CBSE Class 12 Biology (2026–27)
Chapter 7: Human Health and Disease
20 Important Questions and Answers
The chapter covers common human diseases, immunity, AIDS, cancer, and drug/alcohol abuse. These topics remain part of the CBSE Class 12 Biology syllabus for 2026–27.
1. What is health? Mention the factors affecting health.
Answer:
According to the World Health Organization (WHO), health is a state of complete physical, mental, and social well-being and not merely the absence of disease. Good health enables a person to perform daily activities efficiently and maintain a better quality of life. Several factors influence health, including balanced nutrition, personal hygiene, clean surroundings, regular exercise, adequate rest, and emotional stability. Genetic disorders and infectious diseases can also affect health. Social factors such as education, economic conditions, and access to healthcare services play important roles. Therefore, maintaining health requires a combination of healthy lifestyle choices, disease prevention measures, and a supportive environment.
2. Explain amoebiasis and its mode of transmission.
Answer:
Amoebiasis is a disease caused by the protozoan parasite Entamoeba histolytica. It commonly infects the large intestine of humans. The disease spreads through contaminated food and water containing cysts of the parasite. Houseflies act as mechanical carriers and transfer cysts from infected fecal matter to food items. Symptoms include constipation, abdominal pain, cramps, and stools containing mucus and blood. Poor sanitation and unhygienic conditions increase the risk of infection. Prevention involves maintaining personal hygiene, drinking clean water, proper disposal of waste, and protecting food from contamination. Early diagnosis and treatment help prevent complications and reduce the spread of the disease.
3. Write a short note on malaria.
Answer:
Malaria is a serious mosquito-borne disease caused by protozoan parasites of the genus Plasmodium, especially P. vivax and P. falciparum. The disease is transmitted through the bite of an infected female Anopheles mosquito. After entering the human body, the parasite multiplies in liver cells and red blood cells. Symptoms include recurring fever, chills, headache, sweating, and anemia. The rupture of infected red blood cells releases toxins that cause fever attacks. Malaria can be prevented by controlling mosquito breeding sites, using mosquito nets, applying repellents, and maintaining cleanliness in surroundings. Timely treatment is essential to prevent severe complications.
4. What is innate immunity? Explain its barriers.
Answer:
Innate immunity is the natural, non-specific defense mechanism present in the body from birth. It provides immediate protection against pathogens without prior exposure. Innate immunity consists of four main barriers. Physical barriers include skin and mucous membranes that prevent pathogen entry. Physiological barriers involve secretions such as saliva, tears, and stomach acid that destroy microbes. Cellular barriers consist of white blood cells like neutrophils and macrophages that engulf pathogens. Cytokine barriers include proteins such as interferons that inhibit viral multiplication. Together, these barriers form the first line of defense and protect the body from various infections before specific immune responses are activated.
5. Differentiate between active and passive immunity.
Answer:
Active immunity develops when a person’s immune system produces antibodies in response to an infection or vaccination. It takes time to develop but provides long-lasting protection due to the formation of memory cells. Examples include immunity acquired after vaccination against polio or tetanus. Passive immunity occurs when ready-made antibodies are transferred from another source. It provides immediate protection but lasts for a short duration because memory cells are not formed. Examples include antibodies transferred from mother to child through colostrum and injections containing antivenom. Both types of immunity are important for disease prevention and protection against infectious agents.
6. What are antibodies? Mention their functions.
Answer:
Antibodies are specialized proteins called immunoglobulins produced by B-lymphocytes in response to foreign substances known as antigens. They are Y-shaped molecules that specifically recognize and bind to antigens. Antibodies help neutralize toxins and viruses, prevent pathogens from infecting cells, and mark microbes for destruction by immune cells. They also activate the complement system, which enhances pathogen elimination. Antibodies play a crucial role in acquired immunity by providing targeted defense against specific infections. Their presence in blood can indicate immunity to certain diseases or past exposure to pathogens. Vaccination stimulates antibody production and helps prevent infectious diseases.
