NCERT Solutions for Class 12 Biology Chapter 7: Human Health and Disease (NCERT 2026–27)
These Class 12 Biology Chapter 7 solutions cover Human Health and Disease with complete, exam-ready answers to every NCERT exercise question. The chapter explains the difference between infectious and non-infectious diseases, the pathogens that cause common human diseases, the working of innate and acquired immunity, AIDS, cancer, and the abuse of drugs and alcohol. All answers below follow the latest NCERT textbook for the 2026–27 session.
Class: 12Subject: BiologyChapter: 7Chapter Name: Human Health and DiseaseUnit: Biology in Human WelfareSession: 2026–27
Health is far more than the mere absence of disease — it is a state of complete physical, mental and social well-being. Chapter 7, Human Health and Disease, opens the unit on Biology in Human Welfare. It first surveys the common diseases in humans caused by bacteria, viruses, protozoans, helminths and fungi (typhoid, pneumonia, common cold, malaria, amoebiasis, ascariasis, filariasis, ringworm), with their transmission and prevention. It then explains immunity — innate (non-specific) versus acquired (specific, memory-based), the roles of B- and T-lymphocytes, active versus passive immunity, vaccination, allergies, auto-immunity and the lymphoid organs. The chapter closes with two major killers, AIDS (caused by HIV) and cancer (loss of cell-growth control and metastasis), and with the rising problem of drug and alcohol abuse, especially among adolescents, along with measures for its prevention and control.
Key Concepts & Definitions
Health: a state of complete physical, mental and social well-being, not merely the absence of disease.
Pathogen: any disease-causing organism (bacterium, virus, fungus, protozoan, helminth) that harms its host.
Vector: an organism, such as the female Anopheles mosquito, that transmits a pathogen from one host to another.
Immunity: the overall ability of the host to fight disease-causing organisms, conferred by the immune system; it is either innate (non-specific, present at birth) or acquired (pathogen-specific, with memory).
Antibody (H2L2): a protein produced by B-lymphocytes with two light and two heavy peptide chains; types include IgA, IgM, IgE and IgG.
AIDS: Acquired Immuno Deficiency Syndrome, caused by the Human Immunodeficiency Virus (HIV), a retrovirus that destroys helper T-lymphocytes.
Cancer: uncontrolled cell division due to loss of contact inhibition, forming tumours (benign or malignant); spread of malignant cells to distant sites is metastasis.
Drug/alcohol abuse: use of drugs or alcohol for non-medicinal purposes, or in amounts/frequency that impair physical, physiological or psychological function.
NCERT Exercises — Solutions
All questions below are reproduced verbatim from the NCERT textbook (Reprint 2026–27); the answers are original and written in CBSE exam-ready style.
1. What are the various public health measures, which you would suggest as safeguard against infectious diseases?
ANSWERImportant public health measures against infectious diseases are:(i) Maintenance of personal and public hygiene — keeping the body clean and consuming clean drinking water, food, vegetables and fruits; proper disposal of waste and excreta; periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks.(ii) Vaccination and immunisation programmes against infectious diseases such as polio, diphtheria, pneumonia, tetanus and smallpox.(iii) Control and elimination of vectors and their breeding places — avoiding water stagnation, regular cleaning of coolers, use of mosquito nets and wire mesh on doors/windows, introducing larvivorous fish like Gambusia in ponds, and spraying insecticides in ditches and swamps.(iv) Avoiding close contact with infected persons or their belongings in case of air-borne diseases like pneumonia and the common cold.(v) Educating people about diseases and following standard hygiene practices in public catering.
2. In which way has the study of biology helped us to control infectious diseases?
ANSWERAdvances in biological science have armed us to deal effectively with infectious diseases in several ways:(i) The use of vaccines and immunisation programmes has completely eradicated a deadly disease like smallpox and has largely controlled polio, diphtheria, pneumonia and tetanus.(ii) The discovery of antibiotics and various other drugs has enabled us to treat many infectious diseases successfully.(iii) Biotechnology has made possible newer and safer vaccines, including those produced by recombinant DNA technology (e.g. the hepatitis B vaccine produced from yeast), allowing large-scale production and greater availability.(iv) Improved knowledge of pathogens, their life cycles and vectors has helped in developing better diagnostic tests and effective preventive and control measures.
