VBQs Class 12 Biology Human Health and Diseases

Please refer to VBQs for Class 12 Biology Human Health and Diseases. All value based questions for Biology Class 12 have been provided with solutions. We have provided below important values questions and answers. Students should learn these solved VBQs for Class 12 Biology as these will help them to gain more marks and help improve understanding of important topics.

Human Health and Diseases VBQs Class 12 Biology with Answers

Common Diseases in Humans

Very Short Answer Type Questions

Question. Malaria, typhoid, pneumonia and amoebiasis are some of the human infectious diseases.
Which one of these are transmitted through mechanical carriers? 
Answer. Mechanical carrier is one that simply carries pathogens to a susceptible individual and is not essential to the development of the pathogen. The pathogens are simply carried on the mouthparts, legs, body surface of the carrier from an infected to a susceptible host. Amoebiasis and typhoid are carried through mechanical carriers like housefly.

Question. How does malaria differ from chikungunya with reference to their vectors? 
Answer. Malaria is a protozoan disease, transmitted by female Anopheles mosquito while chikungunya is a viral disease transmitted by Aedes aegypti mosquito.

Question. Name any two techniques that serve the purpose of early diagnosis of some bacterial/ viral human diseases. 
Answer. PCR (Polymerase Chain Reaction) and ELISA (Enzyme Linked Immunosorbent Assay) are used for early diagnosis of some bacterial/viral diseases.

Question. Why is Gambusia introduced into drains and ponds? 
Answer. Gambusia is a larvivorous fish. It feeds on mosquito larvae, so introduced in drains and ponds to check spread of mosquito borne diseases.

Question. What causes swelling of the lower limbs in patients suffering fromfilariasis? 
Answer. Filariasis is caused by Wuchereria bancrofti.They normally affect the lymph vessels of the lower limbs causing them to swell like that of an elephant.

Short Answer Type Questions

Question. Name the causative organism, two symptoms and mode of transmission of ringworms.
Answer. Ringworm is a fungal disease caused by dermatophytes, which include Trichophyton, Microsporum and Epidermophyton. Symptoms of ringworm are appearance of dry, scaly lesions on skin, nails, scalp. Ringworm infection is acquired by sharing towels or clothes or comb with infected person.

Question. (a) Name the protozoan parasite that causes amoebic dysentery in humans.
(b) Mention two diagnostic symptoms of the disease.
(c) How is this disease transmitted to others?
Answer.(a) Entamoeba histolytica.
(b) Abdominal pain and blood in faeces.
(c) Amoebic dysentery is transmitted through contaminated food and water.

Question. Define the term ‘health’. Mention any two ways of maintaining it. 
Answer. Health is defined as a state of complete physical, mental and social well being and not merely the absence of disease or infirmity. Balanced diet, personal hygiene and regular exercise are very important to maintain good health.

Question. Write the scientific names of the causal organisms of elephantiasis and ringworm in humans.Mention the body parts affected by them.
Answer. Elephantiasis is caused by Wuchereria bancrofti and mainly affects lower limbs.
Ringworm is caused by Trichophyton and affects skin, hair and nails. 

Question. List the specific symptoms of pneumonia. Name the causative organism.
Answer. Pneumonia is a serious disease of lungs characterised by accumulation of mucus/fluid in alveoli and bronchioles to that extent that breathing becomes dificult. It is caused by Streptococcus pneumoniae or Diplococcus pneumoniae, and Haemophilus influenzae.

Question. Explain what causes chill in humans during malarial attack. Name the causative organism of malignant malaria. 
Answer. Haemozoin released by rupturing of RBCs causes chill in humans during malarial attack. Malignant malaria is caused by Plasmodium falciparum.

Short Answer Type Questions

Question. (a) Write the scientific names of the two species of filarial worms causing filariasis.
(b) How do they affect the body of infected person(s)?
(c) How does the disease spread? 
Answer.(a) Wuchereria bancrofti and Wuchereria malayi.
(b) The filarial worms are deposited near the site of mosquito (Culex) bite. They pass through the punctured skin and reach the lymphatic system where they slowly develop and cause chronic inflammation. They usually infect lymphatic vessels of the lower limbs. The inflammation of lymph nodes and lymph vessels leads to obstruction of lymph vessels which causes thickening of subcutaneous tissues and skin so that swelling of feet, legs, thighs, scrotal sacs occurs.
(c) The pathogens are transmitted to the healthy persons through the bite of the female mosquito Culex.

