Human Health and Disease Important Questions for CBSE Class 12 Biology Health, Common Diseases in Human and Immunity

1.Health is defined as a state of complete physical, mental and social well-being.
(i)The factors which affect human health are:
(a)Genetic disorders  (b) Infections                         (c) Lifestyle.
(ii)Balanced diet, personal hygiene and regular exercise are very important to maintain good health.
(iii) Awareness about diseases and their effect on different body functions, vaccination against infectious diseases, proper disposal of wastes, control of vectors, maintenance of hygienic food and water resources are necessary for achieving good health.

2.Disease is a state when functioning of one or more organs or systems of the body is  adversely affected, characterised by various signs and symptoms.  Diseases can be divided broadly into the following two categories depending on the  modes of transmission
I.Infectious diseases which easily transmit from one person to another, e.g. AIDS, common cold, etc.
II.Non-infectious diseases which does not transmit from one person to another, e.g. cancer, diabetes, etc.
(i)Disease causing organisms are called pathogens, e.g. bacteria, viruses, fungi, protozoans, helminthes, etc.
(ii)The above described pathogens enter the body by direct contact, contaminated food and water, droplet infection, etc
(iii)The pathogens multiply in body cells, interfere with normal vital activities, cause morphological and functional damage.
(iv) Infectious diseases can be divided into certain categories, based on the type of pathogen

3.Some of the common infectious diseases are:
I.Bacterial Diseases

  • Typhoid is caused by bacterium (Salmonella typhi).
  • typhi enters the small intestine through food and water contaminated with them and migrate to other organs through blood.
  • Intestinal perforation and death may occur in severe cases.
  • Widal test is a confirmation test for typhoid.
  • Symptoms are high fever (39-40 °C), weakness, stomach pain, constipation, headache and loss of appetite.

(ii) Pneumonia is caused byStreptococcus pneumoniae and Haemophilus influenzae.

  • These bacteria infect alveoli of the lungs. The alveoli get filled with fluid causing decrease in respiratory efficiency of the lungs.
  • Pneumonia spreads by inhaling droplets/aerosol from infected individuals or even by sharing glasses and utensils with patients.
  • Symptoms of pneumonia are fever, chills, cough, headache, etc.

(iii) Dysentery, plague, diphtheria, etc., are some other examples of bacterial  diseases.
II.Viral Disease
Common cold occurs due to a group of viruses called rhino viruses.

  • These viruses infect the nose and respiratory passage but not the lungs.
  • Common cold is characterised by nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness, etc., which generally last for 3-7 days.
  • The infection occurs due to cough or sneezes of an infected person, either inhaled directly or transmitted through contaminated objects such as pens, books, cups, computer’s keyboard or mouse, etc.

III.Protozoan Diseases
(i)Malaria is caused by a protozoan, Plasmodium (P. vivax, P. malariae and P.falciparum).

  • falciparum causes most serious kind of malaria, i.e. malignant malaria which can be fatal.
  • Female Anopheles mosquito is the vector of Plasmodium, which transfer the sporozoites (infectious form) in human body.


  • The malarial parasite requires two hosts to complete its life cycle, i.e. human and mosquito.
  • Plasmodium enters the human body as sporozoite, through the bite of infected female Anopheles
  • Parasites initially multiply within the liver cells and then attack the Red Blood Cells (RBCs) causing their rupture.
  • Rupture of RBCs release a toxic substance called haemozoin. Haemozoin causes chill and high fever recurring every 3-4 days.
  • When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito’s body and undergo further development.
  • The parasites multiply within them to form sporozoites that are stored in their salivary glands.
  • When these mosquitoes bite a human, the sporozoites are introduced into his/her body, initiating the events mentioned above.

(d)Antimalarial drugs used for the treatment are quinine and chloroquin.
(e)Malaria can be prevented by killing mosquitoes by spraying DDT, BHC, etc., and using insect repellents, mosquito nets, etc.
(iii)Amoebiasis (amoebic dysentery) is caused by an intestinal endoparasite, Entamoeba histolytica, which is found in large intestine of humans.

  • Carrier of pathogen is housefly. It transmits the parasite from faeces of infected person to the food, thereby contaminating them.
  • Infection takes place mainly through the contaminated food and water.
  • Symptoms are abdominal pain, constipation, cramps, faeces with excess mucous and blood clots.

IV.Fungal Disease
Ringworm is caused by many fungi of genera Microsporum, Trichophyton and Epidermophyton.
(i)Infection occurs through contact with an infected person or from soil and through the use of towels, clothes, combs, etc., of an infected person.
(ii)Heat and moisture help these fungi to grow in regions like skin folds as in groin or between the toes.
(iii) Symptoms of ringworm are appearance of dry, scaly lesions on various parts of the body such as skin, nails and scalp accompanied by intense itching.
V.Helminthic Diseases
(i)Ascariasis is caused by an intestinal endoparasite of human, Ascaris lumbricoides commonly called as roundworm.

  • Infection occurs as the eggs of parasite are excreted along with the faeces of infected person, which contaminate water, soil, plants, etc.
  • Infection reaches to human beings through contaminated vegetables, fruits and water, etc.
  • Symptoms of disease are abdominal pain, indigestion, muscular pain, fever, anaemia, nausea, headache and blockage of intestinal passage.

(ii)Filariasis/Elephantiasis is caused by filarial worms, Wuchereria bancrofti and Wuchereria malayi.

  • Culex mosquito (female) is the vector.
  • Genital organs also get affected leading to their deformation.
  • Symptoms are inflammation of organs in which they live for many years, normally affect lymph vessels of lower limbs resulting in swelling hence, called elephantiasis.

