejection, especially in the case of hyperacute rejection, they are not as central as MHC molecules. Antibodies may target antigens on the surface of transplanted cells, leading to immune-mediated damage.

Answer: Pluripotent stem cell

Pluripotent stem cells have the ability to self-renew and differentiate into diverse cell types. These cells can give rise to many different cell types of the body but do not have the potential to develop into all cell types, as seen with totipotent stem cells. Pluripotent stem cells are important in embryonic development and are the basis for the formation of tissues and organs.

The other options are incorrect:

• Adult stem cell: While adult stem cells can self-renew and differentiate into various cell types, their differentiation potential is generally more restricted compared to pluripotent stem cells. They are found in specific tissues and are involved in tissue repair and maintenance.
• Immature blood cells: Immature blood cells, such as hematopoietic stem cells, are a type of adult stem cell found in the bone marrow. They have the ability to differentiate into various blood cell types, but their differentiation potential is limited to the blood cell lineage.

Answer: Helicobacter pylori

Helicobacter pylori is a bacterium that can counteract the acidic environment of the stomach and establish an infection in the stomach lining. It possesses unique mechanisms to survive in the acidic gastric environment, including the production of urease, which helps neutralize stomach acid by converting urea into ammonia. H. pylori is associated with various gastrointestinal disorders, including gastritis and peptic ulcers.

The other options are incorrect:

• Mycobacterium tuberculosis: Mycobacterium tuberculosis is the causative agent of tuberculosis, a respiratory infection. It is not adapted to survive in the acidic environment of the stomach.
• Campylobacter jejuni: Campylobacter jejuni is a common cause of bacterial gastroenteritis, but it does not specifically counter stomach pH. It primarily affects the intestines and is not known for colonizing the stomach lining.
• Salmonella typhi: Salmonella typhi is the bacterium responsible for causing typhoid fever. While it can survive in the acidic environment of the stomach for a short time, its primary site of infection is the small intestine, not the stomach lining.

Answer: Natural active

Natural active immunity is acquired when an individual is exposed to a pathogen in the environment and develops an immune response, leading to the production of antibodies and memory cells. This type of immunity results from natural infection with a pathogen. The immune system recognizes the antigens of the pathogen, mounts a response, and “actively” generates an immune memory.

The other options are incorrect:

• Natural passive: Natural passive immunity occurs when antibodies are transferred from a mother to her offspring through natural processes such as breastfeeding or placental transfer. It does not involve the active participation of the immune system in generating a response.
• Artificial active: Artificial active immunity is induced through vaccination. It involves the administration of vaccines containing weakened or inactivated pathogens or their components to stimulate an immune response. It is not the result of natural infection.
• Artificial passive: Artificial passive immunity is achieved by administering pre-formed antibodies (such as through injections of immune serum or immunoglobulins) rather than relying on the individual’s immune response. It provides immediate protection but does not involve the activation of the individual’s immune system.

Answer: Glycoprotein

Interferon is a signaling protein, a type of molecule made up of chains of amino acids (proteins) with attached sugar molecules (glycosylation). This combination of protein and sugar classifies it as a “glycoprotein.”

The other options are incorrect:

• Lipids: These are fats and oils stored in the body as energy reserves. While some proteins interact with lipids in cellular membranes, interferons themselves are not made of lipids.
• Lipoprotein: These are complexes of lipids and proteins that transport fats in the bloodstream. Interferons, however, are water-soluble proteins and don’t require transportation by lipoproteins.
• Nucleic acid: These molecules like DNA and RNA store genetic information. While interferon’s production is influenced by genes, the protein itself is not formed from nucleic acids.

Answer: Contact dermatitis

Delayed-type hypersensitivity (DTH) is a cell-mediated immune response that takes 24-72 hours to develop after exposure to the allergen. Contact dermatitis, such as a rash from poison ivy, is a classic example of DTH. The immune system reacts to specific components of the plant, causing inflammation and irritation at the site of contact.

