All questions of Immunity for Grade 11 Exam

The Widal test is one method that may be used to help make a presumptive diagnosis of enteric fever, also known as typhoid fever.The test was based on demonstrating the presence of agglutinin (antibody) in the serum of an infected patient, against the H (flagellar) and O (somatic) antigens ofSalmonella typhi.

Its given in 12th NCERT.... widal test for typhoid

When a mosquito feeds on an infected person, the mosquito can become infected and can bite and infect others. The Aedes aegypti and Aedes albopictus mosquitoes transmit chikungunya. They also transmit dengue fever, another disease caused by a virus.

Antibodies are produced by specialized white blood cells called B lymphocytes (or B cells). When an antigen binds to the B-cell surface, it stimulates the B cell to divide and mature into a group of identical cells called a clone.

Human immunodeficiency virus infection and acquired immune deficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV).Following initial infection, a person may not notice any symptoms or may experience a brief period of influenza-like illness. Typically, this is followed by a prolonged period with no symptoms. As the infection progresses, it interferes more with the immune system, increasing the risk of developing common infections such as tuberculosis, as well as other opportunistic infections, and tumors that rarely affect people who have working immune systems.[5] These late symptoms of infection are referred to as acquired immunodeficiency syndrome (AIDS).This stage is often also associated with unintended weight loss.

Sporozoite is the infective stage of the malarial parasite. They are present in the saliva of infected female anopheles mosquito.

Anti venom against snake poison contains antibodies.

Explanation:
Anti venom is a serum that is used to treat snake bites. It contains antibodies that are specifically produced to neutralize the venom of a particular snake species. The antibodies are produced by injecting a small amount of the snake venom into an animal, usually a horse, and then collecting the blood serum from the animal after a certain period of time. This serum contains the antibodies that have been produced in response to the venom.

The antibodies in the anti venom work by binding to the venom molecules and neutralizing their toxic effects. This prevents the venom from causing damage to the body and allows the body's own immune system to clear the venom from the bloodstream.

It is important to note that anti venom is specific to the species of snake that produced the venom. This means that anti venom for one species of snake will not be effective against the venom of another species. It is also important to administer anti venom as soon as possible after a snake bite, as the venom can rapidly spread through the body and cause severe damage if left untreated.

The function of IgE antibody as mediators in allergic reactions of Type I is explained by their ability to interact both with antigen and with receptor molecules on the membrane of blood basophils and tissue mast cells. However, it is not understood how the interaction of an allergen with cell-bound IgE antibody will induce basophil (mast) cells to release a great number of biologically active substances of which some will be further discussed at this meeting, nor is it known what role the IgE-mast cell system plays in the development and control of a normal immune response.

Transmission of Japanese Encephalitis

Japanese Encephalitis is a viral disease that is transmitted by mosquitoes. The Japanese encephalitis virus (JEV) is a flavivirus that is transmitted to humans through the bite of infected mosquitoes. The virus is primarily found in rural and agricultural areas of Asia, but cases have been reported in other parts of the world as well.

Mosquitoes that transmit Japanese encephalitis

The Culex mosquitoes are the primary vector for the transmission of Japanese encephalitis. These mosquitoes are common in rural areas and are most active during the evening and early morning hours. The mosquito becomes infected with the virus when it feeds on an infected animal, usually a pig or a bird. The virus then multiplies in the mosquito's salivary glands and can be transmitted to humans when the mosquito bites a person.

Risk factors for Japanese encephalitis

People who live or travel to areas where Japanese encephalitis is endemic are at risk of contracting the disease. The risk is greatest during the monsoon season when mosquitoes are most active. Children and older adults are at greater risk of developing severe disease if they become infected with the virus.

Prevention of Japanese encephalitis

The best way to prevent Japanese encephalitis is to get vaccinated before traveling to areas where the disease is endemic. Other preventive measures include:

- Wear long-sleeved shirts and pants when outdoors
- Use insect repellent containing DEET on exposed skin
- Use mosquito nets or screens in sleeping areas
- Eliminate standing water around homes where mosquitoes breed

Conclusion

Japanese encephalitis is a serious disease that is transmitted by mosquitoes. The primary vector for the transmission of the virus is the Culex mosquito. People who live or travel to areas where Japanese encephalitis is endemic should take preventive measures to reduce their risk of contracting the disease. Vaccination is the most effective way to prevent Japanese encephalitis.