3. How does the transmission of each of the following diseases take place?
(a) Amoebiasis (b) Malaria (c) Ascariasis (d) Pneumonia
ANSWER(a) Amoebiasis: caused by Entamoeba histolytica. Houseflies act as mechanical carriers and transmit the parasite from the faeces of an infected person to food and food products. Drinking water and food contaminated with faecal matter are the main sources of infection.(b) Malaria: caused by Plasmodium. It is transmitted through the bite of an infected female Anopheles mosquito, which introduces sporozoites (the infectious stage) into the human body.(c) Ascariasis: caused by the roundworm Ascaris. The eggs of the parasite are excreted with the faeces of infected persons and contaminate soil, water and plants. A healthy person acquires the infection through contaminated water, vegetables and fruits.(d) Pneumonia: caused by bacteria such as Streptococcus pneumoniae and Haemophilus influenzae. A healthy person acquires the infection by inhaling droplets/aerosols released by an infected person, or by sharing glasses and utensils with an infected person.
4. What measure would you take to prevent water-borne diseases?
ANSWERWater-borne diseases such as typhoid, amoebiasis and ascariasis spread through contaminated water and food. Preventive measures include:(i) Ensuring the supply of clean, decontaminated drinking water — boiling, filtering or chlorinating water before use.(ii) Proper disposal of waste and excreta so that faecal matter does not contaminate water sources.(iii) Periodic cleaning and disinfection of water reservoirs, tanks, pools and cesspools.(iv) Maintaining personal hygiene — washing hands before eating and after using the toilet — and observing standard hygiene practices in public catering.(v) Consuming clean, properly washed and well-cooked food, vegetables and fruits, and controlling carriers like houseflies.
5. Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.
ANSWERIn a DNA vaccine, a piece of DNA carrying ‘a suitable gene’ is introduced into the host. A suitable gene is one that codes for a specific antigenic protein (antigen) of the pathogen — for example, a surface protein of the disease-causing organism.When this gene is taken up by the host’s cells, the cells produce the corresponding antigenic protein. This antigen stimulates the immune system to produce antibodies and to generate memory B- and T-cells against the pathogen, without causing the actual disease.Thus, the gene must be antigenic enough to trigger a protective immune response, yet harmless on its own. On later exposure to the real pathogen, the primed immune system responds quickly and effectively. (Discuss further examples with your teacher.)
6. Name the primary and secondary lymphoid organs.
ANSWERPrimary lymphoid organs: bone marrow and thymus — here immature lymphocytes differentiate into antigen-sensitive lymphocytes.Secondary lymphoid organs: spleen, lymph nodes, tonsils, Peyer’s patches of the small intestine, and appendix — these provide the sites where lymphocytes interact with antigens and then proliferate to become effector cells.
7. The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form:
(a) MALT (b) CMI (c) AIDS (d) NACO (e) HIV
ANSWER
Abbreviation
Full form
(a) MALT
Mucosa-Associated Lymphoid Tissue
(b) CMI
Cell-Mediated Immunity
(c) AIDS
Acquired Immuno Deficiency Syndrome
(d) NACO
National AIDS Control Organisation
(e) HIV
Human Immunodeficiency Virus
8. Differentiate the following and give examples of each:
(a) Innate and acquired immunity (b) Active and passive immunity
ANSWER(a) Innate vs acquired immunity
Innate immunity
Acquired immunity
Non-specific defence present at the time of birth.
Pathogen-specific defence developed during life.
No memory; response is the same on every exposure.
Has memory; a stronger secondary response on re-exposure.
Works through barriers — physical, physiological, cellular and cytokine.
Works through B- and T-lymphocytes (antibody-mediated and cell-mediated responses).
Example: skin, mucus, acid in the stomach, phagocytes, interferons.
Example: antibodies produced after infection or vaccination (e.g. against measles).
(b) Active vs passive immunity
Active immunity
Passive immunity
Host’s own body produces antibodies in response to antigens.
Ready-made antibodies are directly given to the host.
Slow to develop but long-lasting; provides memory.
Acts immediately but is short-lived; no memory.
Induced by natural infection or by vaccination (immunisation).
Provided by transfer of preformed antibodies.
Example: immunity after suffering from chickenpox, or after a vaccine.
Example: antibodies (IgA) in colostrum and through the placenta to the foetus; anti-tetanus antitoxin; anti-snake-venom serum.
9. Draw a well-labelled diagram of an antibody molecule.
ANSWERAn antibody is a Y-shaped protein molecule with the formula H2L2 — it has four peptide chains: two longer heavy (H) chains and two smaller light (L) chains. Each arm of the ‘Y’ ends in a variable antigen-binding site; the chains are joined by disulphide bonds.For your answer sheet, draw the Y-shape and label: the two heavy chains (the longer chains forming the stem and inner arms), the two light chains (the shorter outer chains), the two antigen-binding sites at the tips of the arms, and the disulphide (–S–S–) bonds linking the chains. (A neat, labelled hand-drawn diagram is required in the exam; refer to Figure 7.4 of the NCERT textbook.)
