NCERT Solutions for Class 12 Biology Chapter 7: Human Health and Disease

Public health measures are community-level, organised interventions — as distinct from an individual’s personal precautions — aimed at blocking the entry, breeding and spread of pathogens before they can reach and infect people on a population scale. NCERT groups these safeguards broadly around sanitation, water/food safety, vector control and immunisation, and a comprehensive answer must cover each category with the diseases it protects against.

1. Sanitation and waste disposal. Proper disposal of waste and excreta, and periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks prevent faecal contamination of the environment. This single measure cuts the transmission chain for every faecal-oral disease — typhoid, amoebiasis and ascariasis all rely on faecally-contaminated food or water to spread.
2. Safe drinking water and food hygiene. Decontaminating drinking water (boiling/chlorination) and observing standard hygiene practices in public catering establishments prevent pathogens from reaching a healthy person’s gut in the first place. Washing vegetables and fruits thoroughly removes Ascaris eggs and amoebic cysts picked up from contaminated soil or water.
3. Vector control. For insect-borne diseases such as malaria and filariasis (and the Aedes-borne dengue and chikungunya that have become widespread in India), the key measure is eliminating the vector and its breeding sites: avoiding stagnant water in and around homes, regular cleaning of household coolers, use of mosquito nets, introducing larvivorous fish like Gambusia in ponds, spraying insecticide in ditches/drains/swamps, and fitting wire mesh on doors and windows to keep mosquitoes out.
4. Immunisation and vaccination programmes. Nationwide vaccination has completely eradicated smallpox and has controlled polio, diphtheria, pneumonia and tetanus to a large extent. Biotechnology is now making newer, safer vaccines available at scale.
5. Avoiding close contact for air-borne diseases. For diseases like pneumonia and the common cold that spread through droplets/aerosols, close contact with infected persons or their belongings (shared glasses, utensils, pens, doorknobs) should be avoided.
6. Treatment infrastructure. The discovery of antibiotics and other drugs has made it possible to treat infectious diseases effectively once they occur, backing up the preventive measures above.

Conclusion: no single measure can protect against all infectious diseases because different pathogens use different transmission routes; effective public health therefore combines sanitation, safe water/food, vector control and immunisation so that every major route of transmission is blocked simultaneously.

The systematic study of biology — particularly microbiology, immunology and biotechnology — has given us the scientific understanding needed to identify disease-causing organisms, learn how they spread, and design rational ways of preventing, diagnosing and treating the diseases they cause. Without this knowledge, control measures would be guesswork; with it, they become targeted and effective.

1. Identification of pathogens and their life cycles. Biology identified the exact organisms responsible for each disease — Salmonella typhi for typhoid, Plasmodium for malaria, Entamoeba histolytica for amoebiasis — and worked out their life cycles. Knowing that Plasmodium needs two hosts (human and female Anopheles mosquito) to complete its life cycle directly told us that eliminating the mosquito vector would break the cycle.
2. Discovery of antibiotics and drugs. The discovery of antibiotics transformed the treatment of bacterial diseases such as typhoid and pneumonia, converting once-fatal infections into curable ones.
3. Vaccines and immunisation. Understanding the memory property of acquired immunity led to vaccination programmes that have eradicated smallpox and controlled polio, diphtheria, pneumonia and tetanus.
4. Diagnostics. Biology-derived diagnostic tests — the Widal test for typhoid and the ELISA test for AIDS — allow early, accurate detection so that treatment or precautions can begin promptly.
5. Recombinant DNA technology. Biotechnology now allows antigenic polypeptides of pathogens to be produced in bacteria or yeast, enabling large-scale, safer vaccine production — e.g., the hepatitis B vaccine produced from yeast.
6. Passive immunisation products. Knowledge of antibodies allowed the preparation of antitoxins (preformed antibodies) for emergencies requiring an immediate response, such as tetanus and snakebite.

Conclusion: biology has controlled infectious diseases by converting ignorance into understanding — once the identity, life cycle and mode of transmission of a pathogen is known scientifically, specific vaccines, drugs, diagnostics and vector-control strategies can be designed, which is why biological research remains central to public health.

Though all four are infectious diseases, each is transmitted by a different pathogen using a different route — faecal-oral, vector-borne or droplet/airborne — and the preventive strategy for each disease follows directly from its specific transmission route.

(a) Amoebiasis. Caused by the protozoan parasite Entamoeba histolytica, which lives in the human large intestine. Houseflies act as mechanical carriers, transferring the parasite from the faeces of an infected person onto food and food products. A healthy person is infected by consuming drinking water and food contaminated by this faecal matter — a classic faecal-oral route.