"HIV " Attacks CD4 cells (T- helper, T- cells) .. this cells plays important role in immune system..

IgG immunoglobin me sabse jyada 80% paye jate h . ye sbse chote imuno globin hote h kyuki enme paratopes kevel 2 hote h upr se ye monovalant hote h. chote size ke karan ye placenta ko cross kr jate h

Thymus gland is the correct option as it is large at the time of birth but reduces to a very small size in adults.

Explanation:

Thymus gland is a specialized gland of the lymphatic system that plays an important role in the development of the immune system. It is located in the upper thorax, behind the sternum, and in front of the heart. The thymus gland is large at the time of birth and continues to grow until puberty. After puberty, the thymus gland begins to shrink and is replaced by fatty tissue. By the age of 20, the thymus gland has reduced to about one-third of its maximum size, and by the age of 50, it has reduced to only a few grams of fatty tissue.

Why is Thymus gland large at the time of birth?

The thymus gland is very active during fetal development and plays a crucial role in the development of the immune system. The thymus gland produces T-lymphocytes, which are immune cells that play a crucial role in fighting infections and diseases. The thymus gland is essential for the development of T-lymphocytes, which are responsible for recognizing and attacking foreign substances in the body. The thymus gland is particularly important during fetal development because the fetus does not have a fully developed immune system and relies on the mother's immune system for protection.

Why does Thymus gland reduce in size in adults?

The thymus gland begins to shrink after puberty because the production of T-lymphocytes decreases with age. As a result, the thymus gland is no longer required to produce large numbers of T-lymphocytes, and its function gradually declines. The thymus gland is gradually replaced by fatty tissue, which is an irreversible process. However, the T-lymphocytes that are produced by the thymus gland during fetal development and childhood continue to circulate in the body and play a crucial role in the immune system throughout life.

Incorrect Immune System Component and Role Match

Explanation:
The immune system is a complex network of cells, tissues, and organs that work together to defend the body against harmful pathogens. The immune system components and their respective roles are as follows:

a) Interferons - Secreted by virus-infected cells and protect non-infected cells from further viral infection. They stimulate the production of antiviral proteins that prevent the virus from replicating in healthy cells.

b) B-lymphocytes - Produce antibodies in response to pathogens into blood to fight with them. B-lymphocytes are a type of white blood cell that recognizes and neutralizes specific pathogens by producing antibodies that bind to and destroy them.

c) Macrophages - Mucus-secreting cells that trap microbes entering in the body. This is an incorrect match as macrophages are actually white blood cells that engulf and digest foreign substances, such as bacteria and viruses, in a process called phagocytosis.

d) IgA - Present in colostrum in early days of lactation to protect infant from diseases. IgA is an antibody that is found in secretions such as tears, saliva, and breast milk. It helps to prevent pathogens from entering the body through the mucous membranes.

In conclusion, the correct match of immune system components and their respective roles is important to understand the functioning of the immune system and to develop effective strategies to combat diseases.

lgE is the most abundant antibody produced against allergens

Allergens are substances that can trigger an allergic response in individuals who are sensitive or allergic to them. When allergens enter the body, they can bind to specific antibodies called immunoglobulin E (IgE) antibodies. IgE antibodies are produced by a type of white blood cell called B cells in response to exposure to allergens. These antibodies are particularly involved in allergic reactions.

Explanation:
There are five major classes of antibodies, also known as immunoglobulins (Ig): IgA, IgD, IgE, IgG, and IgM. Each class of antibody has its own unique structure and function. Among these, IgE is the most abundant antibody produced against allergens.

