Human Health and Disease explains infectious diseases, immunity, AIDS, cancer, and the effects of drug and alcohol abuse.
These NCERT Solutions help Class 12 Biology students write accurate answers using correct examples, terms, routes and mechanisms.
A fever, a mosquito bite, an allergic reaction, a vaccine dose and a cancer test may look like separate topics, but Chapter 7 connects all of them through health and immunity. This chapter is useful for students because it explains disease-causing organisms, how infections spread, how the body defends itself and why prevention matters. The NCERT exercise includes direct questions on public health measures, disease transmission, lymphoid organs, HIV, cancer cells and addiction. These NCERT Solutions Class 12 Biology Chapter 7 give structured answers with causative agents, transmission routes, immune responses and prevention points that students can revise quickly for CBSE 2026 exams.
Key Takeaways
- Health: Health means complete physical, mental and social well-being, not only absence of disease.
- Immunity: Innate immunity is present from birth, while acquired immunity is pathogen-specific and memory-based.
- AIDS: HIV attacks helper T-lymphocytes and causes progressive immune deficiency.
- Cancer: Malignant tumours spread through metastasis and damage normal tissues.
NCERT Solutions Class 12 Biology Chapter 7 Structure 2026
| Exercise Type |
Topic Covered |
Question Count |
| Short Answers |
Public health, disease transmission, water-borne diseases |
5 |
| Concept Answers |
Immunity, lymphoid organs, AIDS, cancer |
8 |
| Application Answers |
Drug abuse, peer pressure, addiction prevention |
4 |
NCERT Solutions for Class 12 Biology Chapter 7 Exercise
Human Health and Disease questions need correct disease examples, causative agents, transmission routes and preventive measures. Answers should use NCERT terms such as pathogen, vector, antibody, MALT, CMI, metastasis and retrovirus.
Q1. What are the various public health measures, which you would suggest as safeguard against infectious diseases?
Answer: Public health measures against infectious diseases include hygiene, sanitation, vector control, vaccination and safe food-water practices.
Important measures are:
- Proper disposal of waste and excreta.
- Regular cleaning and disinfection of water reservoirs, tanks and pools.
- Supply of clean drinking water.
- Maintenance of food hygiene in public catering places.
- Control of vectors such as mosquitoes and houseflies.
- Avoiding stagnation of water near houses.
- Use of mosquito nets, wire mesh and insecticides.
- Vaccination against infectious diseases.
- Avoiding close contact with infected people in air-borne diseases.
- Awareness about disease symptoms, transmission and prevention.
These measures reduce the spread of diseases such as typhoid, amoebiasis, ascariasis, malaria, filariasis, pneumonia and common cold.
Q2. In which way has the study of biology helped us to control infectious diseases?
Answer: The study of biology has helped us understand pathogens, immunity, vaccines, antibiotics and disease transmission.
Biology helped scientists identify bacteria, viruses, protozoans, fungi and helminths that cause diseases. It also explained how pathogens enter the body, multiply and spread from one person to another.
Biological knowledge helped in developing vaccines for diseases such as smallpox, polio, diphtheria, pneumonia and tetanus. It also helped in discovering antibiotics and other drugs for treating infectious diseases.
Biotechnology has enabled the production of safer vaccines, such as recombinant vaccines. Biological understanding of vectors has also helped control mosquito-borne diseases like malaria, dengue, chikungunya and filariasis.
Class 12 Biology Chapter 7 Human Health and Disease Short Answers
Disease transmission questions are scoring when the causative agent, route and carrier are written clearly. Use one disease-specific example in every answer.
Q3. How does the transmission of amoebiasis take place?
Answer: Amoebiasis is transmitted through food and water contaminated with faecal matter.
It is caused by the protozoan parasite Entamoeba histolytica, which lives in the large intestine of humans. Houseflies act as mechanical carriers and transfer the parasite from faeces of infected persons to food and food products.
The main sources of infection are contaminated drinking water and contaminated food.
Q3. How does the transmission of malaria take place?
Answer: Malaria is transmitted through the bite of an infected female Anopheles mosquito.
The disease is caused by Plasmodium species such as Plasmodium vivax, Plasmodium malariae and Plasmodium falciparum. The mosquito injects the infectious sporozoite stage into the human body during a bite.
The parasite multiplies in liver cells and then attacks RBCs. When another female Anopheles mosquito bites the infected person, the parasite enters the mosquito and continues its life cycle.
Q3. How does the transmission of ascariasis take place?
Answer: Ascariasis is transmitted through contaminated food, water, vegetables and fruits.
It is caused by the intestinal helminth Ascaris, commonly called roundworm. Eggs of the parasite are released through the faeces of infected persons. These eggs contaminate soil, water, plants and food items.