The other options are incorrect:

• Penicillin allergy: This is typically a Type I hypersensitivity reaction, mediated by IgE antibodies and mast cells, causing immediate symptoms like hives, swelling, and difficulty breathing.
• Arthus reaction: This is a Type III hypersensitivity reaction, involving circulating immune complexes that activate inflammation in blood vessels, leading to redness, swelling, and pain.
• Anaphylaxis: This is a severe, life-threatening Type I hypersensitivity reaction involving widespread activation of mast cells and release of chemicals, causing symptoms like shock, trouble breathing, and rapid heartbeat.

Answer: all nucleated cells

MHC class I molecules are crucial for the immune system’s cell-mediated immunity. They display peptide fragments of intracellular proteins on the cell surface, allowing cytotoxic T cells to recognize and eliminate infected or abnormal cells. Since all nucleated cells in your body (except red blood cells) can potentially harbor intracellular pathogens, they all express MHC class I molecules to assist in immune defense.

The other options are incorrect:

• B cells: These are lymphocytes involved in humoral immunity and produce antibodies. They lack the machinery to present intracellular peptides and instead express MHC class II molecules for antigen presentation to helper T cells.
• APCs (Antigen-presenting cells): While professional APCs like macrophages and dendritic cells express high levels of MHC class I due to their specialized role in antigen presentation, it’s not exclusive to them. All nucleated cells express a baseline level of MHC class I.
• T cells: These lymphocytes are the ones that recognize and respond to MHC-presented peptides. They themselves don’t express MHC class I for antigen presentation, only MHC class II in specific subsets.

Answer: APCs

MHC class II molecules are specialized for presenting extracellular antigens to helper T cells. These antigens are typically engulfed by APCs (like macrophages and dendritic cells) and processed into peptides before being loaded onto MHC class II molecules and displayed on the cell surface. Helper T cells then recognize these peptides and initiate specific immune responses. Therefore, MHC class II expression is primarily found on APCs.

The other options are incorrect:

• B cells: While B cells express MHC class II, their primary role is in humoral immunity through antibody production. They use MHC class II to present antigens to T cells for T-cell-dependent B cell activation, but their expression level is much lower compared to APCs.
• all nucleated cells: Unlike MHC class I, MHC class II expression is not ubiquitous. It’s mainly confined to professional APCs and some other cell types like B cells, thymic epithelial cells, and activated endothelial cells, based on their specific functions in the immune system.
• T cells: T cells are the ones that recognize and respond to MHC-presented antigens. They require MHC class II presentation for activation but do not express it themselves. They primarily express MHC class I for potential recognition by cytotoxic T cells.

Answer: Tc cells

Humoral immunity is the branch of the adaptive immune system that relies on antibodies produced by B cells and plasma cells to neutralize pathogens and toxins in the body fluids. Tc cells, on the other hand, are part of the cell-mediated immunity arm and directly attack infected cells instead of using antibodies.

The other options are incorrect:

• B cells: These are the lymphocytes that mature into plasma cells and produce antibodies, making them key players in humoral immunity.
• Antibodies: These are the Y-shaped protein molecules secreted by plasma cells that bind to specific antigens on pathogens, marking them for destruction or neutralization.
• Plasma cells: These are specialized B cells that have undergone activation and produce large amounts of antibodies for humoral immune responses.

Answer: γ-globulin injection

Artificial passive acquired immunity refers to the transfer of pre-formed antibodies from one individual to another. γ-globulin injection involves the administration of immunoglobulins, also known as gamma globulins or antibodies, obtained from the blood plasma of immune individuals. This provides immediate protection against certain infections and is a form of passive immunity.