7. What is vaccination? How does it protect the body?
Answer:
Vaccination is the process of administering weakened, killed, or modified pathogens, or their antigens, into the body to stimulate an immune response. Vaccines activate the immune system without causing the disease. As a result, the body produces specific antibodies and memory cells against the pathogen. If the same pathogen enters the body later, the immune system recognizes it quickly and destroys it before it can cause illness. This rapid and enhanced response is called the secondary immune response. Vaccination has successfully controlled many diseases such as polio, smallpox, and hepatitis, making it one of the most effective methods of disease prevention.
8. What are allergies? Mention their symptoms.
Answer:
Allergies are exaggerated immune responses of the body to harmless substances called allergens. Common allergens include pollen grains, dust, pet dander, certain foods, drugs, and insect stings. During an allergic reaction, the immune system releases chemicals such as histamine from mast cells. This causes symptoms like sneezing, watery eyes, skin rashes, itching, nasal congestion, and breathing difficulties. In severe cases, allergies may lead to anaphylaxis, which requires immediate medical attention. Avoiding allergens, maintaining cleanliness, and using prescribed medications can help manage allergic reactions. Allergies occur due to hypersensitivity of the immune system rather than infection by pathogens.
9. What is AIDS? Name its causative agent.
Answer:
AIDS (Acquired Immuno Deficiency Syndrome) is a serious disease that weakens the body’s immune system, making individuals vulnerable to infections and certain cancers. It is caused by the Human Immunodeficiency Virus (HIV), which primarily attacks helper T-lymphocytes. HIV enters immune cells, multiplies, and gradually destroys them, reducing the body’s ability to fight diseases. As immunity declines, the patient becomes susceptible to opportunistic infections. AIDS develops over several years after HIV infection. Although there is no complete cure, antiretroviral therapy (ART) helps control the virus and improves the quality of life of infected individuals.
10. Explain the modes of transmission of HIV.
Answer:
HIV is transmitted through the exchange of infected body fluids. Major modes of transmission include unprotected sexual contact with an infected person, transfusion of contaminated blood, sharing infected needles or syringes, and transmission from an infected mother to her child during pregnancy, childbirth, or breastfeeding. HIV is not spread through casual contact such as shaking hands, sharing food, hugging, or mosquito bites. Awareness, safe sexual practices, screening of blood before transfusion, and using sterile medical equipment are effective preventive measures. Understanding the actual modes of transmission helps reduce stigma and promotes appropriate prevention strategies against HIV infection.
11. Why is cancer called an uncontrolled growth of cells?
Answer:
Cancer is characterized by uncontrolled and abnormal cell division. Normally, cell growth and division are regulated by genes and cellular checkpoints. In cancer, mutations in genes controlling cell division lead to continuous multiplication of cells. These abnormal cells form masses called tumors. Benign tumors remain localized, whereas malignant tumors invade surrounding tissues and spread to other body parts through blood or lymph, a process known as metastasis. Cancer cells compete with normal cells for nutrients and disrupt normal organ function. Environmental factors, radiation, chemicals, tobacco use, and genetic predisposition can contribute to the development of cancer.
12. Distinguish between benign and malignant tumors.
Answer:
Benign tumors are non-cancerous growths that remain confined to their original location. They grow slowly, are usually enclosed within a membrane, and do not spread to other parts of the body. In contrast, malignant tumors are cancerous and grow rapidly. They invade nearby tissues and spread to distant organs through blood or lymphatic circulation. This spreading process is called metastasis. Malignant tumors can seriously impair normal body functions and are often life-threatening if untreated. While benign tumors are generally less harmful and easier to remove surgically, malignant tumors require extensive treatment such as surgery, chemotherapy, and radiotherapy.
13. What is metastasis?
Answer:
Metastasis is the process by which cancer cells spread from the primary tumor site to distant parts of the body. During metastasis, malignant cells detach from the original tumor and enter blood vessels or lymphatic channels. They travel to other organs, where they establish secondary tumors and continue uncontrolled growth. This process makes cancer more dangerous and difficult to treat because multiple organs may become affected. Metastasis is a characteristic feature of malignant tumors and is responsible for many cancer-related complications. Early detection and treatment of cancer can reduce the chances of metastasis and improve patient survival.
