CBSE Class 12 Biology –Chapter 8 Human Health and Disease- Study Materials



· Health is a state of complete physical, mental & social well-being. It is affected by genetic disorders, infections, change in life style (food, water, rest, exercise, habits etc).

· Mind influences immune system (through neural and endocrine systems) and thereby health.

· When the functioning of organs or systems of the body is adversely affected, it is called a disease.

· Diseases may be infectious (transmits from one person to another) or non-infectious (do not transmit. E.g. cancer).

· Disease causing organisms are called Pathogens. Parasites are pathogens as they harm the host.


Good humour hypothesis (by Hippocrates & Indian Ayurveda system): It states that health is a state of body & mind where there is a balance of certain humours. Persons with ‘black bile’ belong to hot personality and would have fevers.

William Harvey disproved this hypothesis. He discovered blood circulation and demonstrated normal body temperature in persons with black bile using thermometer.






a. Typhoid: Pathogen is Salmonella typhi.

· Mode of transmission: It enters small intestine through food & water and migrates to other organs via blood.

· Symptoms: Sustained high fever (39o-40o C), headache, weakness, stomach pain, constipation & loss of appetite. Intestinal perforation and death may occur.

Widal test is used for confirmation of the disease.


Mary Mallon (Typhoid Mary) was a professional cook. She was a typhoid carrier who spread typhoid for several years through the food she prepared.


b. Pneumonia: Pathogen is Streptococcus pneumoniae & Haemophilus influenzae.

It infects lung alveoli. The alveoli get filled with fluid leading to respiratory problems.

· Mode of transmission: Inhaling the droplets/aerosols released by an infected person. Sharing glasses and utensils with an infected person.

· Symptoms: Respiratory problems, fever, chills, cough, headache. In severe cases, lips and finger nails turn grey to bluish colour.

Other bacterial diseases: Dysentery, plague, diphtheria, etc.




a. Common cold: Pathogen is Rhinoviruses.

It infects nose & respiratory passage but not lungs.

· Mode of transmission: Inhaling droplets resulting from cough or sneezes. Through contaminated objects (pens, books, cups, doorknobs, computer accessories) etc.

· Symptoms: Nasal congestion & discharge, fever, headache, sore throat, cough, hoarseness, tiredness etc.

Common cold lasts for 3-7 days.




a. Malaria: Pathogen is Plasmodium sp. (P. vivax, P. malariae & P. falciparum).

Most serious (malignant) malaria is caused by P. falciparum.

· Mode of transmission: By female Anopheles mosquito.

· Symptoms: Haemozoin (toxin released by Plasmodium) causes chill and high fever recurring every 3-4 days.


Life cycle of Plasmodium




b. Amoebiasis (Amoebic dysentery): Pathogen is Entamoeba histolytica.

· Mode of transmission: Houseflies (mechanical carriers) transmit parasites from faeces to food & water.

· Symptoms: Constipation, abdominal pain and cramps, stools with excess mucus and blood clots.




a. Ascariasis: Pathogen is Ascaris (Intestinal parasite).

· Mode of transmission: Soil, water, vegetables, fruits etc. contaminated with faeces containing eggs of parasites.

· Symptoms: Internal bleeding, muscular pain, fever, anaemia and blockage of intestinal passage.

b. Filariasis (Elephantiasis): Pathogen is Filarial worms or Wuchereria (W. bancrofti & W. malayi).

· Mode of transmission: Bite of female Culex mosquito.

· Symptoms: Filarial worms live in lymphatic vessels (usually of lower limbs). It causes chronic inflammation of the organs in which they live for many years. Limbs and genital organs may be deformed.




a. Ring worms: Pathogens are Microsporum, Trichophyton & Epidermophyton. They are seen in groin, b/w toes etc.

· Mode of transmission: From soil or by using towels, cloths, comb etc. Heat and moisture help fungi to grow.

· Symptoms: Dry, scaly lesions on skin, nails, scalp etc. Intense itching.



Personal hygiene


Keep the body clean. Use clean drinking water, food etc.


Public hygiene


a. Proper disposal of wastes and excreta.

b. Periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks.

c. Avoid contact with infected persons or their belongings (to control air-borne diseases).

d. Standard practices of hygiene in public catering.

e. Control and eliminate the vectors (e.g. mosquitoes).

Avoid stagnation of water.

Regular cleaning of household coolers.

Use of mosquito nets.

Introduce larvivorous fishes like Gambusia in ponds.

Spraying insecticides in ditches, drainage and swamps.

Provide doors and windows with wire mesh.

These precautions can avoid vector-borne diseases like Malaria, Filariasis, Dengue & Chikun gunya.

Vaccines & immunisation helped to control diseases like smallpox, polio, diphtheria, pneumonia & tetanus. Drugs like antibiotics also helped to treat infectious diseases.






§ It is the system that gives immunity to the body by recognizing, responding and remembering foreign antigens.

§ It plays role in allergic reaction, auto-immune disease and organ transplantation.

§ It includes lymphoid organs, tissues, cells & antibodies.




These are the organs where origin/maturation & proliferation of lymphocytes occur. 2 types: Primary & Secondary.


a. Primary lymphoid organs

The organs where lymphocytes are matured & differentiated to antigen-sensitive lymphocytes. It is 2 types:

1. Bone marrow: The site of formation of all blood cells including B & T-lymphocytes.

2. Thymus: A bilobed organ seen near the heart and beneath the breastbone. It is large during birth but gradually reduces in size and becomes very small size in puberty. Immature T-lymphocytes from bone marrow is migrated to thymus and matured.

b. Secondary lymphoid organs


The organs, to which matured lymphocytes migrate from primary lymphoid organs, interact with antigens and then proliferate to become effector cells.

E.g. Spleen, lymph nodes, tonsils, Peyer’s patches, Mucosa- associated lymphoid tissue (MALT) & appendix.

Spleen: Bean-shaped organ. Contains lymphocytes and phagocytes. It removes worn-out RBCs & microorganisms from blood. It is a reservoir of erythrocytes in foetus.

Lymph nodes: Found in lymphatic system. They trap microorganisms or other antigens. Trapped antigens activate lymphocytes and cause immune response.

MALT: Located within the lining of respiratory, digestive & urinogenital tracts. It constitutes 50% of lymphoid tissue.



It is the ability of the immune system to fight the pathogens.

It is 2 types: Innate and Acquired.

1. Innate (inborn) immunity


It is the non-specific immunity present at the time of birth.

It includes 4 types of Barriers:

a. Physical barriers: Prevents entry of microbes. E.g. Skin, Mucus coating of the respiratory, gastro-intestinal and urino-genital tracts. Mucus traps microbes.

b. Physiological barriers: They prevent microbial growth. E.g. gastric HCl, saliva, tear etc.

c. Cellular barriers: Phagocytes like WBC [Polymorpho-nuclear leukocytes (PMNL) or neutrophils, monocytes and natural killer lymphocytes], macrophages etc.

d. Cytokine barriers: Virus infected cells secrete a cytokine protein called interferon. It protects non-infected cells from further viral infection.


