Class 12 Biology Chapter 8 Human Health and Disease Notes
8.1 Common Diseases in Humans
Human health is influenced by nutrition, environment, lifestyle and immunity. Diseases may be infectious or non-infectious.
Public Health Measures Against Infectious Diseases
Public health measures help in preventing the spread of infectious diseases at the community level.
Major Measures:
Health Education
Awareness about causes, symptoms and prevention of diseases
Isolation of Infected Persons
Prevents spread of infection
Vaccination
Provides immunity against diseases like TB, typhoid, cholera
Sanitation and Hygiene
Proper disposal of waste and sewage
Clean drinking water
Personal hygiene
Eradication of Vectors
Destruction of breeding sites of mosquitoes, flies etc.
Role of Biology in Control of Infectious Diseases
The study of biology, especially pathology, has helped us to:
Identify disease-causing organisms
Understand mode of transmission
Diagnose diseases from symptoms
Develop vaccines and medicines
Control or eradicate pathogens
Thus, biology plays a vital role in prevention and cure of diseases.
Transmission of Some Common Diseases
| Disease | Mode of Transmission |
|---|---|
| Amoebiasis | Contaminated food & water |
| Malaria | Bite of female Anopheles mosquito |
| Ascariasis | Food & water contaminated with eggs |
| Pneumonia | Droplets, sharing utensils |
Prevention of Water-Borne Diseases
Water-borne diseases can be prevented by:
Supply of clean drinking water
Proper sanitation
Health education
Immunisation
Maintaining general hygiene
DNA Vaccines (Concept)
A DNA vaccine contains a suitable gene that:
Codes for antigenic protein
Is inserted into a plasmid
Produces antigen inside host cells
Triggers immune response
8.2 Immunity
Immunity is the ability of the body to resist disease-causing organisms.
Lymphoid Organs
Primary Lymphoid Organs:
Bone marrow
Thymus
Secondary Lymphoid Organs:
Spleen
Lymph nodes
Tonsils
MALT (Mucosa Associated Lymphoid Tissue)
Types of Immunity
Innate Immunity:
Present from birth
Non-specific
Includes:
Physical barriers (skin)
Physiological barriers (lysozyme, interferon)
Acquired Immunity:
Develops after exposure to antigens
Specific
Memory present
Active vs Passive Immunity
| Active Immunity | Passive Immunity |
|---|---|
| Body produces antibodies | Antibodies transferred |
| Long-lasting | Short-lived |
| Vaccination / infection | Mother → foetus |
Structure of Antibody
Y-shaped protein
Made of two heavy and two light chains
Antigen binding sites at tips
8.3 AIDS (Acquired Immuno Deficiency Syndrome)
Cause:
Human Immunodeficiency Virus (HIV)
Modes of Transmission:
Unprotected sexual contact
Infected blood transfusion
Sharing needles
From mother to child
Mechanism of Immune Deficiency in AIDS
HIV infects helper T-cells
Uses reverse transcriptase
Gradual destruction of immune system
Body becomes vulnerable to opportunistic infections
Death occurs due to secondary infections or cancers
8.4 Cancer
Cancer is a disease of uncontrolled cell division.
Difference Between Normal and Cancer Cells:
| Normal Cell | Cancer Cell |
|---|---|
| Controlled growth | Uncontrolled growth |
| No invasion | Invasive |
| No metastasis | Shows metastasis |
Metastasis
Metastasis is the spread of cancer cells from primary site to distant organs through blood or lymph.
👉 Only malignant tumours show metastasis.
8.5 Drugs and Alcohol Abuse
Harmful Effects of Alcohol Abuse
Damage to liver (cirrhosis)
Gastric ulcers and gastritis
Heart problems
Nervous system damage
Loss of judgement and coordination
Harmful Effects of Drug Abuse
Respiratory and heart failure
Coma and death
Behavioural changes
Increased risk of AIDS & hepatitis B
Violence and criminal behaviour
Role of Friends and Peer Pressure
Friends can influence drug/alcohol intake due to:
Peer pressure
Desire to fit in
Stress or failure
Preventive Measures:
Say NO confidently
Avoid bad company
Seek counselling
Talk to parents and teachers
Medical help if needed
Why Addiction Is Hard to Quit
Psychological dependence
Physiological dependence
Increased tolerance → higher doses
Vicious cycle of abuse
Causes of Drug and Alcohol Abuse in Youth
Stress and frustration
Curiosity
Family problems
Media influence
Lack of awareness
Role of Parents:
Open communication
Monitoring activities
Being good role models
Awareness about drugs
8.6 Summary (Exam Ready ✨)
Public health prevents diseases
Immunity protects body
AIDS weakens immune system
Cancer shows uncontrolled growth
Drug abuse affects physical & mental health
Awareness and education are key
✍️ Top 10 Short Question–Answers
Q1. What is meant by health?
Answer: Health is a state of physical, mental and social well-being.
Q2. What are infectious diseases?
Answer: Diseases caused by pathogens that can spread from one person to another.
Q3. Name any one public health measure to control diseases.
Answer: Vaccination.
Q4. How is malaria transmitted?
Answer: By the bite of female Anopheles mosquito.
Q5. What is immunity?
