Explanation: The immune system is a complex network of cells, tissues, and organs that work together to identify and respond to foreign substances in the body, including bacteria, viruses, parasites, and toxins. Its primary function is to protect the body from infections and other harmful substances.

Incorrect choices:

a. The regulation of body temperature and blood pressure is primarily controlled by the nervous and endocrine systems, not the immune system.

b. Digestion and absorption of nutrients from food are processes mainly controlled by the digestive system, not the immune system.

d. The production of hormones that control bodily functions is primarily the responsibility of the endocrine system, not the immune system.

Explanation: Hormones are chemical messengers produced by the endocrine system to regulate various physiological processes in the body. While the endocrine system and immune system can influence each other's activities, hormones are not considered a direct component of the immune system.

Incorrect choices:

a. Lymphocytes are a type of white blood cell and a critical component of the immune system. They include B cells, T cells, and natural killer cells, which play essential roles in immune responses.

b. Antigens are molecules or substances that can trigger an immune response in the body. They are recognized by the immune system as foreign or non-self and can elicit the production of antibodies.

d. Antibodies are proteins produced by B cells in response to the presence of antigens. They play a vital role in recognizing and neutralizing foreign substances in the body.

Explanation: Active immunity is acquired when the body's immune system is exposed to a specific pathogen or antigen, either through vaccination or natural infection. In response, the immune system produces its antibodies to protect against future encounters with the same pathogen.

Incorrect choices:

a. Innate immunity is the first line of defense against infections and is present at birth. It includes physical barriers, such as the skin and mucous membranes, and non-specific immune responses that do not require prior exposure to a specific pathogen.

c. Passive immunity is the transfer of pre-formed antibodies from one individual to another, providing immediate, temporary protection. This can occur naturally, such as the transfer of antibodies from a mother to her baby during breastfeeding, or through the administration of pre-formed antibodies, as in certain medical treatments.

d. Natural immunity refers to the immunity that is acquired through natural exposure to a pathogen and the subsequent development of an immune response. This includes both active immunity from natural infection and passive immunity from maternal antibodies passed to the baby during childbirth or breastfeeding.

Explanation: B cells are a type of lymphocyte that plays a central role in the adaptive immune response. When activated by the presence of specific antigens, B cells differentiate into plasma cells, which are responsible for producing large quantities of antibodies that can target and neutralize the invading pathogen.

Incorrect choices:

a. T cells are another type of lymphocyte that is involved in cell-mediated immunity, where they directly attack infected or abnormal cells. They do not produce antibodies.

b. Natural killer cells are part of the innate immune system and are responsible for killing infected or cancerous cells. They are not involved in antibody production.

d. Macrophages are phagocytic cells that engulf and destroy pathogens and debris in the body. While they play a crucial role in immune responses, they do not produce antibodies.

Explanation: T cells are a type of lymphocyte that plays a crucial role in cell-mediated immunity. They are responsible for recognizing and directly attacking infected or abnormal cells in the body. There are two main types of T cells: cytotoxic T cells, which directly kill infected cells, and helper T cells, which assist in coordinating the immune response.

Incorrect choices:

a. B cells are responsible for the production of antibodies and are involved in the humoral immune response, which targets pathogens outside of cells. They do not directly recognize and destroy infected cells.

c. Macrophages are antigen-presenting cells that engulf and process pathogens to present their antigens to other immune cells. While they are involved in immune recognition, they do not primarily recognize and destroy infected cells.

d. Neutrophils are a type of white blood cell involved in the innate immune response. They primarily target and destroy bacteria and other foreign invaders in the body, but they do not have the specific recognition capabilities of T cells.

Explanation: B cells are a type of lymphocyte that produces antibodies against specific antigens. When a B cell encounters an antigen that matches its specific receptor, it becomes activated and differentiates into plasma cells, which are responsible for producing large quantities of antibodies that can target and neutralize the antigen.

Incorrect choices:

b. T cells are involved in cell-mediated immunity and do not produce antibodies. They recognize and directly attack infected or abnormal cells in the body.

c. Macrophages are antigen-presenting cells that engulf and process pathogens to present their antigens to other immune cells. They do not produce antibodies themselves but play a role in initiating the immune response.

d. Natural killer cells are a type of lymphocyte involved in the innate immune response. They do not produce antibodies but can directly kill infected or abnormal cells.