Question. At what stage is Plasmodium picked up by the female Anopheles? Describe the life cycle of the parasite in this insect. 
Answer. Female Anopheles mosquito picks up Plasmodium as gametocytes with blood meal. Life cycle of Plasmodium in mosquito is as follows : The gametocytes come out of the RBCs into the lumen of the stomach of the mosquito. Inside the stomach of the mosquito, the male and female gametocytes change into male and female gametes respectively. The gametes fuse (fertilise) to form zygote called oocyst. The nucleus of oocyst divides first by meiosis and subsequently by mitosis, forming large number of small haploid nuclei. At the same time, spindle shaped bodies called sporozoites are formed. When mature oocysts rupture, the sporozoites are liberated into the haemocoel (body cavity filled with blood) of the mosquito. Being motile, the sporozoites move to different organs in the body cavity of the mosquito, but many of them penetrate the salivary glands. The mosquito now becomes infective. When the female Anopheles mosquito bites a healthy person, the sporozoites are injected in his/her blood along with saliva. These sporozoites start the cycle again in human body.

Question. (a) Name the infective stage of Plasmodium which Anopheles mosquito takes in along with the blood meal from an infected human.
(c) Give a flow chart of the part of the lifecycle of this parasite passed in the insect.
Answer.(a) Gametocytes
(b)

Question. At what stage does Plasmodium gain entry into the human body? Write the different stages of its life cycle in the human body.
Answer. The malarial parasite, Plasmodium enters the human body as sporozoites (infectious form) through the bite of infected female Anopheles mosquito (vector). From the human blood sporozoites enter liver cells and multiply here and then attack the red blood cells (RBCs) resulting in their rupture. The rupture of RBCs is associated with release of a toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days. The released parasites from the ruptured RBCs infect new RBCs and develop into gametocytes (male and female). When a female Anopheles mosquito sucks the blood of an infected human host, it receives RBCs containing gametocytes.

Question. Write the scientific name of the pathogen that causes amoebic dysentery. Enumerate four symptoms of the disease. How is the disease transmitted?
Answer. Amoebiasis is caused by monogenic protozoan Entamoeba histolytica. It is characterised by abdominal pain, mild diarrhoea alternating with constipation, passing out of mucus and blood in faeces. The infection occurs by the cysts of Entamoeba present in the stool of infected person, through the agency of houseflies.

Question. (a) State what happens in the human body when malarial parasites infected RBCs burst to release the parasites in the blood.
(b) Mention the specific sites in the host body where production of
(i) sporozoites and
(ii) gametocytes takes place in the life cycle of the malarial parasites.
Answer.(a) When RBCs infected with malarial parasites burst, they release toxin called haemozoin which causes chill and high fever recurring every three or four days.
(b) (i) Production of sporozoites occurs in female Anopheles mosquito, inside oocyst on the surface of stomach.
(ii) Gametocytes formation takes place in human host inside RBCs.

Question. A person is suffering from ascariasis. Mention the pathogen causing the disease and an organ of the body affected, three symptoms and one mode of transmission of the disease.
Answer. Ascariasis is caused by a round worm, Ascaris lumbricoides. It is an endoparasite of small intestine of human beings. Symptoms of ascariasis are abdominal discomfort, fever, anaemia. It is transmitted through contaminated food, water, vegetables etc.

Question. With the help of a flow chart only show the stages of asexual reproduction in the life-cycle of the parasite in the infected human.
Answer.

Long Answer Type Questions

Question. Describe the asexual and sexual phases of life cycle of Plasmodium that cause malaria in humans. 
Answer. Life cycle of Plasmodium requires two hosts for completion, such a two host life cycle is called digenetic.
I. Life cycle of Plasmodium in Man – Asexual phase
(i) Infective stage of Plasmodium is sporozoite.When the mosquito bites another human, sporozoites are injected with bite.
(ii) Parasites (sporozoites) reach the liver through blood.
(iii) The parasite reproduces asexually in liver cells, bursting the cells and releasing into the blood.
(iv) Parasites enter the red blood cells (RBCs) and reproduce asexually there bursting the red blood cells and causing cycles of fever and other symptoms. Released parasites infect new red blood cells.
(v) Sexual stages develop in RBCs.

