NCERT Solutions Class 12 Biology Chapter 7 Human Health and Disease

In Class 12 Biology Chapter 7, Human Health and Disease, students learn how the body maintains health and how different factors can lead to illness. This chapter explains common infectious and non-infectious diseases, their causes, symptoms, and methods of prevention. It also introduces the immune system, different types of immunity, and the role of vaccines in protecting the body, helping students understand how the body defends itself against harmful organisms and conditions.

To help you master these concepts, ALLEN provides high-quality NCERT Solutions that turn complicated theory into clear, logical lessons. Our expert faculty is focused on streamlining complex life cycles and pathways into step-by-step explanations that are easy to remember. These solutions are designed to help you meet the requirements of the CBSE marking scheme, ensuring you can reproduce accurate diagrams and technical terms with confidence during the exams.

1.0Download NCERT Solutions Class 12 Biology Chapter 7 Human Health and Disease : Free PDF

This chapter explains how diseases spread, how the immune system works, and how health can be protected through prevention and care. The NCERT Solutions for Class 12 Biology Chapter 7 Human Health and Disease help students revise key concepts and practise textbook questions easily. Download the free PDF now to study anytime and prepare confidently for exams.

2.0Class 12 Biology Chapter 7 Human Health and Disease : Key Concepts

The chapter focuses on understanding health, disease, and body defence mechanisms. Some of the key lessons covered in this chapter are given below:

• Concept of Health and Disease: Understanding physical, mental, and social aspects of health.
• Pathogens and Infectious Diseases: Learning about bacteria, viruses, fungi, and parasites that cause diseases.
• Non-Infectious Diseases: Studying conditions like cancer, allergies, and lifestyle-related disorders.
• Immune System: Understanding innate and acquired immunity and their roles in body defence.
• Vaccination and Immunisation: Learning how vaccines help prevent infectious diseases.
• Antibiotics and Drug Resistance: Understanding the correct use of medicines and the problem of resistance.
• Public Health Measures: Learning about sanitation, hygiene, and disease prevention at the community level.

3.0NCERT Class 12 Biology Chapter 7 Human Health and Disease : Detailed Solutions

1. What are the various public health measures which you would suggest as safeguard against infectious diseases? 

Ans: Public health measures are crucial to safeguard against the spread of infectious diseases, and maintain a healthy environment.

The major measures include:

• Clean water supply: Ensuring access to safe and potable drinking water to prevent water-borne diseases like cholera, typhoid, and amoebiasis.
• Proper sanitation and waste disposal: Effective systems for sewage treatment and garbage disposal reduce the breeding of disease-causing organisms and vectors.
• Personal hygiene and awareness: Promoting habits such as hand washing, safe food handling, and cleanliness through public education.
• Vaccination and immunisation programmes: Mass immunisation against diseases like polio, measles, tuberculosis, and hepatitis helps build community immunity.
• Vector control: Measures such as spraying insecticides, using mosquito nets, and eliminating stagnant water to control disease carriers like mosquitoes and flies.
• Isolation and quarantine: Separating infected individuals to prevent further transmission of contagious diseases.
• Health education: Creating awareness about modes of transmission, symptoms, and preventive measures through campaigns and schools.

2. In which way has the study of biology helped us to control infectious diseases? 

Ans:

• Identification of pathogens: Biology helps in identifying pathogens like bacteria, viruses, protozoa, and fungi that cause diseases.
• Understanding transmission: It explains how diseases spread through air, water, food, vectors, or direct contact. This helps in designing effective preventive strategies to control their transmission.
• Development of vaccines: Knowledge of the immune system leads to the development of vaccines that provide long-term protection.
• Discovery of medicines: Biological research has contributed to the discovery of antibiotics, antivirals, and other drugs to treat infections.
• Improvement in diagnostics: Techniques like blood tests, microscopy, and molecular methods help in early detection and control of diseases.
• Public health planning: Biological data supports epidemiology and disease surveillance, helping governments plan control programmes.

3. How does the transmission of each of the following diseases take place? 

(a) Amoebiasis 

(b) Malaria 

(c) Ascariasis 

(d) Pneumonia 

Ans:

(a) Amoebiasis: Intake of contaminated food and water containing the cysts of Entamoeba histolytica. 

(b) Malaria : Through the bite of the infected female Anopheles mosquito.