Explanation: Macrophages are a type of white blood cell that plays a crucial role in the innate immune response. They are phagocytes, meaning they engulf and destroy pathogens, cellular debris, and foreign substances in the body. Macrophages are also antigen-presenting cells, as they process and present antigens to other immune cells to initiate an adaptive immune response.

Incorrect choices:

a. B cells produce antibodies against specific antigens but do not directly engulf and destroy pathogens.

b. T cells are involved in cell-mediated immunity and directly attack infected or abnormal cells but do not have phagocytic capabilities like macrophages.

d. Natural killer cells are a type of lymphocyte involved in the innate immune response and can directly kill infected or abnormal cells, but they do not primarily function as phagocytes like macrophages.

Explanation: Macrophages play a dual role in both innate and adaptive immunity. As part of the innate immune response, macrophages act as phagocytes, engulfing and destroying pathogens and debris in the body. They are also antigen-presenting cells, presenting processed antigens to other immune cells to initiate the adaptive immune response.

Incorrect choices:

a. B cells are part of the adaptive immune response and produce antibodies against specific antigens. They are not involved in the innate immune response.

b. T cells are primarily involved in the adaptive immune response and directly attack infected or abnormal cells. They are not part of the innate immune response.

d. Natural killer cells are part of the innate immune response and can directly kill infected or abnormal cells. They do not participate in the adaptive immune response.

Explanation: The immune response is a complex system of defense mechanisms that aim to protect the body from pathogens, such as bacteria, viruses, and other foreign substances. It involves the activation of various immune cells, production of antibodies, and other immune components to recognize and eliminate the invading pathogens.

Incorrect choices:

a. Directly attacking and killing infected cells is the role of cytotoxic T cells during cell-mediated immunity, but it is not the primary purpose of the overall immune response.

b. Antigens are foreign substances that trigger the immune response. They are not produced by the immune response itself but rather recognized by immune cells and antibodies.

c. The immune response is not involved in regulating the body's metabolism. Metabolism regulation is primarily controlled by other systems in the body, such as the endocrine system.

Explanation: B cells are a type of lymphocyte that plays a crucial role in the immune response by recognizing and binding to specific antigens. When a B cell encounters an antigen that matches its specific receptor, it becomes activated and differentiates into plasma cells, which produce antibodies against the antigen.

Incorrect choices:

b. Cytotoxic T cells are responsible for directly attacking and killing infected or abnormal cells during cell-mediated immunity. They do not primarily recognize antigens during the immune response.

c. Macrophages are antigen-presenting cells that engulf and process pathogens to present their antigens to other immune cells, such as T cells and B cells. While they are involved in antigen recognition, they are not the primary cells responsible for this function.

d. Red blood cells do not have a direct role in antigen recognition or the immune response. Their primary function is to transport oxygen throughout the body.

Explanation: B cells recognize antigens by producing specific receptors on their cell surface, known as antibodies or immunoglobulins. When a B cell encounters an antigen that matches its specific antibody, it binds to the antigen, marking it for destruction or neutralization by other immune cells.

Incorrect choices:

a. Engulfing and processing pathogens is the role of antigen-presenting cells like macrophages and dendritic cells. These cells present processed antigens to other immune cells, including B cells, to trigger an immune response.

b. Cytokines are small proteins that serve as signaling molecules in the immune system. They are produced by various immune cells to regulate immune responses, but they are not directly involved in antigen recognition by B cells.

d. Directly attacking and killing infected cells is the role of cytotoxic T cells during cell-mediated immunity, not B cells during the humoral immune response.

Explanation: Antigen recognition during the immune response occurs when antigens bind to specific receptors on immune cells, such as B cell receptors, T cell receptors, or antibodies. This binding is a critical step that triggers the activation of the immune response against the invading pathogen or foreign substance.

Incorrect choices:

a. Activation of regulatory T cells is important for controlling and regulating the immune response but is not directly related to the antigen recognition process.

b. Production of histamines by mast cells is involved in the inflammatory response, but it is not a direct step in the antigen recognition process.

d. Neutrophils are a type of white blood cell involved in the innate immune response. They do not release antibodies, as that function is primarily carried out by B cells and plasma cells.