(b) Malaria. Caused by the protozoan Plasmodium (P. vivax, P. malariae, P. falciparum), transmitted by the bite of an infected female Anopheles mosquito, which acts as the vector. Infectious sporozoites are introduced into the human body through the mosquito’s bite, multiply first in liver cells and then attack red blood cells. When an uninfected female Anopheles bites an infected person, it picks up the parasite, which develops further inside the mosquito into sporozoites stored in its salivary glands, ready to infect the next person. The parasite therefore requires two hosts — human and mosquito — to complete its life cycle.

(c) Ascariasis. Caused by Ascaris, the common round worm, an intestinal parasite. The eggs of the parasite are excreted along with the faeces of an infected person, which contaminate soil, water, vegetables and plants. A healthy person acquires the infection by consuming this contaminated water, vegetables or fruits — again a faecal-oral route, but via soil/produce rather than flies.

(d) Pneumonia. Caused by the bacteria Streptococcus pneumoniae and Haemophilus influenzae, which infect the alveoli of the lungs. A healthy person acquires the infection by inhaling droplets/aerosols released by an infected person (through coughing or sneezing), or even by sharing glasses and utensils with an infected person — an airborne/droplet route.

Conclusion: amoebiasis and ascariasis spread through faecal contamination of food/water, pneumonia spreads through respiratory droplets, while malaria alone requires a mosquito vector and a second host to complete transmission — which is exactly why their respective prevention strategies (sanitation, hygiene, and vector control) differ.

Water-borne diseases such as typhoid, amoebiasis and ascariasis spread when drinking water or food becomes contaminated with the faecal matter of an infected person. Preventing them therefore means breaking this faecal-oral chain at every possible point — from the source of water to the moment it is consumed.

1. Decontaminating drinking water by boiling or chlorination before use, so that pathogens such as Salmonella typhi, Entamoeba histolytica and Ascaris eggs are destroyed before the water is consumed.
2. Proper disposal of excreta and waste through sanitary latrines and sewage systems, so that human faecal matter never reaches open water sources, soil or food in the first place.
3. Periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks, as specifically recommended by NCERT for maintaining public hygiene.
4. Thoroughly washing vegetables and fruits and protecting food from faecal contamination, since Ascaris eggs and amoebic cysts commonly contaminate produce grown using contaminated soil/water.
5. Personal hygiene — washing hands with soap after defecation and before eating/cooking — since houseflies and unwashed hands mechanically carry pathogens from faeces to food.
6. Standard hygiene practices in public catering, so that food served to the public is not a source of mass contamination (as happened in the historical case of ‘Typhoid Mary’, a cook who spread typhoid for years through the food she prepared).
7. Health education of the community about how these diseases spread, so that preventive behaviour becomes routine rather than occasional.

Conclusion: because water-borne diseases depend entirely on faecal contamination of water and food, a combination of safe water treatment, sanitary waste disposal, food hygiene and personal cleanliness together close off every route by which the pathogen could travel from an infected person to a healthy one.

This is a discussion-based NCERT question, but it can be answered precisely using the chapter’s own logic of vaccination. A DNA vaccine works by introducing into the host not the whole pathogen, but only a gene that codes for one of the pathogen’s antigenic proteins. The host’s own cells then use this gene to manufacture that protein, which is recognised by the immune system as foreign and triggers an antibody and memory response — exactly as a conventional vaccine would, but without ever exposing the person to the live, disease-causing organism.

A gene is called ‘suitable’ for this purpose when it satisfies several conditions together:

1. It must code for a strongly antigenic (immunogenic) protein — usually a surface or structural protein of the pathogen that the host’s immune system would naturally recognise and respond to during a real infection, so that the manufactured protein elicits a robust antibody response and generates memory B- and T-cells.
2. It must be safe on its own — the chosen gene should encode only the antigenic protein and not any gene responsible for the pathogen’s virulence or disease-causing ability, so that introducing it cannot itself cause the disease.
3. It must be well characterised and stable in sequence, so that it can be reliably isolated, cloned and expressed using recombinant DNA technology — the same approach by which the hepatitis B vaccine is produced in yeast, as mentioned in this chapter.
4. It should allow large-scale, consistent production of the antigenic protein in a convenient host system (bacteria or yeast), which is precisely why recombinant DNA technology has made modern vaccines more widely available than earlier methods using whole weakened/inactivated pathogens.