II. Life cycle of Plasmodium in female anopheles mosquito – Sexual phase
(i) Female mosquito takes up gametocytes with blood meal.
(ii) Fertilisation and development take place in the mosquito’s stomach.
(iii) The zygote elongates and becomes motile called ookinete.
(iv) The ookinete moves and bores through the wall of the stomach of female Anopheles mosquito. The ookinete changes to oocyst on the surface of the stomach.
(v) Inside the oocyst, sporozoites are formed which are released in the body cavity of the mosquito.
(vi) Mature infective stages (sporozoites) move to different organs of the body cavity but many of them penetrate salivary glands of mosquito.
(vii) When the female Anopheles mosquito bites a healthy person, the sporozoites are injected in his/ her blood alongwith saliva. 

Immunity

Very Short Answer Type Questions

Question. In what way is monocyte a cellular barrier with reference to immunity? 
Answer. Monocytes are motile and phagocytic leucocytes. They engulf bacteria and cellular debris and constitute cellular barriers of innate immunity.

Question. Some allergens trigger sneezing and wheezing in human beings. What causes this type of response by the body? 
Answer.Sneezing and wheezing in human beings to some allergens is caused due to exaggerated response of the immune system.

Question. State two different roles of spleen in the human body. 
Answer.Spleen is the secondary lymphoid organ. It is the site where proliferation and differentiation of B and T lymphocytes takes place and in fetus, spleen produces all types of blood cells.

Question. A boy of ten years had chicken-pox. He is not expected to have the same disease for the rest of his life. Mention how it is possible.
Answer.A body when encounters a pathogen (in this case chicken pox) for first time produces antibodies,that results in memory of the first encounter to protect the body in future from the same disease.

Question. Name any two types of cells that act as ‘cellular barriers to provide innate immunity in humans.
Answer.Certain types of leukocytes (WBCs) like polymorphonuclear leukocytes (PMNLneutrophils) and natural killer cells in the blood are cellular barriers, which provide innate immunity in humans.

Question. How do cytokine barriers help in evading viral infections?
Answer.Interferons are cytokine barriers. These are low molecular weight proteins secreted by virus infected cells, which protect non-infected cells from further viral infection.

Question. Why is secondary immune response more intense than the primary immune response in humans? 
Answer. Secondary immune response is quicker and more intense than the primary immune response because the memory B cells are present to quickly deal with the invading microbes by forming antibodies. Body “remembers” that it previously encountered this type of infection.

Question. What role do macrophages play in providing immunity to humans? 
Answer. Macrophages are phagocytic cells that remove bacteria or other foreign bodies from blood or tissues and display their antigen to alert the lymphocytes and stimulate them.

Question. How do interferons protect us? 
Answer.Virus infected cells produce an antiviral protein called interferon which on reaching the nearby infected cells, make them resistant to viral infection.

Question. What is it that prevents a child to suffer from a disease he/she is vaccinated against? Give one reason. 
Answer. Vaccine is suspension or extract of weakened (attenuated/ dead) pathogens of disease which when injected into healthy person provides it active acquired immunity to the disease.
Vaccination stimulates the antibody production and formation of memory cells without causing the disease. This protects the child by neutralising the pathogenic agents during infection.

Question. It was diagnosed by a specialist that the immune system of the body of a patient has been suppressed. Name the disease the patient has been suffering from and its causative agent.
Answer.In immunodeficiency diseases, the immune system of the body gets weakened, leading to repeated microbial infections. The patient is suffering from AIDS (Acquired Immune deficiency Syndrome) caused by HIV (Human Immunodeficiency Virus).

Question. What is an autoimmune disease? Give an example.
Answer.Autoimmune disease is a condition in which body’s immune system attacks self-cells. E.g., rheumatoid arthritis.

Question. Why is colostrum a boon to the newborn baby?
Answer.Colostrum (mother’s first milk) is rich in IgA antibodies. It provides passive immunity to new born and protects it from various diseases.

Question. When does a human body elicit an anamnestic response? 
Answer.Human body elicits an anamnestic response (secondary response) to the subsequent encounter with the same pathogen to which the body had previously encountered (primary response).

