Immunity Questions in English

(B) The primary lymphoid organs are the sites where immature lymphocytes differentiate into antigen-sensitive lymphocytes. These organs include the $Bone\ marrow$ and the $Thymus$. In the $Bone\ marrow$, both $B$-lymphocytes and $T$-lymphocytes are produced, and $B$-lymphocytes mature there. $T$-lymphocytes migrate to the $Thymus$ for maturation. Therefore, the correct answer is $Bone\ marrow$.

(C) The secondary lymphoid organs,such as the spleen,lymph nodes,tonsils,Peyer's patches of the small intestine,and appendix,provide the sites for the interaction of lymphocytes with the antigen,which then proliferate to become effector cells. Bone marrow and thymus are primary lymphoid organs where lymphocytes mature. Therefore,the spleen is the correct organ among the options provided that acts as a secondary lymphoid organ.

(C) Lymphoid organs are classified into two types: primary and secondary lymphoid organs.
Primary lymphoid organs are the sites where lymphocytes originate and/or mature and differentiate into antigen-specific lymphocytes.
The two main primary lymphoid organs are the $Bone \ marrow$ and the $Thymus$.
In the $Bone \ marrow$, all blood cells including lymphocytes are produced.
In the $Thymus$, $T$-lymphocytes mature.
Secondary lymphoid organs, such as the spleen, lymph nodes, tonsils, and Peyer's patches, provide the sites for interaction of lymphocytes with the antigen.
Therefore, among the given options, the $Thymus$ is a primary lymphoid organ.

(B) The bone marrow is the primary lymphoid organ where all blood cells,including lymphocytes,are produced.
In the bone marrow,hematopoietic stem cells differentiate into various types of blood cells,including red blood cells,white blood cells,and platelets.
Lymphocytes produced in the bone marrow either mature there ($B$-lymphocytes) or migrate to the thymus to mature ($T$-lymphocytes).

(A) The maturation of $T$-lymphocytes occurs in the thymus.
While $T$-lymphocytes originate in the bone marrow,they migrate to the thymus for maturation and differentiation.
Therefore,the thymus is the primary lymphoid organ that provides the specific microenvironment for the maturation of $T$-lymphocytes.

(D) The spleen is a large,bean-shaped organ which mainly contains lymphocytes and phagocytes.
It acts as a filter of the blood by trapping blood-borne microorganisms.
It also has a large reservoir of erythrocytes (red blood cells).

(D) $MALT$ stands for Mucosa-Associated Lymphoid Tissue.
It constitutes about $50\%$ of the lymphoid tissue in the human body.
It is located within the lining of the major tracts in the body, which include the respiratory, digestive, and urogenital tracts.
Therefore, all the given options are correct.

(C) $MALT$ stands for Mucosa-Associated Lymphoid Tissue.
It constitutes about $50\%$ of the lymphoid tissue in the human body.
It is located within the lining of the major tracts in the body,such as the respiratory,digestive,and urogenital tracts.

(D) $MALT$ stands for Mucosa-Associated Lymphoid Tissue.
It is a significant component of the human immune system.
$MALT$ is distributed within the lining of major tracts in the body,such as the respiratory,digestive,and urogenital tracts.
It is estimated that $MALT$ constitutes about $50\%$ of the total lymphoid tissue in the human body.

(C) The correct answer is $C$.
$1$. The thymus is a primary lymphoid organ where $T$-lymphocytes mature. It is quite large at the time of birth but keeps reducing in size with age and becomes very small by the time of puberty.
$2$. The spleen is a large bean-shaped organ which mainly contains lymphocytes and phagocytes. It acts as a filter of the blood by trapping blood-borne microorganisms and is a large reservoir of erythrocytes.
$3$. Bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced.
$4$. The statement that the spleen provides a microenvironment for the maturation of $T$-lymphocytes is false because the thymus is the site for $T$-lymphocyte maturation,not the spleen.

(B) The immune system consists of lymphoid organs,tissues,cells,and soluble molecules like antibodies.
Primary lymphoid organs include the bone marrow and thymus,where lymphocytes mature.
Secondary lymphoid organs include the spleen,lymph nodes,tonsils,Peyer's patches of the small intestine,and the appendix,which provide sites for interaction of lymphocytes with antigens.
The brain is part of the central nervous system and is not considered a lymphoid organ or a primary component of the immune system.