2. Acquired (adaptive) immunity


· It is pathogen specific immunity developed during lifetime.

· It is characterized by memory, i.e. during first encounter of a pathogen, body produces primary response in low intensity. Second encounter of the same pathogen causes a secondary (anamnestic) response in high intensity.

· Primary and secondary immune responses are carried out with B-lymphocytes (B-cells) and T-lymphocytes (T-cells).

a. B-lymphocytes: Produce antibodies. These are the proteins to fight the pathogens.

b. T-lymphocytes: Help B-cells to produce antibodies.


Structure of an antibody molecule


An antibody has 4 polypeptide chains: 2 light chains and 2 heavy chains (H2L2).

Types of antibodies: IgG, IgA, IgM, IgE & IgD.


Types of Acquired immune response


1. Humoral immune response/ Antibody mediated immunity (AMI): It is the immune response mediated by antibodies. Antibodies are found in blood plasma. So called as Humoral immune response.

2. Cell-mediated response / cell-mediated immunity (CMI): It is the immune response mediated by T-lymphocytes (T-cells). The body can differentiate ‘self’ and ‘non-self’ and the CMI causes Graft rejection.

Tissue matching & blood group matching are essential before undertaking any graft/ transplant. After this, the patient should take immuno-suppressants all his life.


Types of Acquired immunity

Acquired immunity is 2 types: Active and passive.


1. Active immunity: It is the immunity in which antibodies are produced in a host body when the host is exposed to antigens (e.g. living or dead microbes or other proteins).

It is a slow process. It is produced by 2 ways:

a. Natural Active Immunity: It is developed during natural infection by microbes.

b. Artificial Active Immunity: It is developed by injecting the microbes deliberately during immunization.


2. Passive immunity: Here, readymade antibodies are directly given to the body. It is 2 types:

a. Natural Passive Immunity: E.g.

§ Antibodies (IgG) from mother → Placenta → Foetus

§ Antibodies (IgA) in colostrum → infants

b. Artificial Passive Immunity: E.g.

§ Anti-tetanus serum (ATS)


This is based on ‘memory’ of the immune system. 2 types:


1. Active Immunization (Vaccination)


§ In this, a preparation of vaccine (antigenic proteins of pathogen or inactivated pathogen) is introduced into the body. It results in the development of antibodies.

§ During actual infection, the antibodies neutralize antigens.

§ The vaccines also generate memory B and T-cells. They recognize the pathogen quickly.

§ E.g. Polio vaccine, Hepatitis B vaccine, DPT vaccine etc.

§ Vaccines are produced using DNA recombinant technology (E.g. Hepatitis B vaccine produced from Yeast).


2. Passive Immunization


§ It is the direct injection of pre-formed antibodies or antitoxin. It is required for quick immune response.

§ E.g. Immunization against Tetanus, snake venom etc.


§ It is the exaggerated response of the immune system to certain antigens present in the environment.

§ Allergens: Substances causing allergy. E.g. mites in dust, pollens, animal dander, fur etc.

§ Antibodies produced against the allergens are IgE type.

§ IgE binds on mast cells to release chemicals like histamine and serotonin from them. It results in allergic reactions.

§ Symptoms: Sneezing, watery eyes, running nose, difficulty in breathing, wheezing, skin rashes etc.

§ Determination of cause of allergy: The patient is exposed to or injected with very small doses of possible allergens, and the reactions studied.

§ Treatment: Drugs like anti-histamine, adrenaline and steroids quickly reduce the symptoms of allergy.

§ Asthma is a respiratory disease due to allergy.

§ Modern-day life style and protected environment provided early in life result in low immunity and more sensitivity to allergens. So, many children in metro cities suffer from allergies and asthma.




In higher vertebrates, memory-based acquired immunity evolved based on the ability to differentiate foreign organisms from self-cells.

Sometimes, due to genetic and other unknown reasons, the body attacks self-cells resulting in damage to the body. It is called auto-immune disease. E.g. Rheumatoid arthritis.


AIDS (Acquired Immuno Deficiency Syndrome)


§ It is the deficiency of immune system.

§ Syndrome means a group of symptoms.

§ It is caused by HIV (Human Immunodeficiency Virus), a retrovirus having RNA genome.

§ AIDS was first reported in America (1981).

§ In the last 25 years, it killed over 25 million persons.




§ Sexual contact with infected person.

§ Transfusion of contaminated blood & blood products.

§ Sharing of infected needles.

§ From infected mother to her child through placenta.

High risk people of getting HIV:

§ Individuals with multiple sexual partners.

§ Drug addicts who take drugs intravenously.

§ Individuals who require repeated blood transfusion.

§ Children born to an HIV infected mother.

HIV does not spread by touch or physical contact. It spreads only through body fluids.

There is a time-lag (from few months to 5-10 years) between the infection and appearance of symptoms.


Replication of retrovirus:



Life cycle of HIV:


HIV enters body → To macrophages (acts as HIV factory) → RNA genome replicates in presence of Reverse transcriptase to form viral DNA → Viral DNA incorporates into host DNA→ Infected cells produce virus particles → HIV enters into helper T-cells (TH lymphocytes) → Replicates & produce progeny viruses → Attack other TH cells → TH cells decrease → Weaken immunity.


§ During this period, the person suffers from fever, diarrhoea and weight loss.

§ Due to deficiency of TH cells, he may be infected with Mycobacterium, viruses, fungi & parasites like Toxoplasma.

§ Diagnosis: ELISA test (Enzyme-linked immuno-sorbent Assay).

§ Treatment: Anti-retroviral drugs are partially effective. They can only prolong the life of the patient.


Prevention of AIDS:


o Educate people about AIDS through organisations like National AIDS Control Organisation (NACO), non-governmental organisations (NGOs), WHO etc.

o Make blood (from blood banks) safe from HIV.

o Use disposable needles and syringes.

o Advocate safe sex and free distribution of condoms.

o Control drug abuse.

o Regular check-ups for HIV in susceptible population.


· Cancer is an abnormal and uncontrolled multiplication of cells resulting in the formation of tumour (masses of cells).

· Normal cells show a contact inhibition (contact with the other cells inhibits their uncontrolled growth). Cancer cells do not have this property.


Types of Tumours


o Benign tumours: Confined to the place of its origin. They do not spread to other parts. Cause little damage.


o Malignant tumours: Mass of proliferating cells (neoplastic or tumour cells) that grow rapidly, invade and damage the surrounding normal tissues. Due to active division and growth, they starve normal cells by competing for nutrients.