Explanation: B cells are part of the adaptive immune system and are responsible for antibody-mediated immunity. They do not directly attack and kill infected cells. Instead, B cells produce antibodies that can recognize and neutralize pathogens or foreign substances.

Incorrect choices:

b. B cells are involved in antibody-mediated immunity, not cell-mediated immunity. They produce antibodies that circulate in the bloodstream and bind to antigens on pathogens, marking them for destruction by other immune cells.

c. Helper T cells, not B cells, primarily recognize antigens presented by antigen-presenting cells like macrophages and dendritic cells.

d. Phagocytosis of pathogens is mainly carried out by macrophages and neutrophils, not B cells.

Explanation: B cells are specialized in producing antibodies against specific antigens. When B cells encounter a pathogen or foreign substance with a matching antigen, they become activated and differentiate into plasma cells. Plasma cells then secrete large amounts of antibodies, which can recognize and neutralize the pathogen.

Incorrect choices:

a. B cells do not directly attack and kill infected cells. That role is primarily performed by cytotoxic T cells during cell-mediated immunity.

c. Regulatory T cells (Tregs) are responsible for regulating the immune response to prevent excessive inflammation and maintain immune homeostasis.

d. B cells recognize antigens presented by antigen-presenting cells like macrophages, but their primary function is to produce antibodies, not to recognize antigens directly.

Explanation: During antibody-mediated immunity, B cells produce antibodies, also known as immunoglobulins. Antibodies are Y-shaped proteins that specifically recognize and bind to antigens on the surface of pathogens or foreign substances. This binding marks the pathogens for destruction by other immune cells or neutralizes their harmful effects.

Incorrect choices:

a. Cytokines are small proteins that serve as signaling molecules in the immune system, regulating the behavior and activity of immune cells. B cells can secrete cytokines, but their primary function is antibody production.

b. Cytotoxic granules contain substances like perforin and granzymes and are released by cytotoxic T cells to induce apoptosis in infected or abnormal cells. B cells do not produce cytotoxic granules.

d. Perforin is a protein released by cytotoxic T cells and natural killer cells to create pores in the membrane of infected cells, leading to cell death. B cells do not produce perforin.

Explanation: The primary role of B cells during the humoral immune response is to produce antibodies against specific antigens on pathogens. When B cells encounter an antigen that matches their specific receptor, they become activated and differentiate into plasma cells, which then secrete large amounts of antibodies into the bloodstream.

Incorrect choices:

a. Antigen presentation to B cells is carried out by antigen-presenting cells, such as macrophages and dendritic cells, not by B cells themselves.

c. Directly attacking and killing infected cells is the role of cytotoxic T cells during cell-mediated immunity, not B cells during the humoral immune response.

d. The regulation of the immune response is mainly the function of regulatory T cells (Tregs) and other immune regulatory mechanisms, not the primary role of B cells.

Explanation: T cells, specifically cytotoxic T cells (CD8+ T cells), are responsible for cell-mediated immunity. They directly recognize and attack infected or abnormal cells, leading to their destruction. This process is crucial in controlling viral infections and cancer cells.

Incorrect choices:
a. B cells, not T cells, are responsible for the production of antibodies during the humoral immune response.
c. Phagocytosis of pathogens is mainly carried out by macrophages and neutrophils, not T cells.
d. Allergic reactions are primarily mediated by a different type of T cells called helper T cells (CD4+ T cells), not cytotoxic T cells.

Explanation: During cell-mediated immunity, T cells recognize antigens that are presented by antigen-presenting cells (APCs) such as macrophages. Macrophages engulf and process pathogens, and then they display fragments of the pathogens' antigens on their cell surface using major histocompatibility complex (MHC) molecules. T cells, specifically helper T cells, interact with these antigen-presenting macrophages and become activated to initiate immune responses.

Incorrect choices:
b. B cells present antigens to helper T cells during the humoral immune response, not during cell-mediated immunity.
c. Plasma cells are not involved in antigen presentation; they are terminally differentiated B cells that produce antibodies during the humoral immune response.
d. Memory cells are formed after the immune system encounters an antigen and are not directly involved in antigen presentation.

Explanation: Helper T cells (CD4+ T cells) play a critical role in the immune response by enhancing the activity of other immune cells. They secrete cytokines that stimulate B cells to produce antibodies, activate cytotoxic T cells to kill infected cells, and promote the function of macrophages in phagocytosis. Helper T cells are essential for coordinating and regulating the immune response.

