Immunity Questions in English

(C) When a quick immune response is required, as in the case of infection by deadly microbes like tetanus or in cases of snakebite, the preformed antibodies or antitoxins are directly injected into the patient. This is known as $Passive \text{ } Immunity$. Since the body does not produce these antibodies itself, it is not active immunity. Therefore, the correct option is $C$.

(C) When pre-formed antibodies (antitoxins) are directly injected into the body,this type of immunity is known as $Passive \text{ } Immunity$. In the case of tetanus,the body does not have enough time to produce its own antibodies against the pathogen,so it is necessary to provide pre-formed antibodies to neutralize the toxins immediately.

(D) Vaccination works on the principle of immunological memory. When a vaccine is introduced into the body, it contains weakened or inactivated pathogens or their antigens. The immune system recognizes these antigens as foreign and triggers an immune response. This response leads to the production of specific antibodies that neutralize the pathogen. Additionally, it creates memory $B$ and $T$ cells, which provide long-term immunity against future infections by the same pathogen.

(A) When preformed antibodies are directly injected into the body to provide a quick immune response, it is known as $Passive \text{ } Immunity$. In the case of a snakebite, the venom is highly toxic and requires an immediate response; therefore, the body cannot wait for the active immune system to produce its own antibodies. Thus, injecting preformed antibodies (antivenom) provides immediate protection, which is a classic example of $Passive \text{ } Immunity$.

(B) Vaccination is a process where a preparation of antigenic proteins of pathogen or inactivated/weakened pathogen (vaccine) is introduced into the body.
In the case of measles,the vaccine contains attenuated (weakened) or inactivated measles viruses.
These act as antigens,which stimulate the immune system to produce specific antibodies and memory $B$ and $T$ lymphocytes.
This provides immunity against future infections by the same pathogen.
Therefore,option $B$ is the correct description of the vaccination process for measles.

(D) Vaccination involves the introduction of antigenic proteins of pathogen or inactivated/weakened pathogen (vaccine) into the body.
This triggers the primary immune response,where the immune system recognizes the antigen as foreign.
As a result,the body produces specific antibodies to neutralize the pathogen.
Simultaneously,the immune system generates $B-$memory cells and $T-$memory cells.
These memory cells remain in the body and provide a rapid and intense secondary immune response upon subsequent exposure to the same pathogen.
Therefore,all the listed components are produced.

(A) Vaccination works on the principle of immunological memory. When a vaccine is introduced into the body,it mimics the pathogen,triggering the immune system to produce $B$ and $T$ memory cells.
These memory cells recognize the specific pathogen upon subsequent exposure and mount a rapid,massive immune response by producing large quantities of antibodies,thereby neutralizing the pathogen.
Thus,Assertion $A$ is true because vaccination provides protection,and Reason $R$ is true because it correctly explains the mechanism of immunological memory involving $B$ and $T$ cells.

(C) The type of immunity where preformed antibodies or antitoxins are directly injected into the body is known as $Passive \text{ } Immunity$.
In cases of $Tetanus$, the pathogen $(Clostridium \text{ } tetani)$ produces a potent toxin.
If a person is injured and there is a risk of infection, immediate protection is required because the body does not have enough time to produce its own antibodies.
Therefore, preformed antibodies (antitoxins) are injected to neutralize the toxins immediately.
This is a classic example of $Passive \text{ } Immunization$.

(C) In the adaptive immune system,memory cells are primarily classified into two main types: $1$. Memory $B$-cells and $2$. Memory $T$-cells. These cells are responsible for the secondary immune response,which is faster and more intense upon re-exposure to the same pathogen.

(C) Memory cells are specialized $B$ and $T$ lymphocytes that are formed after the primary immune response.
When the body encounters a pathogen for the first time,it produces a primary response.
During this process,memory cells are generated that persist in the body for a long time.
Upon subsequent exposure to the same pathogen,these memory cells recognize the pathogen immediately and stimulate $B$-cells to produce a massive amount of antibodies,resulting in a secondary or anamnestic response.