A healthy person gets infected by consuming contaminated food or water.
Q3. How does the transmission of pneumonia take place?
Answer: Pneumonia is transmitted by inhaling droplets or aerosols released by an infected person.
It is caused by bacteria such as Streptococcus pneumoniae and Haemophilus influenzae. These pathogens infect the alveoli of the lungs. A healthy person may also acquire infection by sharing glasses or utensils with an infected person.
Pneumonia spreads through close contact and respiratory secretions.
Q4. What measure would you take to prevent water-borne diseases?
Answer: Water-borne diseases can be prevented by using clean water, proper sanitation and hygienic food practices.
Important measures are:
- Drink boiled, filtered or properly treated water.
- Avoid drinking water from unsafe sources.
- Prevent faecal contamination of water bodies.
- Dispose of sewage and excreta properly.
- Wash fruits and vegetables with clean water.
- Maintain personal hygiene before eating.
- Keep water storage containers covered.
- Clean water tanks and reservoirs regularly.
- Avoid open defecation.
- Follow standard hygiene practices in public food places.
These measures help prevent diseases such as typhoid, amoebiasis and ascariasis.
Q5. Discuss with your teacher what does ‘a suitable gene’ mean, in the context of DNA vaccines.
Answer: In the context of DNA vaccines, a suitable gene means a gene that codes for an antigenic protein of a pathogen.
This gene is selected from the disease-causing organism and introduced into the host through a DNA vaccine. Host cells express the antigenic protein. The immune system recognises this protein as foreign and produces an immune response.
A suitable gene should produce an antigen that can safely trigger protective immunity. It should help the body generate memory B-cells and T-cells against the pathogen.
Human Health and Disease Class 12 NCERT Solutions: Immunity Answers
Immunity answers should clearly separate barriers, organs, cells and antibodies. The immune system works through recognition, response and memory.
Q6. Name the primary and secondary lymphoid organs.
Answer: The primary lymphoid organs are bone marrow and thymus.
The secondary lymphoid organs are spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix.
Primary lymphoid organs are the sites where immature lymphocytes mature into antigen-sensitive lymphocytes. Secondary lymphoid organs are the sites where lymphocytes interact with antigens and become effector cells.
Q7. Expand each abbreviation to its full form.
(a) MALT
Answer: Mucosa-Associated Lymphoid Tissue
(b) CMI
Answer: Cell-Mediated Immunity
(c) AIDS
Answer: Acquired Immuno Deficiency Syndrome
(d) NACO
Answer: National AIDS Control Organisation
(e) HIV
Answer: Human Immunodeficiency Virus
Q8(a). Differentiate between innate and acquired immunity. Give examples of each.
Answer:
| Innate Immunity |
Acquired Immunity |
| It is present from birth. |
It develops after exposure to a pathogen or antigen. |
| It is non-specific. |
It is pathogen-specific. |
| It has no memory. |
It has memory. |
| It works through barriers like skin, mucus, acid, phagocytes and interferons. |
It works through B-lymphocytes, T-lymphocytes and antibodies. |
| Example: Skin prevents entry of microbes. |
Example: Immunity developed after vaccination. |
Innate immunity gives immediate general defence. Acquired immunity gives specific and stronger response after exposure.
Q8(b). Differentiate between active and passive immunity. Give examples of each.
Answer:
| Active Immunity |
Passive Immunity |
| The host produces antibodies after exposure to antigens. |
Ready-made antibodies are given directly. |
| It takes time to develop. |
It gives quick protection. |
| It is usually long-lasting. |
It is usually short-lived. |
| It produces immunological memory. |
It does not produce long-term memory. |
| Example: Immunity after vaccination. |
Example: Antibodies received through colostrum. |
Active immunity is induced by infection or vaccination. Passive immunity is useful when immediate protection is needed, such as in tetanus or snakebite.
Q9. Draw a well-labelled diagram of an antibody molecule.
Answer: Draw a Y-shaped antibody molecule and label these parts:
- Two heavy chains
- Two light chains
- Antigen-binding sites
- Disulfide bonds
- Constant region
- Variable region
Diagram tip: Show the antibody as H₂L₂, because it contains two heavy chains and two light chains.
NCERT Class 12 Biology Chapter 7 Solutions: AIDS
AIDS questions require accurate routes, virus structure and mechanism. Mention that HIV is a retrovirus and affects helper T-lymphocytes.
Q10. What are the various routes by which transmission of human immunodeficiency virus takes place?
Answer: HIV transmission takes place through body fluids.
The main routes are:
- Sexual contact with an infected person.
- Transfusion of contaminated blood and blood products.
- Sharing infected needles, especially among intravenous drug users.
- Transmission from an infected mother to her child through the placenta.
HIV does not spread by touch, handshake, hugging, sharing food or normal social contact.