Answer: The ability of the body to resist disease-causing organisms.
Q6. Name the primary lymphoid organs.
Answer: Bone marrow and thymus.
Q7. What is AIDS caused by?
Answer: Human Immunodeficiency Virus (HIV).
Q8. What is metastasis?
Answer: Spread of cancer cells from one organ to another.
Q9. Name one harmful effect of alcohol abuse.
Answer: Liver damage (cirrhosis).
Q10. Why is drug addiction difficult to quit?
Answer: Due to psychological and physiological dependence.
📝 Long Answer Questions
Q1. Explain public health measures for control of infectious diseases.
Answer:
Public health measures help prevent the spread of diseases at community level.
Major measures include:
Health education: Awareness about causes, symptoms and prevention
Isolation: Separation of infected persons
Vaccination: Provides immunity against diseases
Sanitation & hygiene: Clean water, waste disposal, personal hygiene
Vector control: Destruction of mosquito and fly breeding sites
Q2. Describe immunity and its types.
Answer:
Immunity is the ability of the body to fight pathogens.
Types of immunity:
Innate immunity:
Present from birth
Non-specific
Includes skin, lysozyme, interferon
Acquired immunity:
Develops after exposure
Specific
Has memory
Active immunity:
Body produces antibodies
Long-lasting
Passive immunity:
Antibodies transferred
Short-lived
Q3. Explain AIDS and its effect on immune system.
Answer:
AIDS is caused by HIV.
Transmission:
Unprotected sexual contact
Infected blood transfusion
Sharing needles
Mother to child
Effect on immunity:
HIV infects helper T-cells
Weakens immune system
Body becomes prone to infections
Death occurs due to secondary infections
📝 PYQs (Previous Year Questions)
🔹 1️⃣ Very Short Answer Questions (1 Mark)
What is health?
Name any one public health measure to control infectious diseases.
How is malaria transmitted?
Name the causative agent of AIDS.
Which lymphoid organ produces lymphocytes?
What is immunity?
Define metastasis.
Name any one water-borne disease.
What is a DNA vaccine?
Name any one harmful effect of alcohol.
🔹 2️⃣ Short Answer Questions (2–3 Marks)
Mention any two public health measures to control infectious diseases.
Differentiate between infectious and non-infectious diseases.
Write the modes of transmission of HIV.
What are primary and secondary lymphoid organs? Give examples.
Differentiate between innate and acquired immunity.
What is active immunity? How is it different from passive immunity?
Explain metastasis.
Write any two preventive measures against drug abuse.
What is cancer? Mention two characteristics of cancer cells.
Write two harmful effects of drug abuse.
🔹 3️⃣ Long Answer Questions (3–5 Marks)
Describe public health measures for prevention of infectious diseases.
Explain immunity and its types.
Describe AIDS with reference to cause, transmission and effect on immune system.
Explain cancer and metastasis.
Describe the harmful effects of alcohol and drug abuse.
Explain the role of peers and parents in prevention of drug abuse.
🔹 4️⃣ Difference-Based PYQs (Very Important)
Infectious diseases vs Non-infectious diseases
Innate immunity vs Acquired immunity
Active immunity vs Passive immunity
Normal cells vs Cancer cells
Drug abuse vs Alcohol abuse
🔹 5️⃣ Assertion–Reason / Concept-Based PYQs
Vaccination is an effective method of disease prevention. Justify.
AIDS patients die due to secondary infections. Explain.
Only malignant tumours show metastasis. Give reason.
Drug abuse can increase the risk of HIV infection. Explain.
Public awareness plays an important role in maintaining health. Explain.
🔹 6️⃣ Diagram / Flowchart Based PYQs
Draw a labelled diagram of antibody molecule.
Flowchart showing immune response.
Diagrammatic representation of HIV structure.
❓ FAQs (5)
FAQ 1. How can water-borne diseases be prevented?
By clean drinking water, sanitation, hygiene and immunisation.
FAQ 2. What is a DNA vaccine?
A vaccine containing a gene that produces antigen inside host cells.
FAQ 3. Why is AIDS called an immunodeficiency disease?
Because it weakens the immune system.
FAQ 4. Which tumours show metastasis?
Only malignant tumours.
FAQ 5. How can peer pressure lead to drug abuse?
Desire to fit in, stress and influence of friends.
| Chapter No. | Chapter Name | Visit |
|---|---|---|
| 1 | Reproduction in Organisms | Visit |
| 2 | Sexual Reproduction in Flowering Plants | Visit |
| 3 | Human Reproduction | Visit |
| 4 | Reproductive Health | Visit |
| 5 | Principles of Inheritance and Variation | Visit |
| 6 | Molecular Basis of Inheritance | Visit |
| 7 | Evolution | Visit |
| 8 | Human Health and Disease | Visit |
| 9 | Strategies for Enhancement in Food Production | Visit |
| 10 | Microbes in Human Welfare | Visit |
| 11 | Biotechnology: Principles and Processes | Visit |
| 12 | Biotechnology and its Applications | Visit |
| 13 | Organisms and Populations | Visit |
| 14 | Ecosystem | Visit |
| 15 | Biodiversity and Conservation | Visit |
| 16 | Environmental Issues | Visit |
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