(A) In the case of a snakebite,the patient is injected with preformed antibodies against the snake venom. This is an example of passive immunity. Since the body needs immediate protection against the potent toxins in the venom,injecting preformed antibodies (antivenom) provides an immediate immune response to neutralize the toxins.

(D) Vaccination involves the introduction of antigenic preparations into the body to stimulate the immune system. These preparations can consist of:
$1$. Pathogen proteins (inactivated toxins or specific surface proteins).
$2$. Dead pathogens (inactivated by heat or chemicals).
$3$. Weakened (attenuated) pathogens (live but modified to be non-pathogenic).
By introducing these, the body produces antibodies and memory cells, providing immunity against future infections. Therefore, all the given options are correct.

(A) Memory cells are a specialized type of $B$ and $T$ lymphocytes that are formed during the primary immune response.
These cells persist in the body for a long duration after the initial exposure to an antigen.
Upon subsequent exposure to the same antigen,these cells recognize it rapidly and initiate a secondary immune response,which is much more intense and faster than the primary response.
Therefore,they are defined as cells that possess immunological memory.

(A) Vaccination is the process of introducing a vaccine into the body to stimulate the immune system.
It involves the administration of antigenic proteins of pathogens or inactivated/weakened pathogens (vaccine) into the body.
The immune system recognizes these antigens and produces antibodies against them.
This process generates memory $B$-cells and $T$-cells that recognize the pathogen on subsequent exposure and produce a massive immune response.
Since the body's own immune system is actively involved in producing antibodies and memory cells,vaccination is a form of active immunity.

(C) The principle of vaccination is based on the property of 'memory' of the immune system.
When a vaccine is introduced into the body,the immune system recognizes the antigen and produces antibodies against it.
It also generates memory $B$ and $T$ lymphocytes that recognize the pathogen on subsequent exposure.
This allows the immune system to mount a massive and rapid response upon a real infection,thereby preventing the disease.

(D) Vaccination is a process where a preparation of antigenic proteins of pathogens,inactivated pathogens,or weakened (attenuated) pathogens is introduced into the body. These substances act as antigens and stimulate the immune system to produce antibodies against the specific pathogen without causing the actual disease. This creates immunological memory,which protects the individual from future infections by the same pathogen. Therefore,all the given options are correct.

(C) Vaccination or immunization is based on the property of 'memory' of the immune system.
When a vaccine is introduced into the body,it mimics the pathogen and triggers an immune response.
This process leads to the generation of both $B$-memory cells and $T$-memory cells.
These memory cells recognize the pathogen upon subsequent exposure and produce a massive immune response to neutralize it quickly.

(C) Vaccination works on the principle of immunological memory. When a vaccine is introduced into the body,it contains weakened or dead pathogens or their antigens. The immune system recognizes these antigens as foreign and triggers an immune response. This leads to the production of specific antibodies and memory $B$ and $T$ cells. These memory cells remain in the body and provide long-term protection by producing a rapid and massive response if the same pathogen infects the body in the future.

(A) An autoimmune disease occurs when the immune system loses the ability to distinguish between 'self' and 'non-self' cells. As a result,the body's immune system mistakenly attacks its own healthy cells,tissues,or organs. Examples include Rheumatoid arthritis and Myasthenia gravis.

(B) Autoimmune diseases occur when the immune system fails to distinguish between 'self' and 'non-self' cells,leading to the destruction of the body's own tissues.
$1$. Rheumatoid arthritis is a classic example of an autoimmune disorder where the immune system attacks the joints.
$2$. Insulin-dependent diabetes ($Type-1$ diabetes) is an autoimmune condition where the immune system destroys insulin-producing beta cells in the pancreas.
$3$. Multiple sclerosis is an autoimmune disease where the immune system attacks the protective sheath (myelin) covering nerve fibers.
$4$. Allergy is a hypersensitive reaction of the immune system to harmless environmental substances (allergens),not an autoimmune disease.
Therefore,the correct option is $B$.