(c) Ascariasis : Consumption of food or water contaminated with the eggs of Ascaris lumbricoides.

(d) Pneumonia : Pneumonia is transmitted mainly through inhalation of respiratory droplets released into the air when an infected person coughs or sneezes.

4. What measure would you take to prevent water-borne diseases? 

Ans: Water-borne diseases spread through the consumption of contaminated water, so prevention focuses on ensuring safe water and proper hygiene.

• Use of safe drinking water: Always drink boiled, filtered, or properly treated water to kill harmful microorganisms/pathogens.
• Proper sanitation: Sewage and human waste must be safely disposed to ensure the prevention of contamination of water sources.
• Protection of water sources: Water sources like wells, tanks, and reservoirs should be covered and kept clean to avoid any entry of pollutants and pathogens.
• Personal hygiene: Thoroughly wash hands with soap before eating and after using the toilet to prevent infection.
• Safe food practices: Wash fruits and vegetables before consumption with clean water, and avoid using contaminated water for cooking.
• Community awareness: Create awareness among the community by educating people about clean water practices and hygiene to reduce the spread of diseases.

5. Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines. 

Ans: In the context of DNA vaccines, a “suitable gene” refers to a specific gene selected from a pathogen (virus, bacterium, or parasite) that codes for an antigenic protein capable of stimulating an immune response in the human body.

• This gene is chosen because the protein it produces is recognised by the immune system as foreign and can trigger the formation of antibodies and memory cells without causing the actual disease. 
• The suitable gene is then inserted into a plasmid vector and introduced into the host’s cells. 
• Once inside, the host cells express the antigenic protein, which trains the immune system to recognise and respond quickly if the real pathogen later infects the body.

6. Name the primary and secondary lymphoid organs. 

Ans: Primary Lymphoid Organs:

• Bone Marrow 
• Thymus

Secondary Lymphoid Organs

• Spleen
• LymphNodes
• Tonsils
• Peyer’s Patches
• Appendix

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 

Ans:

(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 

Ans: (a) Innate and Acquired immunity

9. Draw a well-labelled diagram of an antibody molecule. 

10. What are the various routes by which transmission of the human immunodeficiency virus takes place? 

Ans: HIV is transmitted through the exchange of infected body fluids from an infected person to a healthy person. The major routes of transmission are:

• Unprotected sexual contact: HIV can be transmitted during sexual intercourse with an infected person, especially through contact with infected semen or vaginal fluids.
• Transfusion of infected blood or blood products: Receiving HIV-contaminated blood or blood components can transmit the virus.
• Sharing of contaminated needles and syringes: Common among intravenous drug users, where infected needles or syringes are reused.
• Mother-to-child transmission: The virus can pass from an infected mother to her child during pregnancy, childbirth, or breastfeeding.
• Organ or tissue transplantation: Transplantation of infected organs or tissues can also lead to transmission (rare due to screening).

11. What is the mechanism by which the AIDS virus causes a deficiency in the immune system of the infected person? 

Ans: The AIDS virus (HIV) weakens the immune system mainly by attacking and destroying T-helper lymphocytes (CD4⁺ cells), which play a central role in coordinating immune responses.

1. Entry into the body: HIV enters the body through infected body fluids and first infects macrophages and T-helper (CD4⁺) cells by binding to the CD4 receptor on their surface.
2. Replication inside host cells: Inside the cell, the viral RNA is converted into DNA by the enzyme reverse transcriptase. This viral DNA then integrates into the host cell’s DNA and directs the cell to produce new virus particles.
3. Destruction of T-helper cells: As more viruses are produced, the infected T-helper cells are gradually damaged and destroyed, leading to a continuous decline in their number.
4. Failure of immune coordination: Since T-helper cells activate B-lymphocytes (antibody production) and cytotoxic T-cells (cell-mediated immunity), their loss disrupts both humoral and cell-mediated immune responses.

12. How is a cancerous cell different from a normal cell? 

Ans: 

13. Explain what is meant by metastasis. 

Ans: 

• Metastasis is the process by which cancer cells spread from their original (primary) tumour site to distant parts of the body, forming secondary tumours.
• During this process, cancer cells detach from the primary tumour, invade the surrounding tissues, and then enter the blood vessels or lymphatic vessels. 
• These cells are transported to other organs such as the lungs, liver, brain, or bones, where they settle, multiply, and form new tumour masses.