10. What are the various routes by which transmission of human immuno-deficiency virus takes place?
ANSWERTransmission of HIV generally occurs through:(a) Sexual contact with an infected person.(b) Transfusion of contaminated blood and blood products.(c) Sharing infected needles, as in the case of intravenous drug abusers.(d) From an infected mother to her child through the placenta (and also via breast-feeding).It is important to note that HIV/AIDS does not spread by mere touch or physical contact — it spreads only through body fluids.
11. What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
ANSWERAfter entering the body, HIV enters macrophages, where its RNA genome replicates to form viral DNA with the help of the enzyme reverse transcriptase. This viral DNA gets incorporated into the host cell’s DNA and directs the infected cell to produce virus particles, so the macrophage acts like an “HIV factory”.Simultaneously, HIV enters helper T-lymphocytes (TH), replicates inside them and produces progeny viruses. These progeny viruses are released into the blood and attack other helper T-lymphocytes, repeating the cycle.This leads to a progressive decrease in the number of helper T-lymphocytes. As a result, the person becomes severely immuno-deficient and is unable to defend against infections by bacteria (especially Mycobacterium), viruses, fungi and even parasites such as Toxoplasma — infections that would otherwise have been overcome.
12. How is a cancerous cell different from a normal cell?
ANSWER
Normal cell
Cancerous cell
Cell growth and differentiation are highly controlled and regulated.
There is a breakdown of regulatory mechanisms controlling growth.
Shows the property of contact inhibition — contact with other cells stops further division.
Loses contact inhibition and continues to divide, forming masses of cells (tumours).
Remains confined to its proper location.
Malignant cells invade surrounding tissues and may spread to distant sites (metastasis).
Does not starve neighbouring cells.
Grows rapidly, starving normal cells by competing for vital nutrients.
13. Explain what is meant by metastasis.
ANSWERMetastasis is the property of malignant tumours by which cells get sloughed off (detached) from the original tumour, reach distant sites in the body through the blood, and wherever they get lodged, they start a new tumour there.It is the most feared property of malignant tumours because it spreads the cancer to other organs of the body, making the disease difficult to treat.
14. List the harmful effects caused by alcohol/drug abuse.
ANSWERThe harmful effects of alcohol/drug abuse include:(i) Immediate effects: reckless behaviour, vandalism and violence.(ii) Overdosing can lead to coma and death due to respiratory failure, heart failure or cerebral haemorrhage; combining drugs or taking them with alcohol increases this risk.(iii) Intravenous drug use (sharing infected needles) increases the risk of acquiring serious chronic infections like AIDS and hepatitis B.(iv) Chronic use damages the nervous system and the liver (cirrhosis); use during pregnancy adversely affects the foetus.(v) Misuse in sports — anabolic steroids cause masculinisation, aggressiveness, mood swings, abnormal menstrual cycles, excessive body hair and deepening of voice in females; and acne, reduced testicle size, decreased sperm production, breast enlargement and premature baldness in males; in adolescents it may cause stunted growth.(vi) Social and financial harm: drop in academic performance, withdrawal, depression, deteriorating relationships, and even stealing — causing distress to the family and friends.
15. Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
ANSWERYes, friends can strongly influence a young person to take alcohol or drugs. Peer pressure and the perception that it is ‘cool’ or progressive to smoke or use drugs/alcohol are major reasons why youngsters begin these habits.One can protect oneself by:(i) Avoiding undue peer pressure — respecting one’s own choices and not feeling forced to perform beyond one’s limits.(ii) Education and counselling — learning to face problems and accept failures, and channelising energy into healthy pursuits like sports, music, reading and yoga.(iii) Seeking help from parents and peers — sharing problems and feelings of anxiety with trusted friends and elders.(iv) Looking for danger signs and seeking professional/medical help from qualified counsellors when needed. (Your own reasoned views are accepted.)
16. Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.