Cells sloughed from tumours reach other sites via blood where they form a new tumour. This is called metastasis.


Causes of cancer (Carcinogens)


§ Physical agents: E.g. Ionizing radiations like X-rays and gamma rays and non-ionizing radiations like UV.


§ Chemical agents: Tobacco smoke (major cause of lung cancer), vinyl chloride, caffeine, nicotine, mustard gas etc.


§ Biological agents: E.g. oncogenic viruses, c-onc (cellular oncogenes or proto oncogenes) etc. When C-onc in normal cells is activated, the cells become oncogenic.


Cancer detection and diagnosis

o Biopsy: A thin piece of the suspected tissue is stained and examined under microscope (histopathological studies).

In case of leukemia: Biopsy & histopathological studies. Blood & bone marrow tests for increased cell counts.

o Imaging techniques:

§ Radiography: Use of X-rays.

§ CT (Computerized tomography) scan: Uses X-rays to generate a 3D image of the internals of an object.

§ MRI (Magnetic Resonance Imaging): Uses magnetic fields and non-ionising radiations to detect pathological and physiological changes in the living tissue.


o Use of Antibodies against cancer-specific antigens.

o Molecular biology technique: To detect cancer related genes. Such individuals should avoid carcinogens (e.g. tobacco smoke).

Treatment of cancer

o Radiotherapy: Tumour cells are irradiated lethally, without damaging surrounding normal tissues.

o Chemotherapy: Use of chemotherapeutic drugs. Many drugs have side effects like hair loss, anaemia etc.

o Immunotherapy: The patients are given biological response modifiers (e.g. α- interferon) which activates their immune system and helps in destroying the tumour.

o Surgery.

Most cancers are treated by combination of surgery, radiotherapy and chemotherapy.


1. Opioids:


They bind to specific opioid receptors in CNS and gastrointestinal tract. E.g. morphine, heroin, brown sugar.


Morphine is extracted from latex of Papaver somniferum (poppy plant). It is a sedative & painkiller. Used in surgery.

Heroin (smack or diacetylmorphine) is a white, odourless, bitter crystalline compound. It is obtained by acetylation of morphine. It is taken by snorting and injection. Heroin is a depressant and slows down body functions.


2. Cannabinoids:


They interact with cannabinoid receptors in the brain.

Generally taken by inhalation and oral ingestion.

Natural cannabinoids are obtained from inflorescences of Cannabis sativa (Hemp plant). Its flower tops, leaves & resin are used to make marijuana, hashish, charas & ganja.

They affect cardiovascular system.

Cannabinoids are abused by some sportspersons.


3. Coca alkaloid or cocaine (coke or crack):


It is obtained from coca plant Erythroxylum coca.

It interferes with transport of neurotransmitter dopamine.

Cocaine is usually snorted.

It stimulates CNS producing euphoria & increased energy.

Excessive dosage of cocaine causes hallucinations.

Atropa belladona & Datura are also hallucinogenic plants.


Drugs like barbiturates, amphetamines, benzodiazepines, etc. are used as medicines to treat mental illnesses like depression & insomnia. But their abuse causes impairment of physical, physiological or psychological functions.




· Tobacco has been used by human beings for over 400 years.

· It is smoked, chewed or used as a snuff.

· It contains many chemical substances like nicotine (an alkaloid). It stimulates adrenal gland to release adrenaline and nor-adrenaline, causing high BP and heart rate.

· Smoking causes cancers of lung, urinary bladder and throat, bronchitis, emphysema, coronary heart disease, gastric ulcer etc. Tobacco chewing causes oral cancer.

· Smoking increases CO content in blood and reduces oxyhaemoglobin. This causes O2 deficiency in the body.




Adolescence is ‘a period’ and ‘a process’ during which a child becomes mature in terms of his/her attitudes and beliefs for effective participation in society.

Adolescence is a bridge linking childhood and adulthood (period of 12-18 years of age). It is very vulnerable phase of mental and psychological development.


Causes of drug/alcohol use in Adolescence


Curiosity and Experimentation.

Need for adventure and excitement.

To escape facing problems.

Stress from pressure to excel in academics or examination.

Television, movies, newspapers, internet etc.

Unstable or unsupportive family structures & peer pressure.


Addiction and Dependence


· Addiction: It is a psychological attachment (euphoria and a temporary feeling of wellbeing) with drugs and alcohol. With repeated use of drugs, the tolerance level of the receptors increases. Thus the receptors respond only to higher doses leading to greater intake and addiction.

· Dependence: It is the tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome if regular dose of drugs/alcohol is abruptly discontinued. This results in anxiety, shakiness, nausea and sweating.

Dependence leads to social adjustment problems.


Effects of Drug/alcohol abuse


· Reckless behaviour, vandalism and violence.

· Coma and death due to respiratory failure, heart failure or cerebral haemorrhage.

· Drugs mixed with alcohol may cause death.

· Damage of nervous system and liver cirrhosis.

· Mental and social distress to family and friends.

· Social problems like stealing and spread of infectious diseases (e.g. AIDS, hepatitis B).

· Use of drugs and alcohol by pregnant woman affect the foetus (Foetal alcohol syndrome or FAS).

· Loss of sexual drive and necrospermia.

· Misuse of drugs by athletes (e.g. narcotic analgesics, anabolic steroids, diuretics & certain hormones to increase muscle strength and bulk and to promote aggressiveness).


Warning signs of drug/alcohol abuse in Adolescence period


· Drop in academic performance and absence from school.

· Lack of interest in personal hygiene.

· Withdrawal and isolation.

· Depression, fatigue, aggressive and rebellious behaviour.

· Change in sleeping and eating habits.

· Fluctuations in weight, appetite etc.

· Loss of interest in hobbies.

· Deteriorating relationships with family and friends.


Side effects of anabolic steroid abuse

In males:

  • Acne.
  • Mood swings & depression .
  • Increased aggressiveness.
  • Reduced testicles.
  • Decreased sperm.
  • Breast enlargement.
  • Kidney & liver dysfunction.
  • Premature baldness
  • Enlargement of prostate gland.

In females:

  • Masculinisation
  • Mood swings & depression
  • Increased aggressiveness
  • Excessive hair growth
  • Abnormal menstrual cycle
  • Deepening of voice
  • Enlargement of clitoris

In adolescent male & female: Severe facial and body acne, premature closure of the growth centres of the long bones resulting in stunted growth.


Prevention and control


1. Avoid undue peer pressure.

2. Education and counselling.

3. Seeking help from parents and peers.

4. Looking for danger signs.

5. Seeking professional and medical help.

a. Psychologists and psychiatrists.
b. De-addiction and rehabilitation programs.