Conclusion: a ‘suitable gene’ for a DNA vaccine is one that encodes a strongly antigenic but non-disease-causing protein of the pathogen, chosen specifically because it can be produced safely and at scale through recombinant DNA technology while still triggering a full, memory-generating immune response in the host.

Lymphoid organs are the organs where lymphocytes originate, mature, proliferate, or encounter antigen. NCERT classifies them into primary and secondary lymphoid organs based on exactly which of these roles they perform.

Primary lymphoid organs are where immature lymphocytes differentiate into antigen-sensitive lymphocytes. There are two: the bone marrow, which is the main lymphoid organ producing all blood cells including lymphocytes, and the thymus, a lobed organ located near the heart and beneath the breastbone. The thymus is quite large at birth but keeps reducing in size with age, becoming very small by the time puberty is attained. Both the bone marrow and thymus provide the micro-environment needed for the development and maturation of T-lymphocytes.

After maturing in the primary organs, lymphocytes migrate to the secondary lymphoid organs, which provide the sites where lymphocytes interact with antigen and proliferate into effector cells. These are the spleen (a large, bean-shaped organ containing lymphocytes and phagocytes; it filters blood-borne micro-organisms and also serves as a large reservoir of erythrocytes), lymph nodes (small solid structures located at different points along the lymphatic system that trap micro-organisms/antigens from lymph and tissue fluid and activate the lymphocytes present there), tonsils, Peyer’s patches of the small intestine, and the appendix. In addition, mucosa-associated lymphoid tissue (MALT), located within the lining of the respiratory, digestive and urogenital tracts, constitutes about 50 per cent of the lymphoid tissue in the human body and also functions as secondary lymphoid tissue.

Conclusion: the bone marrow and thymus are the body’s primary lymphoid organs where lymphocytes are made and mature, while the spleen, lymph nodes, tonsils, Peyer’s patches, appendix and MALT are the secondary lymphoid organs where these mature lymphocytes actually meet antigens and mount the immune response.

Each of these abbreviations stands for a key concept or organisation introduced in this chapter; expanding them correctly, together with their one-line significance, is essential for exam credit.

Conclusion: these five abbreviations together summarise the chapter’s immunology and AIDS sections — MALT and CMI describe components/mechanisms of the immune system, while AIDS, HIV and NACO describe the disease, its causative virus, and India’s organisational response to it.

(a) Innate immunity is the non-specific defence system that is present at the time of birth, working through four types of barriers — physical (skin, mucus lining the respiratory/GI/urogenital tracts), physiological (acid in the stomach, saliva, tears), cellular (PMNL/neutrophils, monocytes, natural killer cells and macrophages that phagocytose microbes) and cytokine barriers (interferons secreted by virus-infected cells, protecting non-infected cells). Acquired immunity, by contrast, is pathogen-specific and is characterised by memory: the first encounter with a pathogen produces a low-intensity primary response, while a later encounter with the same pathogen produces a much more intense secondary (anamnestic) response. It is carried out by B-lymphocytes (producing antibodies — the humoral response) and T-lymphocytes (cell-mediated immunity).

(b) Active immunity is produced when a host is exposed to antigens (living/dead microbes or other proteins) and the host’s own body produces antibodies in response; because this process takes time, active immunity is slow to give its full effect, but it is long-lasting and carries memory. It is induced by vaccination/immunisation or by natural infection. Passive immunity, in contrast, is conferred when ready-made antibodies are directly given to the body to protect it against a foreign agent — it acts immediately but does not last long and generates no memory. Examples include the colostrum (the yellowish fluid secreted during early lactation, rich in IgA) that protects a new-born, antibodies the foetus receives from the mother through the placenta during pregnancy, and injected antitoxins given for tetanus or snakebite.

Conclusion: innate vs acquired immunity differs in specificity and memory, while active vs passive immunity differs in whether the antibodies are self-made (slow but lasting) or borrowed ready-made (fast but short-lived) — together these four terms describe the complete defence strategy of the human immune system.

An antibody (immunoglobulin) is a protein produced by B-lymphocytes in response to an antigen, and is the key effector molecule of the humoral (antibody-mediated) immune response. Structurally, every antibody molecule is built from four peptide chains: two identical smaller chains called light chains (L) and two identical longer chains called heavy chains (H), held together by disulfide bonds — which is why an antibody is represented by the formula H₂L₂. The whole molecule is shaped like the letter Y: the two arms (formed by the variable regions of the light and heavy chains) carry the antigen-binding sites, while the stem (formed by the constant regions of the heavy chains) is the Fc region. Different classes of antibody exist in the body — IgA, IgM, IgE and IgG — each suited to a different role (for example, IgA is abundant in colostrum, and IgE mediates allergic responses).