4.Prevention measures to avoid infectious diseases are:

  • Maintenance of personal and public hygiene is important.
  • Personal hygiene includes keeping the body clean, consumption of clean drinking water, food, vegetables, fruits, etc.
  • Public hygiene includes proper disposal of waste excreta, periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks.
  • Eradication of vectors and destroying their breeding sites.
  • Mosquito nets, repellants should be used.
  • Vaccination and immunisation programmes for diseases should be strictly followed.
  • Use of antibiotics and other drugs can significantly keep away infectious diseases.

5.Immunity is the capacity of an organism to resist or defend itself from the  development of a disease. It is of the following types, as shown below:
I.Innate immunity is present from birth and is inherited from the parents.
(i)It is non-specific.
(ii)It consists as following types:

  • Physical barriers prevent entry of microorganisms in the body e.g. skin, mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts.
  • Physiological barriers prevent microbial growth in the body, e.g. acid in the stomach, saliva in the mouth and tears from eyes.
  • Cellular barriers phagocytose and destroy microbes. For example, some WBCs like Polymorphonuclear Leukocytes (PMNL), monocytes and natural killer cells (type of lymphocytes) in the blood as well as macrophages in tissues.
  • Cytokine barriers are virus-infected cells, which secrete proteins called They protect non-infeeted cells from further viral infection.

II.Acquired immunity is not present from birth and develops during an individual’s life  time.
(i)It is pathogen specific and characterised by memory.
(ii)When it encounters a pathogen for the first time, it produces a response called  primaiy response, which is of low intensity.
(iii)Further encounter with same pathogen produces highly intensified secondary or  anamnestic response due to memory of the first encounter.
(iv)Immune responses are produced by two types of lymphocytes:

  • B-lymphocytes or B-cells produce an army of proteins (in response to pathogens) called antibodies in blood.
  • T-lymphocytes or T-cells help B-cells to produce antibodies.

(v) Types of acquired immunity:
(a)Humoral immune response or Antibody Mediated Immunity (AMI) It is mediated by antibodies present in blood and lymph.
(b)Cell-mediated immune response or Cell Mediated Immunity (CMI) It is mediated by T-lymphocytes. The graft rejection during organ transplantation, because of the ability to differentiate between self and non-self, is due to the cell-mediated immunity
(vi)Antibodies are immunoglobulin molecules (Ig). These are of five types:  IgA, IgM, IgE, IgG and IgD.
(a)Each antibody molecule has four peptide chains, i.e. two small called  light (L) chains and two longer called heavy (H) chains. Hence, an antibody is represented as H2L2.
(b)An antibody seems like a Y-shaped structure.6.Acquired immunity is as following two types:

7.Vaccination and immunisation The principle is based on the property of memory of immune system.
(i)Vaccination is the process of introduction of weakened or inactivated pathogens or proteins (vaccine) into a person to provide protection against a disease.
(ii)Immunisation is a process by which the body produces antibodies against the vaccine (primary response) and develop the ability to neutralise pathogens during actual infection (secondary response), i.e. the body become immune to that antigen or infection.
(iii)Vaccine generates memory B and T-cells that recognise the pathogens on subsequent exposure and produce an intense immune response.
(iv)In case of requirement of quick immune response like tetanus infection, preformed antibodies are injected into the patient. This is called passive immunisation.
(v)Recombinant DNA technology has produced antigenic polypeptides of pathogen in bacteria or yeast. This allowed large scale production of vaccine, e.g. hepatitis-B vaccine from yeast, etc.

8.Human immune system includes (i) lymphoid organs (ii) immune cells (iii) soluble molecules like antibodies (iv) lymphoid tissues.
Lymphoid organs These are the organs where origin and/or maturation and proliferation of lymphocytes occur. They are as following two types:

  • Primary lymphoid organs are the sites where lymphocytes differentiate and mature to become antigen-sensitive, e.g. bone marrow and thymus.In bone marrow, all blood cells including lymphocytes are produced and B-lymphocytes mature.Thymus is a lobed organ, located near the heart and beneath the breastbone.It reduces as the age increases. T-lymphocytes develop and mature in thymus.
  • Secondary lymphoid organs provide the sites where lymphocytes interact with the antigen and proliferate to become effector cells, e.g. spleen, lymph nodes, tonsils,  Peycr’s patches of small intestine and appendix.Spleen is a large, bean-shaped organ which contains lymphocytes and phagocytes.It acts as a filter to trap blood-borne microbes and contain a large pool of erythrocytes.Lymph nodes are small solid structures along the lymphatic system. Their function is to trap microorganisms or other antigens that enter the lymph and tissue fluid. Mucosal Associated Lymphoid Tissue (MALT) is formed of the masses of lymphoid tissue, lining the mucosa of respiratory, digestive and urogenital tracts. About 50% of lymphoid tissue in human body is formed by MALT.

9.Allergy is a hypersensitive reaction of the immune system to certain antigens present in the environment.
(i)Allergens produce immune response in an individual, e.g. pollen grains, animal dander, dust, feathers, etc.
(ii)IgE antibodies are produced in response to allergens.
(iii)Allergy is due to chemicals like histamine and serotonin released from the mast  cells.             (iv)Symptoms of allergy are sneezing, watery eyes, running nose, difficulty in breathing.
(v)Antihistamine, adrenaline and steroids are taken to reduce the symptoms of allergy.

10.Autoimmunity is an abnormal immune response in which immune system of the body starts arthritis.

11.AIDS or Acquired Immuno Deficiency Syndrome was first reported in 1981 in USA.
(i)The causative agent is Human Immunodeficiency Virus (HIV).
(ii)HIV belongs to the group of viruses called retrovirus. It has RNA genome enclosed in an envelope.
(iii)HIV is transmitted by

  • Sexual contact with infected person.
  • Transfusion of contaminated blood and blood products.
  • Sharing infected needles.
  • Infected mother to unborn child through placenta.