CBSE Class 12 Biology Important Questions Chapter 8 – Human Health and Disease

1 Mark Questions

Chapter 8
Human Health and Disease

1 Marks Questions
1.Name the diagnostic test which confirms typhoid.
Ans.Widal test

2. Name the two major groups of cells required to attain specific immunity.
Ans. B-lymphocytes and T-lymphocytes.

3. You have heard of many incidences of Chickengunya in our country. Name the vector of the disease.
Ans.Aedes mosquitoes.

4. Breast fed babies are more immune to diseases than the bottle fed babies. Why?
Ans.The mother’s milk consists of antibodies (Ig A) such antibodies are notavailable to bottle fed babies.

5. Name the pathogen which causes malignant malaria.
Ans. Plasmodium falciparum.

6. Which microorganism is used to produce hepatitis B Vaccine?
Ans. Yeast.

7. What is the reason of shivering in malarial patient?
Ans.After sparozoite infection, when RBC ruptures, a toxic substance haemozoin is released which cause chilling and high fever.

8.When is a tumourrefered to as malignant?
Ans.A tumour is said to be malignant when grows rapidly, invade & damage the surrounding normal tissues.

9.Why does an AIDS patient suffer from many infections?
Ans.Because in AIDS patient, immune system greatly weakens & cannot fight against any infection.

10.Name two curable sexually transmitted diseases?

11.Name the type of cells that produce antibodies?
Ans.B – lymphocytes.

12.Give the scientific name of causative germ of elephantiasis?

13.Name the fish that help in eradication of mosquito larvae.

2 Mark Questions

Chapter 8
Human Health and Disease

2 Marks Questions
1. Where are B-cells and T-cells formed? How do they differ from each other?
Ans.B-cells and T-cells are formed in bone marrow. B-cells produce antibodies but E-cells do not produce antibodies but help B-cells to produce them.

2. Given below are the pathogens and the diseases caused by them. Which out of these pairs is not correct matching pair and why?
(a) Wuchereria- Filariasis
(b) Microsporum- Ringworm
(c) Salmonella – Common Cold
(d) Plasmodium – Malaria
Ans.Salmonella : Common cold is not a matching pair.

3. What would happen to the immune system, if thymus gland is removed from the body of a person?
Ans.T-lymphocytes are developed and matured in thymus gland, Immune system will become weak on removal of thymus gland.

4. Lymph nodes are secondary lymphoid orgAns. Describe the role of lymph nodes in our immune response.
Ans.Lymph nodes provide the sites for interaction of lymphocytes with the antigen. When the microorganisms enter the lymph nodes, lymphocytes present there are activated and cause the immune response.

5. What is the role of histamine in inflammatory response? Name few drugs which reduce the symptoms of allergy.
Ans.Histamine acts as allergy-mediator which cause blood vessels to dilate. It is released by mast cells. Antihistamine steroids and adrenaline quickly reduce the symptoms of allergy.

6.Differentiate between two different types of tumours?

i) tumour remain confined to place of origin or affected organi) tumour invade surrounding tissue & spread throughout the body.
ii) It is harmlessii) It is harmful
iii) rate of growth of tumour is lowiii) rate of growth of tumour is rapid
iv) causes limited damageiv) Cause uncontrolled damage.

7.What do you mean withdrawal Symptoms? What are its characteristics?
Ans.Withdrawal symptoms refers to the characteristic unpleasant symptoms by body of a drug addict if regular dose of drug is abruptly discontinued. These include anxiety, shakiness, sweating, restlessness, depression, muscular cramps etc.

8.Differentiate between active & passive immunity?

i) when antibodies are developed by our own cells in response to antigeni) when antibodies developed in other vertebrates in response to deliberate infection of antigen
ii) It takes time to develop immunityii) It is used when the immune response has to be faster
iii) It stays for longer periodiii) It stays for short period

9.Enumerate the two properties of cancer cells that distinguish them from normal cell.
Ans.i) uncontrolled proliferation of cells without any differentiation
ii) Ability of these cells to invade other tissues called metastasis.

10.What are allergens? How do they cause inflammatory response inside human body?
Ans.The substance which causes the hypersensitive reaction of the immune system is called an allergeneg. dust, pollen grains etc. These allergens are actually weak antigens. First exposure to allergen does not cause allergy but consequent exposure, allergen combines with Ig E on mast cell. That causes cells to burst & release Histamines which cause inflammatory response.

11.What are autoimmune diseases? Give two examples?
Ans.Immunity is based on ability to differentiate foreign organism from self cells. Sometimes immune system may go off the track & turns against self antigen and elicit immunity. Such conditions are called auto – immune diseases eg. Rheumatoid arthritis, Myasthenia gravis.

3 Mark Questions

Chapter 8
Human Health and Disease

3 Marks Questions
1. What are Cannabinoids? From which plant Cannabinoids are obtained? Which part of the body is affected by consuming these substances?
Ans. – Cannabinoids are a group of chemicals which interact with Cannabinoid receptors present
– Principally in the brain Cannabinoids are obtained from the inflorescences of the plant Cannabis sativa.
– The substances affect the cardiovascular system adversely

2. In the figure, structure of an antibody molecule is shown. Observe it and Give the answer of the following questions.
(i) Label the parts A, B and C.
(ii) Which cells produce these chemicals?
(iii) State the function of these molecules.

Ans.(a) A-Antigen binding site B-Light chain
(b) B-lymphocytes.
(c) Heavy Chain
(d) Antibodies provide acquired immune response.

3. Mention any three causes of drug abuse. Suggest some measures for the prevention and control of drug abuse.
Ans.Reasons to attract towards drug abuse : Curiosity, peer pressure, escape from frustation and failure, family problems, false belief of enhanced performance.
Preventive measures :
– Avoid undue peer pressure
– Education and Counselling
– Seeking help from parents and peers.
– Looking for danger signs
– Seeking professional and medical help

4. A person shows unwelcome immunogenic reactions while exposed to certain substances.
(a) Name this condition.
(b) What common term is given to the substances responsible for this condition?
(c) Name the cells and the chemical substances released which cause such reactions.
Ans.(a) Allergy (b) Allergens
(c) Mast Cells – Histamine, Serotonin

5. Fill in the blanks in the different columns of the table given below to identify the nos 1 to 6.

Name of diseaseCausative organismSymptoms
Typhoid(2)High fever, weakness,headache, stomach pain
(3)RhinovirusesNasal Congestion, anddischarge sorethroat
cough, headache
Ringworm(5)Dry, Scaly lesions onvarious body parts,Intense itching, redness.
(6)EntamoebahistolyticaConstipation, cramps,abdominal pain, Stoolswith excess mucous andblood clots.