Incorrect choices:

a. Cytotoxic T cells (CD8+ T cells) are responsible for directly attacking and killing infected cells, not enhancing the activity of other immune cells.

b. Memory T cells are formed after the immune system encounters an antigen and are not directly involved in enhancing immune cell activity.

d. Suppressor T cells (regulatory T cells) are involved in down-regulating the immune response to prevent excessive inflammation and tissue damage, not in enhancing immune cell activity.

Explanation: Cytotoxic T cells (CD8+ T cells) are the effector cells of cell-mediated immunity. Their primary role is to directly recognize and kill infected or abnormal cells, such as virus-infected cells or cancer cells. Cytotoxic T cells release cytotoxic granules containing perforin and granzymes, which induce apoptosis (cell death) in the target cells.

Incorrect choices:

a. Helper T cells, not cytotoxic T cells, recognize antigens presented by macrophages and play a crucial role in activating other immune cells.

b. B cells are responsible for producing antibodies against pathogens during the humoral immune response, not cytotoxic T cells.

d. Regulatory T cells (suppressor T cells) are involved in regulating the immune response to prevent excessive inflammation and tissue damage, not cytotoxic T cells.

Explanation: Memory in the immune system refers to the ability of immune cells, particularly memory B cells and memory T cells, to recognize and respond more quickly and effectively to specific antigens upon subsequent exposure. This leads to a faster and stronger secondary immune response.

Incorrect choices:
b. The ability of immune cells to differentiate between self and non-self antigens refers to the concept of immune tolerance, which helps prevent the immune system from attacking the body's own cells and tissues.
c. The process of phagocytosis by macrophages is a mechanism by which immune cells engulf and destroy pathogens and cellular debris, but it is not directly related to memory in the immune system.
d. The ability of B cells to produce antibodies is an essential part of the primary immune response, but it is not specific to memory in the immune system.

Explanation: The secondary immune response is faster and more potent than the primary immune response due to the presence of memory B cells and memory T cells. These memory cells "remember" the specific antigen from a previous encounter, allowing for a quicker and more effective immune response upon re-exposure to the same antigen.

Incorrect choices:
a. The secondary immune response is faster and stronger compared to the primary immune response, not delayed and weaker.
b. The secondary immune response involves the activation of memory B cells and memory T cells, not naive B cells and T cells.
d. The primary immune response is characterized by the production of IgM antibodies initially, but during the secondary immune response, the production of IgG antibodies predominates, which are more effective in neutralizing antigens.

xplanation: Memory B cells are formed during the primary immune response and play a critical role in the secondary immune response. When re-exposed to the same antigen, memory B cells quickly differentiate into plasma cells that produce large quantities of specific antibodies, leading to a rapid and robust immune response.

Incorrect choices:
a. The production of antibodies during the primary immune response is primarily carried out by plasma cells, not memory B cells.
b. The activation of helper T cells is essential for coordinating the immune response, but memory B cells are not directly responsible for this process.
c. The initiation of the complement cascade is a separate component of the immune response involving complement proteins, and memory B cells are not directly involved in this process.

Explanation: The secondary immune response provides long-lasting immunity because of the presence of memory B cells and memory T cells. These memory cells "remember" the specific antigen and can quickly mount a strong and effective immune response upon re-exposure to the same antigen, providing long-term protection.

Incorrect choices:

a. The primary immune response is primarily mediated by IgM antibodies, while the secondary immune response involves the predominance of IgG antibodies, which are more effective and provide long-lasting immunity.

b. The secondary immune response occurs after the primary immune response and is faster, not slower, due to the presence of memory cells.

c. Memory cells are a key component of the secondary immune response, playing a central role in providing rapid and robust immunity.

VI. Immune Disorders and Clinical Considerations:

Explanation: Rheumatoid arthritis is an autoimmune disorder in which the immune system mistakenly attacks the synovium (lining of the membranes that surround the joints), causing inflammation, pain, and joint damage.