(C) In the human body,the immune system relies on various types of white blood cells $(WBCs)$.
All blood cells,including lymphocytes ($B$-lymphocytes and $T$-lymphocytes),are produced in the bone marrow through a process called hematopoiesis.
While $T$-lymphocytes migrate to the thymus for maturation,the primary site of production for all immune cells remains the bone marrow.

(B) The correct matching is as follows:
$(A)$ Primary lymphoid organs: These are the sites where lymphocytes originate and/or mature. These include $(iii)$ Bone marrow and $(i)$ Thymus.
$(B)$ $MALT$ (Mucosa-Associated Lymphoid Tissue): It constitutes about $(v)$ $50\%$ of the lymphoid tissue in the human body.
$(C)$ Organ located near the heart: The $(i)$ Thymus is a lobed organ located near the heart and beneath the breastbone.
$(D)$ Bean-shaped organ: The $(ii)$ Spleen is a large, bean-shaped organ which mainly contains lymphocytes and phagocytes.
Therefore, the correct sequence is $(A-iii), (B-v), (C-i), (D-ii)$.

(D) Interferons are a type of cytokine barrier,which is a component of innate immunity.
They are proteins secreted by virus-infected cells that protect non-infected cells from further viral infection.
They also play a role in inhibiting the multiplication of cancer cells.
Mast cells are involved in allergic reactions and secrete histamine and serotonin,not interferons.
Therefore,the statement that interferons are secreted by mast cells is incorrect.

(B) Innate immunity is non-specific and is present at the time of birth. It provides the first line of defense and acts as the primary response against pathogens.
Acquired immunity is pathogen-specific and is characterized by memory. When the body encounters a pathogen for the first time,it produces a primary response. Upon subsequent encounters with the same pathogen,it produces a highly intensified secondary or anamnestic response.
Therefore,Statement $A$ is true as innate immunity acts as the initial barrier. Reason $R$ is also true as acquired immunity is responsible for the secondary response due to immunological memory. However,$R$ does not explain why innate immunity provides a primary response; they are two distinct types of immune responses.
Thus,both $A$ and $R$ are true,but $R$ is not the correct explanation of $A$.

(D) Statement $(i)$ is correct: The skin on our body is the main barrier which prevents the entry of the micro-organisms.
Statement $(ii)$ is correct: Mucus coating of the epithelium lining the respiratory,gastrointestinal,and urogenital tracts also help in trapping microbes entering our body.
Statement $(iii)$ is incorrect: $IgA, IgM, IgE, IgG$ are types of antibodies (immunoglobulins),not $T$-cells.
Statement $(iv)$ is incorrect: The primary immune response is of low intensity,while the secondary immune response is highly intensified due to memory cells.
Therefore,only statements $(i)$ and $(ii)$ are correct.

(B) The statement in option $B$ is incorrect.
Injecting pre-formed antibodies directly into the body is known as passive immunity,not active acquired immunity.
Active immunity involves the body's own immune system producing antibodies in response to an antigen (like a vaccine or natural infection),which is a slow process.
Colostrum,the yellowish fluid secreted by the mother during the initial days of lactation,is rich in $IgA$ antibodies,providing passive immunity to the infant.
Antigens are indeed foreign substances like microbes or proteins that trigger an immune response.

(B) An antigen is defined as any substance that the body recognizes as foreign and that triggers an immune response.
While antigens can be proteins, polysaccharides, or even microorganisms, the most fundamental and defining characteristic of an antigen is that it is a $ \text{foreign molecule} $ to the host organism.
Therefore, among the given options, 'foreign molecule' is the most accurate and encompassing description for an antigen.

(A) Statement $A$ is correct because $B$-lymphocytes are responsible for producing antibodies,and $T$-lymphocytes help $B$-cells in this process. If both are damaged,the humoral immune response is compromised.
Statement $B$ is incorrect because vaccines containing weakened or killed pathogens induce active immunity,not passive immunity.
Statement $C$ is incorrect because the $Hepatitis-B$ vaccine is produced from yeast using recombinant $DNA$ technology,not protozoans.
Statement $D$ is incorrect because antivenom contains pre-formed antibodies,which provides passive immunity,not active immunity.

(C) Immunity is broadly classified into two main types based on how it is acquired:
$1$. Innate Immunity: This is non-specific type of defense that is present at the time of birth.
$2$. Acquired Immunity: This is pathogen-specific and is developed during an individual's lifetime after exposure to a pathogen or through vaccination.