Ans.(i) Alveoli filled with fluid, reduced breathing, fever, chills, cough and headache.
(ii) Salmonella typhi
(iii) Common Cold
(iv) Internal bleeding, muscular pain, anaemia, fever and blockage of the intestinal passage.
(v) Microsporum species/Trichophyton species/Epidermophyton Species.
(vi) Amoebiasis/amoebic dysentery

6. In the given flow diagram, the replication of retrovirus in a host cell is shown. Examine it and answer the following questions
(a) Why is virus called reterovirus?
(b) Fill in (1) and (2)
(c) Can infected cell survie while viruses are being replicated and released by host cell?

Ans.(a) HIV has RNA genome. It produces DNA by reverse transcription.
(b) 1 : Viral DNA is produced by reverse transcriptase.
2 : New Viral RNA is produced by the infected cell.
(c) Infected cell can survive.

7. What is innate immunity? List the four types of barriers which protect the body from the entry of the foreign agents.
Ans.Innate Immunity is non-specific type of defense that is present at the time of birth.
(i) Physical Barriers : Skin, mucous-coated epithelium or respiratory, digestive and urinogenital tract.
(ii) Physiological Barriers : Acidity of Stomach, lysozyme in saliva, tears, sweat.
(iii) Cellular Barrier : Macrophages, neutorophils, monocytes and natural killer lymphocytes..
(iv) Cytokine Barriers :Interferons produced by Viral infected cells, protect the non-infected cells from further Viral infection.

8.How does humoral immune system works when our body is infected?
Ans.Humoral immune response is one in which antibodies are developed which are capable of attacking microbes. Each B-cell has receptors on its surface that recognize a specific antigen. Initial exposure of B-cell to Antigen triggers B-cells to proliferate forming a large clone cell continuous stimulation increases the number of B-lymphocytes which differentiates into smaller antibody producing plasma cells. Each clone of plasma cells manufactures antibodies that specifically react with antigenic determinant that stimulated the initial proliferation. The antibody binds to antigen- forming an antigen-antibody complex which is later digested by phagocytic cells. Some of these plasma cells develops into memory cells which rapidly differentially into plasma cells on later exposure to same antigen.

9.It was diagnosed by a specialist that the immune System of the body of a patient has been suppressed. Describe the infection & the mechanism of its proliferation in the body.

Ans.If the immune system of the patient is found to be suppressed, he is found to suffer from human immunodeficiency virus (HIV). The HIV virus enters into helper T- cells & replicate to produce progeny viruses. The replication of virus involves:-
(i)After viral capsid enters the cell enzyme reverse transcriptase copies single stranded RNA into complementary DNA.
(ii)The RNA is degraded lay ribonuclease H & the DNA strand is duplicated to form double – stranded DNA.
(iii)Proviral DNA is integrated into cells DNA through a complex sequence of reactions catalysed lay Integrase enzyme.
(iv)Once the virus has infected the cell, virus becomes active & large number of virus particles are liberated that can infect other cells.

10.What are carcinogens? What are the different types of carcinogens? Also mention the different methods of treatment of cancer?
Ans.The things that cause cancer are called CARCINOGENS. These agents may be chemical or physical things like:-

  1. Smoking
  2. Tobacco chewing
  3. Radiations eg. uv- x-ray, cosmic rays.
  4. Chemical eg. mustard gas, aflatoxin, cadmium oxide
  5. Biological agents eg. retroviruses
  6. Cellular agents proto-oncogenes which when activated under certain condition may lead to oncogenic transformation of cells.

Treatment of cancer involves :-

  1. SURGERY :- surgical removal of tumour
  2. CHEMOTERAPY : treatment with drugs that can destroy cancer cells
  3. IMMUNOTHERAPY : use of interferons, interleukin, vaccines to generate non-specific defense mechanism
  4. RADIATION THERAPY :- x-ray therapy or radiotherapy use of ionizing radiations to kill cancer cells.
  5. HARMONAL SUPPRESSION : providing or blocking certain hormones.

11.Describe the ill – effects of drug abuse in males & females. Also mention the preventive measures that is to be taken to reduce such effects.
Ans.1) ILL – DEFECTS IN MALES :- acne, increased aggressiveness , mood swing depression reduction of size of testicles, decreased Sperm production, kidney & liver dysfunction, premature baldness.
2) ILL – EFFECTS IN FEMALES :-masculinisation, increased aggressiveness, mood swings, depression abnormal menstrual cycle, excessive hair growth on face & body & deepening of voice.
The following measures are need to be taken to prevent such problems :-

  1. EDUCATION & COUNSELLING :- to face problem or stress, to accept failure as part of life & to channelize child’s energy to some health promoting activities.
  2. AVOID UNDUE PEER PRESSURE :- to pressurize a child to perform beyond his capabilities
  3. SEEKING HELP FROM PARENTS &PEERS :- to share the feeling of anxiety & guilty.
  4. SEEKING PROFESSIONAL FOR MEDICAL HELP :- help available in the form of highly qualified psychiatrist, psychologist etc.

12.What is vaccination? What type of immunity is provided by vaccination?
Ans.Vaccination is a process of development of immunity with administration of vaccines in the body, here weakened pathogen are infected into the body to produce immunity against a particular pathogen. This pathogen stimulates the body to produce antibodies. The antibodies produced against these antigens would neutralize the pathogenic agent. The vaccine also generates memory B – and T – cells that recognize pathogen quickly on subsequent exposure & overwhelm the invaders with massive production of antibodies.
The type of immunity is ACTIVE IMMUNITY.
However, if a person is infected with some deadly microbe to which quick immune response is required, we need to directly injected to patient’s body, This type of immunization is called PASSSIVE IMMUNISATION.

13. (i) Differentiate between communicable & non – communicable diseases?
(ii) Name the body part & the host in which following events takes place in life cycle of plasmodium.
(a) fertilization
(b) Development of Gametophyte :-
(c) Release of sporozoites :-
(d) Asexual Reproduction.
Ans. (i) Communicable diseases are caused lay biological agents & can spread from one person to another or one place to another through air, water, physical contact etc.
Non – communicable diseases are confined to a person & do not easily spread from one person to another.
(ii) (a) in the gut of female anopheles.
(b) in RBCS of Human beings.
(c) Salivary gland of female anopheles.
(d) liver cells of human beings.