Conclusion: an antibody molecule is a Y-shaped H₂L₂ protein made of two heavy and two light peptide chains linked by disulfide bonds, with variable regions at the arm-tips providing antigen specificity and constant regions forming the base that mediates the antibody’s biological effector functions.

HIV (Human Immunodeficiency Virus), the retrovirus that causes AIDS, is transmitted only through specific body fluids under specific circumstances — it is not spread by mere touch or casual physical contact, which is an important public-health clarification made explicitly by NCERT. The recognised routes of transmission are:

1. Sexual contact with an infected person — the most common route globally.
2. Transfusion of contaminated blood and blood products — if blood from an HIV-infected donor is transfused without adequate screening.
3. Sharing of infected needles and syringes — particularly relevant to individuals who take drugs intravenously.
4. From an infected mother to her child through the placenta — vertical/congenital transmission during pregnancy.

Because of these routes, people considered at high risk of HIV infection include individuals with multiple sexual partners, drug addicts who inject drugs intravenously, individuals who require repeated blood transfusions, and children born to an HIV-infected mother.

Conclusion: HIV spreads through four well-defined routes — sexual contact, contaminated blood/blood products, shared needles, and mother-to-child transmission — all of which involve the exchange of body fluids, which is why avoiding casual contact restrictions on infected individuals (while following these specific precautions) is both scientifically correct and socially important.

HIV is a retrovirus — its genome is made of RNA enclosed within a protein envelope. Unlike ordinary infections, HIV does not simply multiply and get cleared by the immune system; instead, it specifically attacks and progressively destroys the very cells that organise the body’s immune response, which is why AIDS is ultimately fatal.

1. After entering the body through one of its transmission routes, the virus first enters macrophages.
2. Inside the macrophage, the viral RNA genome replicates to form viral DNA with the help of the viral enzyme reverse transcriptase.
3. This newly formed viral DNA gets incorporated into the host cell’s own DNA and directs the infected cell to produce new virus particles. The macrophage keeps on producing virus continuously, effectively acting like an ‘HIV factory’ inside the body.
4. Simultaneously, HIV also enters helper T-lymphocytes (T_H), replicates inside them, and produces progeny viruses.
5. These progeny viruses, released into the blood, go on to attack other helper T-lymphocytes. This cycle repeats again and again, leading to a progressive decrease in the number of helper T-lymphocytes in the infected person’s body.
6. During this period, the person suffers from recurring bouts of fever, diarrhoea and weight loss.
7. Because helper T-lymphocyte numbers keep falling, the person becomes progressively immuno-deficient and starts suffering from infections that a healthy immune system would otherwise have overcome easily — caused by bacteria (especially Mycobacterium), viruses, fungi, and even parasites like Toxoplasma. Ultimately the patient is unable to protect himself/herself against these opportunistic infections.

A widely used diagnostic test for AIDS is the enzyme linked immuno-sorbent assay (ELISA). Treatment with anti-retroviral drugs is only partially effective — such drugs can prolong the patient’s life but cannot prevent eventual death, which NCERT describes as ‘inevitable’ once the infection is established.

Conclusion: HIV causes immune deficiency by using macrophages as virus-producing factories and by progressively destroying helper T-lymphocytes, the very cells that coordinate the body’s immune response — so that, over time, the infected person loses the ability to fight off even infections that a healthy immune system would easily overcome.

In a healthy body, cell growth and differentiation are highly controlled and regulated — cells divide only when needed and stop when that need is met. In cancer cells, there is a breakdown of these very regulatory mechanisms, which is the fundamental difference between a cancerous cell and a normal cell.

1. Loss of contact inhibition. Normal cells show a property called contact inhibition, by virtue of which contact with neighbouring cells inhibits their further, uncontrolled growth. Cancer cells appear to have lost this property entirely, so they continue dividing even when surrounded by other cells.
2. Uncontrolled proliferation — tumour formation. Because of this loss, cancerous cells continue to divide indefinitely, giving rise to masses of cells called tumours. A normal cell never forms such a mass.
3. Invasion and damage. While benign tumours remain confined to their original location and cause little damage, cells of malignant tumours (called neoplastic or tumour cells) grow very rapidly, actively invading and damaging the surrounding normal tissue — something a normal cell never does.
4. Competing for nutrients. As malignant cells divide and grow rapidly, they also starve the normal cells around them by competing aggressively for vital nutrients.
5. Metastasis. Cells that slough off a malignant tumour can travel through the blood to distant parts of the body and start new tumours there — a property called metastasis, which normal cells (confined to their tissue of origin) never show.
6. Evasion of immune detection. Tumour cells have been shown to avoid detection and destruction by the immune system, whereas abnormal or damaged normal cells are usually detected and eliminated by immune surveillance.