(iv)People, who are susceptible to infection are:

  • Drug addicts, who take intravenous drug injections.
  • Individuals who are involved with multiple sexual partners.
  • Individuals who require repeated blood transfusion
  • Children born to HIV positive mother.

NOTE Infected cell can survive, while viruses are being replicated and released.
(v)Modes of HIV infection:

  • Virus enters the macrophages, after entering the body of a person.
  • RNA gets replicated to form viral DNA by enzyme reverse transcriptase.
  • Viral DNA gets incorporated into the host cell DNA and directs the infected cells to produce virus particles.
  • Macrophages continue to produce virus particles and thus, acts as HIV factory.
  • These virus particles enter into helper T-lymphocytes (TH cells) in the blood, where they continue to replicate and produce viral progenies.
  • The number of helper T-lymphocytes progressively decreases in the body of the infected person.
  • As the number of T-cells decrease, the immunity also decreases. As a result, person cannot produce any immune response even against common bacteria like Mycobacterium, parasite like Toxoplasma, viruses and fungi.
  • ELISA (Enzyme Linked Immuno Sorbent Assay) is a widely used diagnostic test for AIDS.
  • Treatment with anti-retroviral drugs is only partially effective.

(vi)Preventive measures for HIV infection are:
(a)National AIDS Control Organisation (NACO) set-up in 1991 and other NGOs educate people about AIDS.
(b)Role of WHO to prevent HIV infection:

  • Ensure use of disposable syringes and needles.
  • Ensure keeping blood banks safe from HIV.
  • Free distribution of condoms.
  • Prevention of drug abuse.
  • Discouraging unsafe sex and encouraging regular check-up.

12.Cancer can be defined as an uncontrolled growth or proliferation of cells without any differentiation.
(i)In our body, cell growth and differentiation is highly controlled and regulated.
(ii)The cancer cells divide repeatedly with uncontrolled cell divisions. They do not require extracellular growth factors.
(iii)Cancer cells lost the property of contact inhibition (contact with other cells inhibit the uncontrolled growth).
(iv)The repeated division of cancerous cells, form a large mass of cells called
(v)Cancer cells move from tumour to new sites through blood for forming secondary tumours. This invasion of cancer cells from one part to other parts by the body fluids is called metastasis.
(vi)Types of tumour and differences between them:
(vii)Cancer causing viruses are called oncogenic viruses. They have genes called  viral oncogenes.
(viii) Normal cells have genes called cellular oncogenes (c-onc.) or proto oncogenes, which  are present in inactive state, but under certain conditions (like mutation) could lead  to oncogenic transformation of the cells.
(ix) Carcinogens are cancer causing agents. They may be
(a) Chemicals As in cigarette smoke, benzopyrene, dyes, paints, etc.
(b) Biological Oncogenic viruses, some parasites, etc.
(c) Physical Ionising radiation like X-rays and y-rays, non-ionising radiations like  UV-rays.
(x) Cancer can be detected by the following methods:
(a) Blood and bone marrow tests for increased cell counts.
(b) Biopsy and histopathological studies of the tissue.
(c) Radiography by X-rays, to detect cancer of the internal organs.
(d) Computed Tomography (CT) using X-rays, to generate a 3-D image of internal tissue.
(e) Resonance imaging involves use of non-ionising radiation and strong magnetic field  to detect pathological     and   physiological     changes in living tissue.
(f) Monoclonal antibodies against cancer-specific antigens are also used for cancer  detection.
(xi) Treatment of cancer involves following methods:
(a) Surgery Tumours are removed by surgery to check further spread of cancer cells.
(b) Radiation therapy Tumour cells are irradiated by lethal doses of radiation, taking  care to protect the surrounding normal  cells.
(c) Chemotherapy Several chemotherapeutic drugs are used to kill cancer cells. But,  their side effects like hair loss, anaemia is also reported.Most cancers are treated by the combination of the above three.
(d) Immunotherapy Biological modifiers like a-interferons are used to activate the  immune system and helps in destroying the tumour.

Previous Year  Examinations Questions

1 Mark Questions

1.Why is secondary immune response more intense than the primary immune response in humans?[All India 2014]
Ans. Since, the secondary immune response is based on the memory of primary response,i.e.  first encounter with antigen. The second generated immune response is more fast having higher affinity for antigen, and therefore more intense than primary immune response.

2.Name any two types of cells that act as ‘cellular barriers’ to provide innate immunity in humans.[Delhi 2014]
Ans.Certain type of leucocytes (such as PMNL- neutrophils, monocytes) and natural killer cells are two types of cells that act as ‘cellular barriers’ to provide innate immunity in humans

3.Name the two intermediate hosts on  which the human liver fluke depends to complete its life cycle so as to facilitate parasitisation of its primary host [Delhi 2014]
Ans.The human liver fluke requires two intermediate hosts, i.e. freshwater snail and fish to complete their life cycle and facilitate parasitisation of its primary host

4.How does haemozoin affect the human body when released in blood during malarial infection?  [Foreign 2014]
Ans.The release of toxic haemozoin by the  ruptured RBCs during malarial infection accounts for recurrence of high fever and chill every 3-4 days.

5.What is an autoimmune disease?  Give an example. [Foreign 2014]
Ans.The abnormal response of an immune system in which it fails to recognise ‘self and ‘non-self’ and start destroying its own cells and molecules is called autoimmune disease. Rheumatoid is an example of autoimmune disease which destroys articular cartilage and fusing bones

6.When does a human body elicit an anamnestic response?  [All India 2013; Delhi 2011 C]
Ans.Second encounter of the organism with  same antigen or pathogen elicits anamnestic or secondary response for which body have memory of first encounter.