ANSWEROnce started, the habit is difficult to give up because of the inherent addictive nature of alcohol and drugs, which acts through two linked processes:Addiction: a psychological attachment to the effects of drugs and alcohol — such as euphoria and a temporary feeling of well-being. This drives a person to keep taking them even when not needed or when the use becomes self-destructive.Tolerance: with repeated use, the tolerance level of the receptors in the body increases, so they respond only to higher doses. This leads to greater intake and deepening addiction.Dependence: the body shows an unpleasant withdrawal syndrome (anxiety, shakiness, nausea, sweating) if the regular dose is stopped abruptly, which is relieved only on resuming use. These factors together pull the user into a vicious circle from which it is very hard to escape. (Discuss further with your teacher.)
17. In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
ANSWERMotivating factors: curiosity, the need for adventure and excitement, and the urge to experiment; the desire to escape problems and stresses; pressure to excel in academics or examinations; the perception that drug/alcohol use is ‘cool’ (often promoted by television, movies and the internet); unstable or unsupportive family structures; and peer pressure.How it can be avoided:(i) Avoid undue peer pressure and respect each child’s own personality and choices.(ii) Provide education and counselling to face problems, accept failures, and channelise energy into healthy activities like sports, music, reading and yoga.(iii) Encourage seeking help from parents, teachers and trusted peers.(iv) Alert parents and teachers should look for danger signs, and seek professional and medical help (psychologists, psychiatrists, de-addiction and rehabilitation programmes) when needed. Nurturing parenting with consistent discipline lowers the risk of substance abuse. (Your own reasoned views are accepted.)
Extra Practice Questions
Short Answer Type Questions
Q1. Name the causative organism and one symptom each of typhoid and pneumonia.
ANSWERTyphoid is caused by Salmonella typhi (symptom: sustained high fever of 39–40°C, weakness, stomach pain). Pneumonia is caused by Streptococcus pneumoniae / Haemophilus influenzae (symptom: fever, chills, cough and difficulty in breathing).
Q2. What are the four types of barriers in innate immunity? Give one example of each.
ANSWER(i) Physical barriers — skin and mucus coating of the tracts; (ii) Physiological barriers — acid in the stomach, saliva, tears; (iii) Cellular barriers — neutrophils, monocytes, natural killer cells and macrophages that phagocytose microbes; (iv) Cytokine barriers — interferons secreted by virus-infected cells that protect nearby cells.
Q3. Why is colostrum important for a new-born infant?
ANSWERColostrum, the yellowish fluid secreted by the mother in the first few days of lactation, is rich in antibodies of the IgA type. These ready-made antibodies provide the infant with passive immunity, protecting it against infections until its own immune system matures.
Q4. Name the drugs commonly abused and the plant source of each.
ANSWEROpioids (e.g. heroin/morphine) from the latex of the opium poppy Papaver somniferum; cannabinoids (marijuana, hashish, charas, ganja) from Cannabis sativa; and cocaine (coca alkaloid) from the coca plant Erythroxylum coca.
Q5. What is an allergy and which antibody is responsible for it?
ANSWERAn allergy is the exaggerated response of the immune system to certain antigens (allergens) present in the environment, such as dust mites, pollen and animal dander. It involves the release of histamine and serotonin from mast cells and is mediated by antibodies of the IgE type.
Long Answer Type Questions
Q1. Describe the life cycle of Plasmodium in the human and mosquito hosts.
ANSWERPlasmodium requires two hosts — humans and the female Anopheles mosquito — to complete its life cycle. It enters the human body as sporozoites (the infectious form) through the bite of an infected female Anopheles mosquito. The parasites first multiply within the liver cells and then attack the red blood cells (RBCs), causing them to rupture. This rupture releases a toxic substance, haemozoin, which is responsible for the chill and recurring high fever (every three to four days). When a female Anopheles bites an infected person, the parasites enter the mosquito’s body and undergo further development, multiplying to form sporozoites that are stored in the mosquito’s salivary glands. When this mosquito bites another human, the sporozoites are introduced, restarting the cycle. The female Anopheles mosquito is thus both a host and the vector.
Q2. Explain the structure of the human immune system, naming its lymphoid organs and their functions.
ANSWERThe human immune system consists of lymphoid organs, tissues, cells and soluble molecules like antibodies. Primary lymphoid organs — the bone marrow (where all blood cells, including lymphocytes, are produced) and the thymus (a lobed organ near the heart that reduces in size after puberty) — provide micro-environments for the development and maturation of T-lymphocytes; here immature lymphocytes become antigen-sensitive. Secondary lymphoid organs — the spleen (a large bean-shaped organ that filters blood-borne microbes and stores erythrocytes), lymph nodes (small structures that trap antigens in lymph and tissue fluid and activate lymphocytes), tonsils, Peyer’s patches and the appendix — provide sites for lymphocytes to interact with antigens and become effector cells. In addition, mucosa-associated lymphoid tissue (MALT) lines the respiratory, digestive and urogenital tracts and makes up about 50 per cent of the body’s lymphoid tissue.