(D) Immunity is broadly classified into two main types based on how it is acquired:
$1$. Innate immunity: This is non-specific type of defense that is present at the time of birth.
$2$. Acquired immunity: This is pathogen-specific and is developed during an individual's lifetime after exposure to a pathogen or vaccination.
Therefore,both innate and acquired immunity are the primary types of immunity.

(A) Innate immunity is a type of non-specific defense mechanism that is present at the time of birth.
It is inherited from parents and provides protection against various pathogens from the very beginning of life.
It consists of various barriers like physical,physiological,cellular,and cytokine barriers.

(D) Innate immunity is non-specific type of defense that is present at the time of birth. It provides different types of barriers to prevent the entry of foreign agents into our body. These barriers are categorized into four types:
$1$. Physical barriers (e.g.,skin,mucus coating of the respiratory,gastrointestinal,and urogenital tracts).
$2$. Physiological barriers (e.g.,acid in the stomach,saliva in the mouth,tears from eyes).
$3$. Cellular barriers (e.g.,polymorpho-nuclear leukocytes,monocytes,and natural killer cells).
$4$. Cytokine barriers (e.g.,interferon proteins which protect non-infected cells from further viral infection).
Therefore,the correct answer is $D$ (Barriers).

(D) Innate immunity is non-specific type of defense that is present at the time of birth. It consists of four types of barriers:
$1$. Physical barriers: Skin and mucus coating of the respiratory,gastrointestinal,and urogenital tracts.
$2$. Physiological barriers: Acid in the stomach,saliva in the mouth,and tears from eyes.
$3$. Cellular barriers: Polymorpho-nuclear leukocytes ($PMNL$-neutrophils),monocytes,and natural killer cells.
$4$. Cytokine barriers: Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.
Since all three options mentioned are part of innate immunity,the correct answer is $D$.

(C) Innate immunity is a non-specific type of defense that is present at the time of birth. It consists of four types of barriers:
$1$. Physical barriers: e.g.,skin,mucus coating of the epithelium lining the respiratory,gastrointestinal,and urogenital tracts.
$2$. Physiological barriers: e.g.,acid in the stomach,saliva in the mouth,tears from eyes.
$3$. Cellular barriers: e.g.,polymorpho-nuclear leukocytes ($PMNL$-neutrophils),monocytes,and natural killer cells.
$4$. Cytokine barriers: e.g.,virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.
Since all four options listed (Physical,Physiological,Chemical,and Cellular) are components of innate immunity,the question is technically flawed as all are valid barriers. However,in the context of $NCERT$ classification,'Chemical barriers' are often grouped within 'Physiological barriers'. Therefore,if one must be excluded,'Chemical barriers' is the most appropriate choice.

(C) The human body has several lines of defense against pathogens. The first line of defense consists of physical and physiological barriers. The $Skin$ is the main physical barrier that prevents the entry of microorganisms into the body. Mucus, saliva, and tears are considered physiological or chemical barriers that trap or destroy pathogens.

(D) The innate immunity in humans consists of various barriers that prevent the entry of foreign agents into the body.
Physical barriers include the skin and the mucus coating of the epithelium lining the respiratory,gastrointestinal,and urogenital tracts.
The skin is the primary physical barrier that prevents the entry of microorganisms.
The mucus membrane traps microorganisms entering our body.
Saliva is a physiological barrier (chemical barrier) due to the presence of enzymes like lysozyme.
Therefore,both skin and mucus membrane act as physical barriers.

(A) The human body has innate immunity which consists of four types of barriers:
$1$. Physical barriers: Skin and mucus coating of the epithelium lining the respiratory,gastrointestinal,and urogenital tracts.
$2$. Physiological barriers: Acid in the stomach,saliva in the mouth,and tears from eyes.
$3$. Cellular barriers: Polymorphonuclear leukocytes ($PMNL$-neutrophils),monocytes,and natural killer cells.
$4$. Cytokine barriers: Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.
Therefore,the mucus membrane acts as a physical barrier.

(C) Physiological barriers are part of the innate immunity that prevent microbial growth through chemical or physical conditions.
$1$. Skin is a physical barrier.
$2$. Macrophages are cellular barriers.
$3$. Tears (from eyes) and saliva (in the mouth) are physiological barriers because they contain enzymes like lysozyme that prevent microbial growth.
$4$. Mucus coating of the urogenital tract is a physical barrier.
Therefore,tears are the correct example of a physiological barrier.