Short Answer Type Questions

Question. Write the events that take place when a vaccine for any disease is introduced into the human body.
OR
Why is a person with cuts and bruises following an accident administered tetanus antitoxin?
Give reasons. 
Answer.
In vaccination, a preparation of antigenic proteins of pathogens or weakened pathogen is introduced into the body. These antigens generate the primary immune response, and the memory B and T cells. When the vaccinated person is attacked by the same pathogen again, the existing memory T or B cells recognise the antigen quickly and attack the invaders with massive production of lymphocytes and antibodies.
OR
A person with cuts and bruises following an accident has chances of getting infected from tetanus. So, in this case quick immune response is required which is provided by giving the patient tetanus antitoxin which is a preparation containing preformed antibodies to the toxin. 

Question. How does spleen act as a lymphoid organ? Explain. 
Answer.Spleen acts as secondary lymphoid organ where mature B and T lymphocytes undergo proliferation and differentiation. In spleen, lymphocytes develop acquired immune response to antigens and becomes effector cells.

Question. Name an allergen and write the response of the human body when exposed to it.
Answer. Pollen grain is an allergen. Exposure to pollen causes hay fever. It is the form of allergy due to pollen of grasses, trees and other plants. It is characterised by inflammation of the membrane lining the nose and sometimes of the conjunctiva. The symptoms are sneezing, running nose and watering eyes due to histamine release.

Question. A student on a school picnic to a park on a windy day started sneezing and having dificulty in breathing on reaching the park. The teacher enquired whether the student was allergic to something.
(a) What is an allergy?
(b) Write the two unique characteristics of the system involved in the response observed in the student. 
Answer.(a) Allergy is a hypersensitive response to foreign substances, coming in contact with or entering the body. It is characterised by sneezing, watery eyes, dificulty in breathing etc.
(b) Two unique characteristics of system involved in allergic response are :
(i) The body will produce Ig E antibodies
(ii) The body will release chemicals like histamine and serotonin from the mast cells.

Question. Differentiate between active and passive immunity. 
Answer. The given table shows differences between active and passive immunity:

Question. Name and explain the two types of immune responses in humans. 
Answer. Immune response is the specific reactivity induced in a host by an antigenic stimulus. It is of two types – primary and secondary immune response.
(i) The reaction of the body’s immune system to the first attack of microbes (antigens) is called primary immune response. It takes much longer time to develop because of the requirement of suitable receptor development. This response is feeble and declines rapidly. This produces both receptors and memory cells.
(ii) The reaction of the body’s immune system to any subsequent infection of the same microbe is termed secondary immune response. It is quicker and more intense than primary immune response because memory B cells present quick response against invading microbes.

Question. Name the two types of immune systems in a human body. Why are cell mediated and humoral immunities so called? 
Answer.  Two types of immune systems in human body are : Antibody Mediated Immune System (AMIS) and Cell Mediated Immune System (CMIS). Antibody-mediated (or humoral) immunity is associated with the appearance of antibodies, secreted by B-lymphocytes, in the extracellular fluids such as plasma, lymph and external secretions. Cell-mediated immunity is mediated by T-lymphocytes that defend against pathogens including protists and fungi that enter the cells.

Question. Identify A, D, E and F in the diagram of an antibody molecule given below:

Answer.
A – Antigen binding site
B – Variable region
C – Constant region
D – Light chain
E – Constant region of heavy chain
F – Disulphide bond

Question. List the two types of immunity a human baby is born with. Explain the differences between the two types.
Answer. Two types of immunity with which human baby is born include-
(i) Innate immunity – It is inherited by an organism from the parents and protects it from birth throughout the life. It is not specific to particular pathogen and consists of four types of barriers – physical, physiological, cellular and cytokine.
(ii) Natural passive immunity – It is passively transferred from mother to foetus through placenta, as IgG antibodies can cross placental barrier to reach the foetus.

Question. Why does a doctor administer tetanus antitoxin and not a tetanus vaccine to a child injured in a roadside accident with a bleeding wound?
Explain.
Answer. A child injured in a roadside accident with a bleeding wound has chances of getting infected from tetanus so quick immune response is required, therefore, preformed antibodies, or antitoxin (a preparation containing antibodies to the toxin) is directly injected. In vaccination, a preparation of antigenic proteins of pathogen or inactivated/ weakened pathogen (vaccine) are introduced into the body. The antibodies produced in the body against these antigens would neutralise the pathogenic agents during actual infection. Therefore, vaccine administration would not have given quick relief and thus would not have been effective.