Conclusion: a cancerous cell differs from a normal cell chiefly in having lost contact inhibition and normal growth regulation, which allows it to proliferate uncontrollably, invade surrounding tissue, evade the immune system and, in malignant cases, spread to distant organs through metastasis.

Metastasis is defined by NCERT as the property, shown specifically by malignant tumours, in which cells that are sloughed off from the primary tumour travel through the blood to distant sites in the body, lodge themselves there, and start an entirely new tumour at that distant location. It is described in the textbook as ‘the most feared property of malignant tumours’, because it is what makes cancer spread beyond its original site and become far harder to treat.

This is precisely why benign tumours, which remain confined to their original location, are far less dangerous than malignant tumours — a benign tumour causes localised damage only, while a metastatic malignant tumour can establish new growths in organs completely unrelated to where the cancer originally began, making surgical removal of ‘the whole cancer’ far more difficult once metastasis has occurred.

Conclusion: metastasis is the process by which malignant tumour cells detach, travel via the bloodstream, and establish secondary tumours at distant sites in the body — making it the defining feature that distinguishes a dangerous, spreading malignant cancer from a localised, relatively harmless benign tumour.

NCERT defines drug abuse as taking drugs for a purpose other than medicinal use, or in amounts/frequency that impairs a person’s physical, physiological or psychological functions. Because alcohol and drugs act on the body in several different ways at once, their harmful effects span immediate behavioural changes, severe medical emergencies, chronic organ damage, and even far-reaching social and financial consequences.

1. Immediate behavioural effects: reckless behaviour, vandalism and violence.
2. Acute, life-threatening effects: excessive doses of drugs may cause coma and death due to respiratory failure, heart failure or cerebral haemorrhage; combining drugs with alcohol commonly results in overdosing and death.
3. Warning signs of chronic abuse: drop in academic performance, unexplained absence from school/college, lack of interest in personal hygiene, withdrawal, isolation, depression, fatigue, aggressive and rebellious behaviour, deteriorating relationships with family/friends, loss of interest in hobbies, and changes in sleeping/eating habits and weight/appetite.
4. Infections from intravenous use: those who inject drugs intravenously are far more likely to acquire serious, chronic and ultimately fatal infections like AIDS and Hepatitis B, transmitted by sharing infected needles/syringes (and also via sexual contact or infected blood).
5. Chronic organ damage: long-term use damages the nervous system and the liver (cirrhosis); alcohol use begun in adolescence often leads to heavy drinking in adulthood.
6. Effects on pregnancy: use of drugs/alcohol during pregnancy adversely affects the developing foetus.
7. Sportsperson misuse (anabolic steroids etc.): in females — masculinisation, increased aggressiveness, mood swings, depression, abnormal menstrual cycles, excessive facial/body hair growth, enlargement of the clitoris, deepening of the voice; in males — acne, increased aggressiveness, mood swings, depression, reduced size of testicles, decreased sperm production, potential kidney/liver dysfunction, breast enlargement, premature baldness, enlargement of the prostate gland; these effects can become permanent with prolonged use. In adolescents of either sex, severe facial/body acne and premature closure of the growth centres of long bones may result in stunted growth.
8. Social and financial effects: an abuser unable to fund the habit may turn to stealing; the addict’s behaviour can also cause serious mental and financial distress to the entire family and friends, not just to the user.

Conclusion: alcohol and drug abuse harms the body through acute poisoning risk and chronic organ damage, exposes the user to serious blood-borne infections, and also inflicts lasting social, financial and psychological damage on the user’s family — making it a problem with consequences well beyond the individual.

Yes. NCERT explicitly identifies peer pressure, along with unstable or unsupportive family structures, as one of the key factors associated with drug and alcohol abuse among adolescents. Friends can influence a person to try alcohol or drugs out of curiosity, the desire to fit in, or the perception — often reinforced by television, movies, newspapers and the internet — that using these substances is ‘cool’ or progressive.