(A) Rheumatoid arthritis is a chronic inflammatory disorder that occurs when the immune system mistakenly attacks the body's own tissues,specifically the synovium (the lining of the membranes that surround the joints). Because the body's immune system fails to distinguish between 'self' and 'non-self' and attacks its own cells,it is classified as an autoimmune disease.

(A) Autoimmunity is a condition where the immune system loses its ability to differentiate between self and non-self cells.
This leads the body to attack its own healthy cells and tissues.
Genetic factors and other unknown factors are primarily responsible for the development of autoimmune diseases.
Examples include rheumatoid arthritis and multiple sclerosis.

(D) In higher vertebrates,the immune system has evolved to distinguish between self and non-self cells.
Acquired immunity (also known as adaptive or specific immunity) is the type of immunity that has evolved in higher vertebrates.
It is characterized by its ability to recognize specific pathogens and develop a memory of them,which allows for a faster and stronger response upon subsequent exposures.
Therefore,memory-based acquired immunity is the most advanced evolutionary development in the immune system of higher vertebrates.

(D) Multiple Sclerosis $(MS)$ is a chronic disease of the central nervous system where the immune system mistakenly attacks the protective sheath (myelin) that covers nerve fibers.
This condition is classified as an autoimmune disorder,where the body's immune system fails to distinguish between 'self' and 'non-self' cells,leading to the destruction of its own tissues.
Therefore,the correct cause is autoimmunity.

(B) The immune system is a complex network of cells,tissues,and organs that work together to defend the body against harmful invaders.
Its primary function is to distinguish between 'self' (the body's own cells) and 'non-self' (foreign antigens like bacteria,viruses,and parasites).
Once a foreign antigen is recognized,the immune system initiates a specific response to eliminate or neutralize the threat.
Therefore,the correct statement is that it recognizes foreign antigens and responds to them.

(D) The immune system is a complex network of cells,tissues,and organs that work together to defend the body against pathogens.
It includes:
$1$. Lymphoid organs (like lymph nodes,spleen,thymus,and bone marrow) where immune cells are produced and matured.
$2$. Immune cells (such as lymphocytes like $B$-cells and $T$-cells,macrophages,etc.) that identify and destroy foreign invaders.
$3$. Soluble molecules like antibodies (immunoglobulins) that specifically target and neutralize pathogens.
Therefore,all the given options are components of the immune system.

(D) The immune system consists of lymphoid organs,tissues,cells,and soluble molecules like antibodies that help to recognize foreign antigens.
$1$. Lymphoid organs (like bone marrow and thymus) are sites where lymphocytes originate and mature.
$2$. Lymphocytes ($B$-cells and $T$-cells) are the primary cells of the immune system.
$3$. Antibodies are proteins produced by $B$-lymphocytes in response to pathogens.
$4$. Antigens are foreign substances that trigger an immune response,but they are not a 'component' of the immune system itself; rather,they are the targets that the immune system acts against. Therefore,antigens are not considered a part of the immune system's structural components.

(C) The human immune system consists of lymphoid organs,tissues,cells,and soluble molecules like antibodies and interleukins. Among the given options,antibodies are the soluble protein molecules produced by $B$-lymphocytes in response to pathogens. Lymphoid organs and cells are structural components,not soluble molecules.

(A) The spleen is a large,bean-shaped organ which acts primarily as a reservoir of erythrocytes.
It contains a large pool of blood and is a major lymphoid organ.
It contains lymphocytes and phagocytes,which help in trapping blood-borne microorganisms and filtering the blood.
Therefore,the spleen primarily consists of $(i)$ Phagocytes and $(ii)$ Lymphocytes.

(C) The lymphoid tissue associated with the mucosa is known as $MALT$ (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.