The other options are incorrect:

• Inactivated vaccine: Inactivated vaccines contain killed or inactivated pathogens or their components. They stimulate the immune system to produce an active immune response but do not involve the transfer of pre-formed antibodies. Inactivated vaccines contribute to artificial active acquired immunity.
• Ingestion of colostrum: Colostrum is the early milk produced by mammals, rich in antibodies and nutrients. While the ingestion of colostrum provides passive immunity to newborns, it is a natural form of passive immunity and not an artificial intervention.
• Having infection: Having an infection leads to natural active acquired immunity, where the immune system responds to the infection by producing antibodies and memory cells. It is not considered artificial passive immunity.

Answer: contain heavy & light chains

Antibodies are Y-shaped proteins made up of two heavy chains and two light chains. These chains are linked together by disulfide bonds and play crucial roles in antigen binding and immune function. While carbohydrates are attached to some antibodies (glycosylation), they do not form the core structure of the molecule.

The other options are incorrect:

• are carbohydrates: While some antibodies have carbohydrate moieties attached, these are not the main building blocks. The core structure is formed by the heavy and light chains.
• are made from α & β chains: While amino acids are the building blocks of proteins, they don’t specifically differentiate between α and β chains in the context of antibodies. Both heavy and light chains can be α or β.
• contain no CHOs: This statement is incorrect. Some carbohydrates are attached to certain parts of the antibody molecule, especially the Fc region, contributing to functions like Fc receptor binding and complement activation.

Answer: Humoral immunity

B-lymphocytes, or B cells, are primarily involved in humoral immunity. Humoral immunity is the branch of the immune system that deals with the production of antibodies by B cells and their release into bodily fluids, such as blood and lymph. B cells recognize antigens, differentiate into plasma cells, and produce antibodies that can neutralize pathogens, facilitate their removal, and contribute to immune memory.

The other options are incorrect:

• Cell-mediated immunity: Cell-mediated immunity is primarily mediated by T-lymphocytes (T cells) and does not involve B cells. T cells recognize and directly interact with infected or abnormal cells.
• Active immunity: Active immunity refers to the immune response generated by an individual’s own immune system, either through natural infection or vaccination. B cells play a role in active immunity by producing antibodies.
• Passive immunity: Passive immunity involves the transfer of pre-formed antibodies from one individual to another. B cells are not directly associated with passive immunity, as this process typically involves the administration of antibodies or antibody-containing substances.

Answer: Monoclonal antibodies

The hybridoma technique is used for the production of monoclonal antibodies. In the hybridoma technique, hybrid cells called hybridomas are created by fusing a specific antibody-producing B cell with a myeloma (cancerous plasma cell) to produce a long-lived cell line that continuously produces a single type of antibody. This results in the production of identical (monoclonal) antibodies with high specificity for a particular antigen.

The other options are incorrect:

• Polyclonal antibodies: The hybridoma technique is not used for the production of polyclonal antibodies. Polyclonal antibodies are derived from the immune response of multiple B cells, leading to a mixture of antibodies with different specificities.
• Both “Monoclonal antibodies” and “Polyclonal antibodies”: The hybridoma technique is specifically designed for the production of monoclonal antibodies. While polyclonal antibodies can be generated through other methods, the hybridoma technique is not employed for this purpose.

Answer: All of these

Cell-mediated immunity relies on T cells and other immune cells to directly attack and eliminate infected cells or pathogens. All the listed examples involve this type of immune response:

• Tuberculin skin test: This test measures delayed-type hypersensitivity, a cell-mediated response where T cells react to a specific antigen (tuberculin) introduced under the skin, causing swelling and redness.
• Contact dermatitis: This skin reaction to allergens like poison ivy involves T cells recognizing and attacking skin cells exposed to the allergen, causing inflammation and irritation.
• Granulomatous inflammation: This type of chronic inflammatory response occurs around persistent infections or foreign materials. T cells orchestrate the formation of granulomas, localized areas of immune cells, to isolate and contain the threat.

Answer: Excision repair

In excision repair, a multi-step process is involved in correcting DNA damage, including the removal and replacement of incorrect bases. The first step typically involves the recognition and removal of damaged or incorrect bases by an enzyme complex known as an excision repair complex. After the removal, a second enzyme then fills in the gap with the correct bases, ensuring the integrity of the DNA sequence.