14. List the harmful effects caused by alcohol/drug abuse. 

Ans:

• Physical health problems: Long-term abuse can damage vital organs such as the liver (cirrhosis), brain, heart, and kidneys, and weaken the immune system.
• Mental and behavioural disorders: It can lead to depression, anxiety, memory loss, poor judgment, and aggressive behaviour, affecting decision-making and emotional stability.
• Addiction and dependence: Repeated use results in physical and psychological dependence, making it difficult for the individual to stop without medical help.
• Poor academic and work performance: Substance abuse reduces concentration, motivation, and productivity, leading to failure in studies or job-related problems.
• Social and family problems: It can cause conflicts in relationships, domestic violence, and social isolation.
• Risk of accidents and injuries: Impaired coordination and judgment increase the chances of road accidents, falls, and other injuries.
• Spread of diseases: Sharing needles and unsafe practices can lead to HIV/AIDS, hepatitis, and other infections.
• Financial problems: Continuous spending on substances can cause economic stress and debt for individuals and families.

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? 

Ans: Yes, friends can strongly influence a person to take alcohol or drugs, especially during adolescence. Peer pressure, the desire to fit in, gain acceptance, or appear mature, and curiosity can lead individuals to experiment with substances. Sometimes, misinformation or seeing others use alcohol or drugs without immediate harm can create a false sense of safety, increasing the risk of trying them.

• Develop strong self-confidence: Being clear about one’s values and goals helps in saying “no” firmly without feeling guilty or embarrassed.
• Choose friends wisely: Keeping company with peers who have healthy habits and positive attitudes reduces the chance of being pressured.
• Awareness and education: Knowing the harmful effects of alcohol and drug abuse helps in making informed decisions.
• Seek support from adults: Talking to parents, teachers, or counsellors can provide guidance and emotional support in difficult situations.
• Engage in healthy activities: Participating in sports, hobbies, and creative activities helps reduce stress and keeps the mind positively occupied.

16. Why is it that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher. 

Ans: Once a person starts using alcohol or drugs, the body and mind gradually develop dependence on these substances. This makes quitting difficult due to both physical and psychological factors.

• Physical dependence: Many drugs and alcohol affect the brain’s reward system by increasing the release of chemicals like dopamine, which produces feelings of pleasure and relaxation. Over time, the body becomes used to the substance, and stopping it leads to withdrawal symptoms such as headache, anxiety, sweating, nausea, and restlessness. To avoid these uncomfortable symptoms, the person continues using the substance.
• Psychological dependence: The person may start believing that they cannot function normally without the substance. Alcohol or drugs are often used to cope with stress, sadness, or social situations, which strengthens the emotional attachment to the habit.
• Tolerance: With repeated use, the body develops tolerance, meaning larger amounts of the substance are needed to get the same effect. This further increases dependence and makes quitting harder.
• Social and environmental influence: Continued association with friends or environments where substance use is common can reinforce the habit and make relapse more likely.

17. In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided? 

Ans:  Youngsters may be motivated to take alcohol or drugs due to a combination of social, emotional, and psychological factors. 

• The desire to fit in with friends and avoid rejection often leads to peer pressure.
• Curiosity and the urge to experiment with new experiences can also push them toward trying substances.
• Some young people use alcohol or drugs as a way to cope with stress, academic pressure, family problems, or emotional difficulties.
• Media influence and the portrayal of substance use as fashionable or “cool” can further encourage this behaviour.

How to avoid:

• Creating awareness by teaching youngsters about the harmful effects and long-term consequences of substance abuse helps them make informed choices.
• Providing strong family and social support by having open communication with parents, teachers, and counsellors provides guidance and emotional backing.
• Encouraging friendships with peers who follow healthy lifestyles reduces negative influence.
• Building the ability to say “no” firmly and handle stress through problem-solving skills helps resist peer pressure.
• Participation in sports, hobbies, and community activities keeps youngsters positively occupied and reduces the temptation to experiment.

4.0Key Features and Benefits of Class 12 Biology Chapter 7 Human Health and Disease

• Causes of diseases and immune responses are clearly explained, helping students connect symptoms with underlying processes.
• Practicing these questions strengthen the understanding of immunity types and prevention strategies.
• Regular revision improves recall of medical terms and disease-related concepts.
• Developing strong fundamentals on human health and diseases can also be beneficial in the preparation of competitive exams like NEET.