Q11. What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
Answer: HIV causes immune deficiency by progressively reducing helper T-lymphocytes.
After entering the body, HIV enters macrophages. Its RNA genome is converted into viral DNA by reverse transcriptase. This viral DNA gets incorporated into the host cell DNA and directs the host cell to produce new virus particles.
Macrophages act as HIV factories and continue producing viruses. HIV also enters helper T-lymphocytes, replicates and produces progeny viruses. These new viruses attack more helper T-cells.
As the number of helper T-lymphocytes decreases, the immune system becomes weak. The person becomes susceptible to infections caused by bacteria, viruses, fungi and parasites. This condition is called AIDS.
Class 12 Biology Human Health and Disease Questions and Answers: Cancer
Cancer answers should use terms such as contact inhibition, tumour, malignant, benign, oncogene and metastasis. Early detection is a key point in NCERT.
Q12. How is a cancerous cell different from a normal cell?
Answer: A cancerous cell divides uncontrollably, while a normal cell divides in a controlled and regulated manner.
Normal cells show contact inhibition. This means contact with other cells stops their uncontrolled growth. Cancerous cells lose contact inhibition and continue dividing.
Cancerous cells form masses called tumours. Malignant tumour cells invade surrounding tissues, compete with normal cells for nutrients and may spread to distant organs.
Normal cells remain functionally controlled by the body. Cancerous cells escape normal regulatory mechanisms.
Q13. Explain what is meant by metastasis.
Answer: Metastasis is the spread of cancerous cells from the original tumour site to distant parts of the body.
In malignant tumours, some cells break away from the tumour mass. These cells enter blood or lymph and reach other organs. Wherever they get lodged, they start forming new tumours.
Metastasis is the most feared property of malignant tumours because it spreads cancer throughout the body.
Class 12 Biology Chapter 7 Exercise Answers: Drug and Alcohol Abuse
Application-based answers on substance abuse should include causes, effects, warning signs and prevention. Keep the tone scientific and supportive.
Q14. List the harmful effects caused by alcohol/drug abuse.
Answer: Alcohol and drug abuse harms the body, mind, family and society.
Harmful effects include:
- Reckless behaviour, violence and vandalism.
- Poor academic performance.
- Absence from school or college.
- Lack of interest in personal hygiene.
- Withdrawal, isolation and depression.
- Fatigue and aggressive behaviour.
- Poor relationships with family and friends.
- Change in sleeping and eating habits.
- Weight and appetite fluctuations.
- Coma and death in overdose cases.
- Respiratory failure, heart failure or cerebral haemorrhage.
- Higher risk of AIDS and Hepatitis B through infected needles.
- Damage to nervous system and liver.
- Cirrhosis due to chronic alcohol use.
- Harmful effects on foetus during pregnancy.
Drug or alcohol addiction can also create financial distress and social adjustment problems.
Q15. Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
Answer: Yes, friends can influence a person to take alcohol or drugs through peer pressure.
Young people may start substance use because they want acceptance, adventure, excitement or a “cool” image among friends. They may also imitate peers who smoke, drink or use drugs.
A person can protect himself or herself by:
- Saying no firmly to alcohol or drugs.
- Choosing friends who support healthy habits.
- Avoiding groups where substance use is common.
- Seeking help from parents, teachers or trusted friends.
- Joining sports, music, reading, yoga or other healthy activities.
- Understanding the harmful effects of drugs and alcohol.
- Getting counselling when under stress or pressure.
Strong decision-making and supportive relationships reduce the risk of peer influence.
Q16. Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit?
Answer: It is difficult to stop alcohol or drugs because they cause addiction and dependence.
Addiction is a psychological attachment to the temporary effects of drugs or alcohol, such as euphoria and relief from stress. Repeated use increases the tolerance level of receptors in the body. The person then needs higher doses to get the same effect.
Dependence occurs when the body shows withdrawal symptoms after stopping the substance. These symptoms may include anxiety, shakiness, nausea and sweating. In severe cases, withdrawal can be life-threatening.
This combination of addiction, tolerance and dependence makes it difficult to stop without counselling, medical help and family support.
Q17. In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
Answer: Youngsters may take alcohol or drugs due to curiosity, peer pressure, stress, experimentation and lack of guidance.
Common motivating factors include:
- Need for adventure and excitement.
- Curiosity about the effect of drugs or alcohol.
- Pressure from friends.
- Stress from examinations or competition.
- Desire to escape problems.
- Unstable or unsupportive family environment.
- Influence of media, movies or internet.
- Wrong belief that smoking, drinking or drug use is progressive.
This can be avoided through education, counselling and emotional support. Parents and teachers should identify danger signs early. Students should be encouraged to take part in sports, yoga, music, reading and other healthy activities. Professional and medical help should be taken whenever substance abuse begins.