Incorrect choices:

a. Allergic rhinitis is an allergic response to airborne allergens, such as pollen or pet dander, not an autoimmune disorder.

c. Celiac disease is an autoimmune disorder triggered by the ingestion of gluten, a protein found in wheat, barley, and rye, and it primarily affects the small intestine.

d. Type 1 diabetes mellitus is an autoimmune disorder in which the immune system attacks and destroys insulin-producing beta cells in the pancreas.

Explanation: Fibromyalgia is a chronic pain disorder characterized by widespread pain, fatigue, and tender points in specific areas of the body, such as the neck, shoulders, back, and hips.

Incorrect choices:

a. Systemic lupus erythematosus (SLE) is an autoimmune disorder that can affect multiple organs and systems, including the skin, joints, kidneys, and nervous system.

c. Multiple sclerosis (MS) is an autoimmune disorder that affects the central nervous system, causing symptoms such as fatigue, muscle weakness, and coordination problems.

d. Sjögren's syndrome is an autoimmune disorder that primarily affects the salivary and lacrimal glands, leading to dry eyes and dry mouth.

True or False: Immune disorders can be caused by both genetic and environmental factors.

Explanation: Immune disorders can result from a combination of genetic predisposition and environmental triggers. Some individuals may have a genetic susceptibility to developing certain immune disorders, and exposure to certain environmental factors, such as infections or certain substances, can trigger the immune response leading to the development of the disorder.

Explanation: Sjögren's syndrome is an autoimmune disorder in which the immune system attacks and damages the salivary and lacrimal glands, resulting in dry eyes and dry mouth.

Incorrect choices:

a. Rheumatoid arthritis primarily affects the joints, causing inflammation and joint damage.

c. Crohn's disease is an autoimmune disorder that affects the gastrointestinal tract, leading to inflammation and ulcers.

d. Psoriasis is a chronic skin condition characterized by red, scaly patches on the skin, and it is not related to the salivary and lacrimal glands.

Explanation: Multiple sclerosis (MS) is an autoimmune disorder in which the immune system attacks the myelin sheath, the protective covering of nerve fibers in the central nervous system, leading to communication problems between the brain and the rest of the body.

Incorrect choices:

a. Rheumatoid arthritis primarily affects the joints, not the central nervous system.

b. Sjögren's syndrome primarily affects the salivary and lacrimal glands, not the central nervous system.

d. Crohn's disease is an autoimmune disorder that affects the gastrointestinal tract, not the central nervous system.

Explanation: Celiac disease is an autoimmune disorder in which the immune system attacks and damages the lining of the small intestine in response to the ingestion of gluten, a protein found in wheat, barley, and rye.

Incorrect choices:
a. Rheumatoid arthritis primarily affects the joints, not the small intestine.
b. Sjögren's syndrome primarily affects the salivary and lacrimal glands, not the small intestine.
d. Type 1 diabetes mellitus is an autoimmune disorder in which the immune system attacks and destroys insulin-producing beta cells in the pancreas, not the small intestine.

Explanation: Immune disorders can result from either an overactive immune system (autoimmune disorders) or an underactive immune system (immunodeficiency disorders). In autoimmune disorders, the immune system attacks the body's own tissues, while in immunodeficiency disorders, the immune system is weakened, making the individual more susceptible to infections.

Explanation: Systemic lupus erythematosus (SLE) is an autoimmune disorder that can affect multiple organs and systems, including the skin, joints, kidneys, and nervous system. The presence of a "butterfly rash" on the face, joint pain, and skin lesions are common manifestations of SLE.

Incorrect choices:

b. Fibromyalgia is a chronic pain disorder characterized by widespread pain, fatigue, and tender points in specific areas of the body, but it does not typically present with a "butterfly rash" or skin lesions.

c. Multiple sclerosis (MS) is an autoimmune disorder that affects the central nervous system, causing symptoms such as fatigue, muscle weakness, and coordination problems, but it does not typically present with a "butterfly rash" or joint pain.

d. Sjögren's syndrome is an autoimmune disorder that primarily affects the salivary and lacrimal glands, leading to dry eyes and dry mouth, but it does not typically present with a "butterfly rash" or skin lesions.

VII. Vaccination and Immunization:

Explanation: At 2 months of age, infants are recommended to receive the DTaP vaccine, which protects against diphtheria, tetanus, and pertussis (whooping cough). The MMR vaccine protects against measles, mumps, and rubella and is usually administered at a later age. The hepatitis B vaccine is given shortly after birth, and the varicella vaccine is typically administered at 12 months of age.