The other options are incorrect:

• Light repair: Light repair, also known as photoreactivation, involves the repair of DNA damage caused by exposure to ultraviolet (UV) light. It is not specifically associated with the removal and replacement of incorrect bases.
• Back mutation: Back mutation refers to a mutation that restores the original nucleotide sequence, but it is not a process specifically related to the repair of DNA damage involving the removal and replacement of bases.
• All of these: The correct term for the repair process involving the removal and replacement of incorrect bases is excision repair. While light repair and back mutation are related to DNA repair, they do not specifically involve the described mechanism of excision repair.

Answer: Passive

Antitoxins are pre-made antibodies obtained from another source, typically from animals like horses, that have been immunized against specific toxins. They are used for passive immunization, meaning they provide immediate but temporary protection against the corresponding toxin. Once injected, the antitoxins directly neutralize the toxin in the bloodstream, preventing it from causing harm.

The other options are incorrect:

• Active: Active immunization involves exposing the body to a weakened or inactive form of the pathogen or toxin, triggering the immune system to produce its own antibodies and memory cells. This creates long-term protection against future exposure. Antitoxins, however, do not stimulate the recipient’s immune system.
• Both “Active” and “Passive”: While antitoxin administration can sometimes be followed by active vaccination for long-term protection, the primary purpose of antitoxins is for immediate passive immunization.

Answer: T lymphocytes

The cell-mediated immune response is mainly driven by T lymphocytes, specifically cytotoxic T cells (Tc cells) and helper T cells (Th cells). These specialized cells directly attack infected cells or activate other immune cells like macrophages to eliminate pathogens and tumors. B lymphocytes, on the other hand, are responsible for humoral immunity, which involves producing antibodies to neutralize pathogens in the body fluids.

The other options are incorrect:

• B lymphocytes: While B cells play a crucial role in humoral immunity, they are not directly involved in the cell-mediated immune response.
• B & T lymphocytes: While both cell types contribute to the overall immune system, the cell-mediated response specifically involves the actions of T lymphocytes.
• Endothelial cells: These cells line the blood vessels and play various roles in the body, but they are not directly involved in the immune response.

Answer: Pasteurization

Pasteurization is a process of heat treatment used to reduce the number of microorganisms in food and beverages. However, it is not effective in killing endospores. Pasteurization typically involves lower temperatures and shorter exposure times than methods specifically designed for sterilization.

The other options are incorrect:

• Autoclaving: Autoclaving is an effective method for sterilization and involves the use of steam under pressure. It is capable of killing endospores due to the high temperature and pressure involved.
• Incineration: Incineration, or burning, is a method of sterilization that involves exposing materials to high temperatures. It is effective against endospores and is commonly used for laboratory waste disposal.
• Hot-air sterilization: Hot-air sterilization involves the use of dry heat to kill microorganisms. While it is effective against many types of microorganisms, including vegetative cells and some endospores, it may not be as reliable as methods like autoclaving for complete sterilization.

Answer: Transduction

Transduction is the process by which a virus transfers host DNA from one cell to another. During viral replication, the virus may accidentally package host DNA fragments instead of its own genome. When this virus infects another cell, it can inject the host DNA fragment, potentially integrating it into the new host cell’s genome and altering its genetic makeup.

The other options are incorrect:

• Transformation: This refers to the uptake of free DNA by a cell, directly incorporating the external DNA into its own genome. While viruses can facilitate the entry of foreign DNA, transduction specifically involves the virus packaging and transferring the host DNA.
• Conjugation: This is a bacterial mating process where direct cell-to-cell contact allows the transfer of plasmids (circular DNA molecules) between bacteria. Viruses are not involved in conjugation.
• Integration: This term can have different meanings depending on the context. In the context of viral infections, it often refers to the insertion of viral DNA into the host cell’s genome. However, the question specifies the transfer of host DNA, not viral.