Question. Name and explain the type of barrier of innate immunity where some cells release interferons when infected. 
Answer.  The type of this barrier is called cytokine barrier. Cytokines are protein molecules, released by cells when activated by antigen, that are involved in cell-to-cell communication, acting as enhancing mediators for immune response through interaction with specific cell-surface receptors on leucocytes. Interferons are examples of cytokines. Interferons protect against viral infections of cells.

Question. In an auto immune disorder, a person produces antibodies that mimic the action of TSH. Name the disorder, which results due to this situation.Give its symptoms. 
Answer. A patient with Grave’s disease produces autoantibodies that bind with the receptor for thyroid stimulating hormone (TSH) and mimic the normal action of TSH, activating adenylate cyclase and resulting in production of thyroid hormones. Unlike TSH, auto-antibodies are not regulated, and consequently they overstimulate the thyroid.

Question. The barriers in the innate immunity are given in the following table. Identify a, b, c, and d.

Answer.a – Mucous membrane
b – Lysozyme
c – Cytokine
d – Natural killer cells

Question. Name and explain the type of immunity that is provided by injecting microbes deliberately during immunisation into the human body.
Answer.  Artificial active immunity is the type of immunity that is provided by injecting microbes deliberately during immunisation into the human body. The microbes are injected through vaccines. Vaccine is a suspension of dead/weakened microbes of disease which when injected into healthy person provides artificial active immunity e.g., live BCG vaccine for tuberculosis, MMR vaccine for measles, mumps and rubella.

Question. State the functions of primary and secondary lymphoid organs in humans. 
Answer. There are two types of lymphoid organs : primary lymphoid organs and secondary lymphoid organs. The primary lymphoid organs are those organs where T lymphocytes and B lymphocytes, mature and acquire their antigen-specific receptors. After maturation, the lymphocytes migrate to secondary lymphoid organs e.g., bone marrow and thymus where they undergo proliferation and differentiation. The acquired immune response to antigens usually develops in these organs and become effector cells.

Question. (a) How does a vaccine affect immunity?
(b) How can we get immunised against tetanus? 
Answer.
(a) In vaccination, a preparation of antigenic proteins of pathogens or weakened pathogen is introduced into the body. These antigens generate the primary immune response, and the memory B and T cells. When the vaccinated person is attacked by the same pathogen again, the existing memory T or B cells recognise the antigen quickly and attack the invaders with massive production of lymphocytes and antibodies.
(b) We can get immunised against tetanus either through artificial active immunity which is provided by vaccines or through artificial passive immunity, i.e, by administration of antibodies in the form of antitoxin.

Question. How does a vaccine for a particular disease immunise the human body against that disease?
Answer.  Vaccine is a preparation of dead/weakened germs of a disease which on inoculation into healthy person provides temporary/permanent active/ passive immunity by inducing antibody formation. The antibodies produced in the body against these antigens would neutralise the pathogenic agents during actual infection. The vaccines also generate memory B and T cells that recognise the pathogen quickly on subsequent exposure and attack the invaders with a large production of antibodies.

Question.

(a) What does the above diagram illustrate?
(b) Name the labelled parts ‘A’ and ‘B’.
(c) Name the type of cells that produces this molecule. 
Answer.(a) The given diagram shows structure of an antibody molecule.
(b) ‘A’ is antigen binding site and ‘B’ represents variable region of heavy chain.
(c) B-lymphocytes produce antibodies.

Question. A student on a school trip started sneezing and wheezing soon after reaching the hill station for no explained reasons. But, on return to th plains, the symptoms disappeared. What is such a response called? How does the body produce it? 
Answer. Hill station and plains do have different weather conditions and environment. Sneezing and wheezing on hill station is due to exposure to different allergens, this response is called allergy. It is a hypersensitive response of a person to foreign substance coming in contact with or entering the body. Allergy involves IgE antibodies and release of chemicals like histamine and serotonin from mast cells.