NCERT Solutions Class 12 Biology Human Health and Disease: Important Concepts
Human Health and Disease connects pathogens, immunity, lifestyle and medical prevention. These concepts help students answer both direct and application-based questions.
Common Diseases in Humans
Human diseases may be caused by bacteria, viruses, protozoans, helminths and fungi.
Typhoid is caused by Salmonella typhi. Pneumonia is caused by Streptococcus pneumoniae and Haemophilus influenzae. Common cold is caused by rhinoviruses. Malaria is caused by Plasmodium. Amoebiasis is caused by Entamoeba histolytica. Ascariasis is caused by Ascaris. Filariasis is caused by Wuchereria. Ringworm is caused by fungi such as Microsporum, Trichophyton and Epidermophyton.
Innate Immunity
Innate immunity is present at birth and provides non-specific defence.
It has four barriers:
- Physical barriers: Skin and mucus coating.
- Physiological barriers: Stomach acid, saliva and tears.
- Cellular barriers: Neutrophils, monocytes, natural killer cells and macrophages.
- Cytokine barriers: Interferons secreted by virus-infected cells.
Acquired Immunity
Acquired immunity is pathogen-specific and memory-based.
The first encounter with a pathogen produces a primary response of low intensity. Later exposure to the same pathogen produces a stronger secondary or anamnestic response.
B-lymphocytes produce antibodies. T-lymphocytes mediate cell-mediated immunity and help B-cells produce antibodies.
Vaccination and Immunisation
Vaccination is based on the memory of the immune system.
A vaccine contains antigenic proteins or weakened/inactivated pathogens. It stimulates the body to produce antibodies and memory B-cells and T-cells. During later infection, the immune system recognises the pathogen quickly and produces a strong response.
Hepatitis B vaccine is produced from yeast using recombinant DNA technology.
Allergies and Autoimmunity
Allergy is an exaggerated immune response to environmental antigens called allergens.
Common allergens include dust mites, pollen and animal dander. Allergy symptoms include sneezing, watery eyes, running nose and breathing difficulty. IgE antibodies and chemicals such as histamine and serotonin are involved.
Autoimmunity occurs when the body attacks its own cells. Rheumatoid arthritis is an example of an autoimmune disease.
Cancer Detection and Treatment
Cancer detection is based on biopsy, histopathology, blood tests, bone marrow tests, radiography, CT, MRI and molecular methods.
Cancer treatment includes surgery, radiotherapy, chemotherapy and immunotherapy. Biological response modifiers such as alpha-interferon activate the immune system and help destroy tumour cells.
Human Health and Disease NCERT Solutions: Important Disease Chart
Disease charts help students revise causative agents, symptoms and transmission quickly. These facts are useful for one-mark and short-answer questions.
| Disease |
Causative Agent |
Transmission |
| Typhoid |
Salmonella typhi |
Contaminated food and water |
| Pneumonia |
Streptococcus pneumoniae, Haemophilus influenzae |
Droplets and shared utensils |
| Common cold |
Rhinoviruses |
Droplets and contaminated objects |
| Malaria |
Plasmodium |
Female Anopheles mosquito |
| Amoebiasis |
Entamoeba histolytica |
Contaminated food and water |
| Ascariasis |
Ascaris |
Contaminated food, water and soil |
| Filariasis |
Wuchereria |
Female mosquito bite |
| Ringworm |
Microsporum, Trichophyton, Epidermophyton |
Soil or infected belongings |
Class 12 Biology Chapter 7 NCERT Solutions: Immunity Table
Immunity questions are easier when students revise type, cell and example together. This table covers the main NCERT points.
| Type |
Main Feature |
Example |
| Innate immunity |
Present from birth |
Skin barrier |
| Acquired immunity |
Pathogen-specific memory |
Vaccine response |
| Humoral immunity |
Antibody-mediated |
B-cell antibodies |
| Cell-mediated immunity |
T-cell mediated |
Graft rejection |
| Active immunity |
Host produces antibodies |
Vaccination |
| Passive immunity |
Ready-made antibodies |
Colostrum IgA |
Human Health and Disease Class 12 Questions and Answers: AIDS Prevention
AIDS prevention depends on awareness, safe practices and social support. HIV-positive people need care and dignity.
Important AIDS prevention measures are:
- Use only screened blood for transfusion.
- Use disposable needles and syringes.
- Avoid sharing needles.
- Practise safe sex.
- Promote regular HIV testing in high-risk groups.
- Prevent drug abuse.
- Educate people through NACO, NGOs and public health programmes.
- Support HIV-infected people instead of isolating them.
HIV does not spread through normal touch or social contact.
Useful Links for Class 12 Biology