Answer: Transfection

Transfection refers to the introduction of foreign genetic material, typically DNA or RNA, into eukaryotic cells. This can be achieved through various methods, including physical or chemical techniques, and doesn’t involve direct interaction with viruses (transduction) or bacterial mating (conjugation).

The other options are incorrect:

• Transformation: While also involving the uptake of DNA by cells, transformation typically refers to the natural process of bacteria acquiring DNA from the environment. Eukaryotic cells generally require additional techniques to introduce foreign DNA.
• DNA ligase: This is an enzyme involved in repairing DNA breaks and joining DNA fragments during DNA replication. It’s not a process for introducing new genetic material from the environment.
• Transduction: As mentioned earlier, this refers to the virus-mediated transfer of host DNA between cells, not the acquisition of environmental genetic material.

Answer: Trojan horse vaccine

A Trojan horse vaccine involves inserting genes from a pathogen into a live, non-pathogenic carrier organism. This recombinant carrier then expresses the foreign genes, allowing the immune system to develop a response to the pathogen’s antigens without causing the actual disease.

The other options are incorrect:

• Subunit vaccine: This type of vaccine uses isolated components of a pathogen, like proteins or carbohydrates, rather than the whole organism. While it may include some pathogen genes, it doesn’t involve a live carrier.
• Killed vaccine: This type of vaccine uses an inactivated version of the entire pathogen, preventing it from causing disease but still stimulating the immune system. However, it doesn’t involve manipulating genes or using a live carrier.
• Acellular vaccine: Similar to subunit vaccines, acellular vaccines contain purified components of the pathogen but not the whole organism. They may include some pathogen genes, but not in the context of a live, non-pathogenic carrier.

Answer: Used to participate in helper function

MHC class II proteins are crucial for the immune system’s helper T cell function. They present antigen fragments to helper T cells, allowing them to recognize and activate, which is a key step in coordinating the immune response against pathogens.

The other options are incorrect:

• Recognized by the CD8 protein: This is a function of MHC class I proteins, not MHC class II. CD8 proteins are found on cytotoxic T cells and help them recognize cells presenting antigens on MHC class I molecules.
• Used to mark a cell for killing by cytotoxic T-cells: This is also a function of MHC class I proteins. Cytotoxic T cells recognize infected or abnormal cells by their MHC class I presentation of antigen fragments.
• Not able to carry an antigen fragment: Both MHC class I and II proteins can carry and present antigen fragments. This is their primary function in the immune response.

Answer: Both “Toxoids” and “Subclinical infection”

Active immunity involves the body developing its own long-term immune response against a specific pathogen or toxin. This can be achieved through two main methods:

Toxoids: These are weakened or modified toxins that have lost their harmful effects but retain their antigenicity. When introduced into the body, they trigger the immune system to produce antibodies and memory cells specific to the toxin, providing long-term protection against the active toxin.
Subclinical infection: This occurs when exposure to a weakened or low-dose pathogen results in a mild, undetectable infection. While the infection doesn’t cause noticeable symptoms, the immune system recognizes and responds to the pathogen, generating antibodies and memory cells that offer subsequent protection against the full-blown disease.

The other options are incorrect:

• Antitoxin: This is a passive immunity strategy. Antitoxins are pre-made antibodies obtained from another source and administered to directly neutralize a specific toxin in the body. They provide immediate protection but do not stimulate the recipient’s own immune system for long-term memory.

Answer: IgD

IgD (Immunoglobulin D) is the least abundant immunoglobulin (Ig) in normal adults. IgD is primarily found on the surface of B cells, where it functions as a receptor for antigens. Its exact role in the immune response is not fully understood, but it is believed to play a role in the activation of B cells.

The other options are incorrect:

• IgA: IgA is present in mucosal secretions and is important for mucosal immunity. It is more abundant than IgD.
• IgM: IgM is often the first antibody produced in response to an infection. While IgM levels can vary, it is generally more abundant than IgD.
• IgG: IgG is the most abundant immunoglobulin in the bloodstream and plays a key role in providing long-term immunity. It is more abundant than IgD.