5 Marks Questions

Chapter 8
Human Health and Disease

5 Marks Questions
1. Answer the following with respect to Caner.
(a) How does a cancerous cell differ from a normal cell?
(b) Benign tumor is less dangerous than malignant tumor. Why
(c) Describe causes of cancer.
(d) mention two methods of treatment of the disease.
Ans. (a) In normal cells, growth and differentiation is highly controlled and regulated (contact inhibition). The cancerous cells have lost the property of contact inhibition, hence continue to divide giving rise to masses of cells (tumors).
(b) The benign tumor remains confined in the organ affected as it is enclosed in a connective tissue sheath and does not enter the metastatic stage.
(c) Cancer may be caused due to carcinogens which are physical (radiations), chemicals (Nicotine, Aflatoxin, Cadmium oxide, Asbestos) and biological (viral oncogens).
(d) Surgery, radiotherapy, Chemotherapy

2. The pathogen of a disease depends on RBCs of human for grwoth and reproduction. The person with this pathogen suffers with chill and high fever.
(a) Identify the disease.
(b) Name the pathogen.
(c) What is the cause of fever?
(d) Represent the life cycle of the pathogen diagrammatically.
Ans. (a) Malaria
(b) Different species of Plasmodium viz P. vivax, P. Malariae and P. falciparum.
(c) Malaria is caused by the toxins (haemozoin) produced in the human body by the malarial parasite. This toxin is released by the rupturing of RBCs.
(d) Life cycle of Plasmodium : Fig. 8.1 Page 148, NCERT book, Biology – XII

3. The immune system of a person is supressed. He was found positive for a pathogen in the diagnostic test ELISA.
(a) Name the disease, the patient is suffering from.
(b) Which pathogen is identified by ELISA test?
(c) Which cells of the body are attacked by the pathogen?
(d) Suggest preventive measure of the infection.
Ans. (i) AIDS (Acquired Immuno Deficiency Syndrome)
(ii) HIV (Human Immunodeficiency Virus)
(iii) Helper T-cells, macrophages, B-lymphocytes.
(iv) Preventive measures :
(a) People should be educated about AIDS transmission.
(b) Disposable needles and syringes should be used
(c) Sexual habits should be changed immediately
(d) High-risk groups should be discouraged from donating blood.
(e) Routine screening may be done.

4.Discuss the role of lymphoid organs in the immune response. Explain the different types of lymphoid organs giving two examples of each type in humans.
Ans.Lymphoid organs are organs where origin or maturation & proliferation of lymphocytes occurs. These lymphoid organs are of two types:-
1.PRIMARY LYMPHOID ORGAN: – where immature lymphocytes differentiate into antigen – sensitive lymphocytes. It includes :-

(a)BONEMARROW :– It is the main lymphoid organ present in the thigh region where all types of blood cells including lymphocytes are formed. It provides micro – environment for the development & maturation of B – cells.
(b)THYMUS :- It is located beneath the chest bone near heart. It provides microenvironment for the development & maturation of T – lymphocytes.
2.SECONDAR LYMPHOID ORGAN :- They provide the site for interaction of lymphocytes with antigen which then proliferate to become effector cells. It includes.
(a)SPLEEN :- It is large bean shaped organ & contains mainly lymphocytes & phagocytes. It acts as a filter of blood by trapping blood – bound micro – organism.
(b)LYMPHNODE :- They are small – solid structure located at different points along lymphatic system. It serves to trap antigen which happens to get into lymph & tissue fluid. Antigen trapped in lymph nodes are responsible for activation of lymphocytes,

5.With the help of a well – labelled diagram, Describe the life cycle of malarial parasite.
Ans.Malaria is caused by plasmodium vivax. It has two hosts – female anopheles is the vector of plasmodium while the primary host is man where the parasite maintains an amoeboid stage in RBCS & later produces gametophyte.
Life cycle of plasmodium involves following steps:-

  1. The sporozoites enters the human body, reach the liver through blood & multiply within the liver cells such liver cells burst & release the parasites into blood.
  2. They attack RBCS, multiply & cause their rupture.

The rupturing of RBCS is associated with the release of a toxin called haemozoin, which is responsible for recurring fever & the chill / shivering.

  1. Gametophytes are developed in RBCS.
  2. When a female anopheles mosquito bites an infected person, these parasites enter the mosquito’s body & undergo further development. These parasites multiply within then in the stomach & develop a cyst.
  3. The cyst produces sporozoites which reach salivary gland of mosquito. When such infected Anopheles sucks blood of a healthy person, it transfers. Sporozoites to repeat amoeboid stage again.

6. What do you mean by “Out – breeding”. What are the different methods employed for out breeding.
Ans.Breeding between the unrelated ale & female animals is called Outbreeding. It can be done in following ways:-

  1. OUT CROSS :- The mating of animals within the same breed but do not have any common ancestor on either side of their pedigree for 4-6 generation is called an out cross. It is the best method of breeding of animals that are below average in milk production, growth rate of beef cattle etc.
  2. CROSS–BREEDING :- It is a cross between superior males of one breed & Superior females of another breed. It allows the desirable qualities of two different breeds to be combined & are used for commercial production eg .Hisardale, a new breed of sheep is developed by crossing bikaneri ewes & Marino rams.
  3. INTERSPECIFIC HYBRIDISATION :- male & female animals of two different related species are mated so, that progeny may combine desirable features of both parents eg. mule is produced by crossly donkey & a female house.

7. What is somatic hybridization – Explain the steps involved in the production of somatic hybrids?
Ans.Somatic hybridization is the process of fusing protoplasts of somatic cells derived from two different varieties or species of a plant on a suitable nutrient culture medium under sterile condition. One example of somatic hybrid is topato produced by fusion of protoplast of tomato & potato.
Somatic hybridization involves the following steps:-

  1. Isolation of protoplast from two different varieties of plants – each having a desirable character,
  2. Fusion of cytoplasm of two protoplast results in coalescence of cytoplasm. The nuclei of two protoplasts may or may not fuse together even after fusion of cytoplasm, fusion of protoplast requires a suitable agent called fusogeneg. PEG or polyethylene glycol.
  3. Under favourable conditions, hybrid protoplast synthesise new cell wall around it. Hybrid cell functions as a single cell & then undergo sustained division to form callus.
  4. The regenerated callus is transferred to a new culture plates containing suitable culture media.Here callus divide & form root & shoot after organogenesis.

Human Health and Disease Class 12 Biology MCQs 

1. In the immune system, interferons are a part of
(a) physiological barriers
(b) cellular barriers
(c) physical barriers
(d) cytokine barriers.