Key Points:
- IgE is produced in response to allergen exposure.
- It plays a crucial role in allergic reactions by binding to allergens and triggering the release of chemicals such as histamine from mast cells and basophils.
- Histamine release leads to the typical symptoms of an allergic reaction, such as itching, swelling, redness, and increased mucus production.
- IgE antibodies are involved in allergic diseases such as allergic rhinitis (hay fever), asthma, and atopic dermatitis (eczema).
- The production of IgE antibodies is tightly regulated to prevent unnecessary allergic reactions.
- Individuals with allergies often have higher levels of IgE antibodies in their blood compared to non-allergic individuals.

Conclusion:
In summary, IgE is the most abundant antibody produced against allergens. It plays a key role in allergic reactions by binding to allergens and triggering the release of chemicals that cause allergy symptoms. Understanding the role of IgE antibodies in allergic reactions is important for the development of diagnostic tests and targeted treatments for allergies.

Innate immunity is the first line of defense of our body against pathogens. It consists of physiological and cellular barriers that prevent the entry and growth of microorganisms in our body. These barriers are present in different parts of our body and work together to protect us from infections.

Physiological barriers:

Physiological barriers are the physical and chemical barriers present in our body that prevent the entry and growth of microorganisms. The following statements regarding different physiological barriers of innate immunity are correct:

a) Acid present in the stomach, saliva in the mouth, tears from the eyes prevent the growth of microorganisms and constitute physiological barriers of our body.
- Acid in the stomach kills most of the microorganisms that enter our body through food or water.
- Saliva in the mouth contains enzymes and antibodies that prevent the growth of microorganisms in the oral cavity.
- Tears from the eyes contain lysozyme, an enzyme that can break down the cell wall of bacteria and prevent their growth.

b) Mucous membrane lining the respiratory, gastrointestinal and urinogenital tracts helps in trapping the microbes and constitute physiological barriers of our body.
- This statement is not correct as the mucous membrane is not just a physical barrier but also a site of active immune defense. The mucous membrane contains specialized cells called epithelial cells that secrete mucus, which traps microorganisms and prevents their entry into the body. The mucous membrane also contains immune cells such as macrophages, dendritic cells, and lymphocytes that can recognize and destroy the invading microorganisms.

Cellular barriers:

Cellular barriers are the immune cells present in our body that can recognize and destroy the invading microorganisms. The following statements regarding different cellular barriers of innate immunity are correct:

c) Certain types of leucocytes such as polymorphonuclear leucocytes (PMNL-neutrophils) and lymphocytes such as natural killer cells, constitute cellular barriers of our body.
- Polymorphonuclear leucocytes (PMNL-neutrophils) are the most abundant type of white blood cells in our body. They can recognize and engulf bacteria and other microorganisms.
- Natural killer cells are a type of lymphocyte that can recognize and kill virus-infected and cancerous cells.

d) Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection and constitute cytokine barriers of our body.
- This statement is correct. Interferons are proteins produced by virus-infected cells that activate the immune cells and protect non-infected cells from viral infection. Interferons can induce the expression of antiviral genes in the non-infected cells, which can prevent the replication of the virus.

In conclusion, statement b is not correct as the mucous membrane is not just a physical barrier but also a site of active immune defense.

Allergy and Mast Cells

Allergy is an exaggerated immune response to harmless substances called allergens. These allergens can be anything from pollen to certain foods, medications, or animal dander. During an allergic response, mast cells play an active role in the inflammatory process.

Mast Cells

Mast cells are a type of white blood cell that resides in connective tissues throughout the body, particularly in areas that are exposed to the external environment such as the skin, respiratory tract, and gastrointestinal tract. They are involved in both innate and adaptive immunity.

Role of Mast Cells in Allergy

When an allergen enters the body of an allergic individual, it triggers an immune response. In the case of allergies, the immune system reacts to the allergen as if it were harmful. Mast cells have specific receptors on their surface that recognize and bind to allergens.

Release of Mediators

Upon allergen binding, mast cells release a variety of chemical mediators, including histamine, leukotrienes, and prostaglandins. These mediators are responsible for the symptoms of allergies such as itching, redness, swelling, and increased mucus production.