Answer: Spore

Spores, especially bacterial endospores, are highly resistant to antiseptics and many other physical and chemical agents. Endospores are a dormant, tough, and resistant form of certain bacteria, allowing them to withstand harsh conditions. This resistance is due to the thick and durable spore coat, as well as the presence of various protective factors.

The other options are incorrect:

• Prion: Prions are infectious agents composed of misfolded proteins. They are resistant to many traditional disinfection and sterilization methods, but they are not commonly targeted by antiseptics.
• Cyst: Some cysts, such as those formed by certain protozoa, can be resistant to disinfectants and antiseptics, but they are generally not as resistant as bacterial endospores.
• Fungus: Fungi are typically more susceptible to antiseptics compared to bacterial endospores. While some fungi may have resistant spores, they are not as robust as bacterial endospores in terms of resistance to antiseptics.

Answer: Selenite F broth

Enrichment media are specifically formulated to favor the growth of a particular microorganism or group of microorganisms over others. They often contain specific nutrients, inhibitors, or physical conditions that enhance the target organism’s growth while suppressing or hindering the growth of other bacteria.

The other options are incorrect:

• Chocolate media: This is a selective medium used for growing fastidious bacteria like Neisseria meningitidis, which require specific nutrients for optimal growth. While it favors some bacteria over others, it’s not designed to enrich a specific target organism.
• Egg media: This is a general-purpose medium used for cultivating a wide range of bacteria. It provides various nutrients but doesn’t specifically target or enrich any particular organism.
• Meat extract media: This is another general-purpose medium that provides basic nutrients for bacterial growth. While it may support a variety of organisms, it doesn’t specifically enrich any particular one.

Answer: Freeze-drying

Lyophilization, also known as freeze-drying, is a process of preserving materials by removing water through sublimation. This involves freezing the material, then reducing pressure and applying heat to allow the ice to directly transition from solid to vapor, bypassing the liquid phase. This results in a dry, stable product with minimal physical or chemical changes.

The other options are incorrect:

• Holding at 72° C for 15 seconds: This could be a step in a specific sterilization protocol, but it doesn’t describe the entire process of lyophilization.
• Competitive inhibition: This is a biochemical concept related to enzyme activity, not a preservation technique.
• Sterility testing: This is a quality control procedure to confirm the absence of viable microorganisms, not a preservation method.

Answer: DNA replication

Gene mutation occurs at the time of DNA replication. During DNA replication, errors can occur, leading to changes in the nucleotide sequence of the DNA. Mutations can result from mistakes made by DNA polymerase or from exposure to mutagenic agents during replication.

The other options are incorrect:

• DNA repair: DNA repair mechanisms are involved in correcting damage or errors in the DNA sequence after replication. Mutations may be repaired during these processes, but they are not directly caused during DNA repair.
• Translation: Translation is the process of synthesizing proteins from mRNA. It does not involve changes to the DNA sequence and is not a primary source of gene mutations.
• RNA transcription: RNA transcription is the process of synthesizing RNA from DNA. While errors during transcription can lead to errors in the mRNA sequence, gene mutations primarily occur at the DNA replication stage.

Answer: B-cells

The innate immune system is the first line of defense against pathogens and doesn’t rely on specific antigen recognition. While diverse cell types and mechanisms contribute to this response, B-cells are specifically involved in the adaptive immune system, which develops specialized antibodies to target and neutralize specific pathogens.

The other options are incorrect:

• Alternative pathway of complement system: This is part of the innate immune response. It activates a cascade of proteins that ultimately leads to destruction of pathogens and inflammation.
• Natural killer cells: These are cytotoxic cells that directly attack and kill infected cells or tumor cells. They are crucial players in the innate immune response.
• Macrophages: These are phagocytic cells that engulf and digest pathogens and cellular debris. They are essential components of the innate immune system.