Answer: d

2. The letter T in T-lymphocytes refers to
(a) tonsil
(b) thalamus
(c) thymus
(d) thyroid


Answer: c

3. Use of anti-histamines and steroids gives a quick relief from
(a) allergy
(b) nausea
(c) cough
(d) fever


Answer: a

4. The immunoglobulin abundant in colostrum, is
(a) Ig D
(b) Ig A
(c) Ig G
(d) Ig M


Answer: b

5. Diacetyl morphine is commonly known as
(a) cocaine
(b) hashish
(c) ganja
(d) heroin


Answer: d

6. Opium is extracted from
(a) Atropa belladona
(b) Papaver somniferum
(c) Erythroxylum coca
(d) Cannabis sativa


Answer: b

7. The disease chikungunya is transmitted by
[NCERT Exemplar]
(a) houseflies
(b) Aedes mosquitoes
(c) cockroach
(d) female Anopheles


Answer: b

8. Anti venom against snake poison contains [NCERT Exemplar]
(a) antigens
(b) antigen-antibody complexes
(c) antibodies
(d) enzymes


Answer: c

9. Which of the following glands is large sized at birth but reducies in size with aging? [NCERT Exemplar]
(a) Pineal
(b) Pituitary
(c) Thymus
(d) Thyroid


Answer: c

10. The substance produced by a cell on viral infection that can protect other cells from further infection is [NCERT Exemplar]
(a) serotonin
(b) colostrum
(c) interferon
(d) histamine


Answer: c

11. Many diseases can be diagnosed by observing the symptoms in the patient. Which group of symptoms are indicative of pneumonia? [NCERT Exemplar]
(a) Difficulty in respiration, fever, chills, cough, headache
(b) Constipation, abdominal pain, cramps, blood clots
(c) Nasal congestion and discharge, cough, sorethroat, headache
(d) High fever, weakness, stomach pain, loss of appetite and constipation


Answer: a

12. Transplantation of tissues/organs to save certain patients often fails due to rejection of such tissues/organs by the patient. Which type of immune response is responsible for such rejections? [NCERT Exemplar]
(a) auto-immune response
(b) humoral immune response
(c) physiological immune response
(d) cell-mediated immune response


Answer: d

13. ______ mosquitoes are the vectors of dengue and chikungunya.


Explaination: Aedes.

14. ______ barriers protect the non-infected cells from further viral infections.


Explaination: Cytokine.

15. Cell-mediated immunity is provided by ______ .


Explaination: T-cells.

16. Among non-infectious diseases, ______ is the major cause of death.


Explaination: Cancer.

17. ______ test is performed to confirm typhoid.


Explaination: Widal.

18. Plasmodium enters the human body as ______ .


Explaination: Sporozoite.

19. ______ is the toxin released by the rupture of RBCs into the blood in a malaria- infected person.


Explaination: Hemocoin.

20. _____ is the filarial worm.


Explaination: Wuchereria.

21. ______ are the physical, chemical and biological agents that cause cancer.


Explaination: Carcinogens.

22. Heroin is obtained by _______ of morphine.


Explaination: Acetylation.

23. Match the organisms (Pathogens) in Column I with the diseases they cause in Column II.

Column IColumn II
A. Rhino vims1. Ringworm
B. Plasmodium2. Filariasis
C. Salmonella3. Common cold
D. Trichophyton4. Typhoid
E. Wuchereria5. Malaria
 6. Amoebiasis

Explaination: A – 3, B – 5, C – 4, D-1, E – 2

24. Match the items in Column I with those in Column II.

Column IColumn II
A. Physiological barrier1. Interferons
B. Cytokine barrier2. Skin of the body
C. Cellular barrier3. Tear in the eyes
D. Physical barrier4. Antibodies in colostrum
 5. Polymorpho-nuclear leucocyte

Explaination: A – 3, B – 1, C – 5, D – 2

25. Humoral immunity is responsible for rejection of organ transplants. [True/False]


Explaination: False

26. a-interferon activates the immune system and help to destroy the tumour cells. [True/False]


Explaination: True

27. Cannabinoids affect the digestive system. [True/False]


Explaination: False

28. Nicotine, the alkaloid in tobacco causes the hallucinogenic effect. [True/False]


Explaination: False

29. Colostrum contains antibody IgA and provides passive immunity. [True/False]


Explaination: True

Directions (Q30 to Q33): Mark the odd one in each of the following groups.

30. Saliva in the mouth, Mucus coating in respiratory tract, Tear in the eyes, Acid in the stomach.


Explaination: Mucus coating in respiratory tract

31. Thymus, spleen, appendix, tonsil.


Explaination: Thymus

32. Charas, Heroin, Marijuana, Hashish.


Explaination: Heroin

33. Typhoid, Pneumonia, Diphtheria, Malaria.


Explaination: Malaria

34. Who discovered blood circulation in humans?


Explaination: William Harvey discovered blood circulation in humans.

35. Name one infectious and one non-infectious disease that is the major cause of mortality.


– Infectious disease – AIDS.
– Non-infectious disease – Cancer.

36. 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?


Explaination: It would be confirmed by Widal test.

37. Name one respiratory disease that infects the lung alveoli and one that does not infect the lungs.


– Pneumonia infects lung alveoli.
– Common cold does not infect the lungs.

38. Name two diseases that spread by droplet infection.


Explaination: Common cold and pneumonia.

39. Name two diseases whose spread can be controlled by the eradication of Aedes mosquitoes. [CBSE 2918]
Name two viral diseases transmitted by Aedes mosquito.


Explaination: Dengue and chikungunya.

40. Name the stage of Plasmodium that gains entry into the human, when bitten by an infected female Anopheles. [Delhi 2017C]


Explaination: Sporozoite is the stage.

41. Trace the route of Sporozoite at Plasmodium, when it enters the human body through the bite of female Anopheles, till its entry into RBCs. [Delhi 2017C]


Explaination: Into human blood → Liver cells → blood → RBCs.

42. Name the host where fertilisation occurs in the life cycle of Plasmodium [Delhi 2017C]


Explaination: Anopheles mosquito.

43. How does malaria differ from chikungunya with reference to their vectors? [All India 2010C]


– Anopheles mosquito is the vector of malaria.
– Aedes mosquito is the vector of chikungunya.

44. Malaria, typhoid, pneumonia and amoebiasis are some of the human infectious diseases. Which ones of these are transmitted through mechanical carriers? [Foreign 2011]


Explaination: Amoebiasis, typhoid.

45. How does haemozoin affect the human body, when released in blood during malarial infection? [Foreign 2014]


Explaination: Haemozoin causes the chill and high fever recurring at periodic intervals (of 3-4 days).

46. Why is Gamhusia introduced into drains and ponds? [AH India 2014]


Explaination: Gambusia feeds on the mosquito larvae and thereby helps in eliminating the mosquito vectors of the diseases like Malaria, Chikungunya, dengue, etc.

47. What causes swelling of the lower limbs in patients suffering from filariasis?


Explaination: The filarial worms live for many years in the lymphatic vessels of lower limbs and cause inflammation and swelling there.

48. What role do macrophages play in providing immunity to humans?


Explaination: Macrophages phagocytose and destroy the microbes (pathogens) and provide protection from diseases.

49. How do monocytes act as a cellular barrier in humans to provide innate immunity? [CBSE 2018 C]
In what way is monocyte a cellular barrier w’ith reference to immunity? [Delhi 2015 C]


Explaination: Monocytes are phagocytic and destroy the pathogenic microbes.

50. How do neutrophils act as a cellular barrier to pathogens in humans?


Explaination: Neutrophils phagocytose and destroy the microbes (pathogens).