7.State two different roles of spleen in  the human body?  [All India 2012]
Ans.The two roles of spleen in human body are:
(i) Spleen acts as a filter to trap blood-borne microorganisms.
(ii) It is also a large reservoir of  erythrocytes

8.How do interferons protect us?[All India 2012]
Ans.Interferons produced by virus-infected cells protects the non-infected cells from viral infection by inhibiting its replication and making cells resistant to viral infection

9.Why do pollen grains of some flower trigger sneezing in some people?[Foreign 2012]
Ans.Pollen grains are allergens and cause allergy in some people due to release of chemicals i ike histamine and serotonin from mast cells

10.What is it that prevent a child to suffer from a disease he/she is vaccinated against? Give one reason. [Delhi 2010]
Ans.Vaccination produce antibodies in large numbers, which protect the child by neutralising the pathogenic agents during infection.The vaccine also generate memory B and T-cells.

11.How does malaria differ from chikungunya with reference to their vectors?[All India 2010 C; Delhi 2008]
Ans.Malaria is spread by the vector, i.e. Anopheles mosquite, whereas chikungunya is spread by the vector, i.e. Aedes

12.Malaria, typhoid, pneumonia and  amoebiasis are some of the human infectious diseases. Which one of these are transmitted through mechanical carriers.     [Foreign 2010]
Ans.Amoebiasis is transmitted through mechanical carrier, i.e. houseflies

13.How does colostrum provide initial protection against disease to newborn infants? Give one reason.[Delhi 2009]
Ans.Colostrum contains antibody IgA that  provides protection against disease, thus protecting the newborn infants

14.Some allergens trigger sneezing  and wheezing in human being. What causes this type of response by the body?           [Delhi 2009]
Ans.Immune system of the body produce  exaggerated response (allergy) against allergens and release chemicals like histamines and serotonin from mast cells. This is the cause of sneezing and wheezing, in response to these allergens.

15.Name the type of cells, the AIDS  virus enters into after getting in the human body.                     [All India 2009]
Ans.AIDS virus enter into macrophages after  getting in human body

16.Where are mucosal associated lymphoid tissues present in the human body and why? [All India 2009]
Ans.The Mucosal Associated Lymphoid Tissues (MALT) are present in the lining of the major tracts,i.e.
respiratory, digestive and urogenital tracts. MALT constitutes about 50% of the lymphoid tissue in human body that elicits immune response to antigens along mucosal surfaces.

17.A boy of ten years had chickenpox. He is not expected to have the same disease for the rest of life. Mention how it is possible? [All India 2009]
Ans.(i)The antibodies developed in his body  would circulate in body fluids and neutralise the pathogenic agent during subsequent encounters.
(ii) Further memory B-celis and T-cells are retained in the system, which trigger a more intense and quick response against the same antigen, thus preventing the occurrence of same disease in his life

18.What types of virus causes AIDS? Name its genetic material?[All India 2009]
Ans.Retrovirus causes AIDS. RNA is its genetic  material

19.What causes swelling of lower  limbs in patients suffering from filariasis?           [Delhi 2008]
Ans.Wuchereria bancrofti and Wuchereria malayi, the filarial worm lives for many years in the lymphatic vessels of lower limb, cause inflammation and swelling.

20.What role do macrophages play in providing immunity to humans?[All India 2008]
Ans.Macrophages destroy the microbes (by  phagocytosis) and provide protection against diseases.

21.How do neutrophils act as a cellular barrier to pathogens in humans?[HOTS; All India 2008]
Ans.Neutrophils in blood can phagocytose and  destroy the microbes thus acting as cellular barrier to pathogens.

22.Name the two types of cells in which the HIV multiplies after gaining entry into the human body.[All India 2008]
Ans.HIV multiplies first in macrophages and then in helper T-cells or lymphocytes

23.In what way are monocytes a cellular barrier in immunity? [hots; Foreign 2008]
Ans.Since, monocytes can phagocytose and  destroy the pathogens in blood, they act as cellular barrier

24.High fever, loss of appetite, stomach  pain and constipation are some of the symptoms seen in a patient. How would the doctor confirm that the patient is suffering from typhoid and not amoebiasis? [Foreign 2008]
Ans.Typhoid can be confirmed by widal test.

25.Give the scientific name of the  pathogen causing malignant malaria in humans.[Foreign 2008]
Plasmodium falciparumcauses malignant  malaria in humans.

26.It was diagnosed by a specialist that the immune system of the body of a patient has been suppressed. Name the disease the patient is suffering from and its causative agent.[HOTS; Delhi 2007]
.Patient is suffering from AIDS disease. Where in the immune system gets suppressed making the person susceptible to infections caused by pathogens.  The causative agent of the disease is HIV (Human Immunodeficiency Virus).

27.How do virus infected cells provide innate immunity to healthy cells?[HOTS; Delhi 2007 C]
Ans.Virus-infected cells secrete proteins called interferons, which protect non-infected cells from viral infection. Thus, providing innate immunity to healthy cells

2 Marks Questions

28.List the symptoms of ascariasis. How  does a healthy person acquire this infection? [ All India 2014]
The symptoms of ascariasis, caused by  roundworm include internal bleeding, muscular pain, fever, anaemia and blockage of intestinal passage  A healthy person accquires this infection through consumption of water, vegetables or fruits contaminated with eggs of parasite Ascaris

29.Name an allergen and write the  response of human body when exposed to it [Delhi 2014 C]
Ans.The allergen can be pollen grains, spores or  dust particles.
When the allergens are inhaled or enter body system, they stimulate body to produce IgE antibodies and trriger an anti-allergic reaction. The chemical such as histamine and serotonin are released from mast cells, in respons to allergen, thereby causing dilation of blood vessels. The other symptoms of allergy, i.e. sneezing, watery eyes, running nose, etc

30.Differentiate between active and passive immunity. [Delhi 2014 c]
Ans.Differences between active and passive immunity

31.How does a vaccine for a particular disease immunise the human body against that disease? [Delhi 2013c]
Why is a person with cuts and bruises following an accident administered tetanus antitoxin? Give reasons. [All India 2013]
Ans.During vaccination for a particular disease, an antigen or antigenic protein or pathogen which is in inactive form is introduced into the body which induces mild immuneresponse.
The vaccine generates antibodies that neutralises the toxin/pathogen and produces memory B or T-cells, which recognise the pathogen in the subsequent encounters and produce antibodies.
Tetanus is a disease caused by Mycobacterium tetani. A person with cuts and bruises following an accident is administered tetanus antitoxin because this toxin contains antibody against the pathogen. This inactivates the pathogen (called passive immunity).