Effects on Surrounding Tissues

Histamine, one of the primary mediators released by mast cells, causes blood vessels to dilate and become more permeable. This leads to increased blood flow to the affected area and the leakage of fluid and immune cells into the surrounding tissues. The resulting inflammation contributes to the characteristic symptoms of allergies.

Recruitment of Other Immune Cells

Mast cells also play a role in recruiting other immune cells to the site of the allergic reaction. They release chemotactic factors that attract eosinophils, basophils, and T-cells to the area. These immune cells further contribute to the inflammatory response.

Conclusion

In summary, mast cells actively participate during allergies by recognizing and binding to allergens, releasing chemical mediators that cause inflammation and allergic symptoms, and recruiting other immune cells to the site of the allergic reaction. Therefore, the correct answer to the question is option 'C' - Mast cells.

Humoral immunity is associated with B-cells.

Introduction:
The immune system is responsible for defending the body against external pathogens such as bacteria, viruses, and fungi. The immune system has two major types of immunity, including humoral and cell-mediated immunity. Humoral immunity is a type of adaptive immunity that is mediated by the production of antibodies by B-cells.

B-cells:
B-cells are a type of white blood cell that is responsible for producing antibodies. Antibodies are proteins that are produced by B-cells in response to the presence of foreign antigens. B-cells have receptors on their surface that can recognize specific antigens. Once a B-cell recognizes an antigen, it undergoes a process of activation, proliferation, and differentiation into antibody-secreting cells called plasma cells.

Antibodies:
Antibodies are proteins that are produced by B-cells in response to the presence of foreign antigens. Antibodies have a Y-shaped structure that consists of two heavy chains and two light chains. The tips of the Y-shaped structure contain antigen-binding sites that can recognize specific antigens. Once an antibody binds to an antigen, it can neutralize the antigen or mark it for destruction by other cells of the immune system.

Humoral immunity:
Humoral immunity is a type of adaptive immunity that is mediated by the production of antibodies by B-cells. Humoral immunity is effective against extracellular pathogens such as bacteria and viruses that are circulating in the blood or lymphatic system. In humoral immunity, B-cells recognize foreign antigens and produce antibodies that can neutralize the antigens or mark them for destruction by other cells of the immune system.

Conclusion:
In conclusion, humoral immunity is associated with B-cells. B-cells are responsible for recognizing foreign antigens and producing antibodies in response to the antigens. Antibodies can neutralize or mark the antigens for destruction by other cells of the immune system. Humoral immunity is effective against extracellular pathogens such as bacteria and viruses.

Anatomy of an Antibody

An antibody, also known as an immunoglobulin, is a Y-shaped protein produced by the immune system in response to the presence of antigens. Antibodies play a critical role in the immune response by recognizing and binding to specific antigens, marking them for destruction by other immune cells.

Structure of an Antibody

An antibody consists of two light peptide chains and two heavy peptide chains, making a total of four chains. These chains are held together by disulfide bonds, creating a stable and functional structure. The light chains are shorter in length compared to the heavy chains.

Light Peptide Chains

- An antibody has two identical light peptide chains, also referred to as the L chains.
- Each light chain is composed of approximately 220-230 amino acids.
- Light chains are further divided into two regions: the variable region (VL) and the constant region (CL).
- The variable region contains antigen-binding sites that interact with specific antigens.
- The constant region determines the antibody's class or isotype.

Heavy Peptide Chains

- An antibody has two identical heavy peptide chains, also referred to as the H chains.
- Each heavy chain is longer than the light chain and consists of approximately 440-450 amino acids.
- Similar to light chains, heavy chains are divided into two regions: the variable region (VH) and the constant region (CH).
- The variable region contains antigen-binding sites that complement those of the light chains.
- The constant region determines the antibody's class or isotype.

Role of the Chains

- The heavy and light chains together form the antigen-binding fragment (Fab) of the antibody.
- The Fab region is responsible for recognizing and binding to specific antigens.
- The constant regions of the heavy chains form the antibody's crystallizable fragment (Fc), which interacts with various immune cells and molecules to initiate immune responses.