51. How do cytokine barriers provide innate immunity in humans? [CBSE 2018]
How do cytokine barriers help in evading viral infections? [Delhi 2015 C]
How do interferons protect us? [AH India 2012]


Explaination: Cytokine barriers, i.e. interferons are produced by the body cells in response to viral infection and protect the other non- infected cells from viral infection.

52. Name any two secretions in the body that act as ‘physiological barriers’ of innate immunity.


Explaination: Saliva in the mouth, acid in thestomach and tears from eyes. (any two)

53. Name the kind of barrier of innate immunity, where some cells secrete interferons when infected. [All India 2012]


Explaination: Cytokine barrier.

54. When does a human body elicit an anamnestic response? [AH India 2013]


Explaination: When a human body encounters a pathogen for the second time, it elicits an anamnestic response.

55. Why does a human being elicit an anamnestic response? [Delhi 2011C]


Explaination: Ahuman body elicits an anamnestic response Because our immune system appears to have memory of the first encounter with the same pathogen.

56. Suggest a method to ensure anamnestic response in humans. [Delhi 2017]


Explaination: Giving a booster dose of the vaccine can induce an anamnestic response.

57. Why is secondary immune response more intense than the primary immune response in humans? [All India 2014]


Explaination: Because body appears to have memory of the first encounter (in the form of memory B cells and memory T cells).

58. Why is the antibody-mediated immunity called humoral immunity? [HOTS]


Explaination: Antibodies are the glycoproteins that keep circulating in the body fluids (humors); hence, it is called humoral immunity.

59. Thymus of a new-born child was degenerating right from birth due to a genetic disorder. Predict its two impacts on the health of the child. [CBSE Sample Paper 2016]


– The number of T-lymphocytes will decrease and hence, the immune system will become weak.
– The child will become prone to any infection, which normally could be overcome.

60. Give two examples of passive immunity.


(i) The immunity provided by colostrum to the new-born.
(ii) The immunity provided to the foetus by the antibodies that pass through placenta from the mother.
(iii) Immunity provided against rabies and tetanus through inoculation.

61. Which category of adaptive immunity is provided by vaccination? Why? [HOTS]


Explaination: Active Immunity. It is called so because the antibodies are developed by the vaccinated person’s own cells in response to the antigens.

62. What is it that prevents a child to suffer from a disease he/she is vaccinated against? Give one reason. [Delhi 2010; HOTS]


– His body develops antibodies that circulate in the body fluids and neutralise the pathogenic agent during subsequent encounters.
– Memory B cells and memory T cells are retained in the system.

63. State the function of mast cells in allergy response. [Foreign 2013]


Explaination: Mast cells release chemicals like serotonin and hlitaminc, which cause allergy.

64. Why do pollen grains of some flowers trigger ‘sneezing’ in some people? [Foreign 2012]


Explaination: Pollen grains are allergens and cause allergic reactions in some people by causing release of histamine and serotonin from the mast cells.

65. Name the condition in vertebrates, where the body attacks self-cells. [All India 2017C]


Explaination: Autoimmunity.

66. Name the category of disease in which ’ ‘Rheumatoid arthritis’ in human, put under. [All India 2017 C]
Name the category of the disease, rheumatoid arthritis. [Foreign 2012]


Explaination: Autoimmune disease.

67. What is an autoimmune disease? [All India 2017C]


Explaination: An autoimmune disease is the one caused when the immune system of the body goes off the track and attacks ‘self’ cells.

68. What would happen to the immune system, if thymus gland is removed from the body of a person?


– Thymus is a primary lymphoid organ.
– If that is removed, T-lymphocytes cannot differentiate and their number decreases; so the immune system becomes weak and the person is prone to any infection.

69. Where are mucosal associated lymphoid tissues present in the human body and why?


Explaination: Mucosal associated lymphoid tissues are present within the lining of the respiratory, digestive and urinogenital tracts; they con-stitute about 50 per cent of the lymphoid tissue.

70. Name the two types of cells in which HIV multiplies, after gaining entry into the human body.


Explaination: Macrophages and Helper T-lymphocytes.

71. Retroviruses have no DNA. However, the DNA of the infected host cell does possess viral DNA. How is it possible? [All India 2015; HOTS]


Explaination: Retroviruses carry out reverse transcription (formation of DNA on RNA template) as they possess the enzyme, reverse transcrip-tase; the DNA is integrated with host DNA.

72. Why is sharing of injection needles between two individuals not recommended? [Delhi 2013]


Explaination: It is to prevent the spread of HIV or hepatitis B through contaminated needles.

73. Why does an AIDS patient suffer from many other infections? [HOTS]


Explaination: Due to reduction in the number of helper T-cells, the immune system of the person is weak and he suffers from infections that otherwise could have been overcome.

74. What are protooncogenes?


Explaination: Protooncogenes are the genes in normal cells, which when activated under certain conditions, could lead to oncogenic trans-formation of the cells.

75. Indiscriminate diagnostic practices using X-rays, etc. should be avoided. Give one reason. [Delhi 2015]


Explaination: X-rays are ionising radiations and can prove to be carcinogenic, i.e. cancer-causing.

76. Mention the useful as well as the harmful drug obtained from the latex of poppy plant. [Foreign 2012]


Explaination: Morphine.

77. Write the chemical structure of morphine.


Biology MCQs for Class 12 with Answers Chapter 8 Human Health and Disease 1

78. What is heroin chemically?


Explaination: Diacetylmorphine.

79. What is meant by drug abuse?


Explaination: When drugs are taken for a purpose other than their normal clinical use and in amounts/concentrations or frequency that impair one’s physical, physiological and psychological functions, it constitutes drug abuse.

80. Write the structural formula of a cannabinoid molecule.


Biology MCQs for Class 12 with Answers Chapter 8 Human Health and Disease 2

81. (a) Where are cannabinoid receptors present in a human body?
(b) Name the body system affected by cannabinoids.


(a) Cannabinoid receptors are present in the brain.
(b) They affect the cardiovascular system.

82. Name two plants other than coca plant that have hallucinogenic properties.


Explaination: Atropa belladona and Datura.

83. How does smoking tobacco in human lead to oxygen deficiency in their body? [Delhi 2012]


Explaination: Smoking increases the carbon monoxide content of the blood, which reduces the concentration of haem bound oxygen; hence there is oxygen deficiency in their body.

84. Define adolescence.


Explaination: Adolescence refers to the period and process of rapid growth and physical and mental development (attitudes and beliefs) from childhood to adulthood.

85. Why do the doses of drugs keep on increasing or lead to greater intake and addiction? [HOTS]


Explaination: It is because the tolerance level of the receptors in our body increases; they start responding to higher doses only and hence there is greater intake.

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