(C) Lymphoid organs are the sites where origin and/or maturation and proliferation of lymphocytes occur.
Primary lymphoid organs include the bone marrow and the thymus.
In these organs,immature lymphocytes differentiate into antigen-sensitive lymphocytes.
After maturation,the lymphocytes migrate to secondary lymphoid organs like the spleen,lymph nodes,tonsils,Peyer's patches of the small intestine,and the appendix.
Therefore,bone marrow is classified as a primary lymphoid organ.

(D) Mucosa-Associated Lymphoid Tissue $(MALT)$ constitutes about $50\%$ of the lymphoid tissue in the human body.
It is located within the lining of the major tracts in the body, specifically the digestive, respiratory, and urogenital tracts.
It is $NOT$ present in the circulatory tract (blood vessels or heart).
Therefore, the correct option is $D$.

(D) Mucosa-associated lymphoid tissue $(MALT)$ constitutes about $50\%$ of the lymphoid tissue in the human body.
It is located within the lining of the major tracts in the body,specifically the respiratory,digestive,and urogenital tracts.
Therefore,all the given options are correct sites where $MALT$ is present.

(B) The primary lymphoid organs are the sites where lymphocytes originate and/or mature and proliferate.
$T$-lymphocytes originate in the bone marrow but migrate to the thymus gland for maturation.
Therefore,the bone marrow and the thymus gland provide the necessary microenvironment for the maturation of $T$-lymphocytes.
Thus,the correct option is $B$.

(B) Lymphocytes are specialized white blood cells that play a central role in the immune system.
They are specifically sensitive to $Antigens$.
An $Antigen$ is a molecule or molecular structure,such as may be present at the outside of a pathogen,that can be bound by an antigen-specific antibody or $B$-cell antigen receptor.
When lymphocytes encounter an $Antigen$,they become activated to initiate an immune response,which includes the production of antibodies (immunoglobulins).
Therefore,lymphocytes respond to the presence of $Antigens$.

(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 acts as a large reservoir of erythrocytes (Red Blood Cells).
Since it contains lymphocytes and phagocytes,it is considered a secondary lymphoid organ.
However,the site of maturation for lymphocytes is the primary lymphoid organs (bone marrow and thymus),not the spleen.
Therefore,the statement that the spleen is the site of maturation for lymphocytes is incorrect.

(B) Primary lymphoid organs are the sites where lymphocytes originate and/or mature and differentiate into antigen-sensitive lymphocytes. The two main primary lymphoid organs in humans are the $Bone \text{ } marrow$ and the $Thymus \text{ } gland$. In the bone marrow, all blood cells including lymphocytes are produced. The thymus is the site where $T$-lymphocytes mature. Therefore, the correct option is $B$.

(A) The lymphoid organs are the sites where origin and/or maturation and proliferation of lymphocytes occur.
Secondary lymphoid organs,such as the spleen,lymph nodes,tonsils,Peyer's patches of the small intestine,and the appendix,provide the sites for the interaction of lymphocytes with antigens,which then proliferate to become effector cells.
Among the given options,the small intestine (specifically Peyer's patches located in the small intestine) serves as a secondary lymphoid organ where this interaction occurs.
Thymus is a primary lymphoid organ where $T$-lymphocytes mature.

(A) Lymphocytes are a type of white blood cell that plays a crucial role in the immune system.
There are two main types of lymphocytes: $B$-lymphocytes and $T$-lymphocytes.
$B$-lymphocytes mature in the bone marrow,while $T$-lymphocytes migrate to the thymus for maturation.
However,in the context of general biology questions regarding the primary site of lymphocyte production and maturation of $B$-cells,the bone marrow is the correct answer.

(C) The $Spleen$ is a large,bean-shaped lymphoid organ.
It primarily 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.