(D) Physiological barriers are part of the innate immunity system that prevent microbial growth through chemical or physical conditions.
$1$. Acid in the stomach $(HCl)$ kills pathogens.
$2$. Saliva in the mouth prevents bacterial growth.
$3$. Tears from the eyes wash away pathogens and contain enzymes.
$4$. Mucus coating is a physical barrier,not a physiological one,as it traps microorganisms in the respiratory,gastrointestinal,and urogenital tracts.

(A) Phagocytosis is a process by which cells engulf and destroy pathogens or cellular debris.
$PMNL$ (Polymorphonuclear leukocytes),such as neutrophils,are well-known phagocytic cells.
Monocytes also differentiate into macrophages,which are professional phagocytes.
Natural Killer $(NK)$ cells are a type of lymphocyte that primarily targets virus-infected cells and tumor cells through cytotoxic mechanisms,but they are not considered professional phagocytes in the same sense as neutrophils or macrophages.
However,in the context of innate immunity,$PMNL$ and Monocytes are the primary phagocytic cells.
Given the options provided in standard biological contexts,$PMNL$ and Monocytes are phagocytic,while $NK$ cells are cytotoxic.
Since the question asks for cells that act as phagocytes,and $PMNL$ and Monocytes are clearly phagocytic,the most appropriate answer is that both $PMNL$ and Monocytes perform this function.

(C) Acquired immunity is characterized by memory. When the body encounters a pathogen for the first time,it produces a primary response of low intensity. Subsequent encounters with the same pathogen elicit a highly intensified secondary or anamnestic response due to the memory of the first encounter.

(A) Immunity is broadly classified into two types: Innate and Acquired.
$1$. Innate immunity is present at the time of birth and is non-specific.
$2$. Acquired immunity is pathogen-specific and is developed by the body after birth during its lifetime upon exposure to pathogens or through vaccination.
Therefore,the immunity developed after birth to combat diseases is called Acquired immunity.

(B) When our body encounters a pathogen for the first time,it produces a response of low intensity. This is called the $Primary \text{ response}$. Subsequent encounters with the same pathogen elicit a highly intensified $Secondary \text{ or } Anamnestic \text{ response}$ due to the memory of the immune system.

(A) The immune response is categorized into primary and secondary based on the encounter with an antigen.
$1$. When the body encounters a pathogen for the first time,it produces a $Primary \ immune \ response$. This response is characterized by low intensity and a slower rate of antibody production.
$2$. When the same pathogen enters the body again,the immune system recognizes it due to immunological memory,triggering a $Secondary \ immune \ response$ (also known as an anamnestic response). This response is much faster and of higher intensity compared to the primary response.

(A) The correct matches are as follows:
$1$. Physical barrier: The skin is the primary physical barrier that prevents the entry of microorganisms into the body. Thus, $(a-y)$.
$2$. Physiological barrier: Acid in the stomach, saliva in the mouth, and tears from eyes prevent microbial growth. Thus, $(b-w)$.
$3$. Cellular barrier: Certain types of leukocytes (WBCs) like polymorphonuclear leukocytes ($PMNL$-neutrophils) and monocytes are examples of cellular barriers. Thus, $(c-z)$.
$4$. Cytokine barrier: Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection. Thus, $(d-x)$.
Therefore, the correct sequence is $(a-y), (b-w), (c-z), (d-x)$.

(C) The correct answer is $C$.
$1$. Physical barriers include skin and mucus coating of the respiratory,gastrointestinal,and urogenital tracts.
$2$. Physiological barriers include acid in the stomach,saliva in the mouth,and tears from the eyes.
$3$. Cellular barriers include polymorphonuclear leukocytes ($PMNL$-neutrophils),monocytes,and natural killer cells.
$4$. Cytokine barriers include proteins called interferons which protect non-infected cells from further viral infection.
Therefore,'Cellular barrier – Tears from the eyes' is mismatched because tears are a physiological barrier,not a cellular one.

(B) Innate immunity is a non-specific type of defense that is present at the time of birth. It provides protection against pathogens by preventing their entry into the body or by eliminating them if they enter. It does not involve the production of antibodies by the body (which is a feature of adaptive immunity) nor does it involve the introduction of ready-made antibodies (which is passive immunity). Therefore,the correct description is that it is present from birth.