14. Mention any three methods used in cancer treatment.
Answer:
Three major methods used in cancer treatment are surgery, radiotherapy, and chemotherapy. Surgery involves the physical removal of tumors from the body and is most effective when cancer is localized. Radiotherapy uses high-energy radiation to destroy cancer cells and reduce tumor size. Chemotherapy involves the administration of anti-cancer drugs that kill rapidly dividing cells. In some cases, immunotherapy and targeted therapy are also used to enhance treatment effectiveness. The choice of treatment depends on factors such as cancer type, stage, location, and overall health of the patient. Early diagnosis greatly improves treatment outcomes and survival rates.
15. What are drugs? How do they affect the nervous system?
Answer:
Drugs are chemical substances that alter the normal functioning of the body and mind when consumed. Many addictive drugs affect the central nervous system by influencing neurotransmitter activity in the brain. They may produce feelings of pleasure, relaxation, excitement, or altered perception. Repeated use can lead to dependence, tolerance, and addiction. Drug abuse may impair memory, judgment, coordination, and decision-making abilities. Long-term use can damage vital organs and negatively affect mental health. Adolescents are particularly vulnerable due to peer pressure and curiosity. Education, awareness, and strong family support play important roles in preventing drug abuse.
16. What are opioids? Give examples.
Answer:
Opioids are narcotic drugs derived from the opium poppy plant or synthesized chemically. They act on opioid receptors present in the brain and nervous system, producing pain relief and feelings of euphoria. Common examples include morphine, heroin, codeine, and certain prescription painkillers. Although opioids are useful in medicine for managing severe pain, their misuse can lead to addiction and dependence. Excessive use may cause respiratory depression, impaired judgment, and even death in severe cases. Because of their addictive nature, opioid drugs should be used only under medical supervision and according to prescribed guidelines.
17. Explain the harmful effects of alcohol abuse.
Answer:
Alcohol abuse negatively affects both physical and mental health. Excessive alcohol consumption can damage the liver, leading to conditions such as fatty liver, hepatitis, and cirrhosis. It also impairs brain function, affecting memory, concentration, coordination, and decision-making abilities. Long-term alcohol abuse increases the risk of heart disease, digestive disorders, and certain cancers. Social consequences include poor academic performance, family conflicts, accidents, and financial problems. Alcohol dependence can develop when individuals become unable to function normally without drinking. Awareness, counseling, healthy lifestyle choices, and support from family and friends are important in preventing alcohol abuse.
18. Why are adolescents more vulnerable to drug and alcohol abuse?
Answer:
Adolescents are more vulnerable to drug and alcohol abuse because this stage of life involves curiosity, emotional changes, and a desire for social acceptance. Peer pressure often encourages experimentation with harmful substances. Stress related to studies, relationships, or family issues may also contribute. Lack of awareness about long-term consequences increases the risk of substance abuse. Adolescents may mistakenly believe that drugs improve performance or provide relief from problems. However, repeated use can lead to addiction, health complications, and behavioral changes. Proper guidance, education, positive social environments, and strong family support can help adolescents avoid substance abuse.
19. What preventive measures can be taken against infectious diseases?
Answer:
Prevention of infectious diseases requires a combination of personal and public health measures. Maintaining personal hygiene, washing hands regularly, consuming safe drinking water, and eating hygienically prepared food reduce the risk of infection. Vaccination protects against many communicable diseases. Proper sanitation and waste disposal help control disease-causing organisms and vectors. Avoiding contact with infected individuals and using protective measures during outbreaks are also important. Public awareness programs and early diagnosis contribute significantly to disease prevention. A healthy lifestyle, balanced diet, and regular exercise strengthen immunity and enhance the body’s ability to resist infections.
20. Differentiate between infectious and non-infectious diseases.
Answer:
Infectious diseases are caused by pathogens such as bacteria, viruses, fungi, protozoa, and parasites. They can spread from one individual to another through air, water, food, vectors, or direct contact. Examples include malaria, tuberculosis, and AIDS. Non-infectious diseases are not caused by pathogens and do not spread between individuals. They may result from genetic factors, lifestyle choices, nutritional deficiencies, or environmental influences. Examples include cancer, diabetes, and hypertension. Infectious diseases can often be prevented through vaccination and hygiene, whereas prevention of non-infectious diseases mainly involves healthy living, regular medical checkups, and risk factor management.