Answer: T cell

The cellular immune response, also known as cell-mediated immunity, is primarily mediated by T cells. T cells are a type of lymphocyte that plays a central role in recognizing and responding to infected or abnormal cells. There are two main types of T cells involved in the cellular immune response: cytotoxic T cells (CD8+ T cells), which directly kill infected cells, and helper T cells (CD4+ T cells), which assist and coordinate various immune responses.

The other options are incorrect:

• B cells: B cells are primarily involved in humoral immunity, where they produce antibodies that target pathogens in body fluids. They are not the main mediators of the cellular immune response.
• B & T cells: While both B and T cells are essential components of the immune system, the cellular immune response specifically refers to the role of T cells in recognizing and responding to infected or abnormal cells.
• Endothelial cells: Endothelial cells are cells lining blood vessels and are not immune cells. They are not the mediators of the cellular immune response.

Answer: Both ‘Inheritable’ & ‘Permanent’

utations in microbes can influence their characteristics only if they meet two key criteria:

Inheritable: The mutation must be incorporated into the microbial DNA and passed on to future generations during cell division. Otherwise, the mutation will disappear when the individual microbe dies.
Permanent: The mutation should not be corrected by repair mechanisms within the cell. If the mutation gets repaired back to the original DNA sequence, it won’t have any lasting impact on the microbe.

The other options are incorrect:

• Beneficial: While beneficial mutations are important for microbes to adapt and thrive, not all mutations are beneficial. Even neutral or harmful mutations can be inheritable and permanent, still influencing the microbe’s characteristics.

Answer: It is required for normal cell function.

Plasmids are extrachromosomal, circular pieces of DNA found in bacteria and some other organisms. While plasmids can confer various advantages to bacteria, such as antibiotic resistance or the ability to produce toxins, they are not required for normal cell function. Chromosomal DNA contains essential genetic information for normal cellular processes, and plasmids are separate entities that may provide additional functionalities but are not essential for basic cellular functions.

The other options are incorrect:

• It is a circular piece of DNA: This is true. Plasmids are typically circular, double-stranded DNA molecules.
• It is found in bacteria: This is true. Plasmids are commonly found in bacteria and contribute to their genetic diversity.
• It can be transferred from cell to cell: This is true. Plasmids can be transferred between bacterial cells through processes like conjugation, allowing the spread of genetic information.

Answer: Gene

The smallest unit of heredity is a gene. Genes are segments of DNA that contain the instructions for the synthesis of specific proteins or functional RNA molecules. Genes are the fundamental units that carry genetic information and are passed from one generation to the next.

The other options are incorrect:

• Chromosome: Chromosomes are structures made up of DNA and proteins that carry multiple genes. While chromosomes contain genes, they are not the smallest unit of heredity.
• Codon: A codon is a sequence of three nucleotides in DNA or RNA that codes for a specific amino acid in protein synthesis. It is part of the genetic code, but it is not the smallest unit of heredity.
• Nucleotide: A nucleotide is the basic building block of nucleic acids, including DNA. It consists of a phosphate group, a sugar molecule, and a nitrogenous base. While nucleotides are essential components of genes, they are not the smallest unit of heredity.

Answer: Malaise

Malaise refers to a general feeling of illness, discomfort, or uneasiness without the presence of specific symptoms. It is a non-specific term that describes a sense of not feeling well or being in a state of overall discomfort. Malaise can be a symptom of various underlying health conditions.

The other options are incorrect:

• Cystitis: Cystitis is the inflammation of the bladder, often caused by a urinary tract infection. It is characterized by symptoms such as urinary urgency, frequency, and pain during urination.
• Arthritis: Arthritis is the inflammation of one or more joints, leading to pain, swelling, and decreased joint mobility. It is a specific condition affecting the joints.
• Lymphopenia: Lymphopenia is a condition characterized by a low level of lymphocytes (a type of white blood cell) in the blood. It is a specific hematological abnormality rather than a general feeling of illness.