32.A patient showed symptoms of sustained high fever, stomach pain and constipation, but no blood clot in stools. Name the disease and its pathogen. Write the diagnostic test for the disease. How does the disease get transmitted?[Delhi 2013 C]
Ans.Typhoid is the disease that show symptoms, i.e. high fever, stomach pain and constipation.
Its causative agent is Salmonella typhi. Widal test is used for its diagnosis.Typhoid is transmitted through contaminated food and water

33.(i) Highlight the role of thymus as a  lymphoid organs.
(ii) Name the cells that are released from the above mentioned gland. Mention how they help in immunity?   [Delhi 2012]
Ans.(i)Thymus is a primary lymphoid organ of  the immune system. Maturation of lymphocytes occur in it. T-cells produced in the bone marrow get mature in thymus and are released from here.
(ii) T-cells are released from thymus, upon maturation. They themselves do not produce antibodies, but help B-cells to produce them. They are also responsible for Cell Mediated Immune (CMI) response.

34.Name the parasite that causes filariasis in humans. Mention its two diagnostic symptoms. How is this transmitted to others?[Delhi 2012]
Ans.Wuchereria (W. bancrofti and W. malayi)  are the filarial worms that cause filariasis in humans.
Diagnostic Symptoms
(i) Collection of fluid causes swelling in arms, breasts, legs and genital region.
(ii) Inflammation in lower limbs, resulting in deformities.
It is transmitted to a healthy person through the bite of the female mosquito vector, Culex.

35.(i) Name the protozoan parasite  that causes amoebic dysentery in humans.
(ii)Mention two diagnostic symptoms of the disease.
(iii)How is this disease transmitted  to Others?  [Delhi 2012,2009]
Ans.(i)Entamoeba histolytica is a protozoan  parasite in the large intestine of human, which causes amoebiasis (amoebic dysentery).
(ii) Diagnostic Symptoms

  • Abdominal pain and cramps.
  • Stools with excess mucous and blood  clots.

(iii) The disease is transmitted by houseflies. They act as mechanical carrier as they transmit the parasite from faeces of infected persons to food products, thereby contaminating them

36.Name the two special types of  lymphocytes in humans. How do they differ in their roles in immune response?     [All India 2012]
Ans.Two types of lymphocytes are:
(i) B-lymphocytes or B-cells (ii) T-lymphocytes or T-cells
B-lymphocytes and T-lymphocytes are:

37.(i) Name the group of virus responsible  for causing AIDS in humans. Why are these virus so named?
(ii)List any two ways of transmission of HIV infection in humans other than sexual contact? [All India 2012]
Ans.(i)Retrovirus is the group of virus causing  AIDS in humans. They contain RNA as genetic material and with the help of enzyme reverse transcriptase they make DNA on RNA template. Thus, they are called retrovirus.
(ii) (a) By sharing infected needles.
(b) By transfusion of blood contaminated with HIV

38.Why is an antibody represented H2L2 ?[Foreign 2012]
Ans.Antibody is represented as H2L2 because  each antibody molecule has four peptide chains, i.e. two small light (L) chains and two longer heavy (H) chains.

39.Name the different types of cell providing cellular barrier responsible for innate immunity in humans.[Foreign 2012]
Ans.Cellular barriers are provided by:
(i) Certain types of WBC like  polymorphonuclear leukocytes and monocytes in blood.
(ii) Macrophages in tissue

40.List any two emergent circumstances,  when a medical doctor would recommend injection of a pre-formed antibody into the body of a patient and why?     [HOTS; Delhi 2011C]
Ans.(i) In case of snake bite, quick immune  response is required and we cannot wait for the body to produce antibodies.
(ii) In tetanus, it is infected with some deadly microbes to which quick immune  response is required

41.How is an allergic reaction caused by an allergen? Name the drug that can reduce the symptoms of allergy?  [All India 2011 C]
Ans.Allergens can produce IgE type of antibodies. There is release of histamine and serotonin like chemicals from mast cells, which cause allergic reactions.The use of drug anti-histamine, adrenalin and steroids quickly reduce the symptoms of allergy.

42.Name the two types of immunity in a human body. Why are cell mediated and humoral immunities so called?[Delhi 2011]
Ans.Types of immunity system in human are:
(i) Innate immunity, acquired immunity or humoral immunity system and cell mediated immunity system.
(ii) Cells mediated immunity is so called as it involves specialised cells, the T-lymphocytes.  Humoral immunity is so called because it includes antibodies, which are found circulating in body fluid, the blood (humors-body fluids).

43.Write the scientific names of the causal  organisms of elephantiasis and ringworm in humans. Mention the body parts affected by them.         [Delhi 2011]
Ans.(i)Elephantiasis is caused by Wuchereria  bancrofti and W. malayi. These affect lower limbs and genital organs.
(ii) Ringworm is caused by Microsporum, Trychophyton and Epidermophyton. They affect the skin, nails and scalp.

