Health is one of the most valuable assets of human life. According to the World Health Organization (WHO), health is defined as a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity. Diseases can result from infections, improper lifestyle, environmental factors, or genetic causes.
In Class 12 Biology, the chapter Human Health and Disease covers various aspects of health, pathogens, immunity, common diseases, prevention methods, and the importance of vaccination and drugs. This topic is extremely important from both an academic and real-life perspective.
Human Health and Disease Class 12 Biology Notes | Detailed Explanation, MCQs & FAQs
Health and Its Importance
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Health is influenced by genetic factors, environmental conditions, nutrition, and social lifestyle.
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A healthy person can resist infections, perform tasks efficiently, and maintain emotional balance.
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Factors affecting health:
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Balanced diet
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Good hygiene
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Healthy environment
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Proper exercise and rest
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Mental stability
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Diseases
What is Disease?
A disease is a condition in which the body or a part of it does not function properly. It can be infectious (caused by pathogens) or non-infectious (caused by genetic, metabolic, or lifestyle issues).
Types of Diseases
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Infectious Diseases – Caused by pathogens such as bacteria, viruses, fungi, protozoa, and worms.
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Non-Infectious Diseases – Caused due to genetic disorders, lifestyle factors, nutritional deficiencies, or metabolic errors.
Common Infectious Diseases
Bacterial Diseases
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Typhoid – Caused by Salmonella typhi. Spread through contaminated food and water. Symptoms: fever, weakness, abdominal pain, constipation. Diagnosed by Widal test.
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Pneumonia – Caused by Streptococcus pneumoniae and Haemophilus influenzae. Spread by droplets. Symptoms: fever, chills, cough, fluid-filled alveoli.
Viral Diseases
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Common Cold – Caused by Rhinoviruses. Symptoms include nasal congestion, sore throat, cough, and tiredness.
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Dengue – Spread by Aedes aegypti mosquito carrying dengue virus. Symptoms: high fever, severe headache, joint pain, and rash.
Protozoan Diseases
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Malaria – Caused by Plasmodium species (vivax, falciparum, malariae, ovale). Spread by female Anopheles mosquito. Symptoms: fever with chills, sweating, and weakness.
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Amoebiasis – Caused by Entamoeba histolytica. Spread through contaminated water and food. Symptoms: abdominal pain, dysentery, constipation.
Helminthic Diseases
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Ascariasis – Caused by Ascaris lumbricoides (roundworm). Spread through contaminated food and water. Symptoms: abdominal pain, anemia, weakness.
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Elephantiasis – Caused by Wuchereria bancrofti or Wuchereria malayi spread by mosquitoes. Causes inflammation and enlargement of body parts, especially legs.
Fungal Infections
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Ringworm – Caused by Microsporum, Trichophyton, and Epidermophyton. Spread through contact with infected persons or soil. Causes itchy circular patches on skin.
Immunity
What is Immunity?
Immunity is the body’s ability to resist infection or disease-causing organisms.
Types of Immunity
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Innate Immunity – Present from birth, non-specific defense against pathogens. Includes:
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Physical barriers (skin, mucous)
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Physiological barriers (HCl in stomach, saliva)
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Cellular barriers (phagocytes, WBCs)
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Cytokine barriers (interferons against viruses)
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Acquired Immunity – Developed during lifetime, specific and has memory.
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Active Immunity – Produced by body after infection or vaccination.
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Passive Immunity – Provided by pre-formed antibodies, e.g., mother to child through colostrum.
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Vaccination and Immunization
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Vaccination is the introduction of a weakened or killed pathogen to stimulate the immune system.
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Immunization develops memory cells that protect the body from future infections.
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Examples: BCG (tuberculosis), OPV (polio), Hepatitis B vaccine, MMR vaccine.
Allergies
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Allergy is the hypersensitive response of the immune system to allergens (e.g., pollen, dust, animal dander).
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Symptoms: sneezing, watery eyes, breathlessness, skin irritation.
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Mediated by IgE antibodies and histamines.
Autoimmunity
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The condition in which the immune system attacks the body’s own cells.
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Examples: Rheumatoid arthritis, Multiple sclerosis, Myasthenia gravis.
Cancer
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Cancer is uncontrolled cell division that forms tumors.
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Types: benign (non-spreading) and malignant (spreading).
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Causes: carcinogens, radiation, viruses, genetic mutations.
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Treatment: Surgery, chemotherapy, radiation therapy, immunotherapy.
Drugs and Alcohol Abuse
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Adolescents are vulnerable to drug and alcohol addiction.
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Commonly abused drugs: opioids (heroin), cannabinoids, cocaine, hallucinogens.
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Alcohol affects the liver, brain, and nervous system.
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Prevention: Education, counseling, parental support, peer resistance.