Summary

An antibody is composed of two light peptide chains and two heavy peptide chains. The light chains are shorter and consist of variable and constant regions, while the heavy chains are longer and also have variable and constant regions. Together, these chains form the antigen-binding fragment (Fab) and the crystallizable fragment (Fc), allowing antibodies to recognize and neutralize specific antigens.

Spleen is an important organ of the lymphatic system that helps in filtering the blood and fighting against infections. Let's discuss the given statements and understand which ones are correct.

(i) Spleen is a large bean-shaped organ which mainly contains lymphocytes and phagocytes.
This statement is correct. Spleen contains lymphocytes and phagocytes which help in fighting against infections and foreign particles.

(ii) Spleen is a large reservoir of erythrocytes.
This statement is incorrect. Although spleen does store some erythrocytes, it is not a primary reservoir of erythrocytes. Its main function is to filter the blood and remove old or damaged erythrocytes.

(iii) Spleen is a primary lymphoid organ.
This statement is incorrect. Spleen is not a primary lymphoid organ. Primary lymphoid organs are bone marrow and thymus, where lymphocytes are produced and matured.

(iv) Spleen acts as a filter of the blood by trapping blood-borne microorganisms.
This statement is correct. Spleen acts as a filter of the blood by trapping blood-borne microorganisms and removing them from the circulation.

Therefore, the correct option is (d) (i), (ii) and (iv).

Active Immunization

Active immunization is a method of inducing immunity in an individual by introducing a vaccine into their body. The vaccine contains weakened or killed forms of the pathogen or its components, which stimulates the immune system to produce an immune response. The vaccine against polio viruses is an example of active immunization.

The Polio Vaccine

The polio vaccine is a preventive measure used to protect individuals from poliovirus infection, which can cause poliomyelitis, a highly infectious disease that affects the nervous system. There are two types of polio vaccines: the inactivated polio vaccine (IPV) and the oral polio vaccine (OPV).

IPV - Inactivated Polio Vaccine

The IPV is an injectable vaccine that contains inactivated (killed) poliovirus. When administered, it stimulates the immune system to produce an immune response against the virus. This response includes the production of poliovirus-specific antibodies and the activation of immune cells. These immune responses help protect the individual from future poliovirus infection.

OPV - Oral Polio Vaccine

The OPV is an oral vaccine that contains weakened (attenuated) poliovirus strains. When taken orally, the attenuated viruses replicate in the intestine, stimulating a strong immune response. This response results in the production of antibodies and activation of immune cells, providing protection against poliovirus infection.

Advantages of Active Immunization

Active immunization through vaccination offers several advantages:

1. Long-lasting protection: Vaccines stimulate the immune system to produce memory cells. These cells "remember" the pathogen and can mount a rapid and effective response if re-exposed to the same pathogen in the future.

2. Herd immunity: Vaccination not only protects vaccinated individuals but also contributes to herd immunity. When a significant proportion of the population is immune to a particular infectious disease, it reduces the overall transmission of the pathogen and protects those who cannot be vaccinated, such as infants or individuals with weakened immune systems.

3. Eradication of diseases: Active immunization has been instrumental in eradicating diseases such as smallpox and nearly eradicating others like polio. By vaccinating large populations, the transmission of the pathogen can be interrupted, leading to the elimination or eradication of the disease.

In conclusion, the polio vaccine is an example of active immunization. It utilizes the IPV or OPV to stimulate the immune system and induce a protective immune response against poliovirus infection. Active immunization through vaccination offers long-lasting protection, contributes to herd immunity, and has been successful in eradicating or controlling many infectious diseases.

The correct answer is option A: (ii), (iv), and (v).

Explanation:

(i) Innate immunity is a specific type of defence, that is present at the time of birth.
This statement is incorrect. Innate immunity is a non-specific type of defense mechanism that is present at birth. It provides the first line of defense against pathogens and is not specific to any particular pathogen. It includes physical barriers like the skin, mucous membranes, and chemical barriers like enzymes and antimicrobial peptides.

(ii) Malignant malaria is caused by Plasmodium falciparum.
This statement is true. Malignant malaria, also known as cerebral malaria, is a severe form of malaria caused by the Plasmodium falciparum parasite. It is characterized by the invasion of the brain by the parasite and can lead to coma and death if not treated promptly.

(iii) Malaria could be confirmed by Widal test.
This statement is incorrect. The Widal test is not used to confirm malaria. It is a serological test used to diagnose typhoid fever caused by the Salmonella bacteria. Malaria is diagnosed through microscopic examination of blood smears or through rapid diagnostic tests that detect specific malaria antigens.

(iv) Active immunity is slow and takes time to give its full effective response.
This statement is true. Active immunity is acquired when the immune system is exposed to a pathogen or a vaccine and produces its own immune response. This process takes time as the immune system needs to recognize the pathogen, activate immune cells, and produce antibodies. It usually takes several days to weeks for the immune response to reach its full effectiveness.

(v) Saliva in the mouth acts as a physiological barrier for pathogens.
This statement is true. Saliva contains various components that act as a physiological barrier for pathogens. It contains enzymes like lysozyme and lactoferrin that can kill or inhibit the growth of bacteria. It also contains antibodies and antimicrobial peptides that can neutralize or destroy pathogens. Additionally, saliva helps to wash away pathogens from the oral cavity, reducing the risk of infection.

The first line of defence in the immune system is provided by the skin and mucous membranes.

The immune system is a complex network of cells, tissues, and organs that work together to protect the body from harmful pathogens such as bacteria, viruses, and parasites. The immune system has two main lines of defence: the innate immune system and the adaptive immune system. The first line of defence is the innate immune system, which provides immediate, non-specific protection against pathogens.

The skin and mucous membranes are the first line of defence in the immune system because they act as physical barriers that prevent pathogens from entering the body.

Role of the skin:
The skin is the largest organ in the body and serves as a physical barrier between the internal organs and the external environment. It consists of multiple layers of cells that are tightly packed together, making it difficult for pathogens to penetrate. The outermost layer of the skin, called the epidermis, is composed of dead skin cells that provide an additional layer of protection. The skin also produces sweat and sebum, which contain antimicrobial substances that can kill or inhibit the growth of pathogens.

Role of mucous membranes:
Mucous membranes are found in various parts of the body, including the respiratory tract, gastrointestinal tract, and genitourinary tract. They are made up of a layer of epithelial cells that secrete mucus, a sticky substance that traps pathogens and prevents them from entering the body. Mucous membranes also contain specialized immune cells, such as macrophages and neutrophils, which can detect and eliminate pathogens.

The importance of the first line of defence:
The skin and mucous membranes play a crucial role in protecting the body from pathogens. By preventing pathogens from entering the body, they reduce the risk of infection and disease. However, if the first line of defence is breached and pathogens manage to enter the body, the second line of defence, which includes the inflammatory response and the complement system, is activated to eliminate the pathogens.

In conclusion, the skin and mucous membranes serve as the first line of defence in the immune system by acting as physical barriers and preventing pathogens from entering the body. They play a crucial role in protecting the body from infection and disease.

Innate immunity is the first line of defense mechanism against pathogens and foreign substances in the body. It is non-specific and present at birth. The components of innate immunity include:

1. Phagocytes: Neutrophils and macrophages are phagocytes that engulf and digest pathogens.

2. Natural killer cells: These cells recognize and destroy virus-infected cells and cancer cells.

3. Complement system: It is a group of proteins that work together to destroy pathogens.

4. Interferons: These are proteins that are released in response to viral infections and prevent the spread of the virus to other cells.

5. Inflammation: It is a response to tissue damage or infection and involves the release of chemical mediators that cause vasodilation, increased permeability, and recruitment of immune cells to the site of infection.

However, B-lymphocytes are part of the adaptive immune system and do not participate in innate immunity. They produce antibodies that specifically recognize and bind to antigens on pathogens, marking them for destruction by phagocytes or complement proteins. B-lymphocytes are activated by the presence of antigens and undergo clonal expansion to produce a large number of identical cells that can recognize and respond to the antigen. Therefore, B-lymphocytes are not part of the initial response to infection and take time to produce an effective response.