Question. A young boy when brought a pet dog home started to complain of watery eyes and running nose. The symptoms disappeared when the boy was kept away from the pet.
(a) Name the type of antibody and the chemicals responsible for such a response in the boy.
(b) Mention the name of any one drug that could be given to the boy for immediate relief from such a response.
Answer.(a) Such a response in the boy is called allergy which occurs due to production of IgE antibodies and chemicals like histamine and serotonin from the mast cells.
(b) Anti-histamine could be given to the boy for immediate relief from such a response.

Question. (a) Name the lymphoid organ in humans where all the blood cells are produced.
(b) Where do the lymphocytes produced by the lymphoid organ mentioned above migrate and how do they affect immunity? 
Answer.(a) Bone marrow.
(b) The lymphocytes produced migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix. The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells which then affect immunity.

Question. What is colostrum? Why is it important to be given to the newborn infants? 
Answer. Colostrum (mother’s First milk) is rich in IgA antibodies. It provides passive immunity to new born and protects it from various diseases.

Question. (a) Highlight the role of thymus as a lymphoid organ.
(b) Name the cells that are released from the above mentioned gland. Mention how they help in immunity. 
Answer.(a) Thymus is a primary lymphoid organ where the maturation of T-lymphocytes takes place.
Thymus atrophies with age.
(b) T-lymphocytes are released from thymus. T cells provide cell-mediated immunity and defend against pathogens including protists and fungi that enter the cells.

Question. Name the type of immunity that is present at the time of birth in humans. Explain any two ways by which it is accomplished. 
Answer.  Innate immunity is the resistance to infection, which an individual possesses by virtue of his genetic make up, that is it comprises all those defence elements with which an individual is born It is accomplished by certain barriers such as physical, physiological, cellular and cytokine barriers.

Short Answer Type Questions

Question. Why are lymph nodes and bone marrows called lymphoid organs? Explain the functions of each one. 
Answer.  Lymph nodes and bone marrow are called lymphoid organs as these are the sites for proliferation and maturation of lymphocytes respectively. Lymph nodes are secondary lymphoid organs where mature B- and T-lymphocytes undergo proliferation and differentiation. Bone marrow is a primary lymphoid organ where B cells mature and acquire their antigen-specific receptors.

Question. A heavily bleeding and bruised road accident victim was brought to a nursing home. The doctor immediately gave him an injection to protect him against a deadly disease.
(a) Write what did the doctor inject into the patient’s body.
(b) How do you think this injection would protect the patient against the disease?
(c) Name the disease against which this injection was given and th kind of immunity it provides. 
Answer.(a) Doctor injected anti-tetanus toxin into patient’s body.
(b) Injection containing preformed antibodies or antitoxin (preparation containing antibodies to toxin) would neutralise the pathogenic agents and would give quick relief.
(c) Injection was given against tetanus and it provides artificial passive immunity.

Question. What is the functional difference between B-cells and T-cells? 
Answer. Differences between B-Lymphocytes (B-cells) and T-Lymphocytes (T-cells)

Question. (a) List any two situations when a medical doctor would recommend injection of preformed antibodies into the body of a patient.
Name this kind of immunisation and mention its advantages.
(b) Name the kind of immunity attained when instead of antibodies weakened antigens are introduced into the body.
 Answer. 
(a) If a person is infected with some deadly microbes to which quick immune response is required as in tetanus, we need to directly inject the preformed antibodies or antitoxin. Even in the cases of snakes bites the injection which is given to the patients, contain preformed antibodies against the snake venom. This type of immunisation is called artificial passive immunisation. It provides immediate relief but may cause some problems.
(b) In vaccination, a preparation of inactivated/ weakened antigenic proteins of pathogens are introduced into the body. This produces immune response and the type of immunity is called artificial active immunity.

Question. (a) Name and explain giving reasons, the type of immunity provided to the newborn by the colostrum and vaccinations.
(b) Name the type of antibody
(i) present in colostrum
(ii) produced in response to allergens in human body. 
Answer.(a) Colostrum (mother’s first milk) rich in IgA antibodies provides natural passive immunity to new born. In passive immunity, ready-made antibodies are directly injected into a person to protect the body against foreign agents.
Through vaccination artificial active immunity, will be provided to the newborn in which his own cells will produce antibodies in response to vaccine. E.g.,BCG vaccine for tuberculosis.
(b) (i) IgA
(ii) IgE

Question.