Incorrect choices:

a. The MMR vaccine protects against measles, mumps, and rubella, not whooping cough (pertussis).

b. The hepatitis B vaccine is typically given shortly after birth, not at 2 months of age.

d. The varicella vaccine is usually administered at 12 months of age, not at 2 months.

Explanation: Vaccinations are made from either weakened or killed pathogens or parts of pathogens, which cannot cause the disease they are meant to protect against. However, they stimulate the body's immune system to produce a protective response, providing immunity against the specific disease.

Explanation: Live attenuated vaccines use a weakened form of the pathogen that is still capable of replicating but does not cause severe illness in healthy individuals. This type of vaccine can provide long-lasting immunity with a single dose.

Incorrect choices:

a. Inactivated vaccines use killed pathogens, not weakened forms.

b. Subunit vaccines use only specific parts of the pathogen, not weakened forms.

d. Toxoid vaccines use inactivated toxins produced by the pathogen, not weakened forms of the pathogen itself.

Explanation: Booster doses of vaccines are recommended to reinforce and extend the duration of immunity provided by the initial vaccination. They help the immune system to maintain a higher level of protection against the disease over time.

Incorrect choices:

a. The number of antibodies in the blood is not increased by booster doses; rather, the immune system's memory is reinforced.

b. Booster doses do not decrease the risk of adverse reactions; they are given to maintain immunity.

d. Booster doses do not reduce the number of required vaccine doses; they are additional doses given to maintain immunity over time.

Explanation: The pneumococcal polysaccharide vaccine is recommended for older adults to protect against pneumonia caused by Streptococcus pneumoniae bacteria. The influenza vaccine is recommended annually for people of all ages to prevent the flu.

Incorrect choices:

a. The hepatitis B vaccine is not specifically recommended for older adults to prevent pneumonia.

b. The influenza vaccine protects against the flu, not pneumonia.

d. The HPV vaccine is recommended for adolescents and young adults, not older adults, and does not protect against pneumonia.

Explanation: Active immunity is acquired when the body's immune system is exposed to a pathogen through vaccination or natural infection and produces an immune response to provide protection against future infections.

Incorrect choices:

b. Passive immunity is acquired when preformed antibodies are transferred to an individual, providing immediate but temporary protection against a specific pathogen.

c. Natural immunity refers to immunity that is acquired through natural exposure to a pathogen, either through infection or vaccination.

d. Herd immunity is the indirect protection that occurs when a large percentage of a population becomes immune to a disease, either through vaccination or previous infection, reducing the likelihood of transmission to susceptible individuals.

Explanation: Healthcare workers are recommended to receive the hepatitis B vaccine to protect against hepatitis B virus (HBV) infection, which can be transmitted through contact with infected blood or body fluids.

Incorrect choices:

a. The influenza vaccine is recommended annually for healthcare workers to protect against seasonal flu, not hepatitis B.

b. The tetanus toxoid vaccine protects against tetanus, not hepatitis B.

d. The pneumococcal polysaccharide vaccine protects against pneumonia caused by Streptococcus pneumoniae bacteria, not hepatitis B.

Explanation: Passive immunity is acquired when preformed antibodies are transferred to an individual, providing immediate but temporary protection against a specific pathogen. This can occur naturally from a mother to her newborn or artificially through administration of specific antibodies.

Incorrect choices:

a. Active immunity is acquired when the body's immune system is exposed to a pathogen and produces an immune response to provide protection against future infections.

c. Natural immunity refers to immunity that is acquired through natural exposure to a pathogen, either through infection or vaccination.

d. Herd immunity is the indirect protection that occurs when a large percentage of a population becomes immune to a disease, either through vaccination or previous infection, reducing the likelihood of transmission to susceptible individuals.

Explanation: The human papillomavirus (HPV) vaccine is recommended for adolescents to protect against certain types of HPV infections, which can lead to cervical, vaginal, vulvar, penile, anal, and throat cancers.

Incorrect choices:

a. The hepatitis B vaccine is typically given in infancy and does not protect against certain types of cancer.

b. The influenza vaccine is recommended annually for people of all ages to prevent the flu, not certain types of cancer.

d. The meningococcal vaccine protects against meningococcal infections, not certain types of cancer.