Q3. Describe the causes, detection and treatment of cancer.
ANSWERCauses: Normal cells transform into cancerous (neoplastic) cells under the action of carcinogens — physical agents (ionising radiations like X-rays and gamma rays, and non-ionising UV that damage DNA), chemical agents (e.g. carcinogens in tobacco smoke, a major cause of lung cancer) and biological agents (oncogenic viruses carrying viral oncogenes). Normal cells also contain cellular oncogenes (proto-oncogenes) that can trigger transformation when activated. Detection and diagnosis: done by biopsy and histopathological studies of tissue, and blood and bone-marrow tests for raised cell counts in leukaemia; imaging techniques like radiography (X-rays), CT and MRI detect cancers of internal organs; antibodies against cancer-specific antigens and molecular biology techniques identify cancers and inherited susceptibility. Treatment: the common approaches are surgery, radiation therapy (radiotherapy), chemotherapy (using drugs that kill cancer cells, often with side effects like hair loss and anaemia) and immunotherapy using biological response modifiers such as α-interferon to activate the patient’s immune system. Most cancers are treated by a combination of surgery, radiotherapy and chemotherapy.
For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.
A-R 1. Assertion: Vaccination provides protection against many infectious diseases.
Reason: Vaccines generate memory B- and T-cells that respond rapidly on later exposure to the pathogen.
A-R 2. Assertion: Passive immunity is long-lasting and produces memory.
Reason: In passive immunity the body produces its own antibodies in response to antigens.
A-R 3. Assertion: HIV/AIDS does not spread by mere touch or physical contact.
Reason: HIV spreads only through body fluids such as blood, semen and from infected mother to child.
A-R 4. Assertion: Benign tumours are generally less dangerous than malignant tumours.
Reason: Benign tumours remain confined to their original location and do not show metastasis.
A-R 5. Assertion: With repeated drug use, a person needs higher doses to get the same effect.
Reason: Repeated use raises the tolerance level of receptors, which then respond only to higher doses.
Answer key: 1-(A), 2-(D), 3-(A), 4-(A), 5-(A).
Common Mistakes to Avoid
Watch out for these
Confusing the vector with the pathogen — in malaria, Plasmodium is the pathogen while the female Anopheles mosquito is the vector.
Mixing up active and passive immunity — in active immunity the body makes its own antibodies; in passive immunity ready-made antibodies are given.
Writing that HIV destroys all WBCs — it specifically destroys helper T-lymphocytes (and infects macrophages).
Forgetting that AIDS is acquired, not congenital, and is not spread by touch.
Saying cancer cells “stop dividing” — in fact they lose contact inhibition and divide uncontrollably.
Listing the wrong plant source for an abused drug — heroin/morphine from Papaver somniferum, cannabinoids from Cannabis sativa, cocaine from Erythroxylum coca.
How to score full marks in this chapter
Tabulate differences (innate vs acquired, active vs passive, normal vs cancer cell) for clear, high-scoring answers. Always give the scientific name of the causative organism with its disease, and name the vector separately. For HIV, state the sequence: macrophage → reverse transcriptase → viral DNA into host genome → attack on helper T-cells. Use the exact abbreviations (MALT, CMI, NACO) with full forms. For the antibody diagram, label heavy chains, light chains, antigen-binding sites and disulphide bonds neatly.
Frequently Asked Questions
What is Class 12 Biology Chapter 7 about?
Chapter 7, Human Health and Disease, covers common human diseases caused by bacteria, viruses, protozoans, helminths and fungi; innate and acquired immunity; active and passive immunity; vaccination, allergies and auto-immunity; the lymphoid organs; AIDS; cancer; and drug and alcohol abuse with its prevention.
How does HIV cause immune deficiency?
HIV enters macrophages and helper T-lymphocytes, where reverse transcriptase forms viral DNA that integrates into the host genome and produces new viruses. These progressively destroy helper T-lymphocytes, leaving the person unable to fight infections that could otherwise be overcome.
What is the difference between a benign and a malignant tumour?
A benign tumour stays confined to its original location and causes little harm, whereas a malignant tumour invades surrounding tissues and spreads to distant sites through the blood — a property called metastasis — making it far more dangerous.
Are these Class 12 Biology Chapter 7 solutions free?
Yes. All solutions are free and follow the official NCERT Biology textbook for the 2026–27 session.