44.Identify A, D, Eand Fin the diagram of a antibody molecule given below:
Ans.A-Antigen binding region D-Light chain
E -Heavy chain
F -Disulphide bond/bridge

45.Name the host and the site, where the following occur in the life cycle of a malarial parasite
(i)Formation of gametocytes
(ii)Fusion of gametocytes [Delhi 2010]
Ans.(i)Formation of gametocytes occurs in  erythrocytes (RBC) of human beings.
(ii) Fusion of gametocytes occurs in the intestine of mosquito

46.Define the term health. Mention any two ways of maintaining it.[All India 2010]
Ans.Health can be defined as a state of complete physical, mental and social well-being. It can be maintained by taking balanced diet, maintaining personal hygiene, regular exercise/yoga, vaccination against infectious diseases, etc

47.Why does a doctor administer tetanus antitoxin and not a tetanus vaccine to a child injured in a roadside accident with a bleeding wound?[HOTS; All India 2010]
Ans.In case of injury, tetanus antitoxin, i.e. preformed antibodies for tetanus are injected, as the child is infected with deadly microbes (tetanus-bacteria) to which fast immunisation is required.
If tetanus vaccine is injected, it will take sometime for the body to develop immunity and that will be too late and may prove fatal.

48.Identify A, B,C and D in the following table

Ans.A – Small intestine B – Rhinovirus
C – Nose, respiratory passage D – Alveoli of lungs.

49.The barriers in the innate immunity are given in the following table. Identify A, B, C and D.  [Delhi 2010 c]
Ans.A-Lining of epithelium B-Tears C-Cytokine
D-Polymorphonuclear leukocytes

50.(i) How does a vaccine affect immunity?
(ii) How can we get  immunisation against tetanus?       [All India 2010]
Ans.(i) 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. The vaccines also generate memory B and T-cells.
(ii) Preformed antibodies for tetanus are directly injected to acquire quick immune response. This is called passive immunisation.

51.Why do normal cells do not show cancerous growth? [hots; ah India 2010]
Ans.Normal cells do not show cancerous growth as:
(i) Their growth and division are regulated by certain regulatory mechanisms.
(ii) They show the property of contact inhibition, by  virtue of which contact with other cells inhibit their uncontrolled growth.

52.How do macrophages in the human body act as HIV factory?[All India 2010]
Ans.After entering the macrophage, the RNA of the virus replicates to form viral DNA by enzyme reverse transcriptase.
This viral DNA gets into the DNA of host cell and directs it to produce viral particles. The macrophages continues to produce virus and in this way acts as HIV factory

53.(i) What does the below diagram  illustrate?
(ii)Name the parts labelled A and B
(iii)Name the type of cells that produce this molecule. [Delhi 2009]
Ans.(i)It shows antibody molecule.
(ii) A – Antigen-binding site  B – Heavy chain
(iii) B-lymphocytes (B-cells) produce  antibodies

54.State the effect of carcinogens on human body. Name the carcinogenic ionising and non-ionising radiations. Mention their carcinogenic effect.  [All India 2010 C]
Ans.Carcinogens can transform normal cell into  cancerous neoplastic cell.  Carcinogenic ionising radiations are X-rays and gamma rays.  Carcinogenic non-ionising radiations are UV-rays.These radiations cause damage to DNA, i.e. mutations that leads to transformation of normal cells into cancerous cell

55.list the specific symptoms of typhoid. Name its causative agent.[All India 2009]
Ans.Symptoms of typhoid are:
(i) Constant high fever (39-40 °C)
(ii) Weakness and headache
(iii) Stomach pain
(iv) Loss of appetite
Intestinal (small intestine) perforation in severe cases which may cause death. Causative agent – Salmonella typhi

56.(i) Explain the property that  prevents normal cells from becoming cancerous.
(ii)All normal cells have inherent characteristic of becoming cancerous. Explain.[HOTS; Foreign 2009]
Ans.(i)Contact inhibition is the property shown  by normal cells. Due to contact with other cells, they inhibit their uncontrolled proliferation and growth.
(ii) All normal cells have oncogenes (c-onc) or protooncogenes. When activated under certain conditions, such genes could lead to oncogenic transformation of cells, i.e. they become cancerous,

57.What is colostrum? Why is it important to be given to the newborn infants?[Foreign 2009, Delhi 2009]
Ans.Colostrum is the milk produced by mother during initial days of lactation.Colostrum contains antibody IgA that  provides protection against disease, thus protecting the newborn infants

58.How does spleen act as lymphoid  organ? Explain. [Foreign 2009]
Ans.Spleen is a large, bean-shaped organ,  which contain lymphocytes and phagocytes. It act as a filter to trap blood-borne microbes and contain large pool of erythrocytes, thus acts as secondary lymphoid organs.

59.Explain the response initiated when  a dose of vaccine is introduced into the human body.    [Delhi 2009]
Ans.When a dose of vaccine is administered in the human body, antibodies are produced in the body against these antigens. They 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

60.How do normal cells get transformed into cancerous neoplastic cells? Mention the difference between viral oncogenes and cellular oncogenes. [Foreign 2008]
Ans.Normal cells are transformed into cancerous neoplastic cells due to physical, chemical or biological agents, which are known as carcinogens.
(i) Viral oncogenes Genes of viruses, which cause cancer.
(ii) Cellular oncogenes Genes present in normal cells, which become activated under certain conditions and cause oncogenic transformation of the cell.

3 Marks Questions

61.Community service department of your school plans a visit to a slum near the school with an objective educate the slum dwellers with respect to health and hygiene.
(i)Why is there a need to organise such visits?
(ii)Write the steps you will highlight, as a member of this department, in your interactions with them to enable them to lead a healthy life.[All India 2014]
Ans.(i)Slums are generally unauthorised and  encroached colonies with no public facilities and organisation. Due to lack of education, cleanliness and other facilities and the poor living standard in terms of health, hygiene and nutrition such people are always at risk of acquiring infections. Therefore, there is a need to organise visits to slums so as to educate and crate awareness among them regarding the importance of hygiene.
(ii) The points to be highlighted while interacting with the slum people may be.