Introduction:
Antibodies, also known as immunoglobulins, are proteins that are secreted by B lymphocytes (B cells). They play a crucial role in the immune response by recognizing and binding to specific foreign substances, known as antigens, in order to neutralize or eliminate them. Understanding the source of antibodies is important in understanding the immune system and its response to pathogens.

B lymphocytes:
- B lymphocytes are a type of white blood cell that are part of the adaptive immune system.
- They are produced in the bone marrow and mature in the lymphoid organs, such as the spleen and lymph nodes.
- Once mature, B cells circulate in the blood and lymphatic system, constantly surveilling for antigens.
- When a B cell encounters an antigen that matches its specific receptor, it undergoes activation.

Activation of B lymphocytes:
- The activation of B cells occurs through a complex series of interactions with other immune cells.
- Once activated, B cells differentiate into plasma cells, which are specialized in secreting antibodies.
- Plasma cells are highly active in antibody production and can secrete large quantities of antibodies into the bloodstream.

Antibody secretion:
- Antibodies are secreted by plasma cells in response to antigen stimulation.
- These plasma cells are derived from activated B lymphocytes.
- The antibodies produced by plasma cells are specific to the particular antigen that triggered their activation.
- Antibodies are released into the blood and other body fluids, where they can bind to antigens and initiate immune responses.

Function of antibodies:
- Antibodies have various functions in the immune response, including neutralizing pathogens, promoting phagocytosis, activating complement system, and facilitating antigen presentation.
- They can bind to antigens on the surface of pathogens, preventing them from infecting cells and marking them for destruction by other immune cells.
- Antibodies can also enhance phagocytosis, where immune cells engulf and destroy pathogens.
- Additionally, antibodies can activate the complement system, a group of proteins that can directly kill pathogens and enhance the immune response.
- Antibodies can also facilitate antigen presentation, a process in which antigens are displayed to other immune cells, such as T lymphocytes, to initiate a coordinated immune response.

Conclusion:
In conclusion, antibodies are secreted by B lymphocytes, which differentiate into plasma cells upon activation. These antibodies are essential components of the immune response and play a crucial role in recognizing and eliminating pathogens. Understanding the source and function of antibodies is important in understanding the immune system's ability to fight off infections.

Introduction:
Vaccines and immunization programs have been crucial in controlling the spread of infectious diseases. They work by stimulating the immune system to recognize and destroy specific pathogens, preventing the onset of infection or reducing its severity. Several diseases have been successfully controlled through vaccination efforts.

Polio and Tetanus:
- Polio is a highly contagious viral infection that can lead to paralysis or even death. The polio vaccine, introduced in the 1950s, has been instrumental in eliminating polio in many parts of the world. Through widespread immunization campaigns, the number of polio cases has significantly decreased.
- Tetanus is caused by the bacterium Clostridium tetani, which enters the body through wounds. It can cause severe muscle stiffness and spasms, leading to respiratory failure. The tetanus vaccine, often administered in combination with other vaccines, has been effective in preventing this disease. Immunization programs have played a vital role in controlling tetanus.

Diphtheria and Pneumonia:
- Diphtheria is an acute bacterial infection that primarily affects the respiratory system. It can lead to the formation of a thick grayish coating in the throat, making it difficult to breathe. The diphtheria vaccine has proven highly effective in preventing the disease. Vaccination campaigns have significantly reduced the incidence of diphtheria worldwide.
- Pneumonia is an infection that inflames the air sacs in one or both lungs, leading to cough, fever, and difficulty breathing. While vaccines do not directly target pneumonia, they can prevent the primary causes of pneumonia, such as Streptococcus pneumoniae and Haemophilus influenzae. Vaccines against these pathogens, like the pneumococcal and Hib vaccines, have helped control pneumonia cases.

Cancer and AIDS:
- Cancer and AIDS are not infectious diseases caused by specific pathogens. Cancer arises due to uncontrolled growth of cells, while AIDS is caused by the human immunodeficiency virus (HIV). Vaccines have not yet been developed to directly prevent these conditions, although research is ongoing to develop an HIV vaccine.