Conclusion xx

Explanation: Passive immunity is the temporary immunity that is acquired from an external source, such as the transfer of antibodies from a mother to her baby through the placenta during pregnancy or through breastfeeding. This type of immunity provides immediate protection but does not result in the production of memory cells.

Incorrect choices:

a. The body's response to a vaccine is an example of active immunity, where the body produces its own antibodies in response to exposure to a weakened or inactive form of a pathogen.

c. The activation of T cells in response to an infection is part of the body's adaptive immune response, contributing to active immunity.

d. The production of memory cells after exposure to a pathogen is also a characteristic of active immunity, as it allows the body to recognize and respond more quickly to future infections with the same pathogen.

Explanation: Numerous scientific studies have found no link between vaccines and autism. The notion that vaccines cause autism was based on a discredited and fraudulent study, and subsequent research has shown no evidence of such a link.

Explanation: Memory cells are a type of immune cell that are formed during the body's initial encounter with a pathogen. They "remember" the specific antigen of the pathogen and allow the immune system to respond more rapidly and effectively if the same pathogen is encountered again in the future. Memory cells are responsible for providing long-term immunity.

Incorrect choices:

a. Engulfing pathogens and foreign invaders is the role of phagocytes, such as macrophages and neutrophils.

b. Initiating the inflammatory response is carried out by various immune cells, including mast cells and basophils, as part of the innate immune response.

c. Producing antibodies in response to infection is the primary role of B cells in the immune system.

Explanation: Antigens are unique molecules or proteins present on the surface of cells, including pathogens. The immune system can recognize these antigens as "non-self" and mount an immune response to eliminate them while sparing the body's own cells, which display different antigens that are recognized as "self."

Incorrect choices:

b. Recognizing different blood types is relevant for blood transfusions but not a primary mechanism of distinguishing self from non-self by the immune system.

c. Monitoring hormone levels in the body is not directly related to the immune system's ability to distinguish between self and non-self.

d. Cytokines are signaling molecules released by immune cells to regulate the immune response but are not the primary means of distinguishing self from non-self.

Explanation:The body's ability to produce antibodies against specific pathogens. Immunity refers to the body's ability to recognize and respond to specific pathogens, such as bacteria or viruses, by producing antibodies that target and neutralize these invaders.

Incorrect choices:

a. The body's ability to tolerate foreign substances without a response is not immunity but rather the concept of immunological tolerance, which prevents the immune system from attacking the body's own cells and tissues.

c. Immunity does not guarantee the prevention of infections, but it provides protection and reduces the severity of infections upon subsequent exposures to the same pathogen.

d. While the immune system is designed to fight off infections, it is not capable of fighting off all types of infections equally. The immune response is specific to the type of pathogen encountered.

Explanation: Active immunity. Active immunity is acquired when the immune system is exposed to a pathogen, either through natural infection or vaccination. It results in the production of memory cells that provide long-term protection against future exposures to the same pathogen.
Incorrect choices:

a. Passive immunity is acquired when preformed antibodies are transferred from one individual to another. It provides immediate but temporary protection and does not involve the production of memory cells.

b. Innate immunity is the body's first line of defense against infections and provides immediate, non-specific protection, but it does not involve the production of antibodies specific to a particular pathogen.

d. Acquired immunity is a general term that includes both active and passive immunity, but it does not specifically describe the type of immunity acquired through vaccination or exposure to a specific pathogen.

Explanation: Todirectly destroy pathogens and infected cells. Antibodies are Y-shaped proteins produced by B cells in response to a specific pathogen. They bind to the surface of the pathogen and mark it for destruction by other components of the immune system or directly neutralize the pathogen.

Incorrect choices:

b. While antibodies can attract white blood cells to the site of infection, their primary role is not to do so but rather to directly target and neutralize pathogens.

c. Antibodies do not produce hormones but are part of the humoral immune response, which involves the production of antibodies to fight off infections.

d. Antibodies do not play a role in maintaining body temperature during infections; instead, fever is a response triggered by the release of certain chemicals called pyrogens during infections.

Explanation: Recognizing and responding to specific antigens. T cells are a type of lymphocyte that plays a central role in cell-mediated immunity. They recognize and respond to specific antigens presented by infected or abnormal cells, leading to their destruction.