  • Importance of cleanliness and hygiene of body as well as surroundings.
  • Awareness and prevention of infectious diseases.
  • Use of public facilities, i.e. toiletries.
  • Consumption of properly cooked and hygienic food and water.
  • Administration of vaccines to  newborn children so as to prevent diseases.

62.(i) Name and explain going reason,  the type of immunity provided to the newborn by the colostrum and vaccinations
(ii)Name the type of antibody:

  • present in colostrum
  • produced in response to allergens in human body.[Foreign 2014]

Ans.(i) The immunity provided to the newborn  by colostrum and vaccinations is called passive immunity. This is because both in colostrum and vaccines the antibodies conferred are not produced by own body but are rather transferred passively to recipient’s body. Such as IgA antibodies pass across the placenta or through milk (colostrum) to infants and provides passive immunity against infection.
(ii) The type of antibody present in

  • colostrum is IgA.
  • response to allergens in human body  is IgE

63.(i)Name the causative organisms  for the following diseases.
(ii)How can public hygiene help control such diseases? [Delhi 2014C]
Ans.(i)The causative agent or organism forfollowing diseases are:
(a)Elephantiasis is caused by Wuchereria  bancrofti and W. malayi. These affect lower limbs and genital organs.
(b) Ringworm is caused by Microsporum, Trychophyton and Epidermophyton. They affect the skin, nails and scalp.
(c)Entamoeba histolytica is a protozoan  parasite in the large intestine of human, which causes amoebiasis (amoebic dysentery).
(ii) Maintenance of public hygiene such as:

  • keeping body and surroundings clean.
  • consumption of clean drinking water, fruits and vegetables, etc.
  • regular cleaning and disinfection of tanks and other water reservoirs, etc.
  • All the above measures help controlproper disposal of waste and excreta.the increase in vectors of infectious diseases and their breeding places. Thus, there would be reduced chances of transmission of infectious diseases.

64.Name the cells HIV attacks first when it gains entry into a human body. How does this vims replicate further to cause immunodeficiency in the body?[Delhi 2013 C, 2010; All India 2010 C]
Trace the events occur in human body to cause immunodeficiency, when HIV gains entry into the body.[Delhi 2011; Foreign 2009]
Ans.The HIV virus attacks the macrophages  cells in human body.
(i) RNA is replicated to form viral DNA by the enzyme reverse transcriptase.
(ii) Viral DNA now gets incorporated into the host cell’s DNA and directs the infected cells to produce viruses.
(iii) Macrophages continue to produce virus particles and function as HIV factories.
(iv) The virus particles enter helper T-lymphocytes in the blood, where they continue to replicate and produce viral progenies.
(v)The number of helper T-lymphocytes progressively decreases in the body of the infected person.
(vi) With the decrease in number of T-cells, the immunity also decreases. The person is unable to produce any immune response even against common bacteria like Mycobacterium, parasites like Toxoplasma, viruses and fungi.

65.Trace the life cycle of malarial parasite in human body, when bitten by infected female  [All India 2012]
Ans.Life Cycle of Malarial Parasite  (Plasmodium) in Human Body

66.Study a part of the life cycle of malarial parasite given below.
(i)Mention the roles of A in the life cycle of the malarial parasite.
(ii)Name the event C and the organ where this event occurs.
(iii)Identify the organ B and name the cells being released from it.[Delhi 2012]
Ans.(i)A is female Anopheles mosquito, these  mosquito act as vectors and transmit the disease from patients to healthy individuals.
(ii) The event C is fertilisation. It occurs in the intestinal wall of mosquito.
(iii) B is salivary glands, sporozoites cells are released from it.

67.(i) Name the causative agent of  typhoid in humans.
(ii) Name the test administered to confirm the disease.
(iii)How does the pathogen gain entry into the human body? Write the diagnostic symptoms and mention  the body organ that gets affected in severe cases?[All India 2011]
Ans.(i) Salmonella typhi.
(ii) Widal test.
(iii) Pathogens enter the human body through  contaminated food and water.
Symptoms of typhoid are:
(a) Constant high fever (39-40 °C)
(b) Weakness and headache
(c) Stomach pain
(d) Loss of appetite
Intestinal (small intestine) perforation in severe cases which may cause death. Causative agent – Salmonella typhi

68.Study the diagram showing replication of HIV in humans and answer the following questions accordingly.
(i)Write the chemical nature of the coat
(ii)Name the enzyme B acting on X to produce molecule C. Name C.
(iii)Mention the name of the host cell D the HIV attacks first when it enters into the human body.
(iv)Name the two different cells the  new viruses E subsequently attack.       [All India 2011]
Ans.(i)A – Protein coat
(ii) B – Reverse transcriptase  C – It is viral DNA
(iii) Macrophage (animal or human cell)
(iv)Macrophages and helper T-cells.

69.Identify A, B and C in the schematic diagram of an antibody given above and answer the questions.
(i)Write the chemical nature of an antibody.
(ii)Name the cells that produce antibodies in humans.
(iii)Mention the type of immune response provided by an antibody.[Delhi 2010]
Ans.A – Antigen binding site B – Light chain  C – Heavy chain
(i) Antibodies are proteinaceous in nature.
(ii) B-lymphocytes
(iii) Humoral immune response

70.An antibody molecule is represented as H2L2. Explain. [Delhi 2010,2009 c]
Ans.Antibody is represented as H2L2 because  each antibody molecule has four peptide chains, i.e. two small light (L) chains and two longer heavy (H) chains.