Conclusion:
Vaccines and immunization programs have been successful in controlling infectious diseases like polio, tetanus, diphtheria, and pneumonia. These programs have significantly reduced the incidence of these diseases and prevented their severe consequences. However, it is important to note that vaccines are not yet available for all infectious diseases, and continued research and immunization efforts are required to combat emerging and existing infections.

The correct answer is option 'A' (i), (ii), and (iii). Let's discuss each statement in detail:

(i) Cell-mediated immunity is responsible for acquired immunity:
Cell-mediated immunity is one of the two arms of acquired immunity, the other being humoral immunity. Acquired immunity is the immunity that develops after exposure to an antigen. Cell-mediated immunity involves the activation of T lymphocytes, which directly attack infected cells or cancer cells. These T cells recognize antigens presented by antigen-presenting cells (APCs) and initiate an immune response.

(ii) It produces a primary response of low intensity:
The primary immune response is the initial response of the immune system to an antigen. It occurs when the immune system encounters a specific antigen for the first time. During the primary response, there is a lag period before antibodies are produced, and the intensity of the response is relatively low. It takes time for B cells to differentiate into plasma cells and secrete antibodies. However, the primary response leads to the development of memory cells, which are responsible for faster and stronger secondary immune responses upon subsequent exposure to the same antigen.

(iii) Active and passive immunity are types of acquired immunity:
Active immunity is the immunity that develops in response to an antigen exposure. It can occur naturally through infection or artificially through vaccination. When a person is exposed to an antigen, their immune system produces antibodies and memory cells, providing long-term protection against that specific antigen.

Passive immunity, on the other hand, is the temporary immunity that is acquired from another source. It can be acquired naturally, such as the transfer of antibodies from a mother to her fetus through the placenta or breast milk, or artificially, through the administration of preformed antibodies (e.g., immune globulins). Passive immunity provides immediate but short-lived protection, as the transferred antibodies are eventually cleared from the body.

(iv) Polymorphonuclear leucocytes and natural killer cells are involved in acquired immunity:
This statement is incorrect. Polymorphonuclear leukocytes, such as neutrophils, basophils, and eosinophils, are mainly involved in innate immunity, the non-specific defense mechanism that provides immediate, but short-lived protection against a wide range of pathogens. Natural killer (NK) cells are also part of the innate immune system and play a role in the early defense against viral infections and some types of cancer cells. However, acquired immunity primarily involves the activation of lymphocytes, including B cells and T cells.

In conclusion, the correct statements regarding the characteristics of acquired immunity are (i) Cell-mediated immunity is responsible for acquired immunity, (ii) It produces a primary response of low intensity, and (iii) Active and passive immunity are types of acquired immunity.

Life Cycle of Plasmodium
The life cycle of Plasmodium, the parasite responsible for malaria, involves two hosts: humans and female Anopheles mosquitoes. The correct sequence of the life cycle is crucial for understanding malaria transmission.
Sporozoites in Humans
- Plasmodium enters the human body through the bite of an infected female mosquito, introducing sporozoites into the bloodstream.
Liver Cells
- The sporozoites travel to the liver, where they invade liver cells (hepatocytes) and undergo asexual reproduction, developing into merozoites.
RBCs (Red Blood Cells)
- Merozoites are released into the bloodstream and invade red blood cells, where they multiply further, leading to the clinical symptoms of malaria.
Gametocytes in Blood
- Some of these merozoites differentiate into gametocytes, which are the sexual forms of the parasite found in the blood.
Blood Meal by Female Mosquito
- When a female mosquito takes a blood meal from an infected human, she ingests these gametocytes.
Fertilization in Mosquito
- In the mosquito’s gut, gametocytes undergo fertilization, forming zygotes, which develop into ookinetes and then oocysts.
Sporozoites in Mosquito
- These oocysts multiply and eventually release sporozoites, which migrate to the mosquito's salivary glands, ready to infect another human when the mosquito bites again.
Conclusion
Option B accurately describes this life cycle by outlining the critical stages: sporozoites infect liver cells, move to RBCs, form gametocytes, are taken up by a mosquito, and finally develop back into sporozoites, completing the cycle.