Incorrect choices:

a. T cells are not responsible for the production of antibodies, but that is the role of B cells in the humoral immune response.

b. While T cells are involved in directly attacking and destroying infected cells, their main function is to recognize specific antigens rather than directly attacking pathogens.

c. Marking pathogens for destruction by phagocytes is primarily a function of antibodies and complement proteins, not T cells.

Explanation: Passive immunity. Passive immunity is acquired when preformed antibodies are transferred from one individual to another. In this case, the mother's antibodies are transferred to her baby through breast milk, providing temporary protection against certain infections.

Incorrect choices:

a. Active immunity is acquired when the immune system is exposed to a pathogen or vaccination, leading to the production of memory cells and long-term protection.

b. Innate immunity is the body's first line of defense against infections and is not transferred from the mother to the baby but rather present from birth.

c. Adaptive immunity is another term for acquired immunity and involves the production of memory cells after exposure to a specific pathogen or vaccination. It is not transferred through breast milk.

Explanation: Receiving antibodies through placenta during pregnancy. Passive immunity is acquired when preformed antibodies are transferred from one individual to another, providing immediate but temporary protection. This can occur naturally through breastfeeding or artificially through administration of preformed antibodies, as in the case of placental transfer of antibodies from a mother to her baby.

Incorrect choices:

a. Receiving a flu vaccine involves active immunity, where the body is exposed to an attenuated or inactivated pathogen to stimulate the production of antibodies and memory cells for long-term protection.

b. Developing immunity after recovering from a viral infection is an example of active immunity, where the body mounts an immune response and produces memory cells to provide long-lasting protection against the pathogen.

d. Producing memory cells after exposure to a pathogen is part of the adaptive immune response and contributes to long-term immunity, not passive immunity.

Explanation:Innate immunity. Innate immunity is the body's first line of defense and provides immediate protection against infections without prior exposure to the pathogen. It includes physical barriers, such as the skin, and various cellular and chemical components.

Incorrect choices:

a. Adaptive immunity is the acquired immunity that develops after exposure to a specific pathogen or vaccination. It takes some time to mount a response and produce antibodies or memory cells.

b. Humoral immunity is a component of adaptive immunity that involves the production of antibodies by B cells to neutralize pathogens.

d. Cell-mediated immunity is another component of adaptive immunity, where T cells directly attack infected or abnormal cells.

Explanation:Destroying infected cells. Antibodies are produced by B cells in response to a specific pathogen and play a crucial role in identifying and neutralizing the invading pathogens, including infected cells.

Incorrect choices:

b. Attracting white blood cells to the site of infection is not the primary role of antibodies. White blood cells are attracted to the site of infection by chemical signals released by damaged tissues or pathogens.

c. Antibodies do not produce hormones. Hormones are chemical messengers produced by endocrine glands to regulate various bodily functions.

d. Antibodies do not regulate body temperature. Body temperature regulation is mainly controlled by the hypothalamus in the brain.

Explanation: T cells are a type of lymphocyte that plays a central role in cell-mediated immunity. They can recognize and destroy abnormal cells, including cancer cells, through direct cell-to-cell interactions.

Incorrect choices:

b. B cells produce antibodies in response to specific pathogens, but they do not directly attack cancer cells.

c. Antibodies are protein molecules that can bind to specific antigens on pathogens, but they do not have a direct role in attacking cancer cells.

d. Macrophages are phagocytic cells that engulf and destroy foreign substances, including pathogens, but they are not the primary cells responsible for recognizing and attacking cancer cells.

Explanation: Memory cells recognize and respond rapidly to previously encountered pathogens. Memory cells are a type of immune cell that are formed after an initial infection or vaccination. They "remember" the specific pathogen and allow the immune system to mount a faster and stronger response upon subsequent exposures to the same pathogen, providing long-term immunity.

Incorrect choices:

a. Memory cells do not directly attack pathogens in the body. They serve as a form of immune "memory" to help the body respond more effectively to future infections.

b. Memory cells do not produce antibodies upon initial pathogen exposure. B cells are responsible for producing antibodies in response to the pathogen.

d. Memory cells do not regulate the body's temperature during an infection. Temperature regulation is mainly controlled by the hypothalamus in the brain in response to infection or other stimuli.