(D) Interferons $(IFNs)$ are cytokine barriers secreted by virus-infected cells. When a cell is infected by a virus,it releases interferons. These proteins protect the surrounding non-infected cells from viral infection and prevent them from further infection. Therefore,the correct option is $D$.

(D) Interferons are a group of signaling proteins made and released by host cells in response to the presence of several pathogens,such as viruses,bacteria,parasites,or tumor cells. Specifically,in the context of human immunity,virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection. Therefore,among the given options,the production of interferons is a response to viral infection.

(B) The $Secondary$ $immune$ $response$ (also known as the $anamnestic$ $response$) occurs upon subsequent encounter with the same pathogen.
It is characterized by a rapid,high-intensity,and long-lasting production of antibodies due to the presence of memory $B$ and $T$ cells generated during the primary exposure.
In contrast,the primary immune response is slower,less intense,and shorter-lived.

(D) The correct matching is as follows:
$1$. Physical barrier: Skin $(A-i)$ acts as a primary physical barrier to prevent the entry of pathogens.
$2$. Physiological barrier: Saliva in the mouth $(B-iv)$ and acid in the stomach are physiological barriers that prevent microbial growth.
$3$. Cellular barrier: Mucus coating $(C-iii)$ is often associated with the lining of respiratory and gastrointestinal tracts, but in the context of cellular immunity, leukocytes like $PMNL$-neutrophils and monocytes act as cellular barriers.
$4$. Cytokine barrier: Interferons $(D-ii)$ are proteins secreted by virus-infected cells which protect non-infected cells from further viral infection.
Thus, the correct sequence is $A-i, B-iv, C-iii, D-ii$.

(D) Memory cells are a type of $B$ and $T$ lymphocytes that are generated during the primary immune response to an antigen.
When the body is first exposed to a pathogen,lymphocytes proliferate and differentiate into effector cells and memory cells.
These memory cells persist in the body for a long time and provide a rapid and intense secondary immune response upon subsequent exposure to the same pathogen.

(B) An antibody is a specialized protein molecule,also known as an immunoglobulin $(Ig)$,produced by $B$-lymphocytes in response to the presence of an antigen.
These proteins specifically bind to antigens to neutralize them or mark them for destruction by other immune cells.
Therefore,an antibody is a protein that inactivates antigens.

(D) Vaccination is based on the property of 'memory' of the immune system.
When a vaccine is introduced into the body,it mimics an infection,causing the immune system to produce antibodies and generate memory $B$ and $T$ lymphocytes.
These memory cells remain in the body and recognize the specific pathogen upon subsequent exposure.
This allows the immune system to mount a faster and more intense secondary immune response,thereby preventing the disease.

(C) -cells are a type of white blood cell (lymphocyte) that play a crucial role in the humoral immune response. When they encounter a pathogen,they differentiate into plasma cells,which produce and secrete large quantities of specialized proteins called antibodies. These antibodies act as an 'army of proteins' that specifically target and neutralize pathogens such as bacteria and viruses in the body fluids.

(B) Antibodies are specialized proteins produced by the immune system to identify and neutralize foreign pathogens like bacteria and viruses.
In the human body,$B$-lymphocytes (or $B$-cells) are the specific type of white blood cells responsible for the production of antibodies.
When $B$-cells encounter an antigen,they differentiate into plasma cells,which then secrete large quantities of antibodies into the blood and lymph.
$T$-cells,on the other hand,are involved in cell-mediated immunity but do not produce antibodies themselves.

(A) The immune system consists of two main types of lymphocytes: $B$-cells and $T$-cells.
$B$-cells are responsible for the production of antibodies (humoral immune response).
$T$-cells do not produce antibodies themselves.
However,helper $T$-cells ($T_h$ cells) play a crucial role by releasing cytokines that stimulate and assist $B$-cells to proliferate and differentiate into plasma cells,which then secrete antibodies.
Therefore,$T$-cells are the cells that assist $B$-cells in antibody production.

(C) Each antibody molecule is represented by the formula $H_2L_2$.
This means it consists of four polypeptide chains: two identical light chains $(L)$ and two identical heavy chains $(H)$.
These chains are held together by disulfide bonds to form a $Y$-shaped structure.

(C) An antibody molecule is represented as $H_2L_2$.
It consists of four polypeptide chains: two small chains called light $(L)$ chains and two longer chains called heavy $(H)$ chains.
These chains are held together by disulfide bonds to form a $Y$-shaped structure.