71.Mention the name of the causal  organism, symptoms and the mode of transmission of the disease amoebiasis.         [All India 2010]
Ans.Causal organism of amoebiasis -Entamoeba histolytica.
(i) Symptoms are constipation, abdominal  pain and cramps, stool with excess mucus and blood clots.
(ii) Mode of transmission is through  contaminated food and water.

72.(i) All human beings have cellular  oncogenes but only few suffer from cancer disease.Give reasons.
(ii)How is a malignant tumour different from a benign tumour?[Foreign 2010]
Ans.(i) All cells have cellular oncogenes or proto-oncogene, which code for certain growth factors. Under certain conditions, they get activated and lead to oncogenic transformation causing cancer.
This transformation is induced by physical, chemical and biological factors called  carcinogens.
(ii) Differences between benign and malignant tumour are:

73.Trace the life cycle of Plasmodium in humans from the stage of entry until it is picked up by the female Anopheles. [All India 2010; Delhi 2008]
Ans.  Life cycle of Plasmodium (malarial parasite)
(i) The infected female Anopheles mosquito transfers the infectious form of Plasmodium, i.e. sporozoites to the human body by biting.
(ii) Sporozoites reach the liver cells, where they multiply.
(iii) This is followed by their attack on red blood cells resulting in the rupture of RBCs.
(iv) Ruptured RBCs release a toxin called  haemozoin, responsible for recurring fever, chills and shivering.
(v)The parasite enter female Anopheleswhen they bite an infected person.
(vi)In the body of mosquito, they fertilise and multiply in stomach wall.
(vii)Sporozoites are then again transferred to the human body by mosquito bite.

74.Give the scientific name of the parasite that causes malignant malaria in humans.At what stage does this parasite enter the human body? Trace its life cycle in human body. [Delhi 2009]
Ans.Plasmodium falciparumcauses  malignant malaria. It enters into human body in sporozoites form.
Plasmodium  Life Cycle of Malarial Parasite  (Plasmodium) in Human Body

75.(i) Name the respective forms in  which the malarial parasite gains entry into.
(a)Human body
(b)Body of female
(ii)Name the hosts where the sexual and asexual reproduction occur respectively.
(iii)Name the toxin responsible for the appearance of symptoms of malaria in human. Why do these symptoms occur periodically?[Delhi 2003]
Ans.(i) (a) Sporozoite
(b) Gametocytes
(ii) Sexual reproduction occurs iri mosquito and asexual reproduction takes place in human body.
(iii)Haemozoin is the toxin. The parasites after entering the fresh RBCs take 48-72 hours to complete the erythrocytic cycle. Then they burst to release toxic substance called  haemozoin. So, the symptoms like chill and high fever occur  periodically

76.(i) Why do the symptoms of malaria  not appear immediately after the entry of sporozoites into the human body when bitten by female Anopheles? Explain.
(ii) Give the scientific name of the malarial parasite that causes malignant malaria in humans.[HOTS; All India 2009]
Ans.(i)Malarial parasite completes its asexual  cycle in liver cells and then it attacks the Red Blood Cells (RBCs) resulting in their rupture. The ruptured RBCs release toxic substance called  haemozoin that is responsible for the symptoms of malaria like chill and high fever. Thus, no symptoms appear in the infected person between the period, the parasite enters the body and till RBCs release haemozoin,
(ii)  Plasmodium falciparumcauses  malignant malaria. It enters into human body in sporozoites form.
Plasmodium  Life Cycle of Malarial Parasite  (Plasmodium) in Human Body

77.A person is suffering from amoebiasis. Mention the pathogen that causes it and one organ of the body that get affected. Give three symptoms and one mode of its transmission. [All India 2009 c, 2008]
Ans.Amoebiasis is caused by Entamoeba  histolytica, Organ infected-small intestine, which gets perforated or blocked in severe cases  Symptoms Constipation, abdominal pain, stool with excess mucus and blood clots.  It can be transmitted by carriers as houseflies form infected faeces to food products and water.

78.How is innate immunity different from the immunity that you require through vaccines? Describe any two ways by which innate immunity can be accomplished?[Foreign 2009; All India 2008]
Ans.Differences between innate immunity and acquired immunity are
Innate immunity can be accomplished by:
(i) Physiological barriers like tears in eyes, acid in stomach, saliva in mouth, etc
(ii) Cytokinine barriers, i.e. interferons produced by virus-infected cells to protect non-infected cells from viral infection

79.A person is suffering from ascariasis. Mention the pathogen causing the disease and an organs of the body affected. Write three symptoms and one mode of transmission of the disease.[All India 2009 C]
Ans.Pathogen for ascariasis – Ascaris lumbricoides.
(i) Organ affected – Intestine.
(ii) Symptoms – Abdominal pain,  indigestion, muscular pain, fever, etc.
(iii) Mode of transmission – Through contaminated vegetables, fruits and water

80.(i) Name the infective stage of  Plasmodium, which Anopheles mosquito takes in along with the blood meal from an infected human.
(ii)Why does the infection cause fever in humans?
(iii)Give a flow chart of the part of the life cycle of this parasite passed in this insect.[Foreign 2008; All India 2008]
Ans.(i) Gametocyte.
(ii) The parasites first multiply within the  liver cells and then attack red blood cells resulting in their rupture. This cell bursting leads to the chill/shivering and fever due to the release of toxic chemical substance haemozoin.

81.(i) 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.
(ii) Name the kind of immunity attained when instead of antibodies, weakened antigens are introduced into the body.  [Delhi 2008 C]
Ans.(i)A doctor would recommend preformed  antibodies in injured person in an accident on snake bites and tetanus.  Type of immunisation is passive immunisation.
Its advantages are:
(a)Provides immediate relief.
(b)Used either prophylactically or  therapeutically.
(ii)This type of immunit