Multiple Choice Questions (MCQs)
Q1. The causative organism of Typhoid is:
a) Plasmodium vivax
b) Salmonella typhi
c) Entamoeba histolytica
d) Wuchereria bancrofti
Answer: Salmonella
Q2. Which test is commonly used for the diagnosis of Typhoid?
a) ELISA test
b) Widal test
c) Mantoux test
d) Vidal test
Answer: Widal
Q3. Pneumonia is caused by:
a) Rhinovirus
b) Streptococcus pneumoniae
c) Dengue virus
d) Ascaris lumbricoides
Answer: Streptococcus
Q4. Malaria is transmitted by which mosquito?
a) Aedes aegypti
b) Anopheles
c) Culex
d) Mansonia
Answer: Anopheles
Q5. Which protozoan causes Amoebiasis?
a) Plasmodium falciparum
b) Entamoeba histolytica
c) Giardia lamblia
d) Trypanosoma gambiense
Answer: Entamoeba
Q6. Elephantiasis is caused by:
a) Ascaris
b) Wuchereria
c) Plasmodium
d) Microsporum
Answer: Wuchereria
Q7. Common cold is caused by:
a) Influenza virus
b) Rhinovirus
c) Dengue virus
d) Hepatitis virus
Answer: Rhinovirus
Q8. Dengue is spread by which mosquito?
a) Anopheles
b) Culex
c) Aedes
d) Mansonia
Answer: Aedes
Q9. Ringworm is caused by which type of pathogen?
a) Bacteria
b) Virus
c) Fungus
d) Helminth
Answer: Fungus
Q10. Which cell type provides innate immunity?
a) B-lymphocytes
b) T-lymphocytes
c) Phagocytes
d) Memory cells
Answer: Phagocytes
Q11. Which antibody is responsible for allergy?
a) IgA
b) IgE
c) IgG
d) IgM
Answer: IgE
Q12. The first vaccine developed by Edward Jenner was for:
a) Tuberculosis
b) Smallpox
c) Polio
d) Hepatitis B
Answer: Smallpox
Q13. Which of the following provides passive immunity?
a) Vaccination
b) Colostrum
c) Infection
d) Immunization
Answer: Colostrum
Q14. Which cells are called the soldiers of the body?
a) RBC
b) WBC
c) Platelets
d) Neurons
Answer: WBC
Q15. The uncontrolled cell division is called:
a) Immunity
b) Allergy
c) Cancer
d) Tumor
Answer: Cancer
Q16. The causative agent of Ascariasis is:
a) Plasmodium
b) Wuchereria
c) Ascaris
d) Trichophyton
Answer: Ascaris
Q17. Which of the following is an example of autoimmune disease?
a) Amoebiasis
b) Tuberculosis
c) Rheumatoid arthritis
d) Malaria
Answer: Arthritis
Q18. The BCG vaccine is given for prevention of:
a) Polio
b) Tuberculosis
c) Tetanus
d) Hepatitis
Answer: Tuberculosis
Q19. Which drug is derived from Papaver somniferum?
a) Cocaine
b) Morphine
c) Cannabis
d) LSD
Answer: Morphine
Q20. Which mosquito is responsible for spreading filariasis?
a) Aedes
b) Culex
c) Anopheles
d) Mansonia
Answer: Culex
Short Answer Questions
Q1. Define health according to WHO.
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 or infirmity.
Q2. What is immunity?
Answer: Immunity is the ability of the body to resist harmful effects of disease-causing microorganisms and toxins, either through innate mechanisms or acquired responses.
Q3. Name the causative organism of malaria.
Answer: Malaria is caused by protozoans belonging to the genus Plasmodium such as Plasmodium vivax, Plasmodium falciparum, Plasmodium malariae, and Plasmodium ovale.
Q4. What is allergy?
Answer: Allergy is an exaggerated immune response of the body to harmless substances like pollen, dust, or animal dander, mediated by IgE antibodies and histamines.
Q5. Mention one difference between innate and acquired immunity.
Answer: Innate immunity is non-specific and present from birth, while acquired immunity is specific, develops during life, and has memory against particular pathogens.
Q6. What is the role of BCG vaccine?
Answer: BCG (Bacillus Calmette–Guérin) vaccine is given for the prevention of tuberculosis by stimulating the immune system to produce resistance against Mycobacterium tuberculosis.
Q7. Name any two autoimmune diseases.
Answer: Two examples of autoimmune diseases are Rheumatoid arthritis and Multiple sclerosis.
Q8. What is the causative agent of Amoebiasis?
Answer: Amoebiasis is caused by the protozoan parasite Entamoeba histolytica, which spreads through contaminated food and water.
Q9. Which mosquito spreads dengue fever?
Answer: Dengue fever is spread by the bite of the Aedes aegypti mosquito carrying dengue virus.
Q10. What is the difference between benign and malignant tumors?