One can protect oneself from such influence using the very prevention measures the chapter lists for adolescents:

1. Avoid undue peer pressure — recognise that every individual has their own choice and personality, which deserves respect; one should not feel pushed to perform or conform beyond one’s own comfort, whether in this context or in studies/sports.
2. Seek education and counselling to learn healthier ways of facing stress, disappointment and failure, and to channel one’s energy into constructive pursuits like sports, reading, music and yoga instead of substances.
3. Seek help from parents and trusted peers immediately when feeling pressured, rather than isolating oneself — sharing the problem helps in getting proper guidance and in venting feelings of anxiety.
4. Build the confidence to say no and recognise, early, the warning signs of being drawn into such company.
5. Seek professional and medical help if the pressure or temptation becomes difficult to resist alone — qualified psychologists and counsellors can help an adolescent build resistance to peer influence.

Conclusion: friends and peer pressure can and do influence adolescents toward alcohol and drug use, but this influence can be resisted by respecting one’s own choices, seeking guidance from parents, teachers and counsellors, and channelling energy into healthy activities instead.

Once started, alcohol or drug use becomes difficult to stop because of three linked biological phenomena described in this chapter — addiction, tolerance and dependence — which together trap the user in what NCERT calls a ‘vicious circle’.

1. Addiction is a psychological attachment to the effects of the drug or alcohol — such as the euphoria and temporary feeling of well-being it produces. This attachment drives the person to keep taking the substance even when it is not needed, or even after its use has become self-destructive.
2. Tolerance develops with repeated use: the receptors in the body become progressively less responsive, so they respond only to higher doses of the drug or alcohol over time. This pushes the user toward greater and greater intake, deepening the addiction further.
3. Dependence is the body’s tendency to show a characteristic and unpleasant withdrawal syndrome — anxiety, shakiness, nausea and sweating — if the regular dose is suddenly stopped. In some cases withdrawal can even be severe and life-threatening. Because resuming use relieves these unpleasant symptoms, the person is pulled back into using the substance again and again.
4. Importantly, NCERT notes that even a single use of these substances can be a ‘fore-runner to addiction’ — so the risk begins from the very first instance of use, not only after repeated use.
5. In the absence of guidance or counselling, the person has no means of breaking out of this self-reinforcing cycle and becomes fully dependent.

Conclusion: giving up alcohol or drugs is difficult because addiction creates a psychological pull toward the substance, tolerance forces ever-increasing doses, and dependence produces a painful withdrawal syndrome on stopping — together forming a self-reinforcing vicious circle that usually requires professional guidance and counselling to break.

Adolescence (roughly 12–18 years of age) is described by NCERT as a ‘bridge linking childhood and adulthood’ — a biologically and behaviourally vulnerable phase during which several factors together motivate youngsters toward alcohol or drug use.

Motivating factors:

1. Curiosity, need for adventure/excitement and natural experimentation — a child’s natural curiosity often motivates the first try.
2. Perceived benefits such as relief from stress, which later leads the child to use these substances to escape facing problems rather than out of curiosity alone.
3. Academic/examination and competition-related stress, which NCERT specifically names as having played a significant role in recent years.
4. The perception that it is ‘cool’ or progressive to smoke, drink or use drugs — a perception actively promoted by television, movies, newspapers and the internet.
5. Unstable or unsupportive family structures and peer pressure.

How this can be avoided — NCERT’s section on Prevention and Control lists five concrete measures:

1. Avoid undue peer pressure — every child has their own choice and personality, which should be respected and nurtured rather than pushed beyond their threshold in studies, sports or other activities.
2. Education and counselling — helping the child learn to face stress and accept disappointments/failures as a normal part of life, and channelling their energy into healthy pursuits like sports, reading, music, yoga and other extracurricular activities.
3. Seeking help from parents and peers — immediately, so appropriate guidance can be given and the young person can vent feelings of anxiety and guilt to trusted people.
4. Looking for danger signs — alert parents, teachers and even friends should watch for the warning signs of abuse and not hesitate to bring them to the notice of parents/teachers in the best interest of the person concerned.
5. Seeking professional and medical help — from psychologists, psychiatrists, and de-addiction and rehabilitation programmes; with sufficient effort and willpower, an affected individual can get rid of the problem completely and lead a normal, healthy life.

Conclusion: youngsters are drawn toward alcohol and drugs by a mix of curiosity, stress, social perception and peer/family pressure during the vulnerable adolescent phase, but this can be substantially prevented through respectful parenting, education and counselling, timely help-seeking, early recognition of danger signs, and professional de-addiction support when needed.