(A) The spleen is a large,bean-shaped organ that primarily contains lymphocytes and phagocytes.
It acts as a filter of the blood by trapping blood-borne microorganisms.
It is considered a secondary lymphoid organ,not a primary one.
Primary lymphoid organs are the bone marrow and thymus,where lymphocytes mature.
Therefore,the correct statement is that it removes microorganisms from the blood.

(A) $MALT$ 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.

(A) In the human body,primary lymphoid organs are the sites where immature lymphocytes differentiate into antigen-sensitive lymphocytes. The two primary lymphoid organs are the bone marrow and the thymus. In the thymus,$T$-lymphocytes mature and differentiate. Therefore,the correct answer is the thymus.

(C) The $Thymus$ is a primary lymphoid organ that plays a crucial role in the development and maturation of $T$-lymphocytes.
It is quite large at the time of birth but gradually decreases in size with increasing age.
By the time puberty is reached,it becomes significantly reduced in size and is eventually replaced by adipose tissue in older adults.

(A) In the human immune system,primary lymphoid organs are the sites where immature lymphocytes differentiate into antigen-sensitive lymphocytes.
These organs include the bone marrow and the thymus.
After maturation,these lymphocytes migrate to secondary lymphoid organs like the spleen,lymph nodes,tonsils,Peyer's patches of the small intestine,and the appendix,where they interact with antigens and proliferate to become effector cells.

(C) Lymphoid organs are the organs where origin,maturation,and proliferation of lymphocytes occur.
$1$. Primary lymphoid organs (like bone marrow and thymus) are sites where lymphocytes originate and mature.
$2$. Secondary lymphoid organs (like spleen,lymph nodes,tonsils,Peyer's patches,and appendix) provide the sites for interaction of lymphocytes with antigens,which then proliferate to become effector cells.
$3$. Antibodies are produced by plasma cells (differentiated $B$-lymphocytes) in response to antigens,but the lymphoid organs themselves are not the 'site of origin' of antibodies; rather,they are the sites where the immune response is initiated. Therefore,option $C$ is the correct answer as it is not a primary function or definition associated with lymphoid organs.

(D) The bone marrow is the primary lymphoid organ where all blood cells,including lymphocytes,are produced. In humans,$B$-lymphocytes mature in the bone marrow,while $T$-lymphocytes mature in the thymus. The secondary lymphoid organs,such as the spleen,lymph nodes,and $MALT$,provide the sites for the interaction of lymphocytes with antigens,which then proliferate to become effector cells. Therefore,providing a site for lymphocytes to interact with antigens is a function of secondary lymphoid organs,not the bone marrow.

(D) Lymphoid organs are the organs where origin and/or maturation and proliferation of lymphocytes occur.
Primary lymphoid organs like bone marrow and thymus provide the micro-environment for the development and maturation of lymphocytes into antigen-sensitive lymphocytes.
After maturation,the lymphocytes migrate to secondary lymphoid organs like spleen,lymph nodes,tonsils,Peyer's patches of small intestine,and appendix,where they interact with the antigen and then proliferate to become effector cells.

(C) Primary lymphoid organs are the sites where lymphocytes originate and/or mature and become antigen-specific.
In humans,the primary lymphoid organs are the bone marrow and the thymus.
$B$-lymphocytes mature in the bone marrow,while $T$-lymphocytes mature in the thymus.
Spleen,lymph nodes,and tonsils are secondary lymphoid organs where lymphocytes interact with antigens and proliferate.
Therefore,bone marrow is the correct answer.

(A) Lymphoid organs are classified into primary and secondary lymphoid organs.
Primary lymphoid organs include the bone marrow and thymus,where immature lymphocytes differentiate into antigen-sensitive lymphocytes.
Secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen,which then proliferate to become effector cells.
Examples of secondary lymphoid organs include the spleen,lymph nodes,tonsils,Peyer's patches of the small intestine,and appendix.
Since the thymus is a primary lymphoid organ,it is not a secondary lymphoid organ.