Answer: Benign tumors do not spread to other body parts and remain localized, while malignant tumors spread rapidly through blood or lymph and cause cancer.
Long Answer Questions
Q1. Explain the types of immunity in detail.
Answer: Immunity is of two main types – Innate immunity and Acquired immunity. Innate immunity is the natural defense present at birth. It includes physical barriers like skin and mucous, physiological barriers like HCl in the stomach, cellular barriers like phagocytes, and cytokine barriers like interferons. Acquired immunity develops during life and is specific to pathogens. It is of two types – active immunity, which develops after infection or vaccination and lasts longer, and passive immunity, which is provided by ready-made antibodies such as those from mother to child via colostrum.
Q2. Describe the life cycle of Plasmodium in humans.
Answer: When an infected female Anopheles mosquito bites a human, it injects sporozoites of Plasmodium. These sporozoites infect liver cells and multiply, later entering red blood cells (RBCs). Inside RBCs, the parasite grows and divides, causing rupture of RBCs, which leads to the release of toxins and periodic fever with chills. Gametocytes formed in human blood are taken up by another mosquito during a bite, where they undergo sexual reproduction, completing the life cycle.
Q3. Explain the causes, symptoms, and prevention of Typhoid.
Answer: Typhoid is caused by Salmonella typhi and spreads through contaminated food and water. Symptoms include prolonged fever, weakness, abdominal pain, constipation, headache, and loss of appetite. The Widal test is used for diagnosis. Prevention can be achieved by maintaining hygiene, drinking clean water, vaccination, and avoiding contaminated food.
Q4. What is cancer? Describe its causes and treatment.
Answer: Cancer is uncontrolled cell division that leads to the formation of tumors. Causes include exposure to carcinogens, radiation, genetic mutations, and certain viruses. Benign tumors remain localized, while malignant tumors spread and invade other tissues. Treatments include surgery, chemotherapy, radiation therapy, and immunotherapy. Early detection increases the chances of successful treatment.
Q5. Discuss the harmful effects of drug and alcohol abuse.
Answer: Drug and alcohol abuse severely affect physical, mental, and social health. Drugs such as opioids, cannabinoids, and hallucinogens impair brain function, cause addiction, and damage organs like the liver, lungs, and heart. Alcohol abuse leads to liver cirrhosis, brain damage, and loss of self-control. Socially, it results in poor academic performance, financial issues, and disturbed family relations. Prevention includes education, counseling, family support, and strict law enforcement.
Frequently Asked Questions (FAQs)
Q1. What is the difference between health and disease?
Answer: Health is a state of complete physical, mental, and social well-being, whereas disease is a condition in which the body or a part of it is not functioning properly due to infection, genetic defect, or lifestyle issues.
Q2. Which vaccine is given to prevent polio?
Answer: The Oral Polio Vaccine (OPV) is given to prevent polio, which provides active immunity against the poliovirus.
Q3. What are antibiotics?
Answer: Antibiotics are chemical substances produced by microorganisms that kill or inhibit the growth of certain pathogenic bacteria. For example, Penicillin discovered by Alexander Fleming.
Q4. Why is Plasmodium falciparum more dangerous than other species?
Answer: Plasmodium falciparum is considered the most dangerous species because it causes malignant malaria, which can lead to cerebral malaria, severe anemia, and even death if untreated.
Q5. What are carcinogens?
Answer: Carcinogens are substances that cause cancer by inducing uncontrolled cell division. Examples include tobacco smoke, UV radiation, asbestos, and certain viruses.
Q6. How does vaccination protect us from diseases?
Answer: Vaccination introduces a weakened or killed form of a pathogen into the body, stimulating the immune system to produce memory cells. These memory cells provide quick and effective defense if the body encounters the pathogen in the future.
Q7. What is the main cause of common cold?
Answer: The common cold is mainly caused by Rhinoviruses, which infect the nose and respiratory tract, leading to nasal congestion, sneezing, and sore throat.
Q8. Which immune cells are destroyed by HIV?
Answer: HIV specifically attacks and destroys CD4+ T-lymphocytes, weakening the immune system and making the body prone to opportunistic infections.
Q9. How can drug abuse be prevented among adolescents?
Answer: Drug abuse can be prevented through proper education, awareness programs, family support, counseling, healthy peer groups, and strict laws against drug trafficking and consumption.
Q10. What is the role of interferons?
Answer: Interferons are proteins produced by virus-infected cells that prevent the multiplication of viruses in neighboring cells, thus acting as part of innate immunity.
Conclusion
The study of Human Health and Disease provides an understanding of how diseases spread, how our immune system defends the body, and how we can prevent infections through vaccination, hygiene, and healthy habits. Awareness about drug and alcohol abuse also highlights the importance of mental and physical health for a better quality of life.
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