(i) Identify the molecule shown and the site labelled ‘A’.
(ii) Why is this molecule referred to as H₂L₂? Explain.
Answer.(i) Given figure shows an antibody molecule,and A is antigen binding site.
(ii) An antibody molecule consists of four peptide chains, two small light chains and two longer heavy chains. Hence, an antibody is represented as H₂L₂

Question. (a) It is generally observed that the children who had suffered from chicken-pox in their childhood may not contract the same disease in their adulthood. Explain giving reasons the basis of such an immunity in an individual.Name this kind of immunity.
(b) What are interferons? Mention their role.
Answer.
(a) Children who had suffered from chickenpox may not contract the same disease in their adulthood because of development of memory cells. These type of cells develop during first encounter with the pathogen. Memory cells are highly specific and may remain in body for decades. Subsequent encounter with the same pathogen elicits a highly intensified secondary or anamnestic response. This type of immunity is known as acquired natural active immunity.
(b) Interferons are the proteins produced by virus infected cells. They protect non-infected cells from further viral infection.

Question.

Identify a, b and c in the schematic diagram of an antibody given above and answer the questions.
(a) Write the chemical nature of an antibody.
(b) Name the cells that produce antibodies in humans.
(c) Mention the type of immune response provided by an antibody.
Answer. In the given structure of an antibody molecule, ‘a’ is the antigen binding site, ‘b’ is constant region of light chain and ‘c’ is constant region of heavy chain.
(a) Antibodies are protein in nature.
(b) B-cells produce antibodies.
(c) Humoral immune response is an antibody mediated immune response.

Long Answer Type Questions

Question. A youth in his twenties met with an accident and succumbed to the injuries. His parents agreed to donate his organs. List any two essential clinical steps to be undertaken before any organ transplant. Why is the transplant rejected sometimes? What views would you share with your health club members to promote organ
donation? 
Answer. Organ transplantation involves the removal of damaged/injured tissues or organs from the body of a person and their substitution by similar tissues/organs from a donor. Tissue matching, blood group matching are essential clinical steps before undertaking any graft/ transplant. Transplantation may result in the rejection of transplanted organs as the immune system recognises the protein in the transplanted tissue or organs as foreign and initiates cellular immunity.
We should raise and promote awareness about organ donation, about need of organ and tissue donors. There are lakhs of people waiting for organ donation and many people die daily while waiting for transplant. Organs and tissues from one donor can save upto 40-50 lives. So, we should encourage and get registered for organ donation to save many lives. 

Question. (a) Name and explain any four lymphoid organs present in humans.
(b) Categorise the named lymphoid organs as primary or secondary lymphoid organs, giving reasons.
Answer. (a) Four lymphoid organs are :
(i) Bone marrow : It is the main lymphoid organ where all blood cells including lymphocytes are formed. Maturation of B-lymphocytes occurs here.
(ii) Thymus : It is the site of T lymphocyte maturation. Thymus is situated near the heart and is quite large in size at the time of birth but keeps reducing with age.
(iii) Lymph nodes: These are small solid structures found at intervals along the lymphatic system. They are composed of lymphoid tissue and act as filters for the lymph, preventing foreign particles from entering the bloodstream. Lymph nodes also produce lymphocytes and plasma cells.
(iv) Spleen: It is a bean shaped organ which is the largest single mass of lymphoid tissue in the body. In foetus the spleen produces all types of blood cells but in adult it only produces lymphocytes. Macrophages of spleen are phagocytic.
(b) Lymphoid organs are those organs where the maturation and proliferation of lymphocytes takes place.There are two types of lymphoid organs :
primary and secondary.
Primary lymphoid organs are those where T lymphocytes and B lymphocytes mature and acquire their antigen-specific receptors. Bone marrow and thymus are primary lymphoid organs. B-lymphocytes mature in bone marrow and T-lymphocytes mature in thymus.
Secondary lymphoid organs are those where B lymphocytes and T lymphocytes undergo proliferation and differentiation. They acquire immune response in these organs and become effector cells. Lymph nodes and spleen are secondary lymphoid organs.

Question. Under polio prevention programme, infants in India were given polio vaccines on a large scale at regular intervals to eradicate polio from the country.
With the help of an example each, differentiate between active and passive immunity. 
Answer. The given table shows differences between active and passive immunity: