Why Do We Fall Ill? — AP Class 8 Biological Science
'Health is not just the absence of disease — it is a state of complete physical, mental, and social well-being.'
1. Health and Its Importance
What is Health?
According to the World Health Organisation (WHO): 'Health is a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.'
Factors Affecting Health
| Factor | Examples |
|---|---|
| Personal hygiene | Bathing, hand washing, clean clothes |
| Nutrition | Balanced diet with proteins, vitamins, minerals |
| Environment | Clean air, safe water, proper sanitation |
| Economic status | Ability to afford nutritious food and healthcare |
| Mental well-being | Stress management, emotional support |
| Social connections | Family support, community, friends |
'Key Point: A person may be free of disease but still not be 'healthy' if they are stressed, anxious, or socially isolated.'
2. Disease — Definition and Classification
What is a Disease?
A disease is any condition that impairs the normal functioning of the body or mind, causing physical or mental discomfort.
Classification of Diseases
| Classification | Type | Description | Examples |
|---|---|---|---|
| Duration | Acute | Sudden onset, short duration (days to weeks) | Common cold, diarrhoea, sore throat |
| Duration | Chronic | Long duration (months to years) | Tuberculosis, diabetes, arthritis, cancer |
| Cause | Infectious | Caused by pathogens — can spread from person to person | Cholera, malaria, COVID-19 |
| Cause | Non-infectious | Not caused by pathogens — cannot spread | Diabetes, cancer, heart disease, hypertension |
Acute vs Chronic — Comparison Table
| Feature | Acute Disease | Chronic Disease |
|---|---|---|
| Duration | Short (days) | Long (months/years) |
| Onset | Sudden | Gradual |
| Effect on body | Temporary weakness, then recovery | Long-term damage, persistent weakness |
| Treatment | Usually curable | Often managed, not fully cured |
| Example | Common cold, fever | Tuberculosis, diabetes |
'AP Board Focus: Understand the difference between acute and chronic — a common exam question. Chronic diseases cause MORE long-term harm than acute ones.'
3. Infectious Diseases — Caused by Pathogens
Types of Pathogens
| Pathogen | Type | Example Disease |
|---|---|---|
| Bacteria | Prokaryotic, single-celled, living | Cholera, Typhoid, Tuberculosis, Tetanus |
| Virus | Non-living outside host, nucleic acid + protein coat | Common cold, COVID-19, Polio, AIDS, Chickenpox |
| Protozoa | Eukaryotic, single-celled | Malaria, Amoebic dysentery, Giardia |
| Fungi | Eukaryotic, can be multi-cellular | Ringworm, Athlete's foot, Yeast infection |
| Helminths (Worms) | Multicellular parasites | Tapeworm, Roundworm, Hookworm |
Detailed Disease Table
| Disease | Causing Agent | Pathogen Type | Mode of Transmission | Symptoms |
|---|---|---|---|---|
| Common Cold | Rhinovirus | Virus | Airborne (sneezing/coughing) | Runny nose, sore throat, sneezing, cough |
| Cholera | Vibrio cholerae | Bacteria | Contaminated water/food | Severe diarrhoea, dehydration, vomiting |
| Typhoid | Salmonella typhi | Bacteria | Contaminated food/water | High fever, stomach pain, weakness |
| Tuberculosis (TB) | Mycobacterium tuberculosis | Bacteria | Airborne (coughing) | Persistent cough, blood in sputum, weight loss, night sweats |
| Malaria | Plasmodium | Protozoa | Mosquito bite (Anopheles — female) | Fever with chills, sweating, headache |
| Amoebic Dysentery | Entamoeba histolytica | Protozoa | Contaminated food/water | Bloody diarrhoea, stomach cramps |
| Ringworm | Trichophyton | Fungi | Skin contact, contaminated surfaces | Itchy, ring-shaped red patches on skin |
| Dengue | Dengue virus | Virus | Mosquito bite (Aedes aegypti) | High fever, severe headache, joint pain, rash |
| COVID-19 | SARS-CoV-2 | Virus | Airborne droplets | Fever, cough, loss of smell/taste, breathing difficulty |
Means of Disease Spread
| Mode | How it Spreads | Examples |
|---|---|---|
| Airborne | Sneezing, coughing, talking — droplets containing pathogens | Cold, Flu, TB, COVID-19 |
| Waterborne | Contaminated drinking water — sewage mixing with water sources | Cholera, Typhoid, Hepatitis A |
| Foodborne | Contaminated or improperly cooked food | Amoebic dysentery, Food poisoning |
| Vector-borne | Insects (mosquitoes, flies, ticks) transfer pathogens | Malaria (Anopheles), Dengue (Aedes), Plague (flea) |
| Contact | Direct physical contact (skin, sexual, blood) | Ringworm, AIDS, Conjunctivitis |
| Blood | Blood transfusion, needle sharing, mother to child | HIV/AIDS, Hepatitis B |
'Remember: A 'vector' is an organism that carries a pathogen from one host to another — it does NOT cause the disease itself. The female Anopheles mosquito is the vector for malaria.'
4. Non-Infectious Diseases
| Disease | Cause | Risk Factors | Prevention |
|---|---|---|---|
| Diabetes | Insufficient insulin production or response | Obesity, family history, poor diet | Healthy diet, exercise, weight management |
| Cancer | Uncontrolled cell division | Smoking, pollution, genetics, UV radiation | Avoid tobacco, limit alcohol, sunscreen |
| Heart disease | Blockage in arteries | High cholesterol, smoking, lack of exercise | Regular exercise, balanced diet, no smoking |
| Hypertension | High blood pressure | Salt intake, stress, obesity | Low-salt diet, stress management |
| Anaemia | Iron deficiency | Poor diet, blood loss | Iron-rich foods (spinach, jaggery, dates) |
| Goitre | Iodine deficiency | Lack of iodine in diet | Iodised salt |
5. Prevention of Diseases
General Principles of Prevention
- Hygiene: Wash hands before eating and after using the toilet
- Safe water: Drink boiled or purified water
- Proper food: Eat clean, properly cooked food — cover food to protect from flies
- Mosquito control: Use mosquito nets, repellents, remove stagnant water
- Ventilation: Keep rooms well-ventilated — airborne pathogens spread less
- Isolation: Stay home when sick to avoid infecting others
Vaccination and Immunisation
| Term | Definition |
|---|---|
| Vaccine | A preparation of weakened or dead pathogens that stimulates the body to produce antibodies |
| Vaccination | The act of administering a vaccine |
| Immunisation | The process by which the body becomes protected against a disease through vaccination |
How Vaccination Works
- Weakened/dead pathogen (vaccine) is introduced into the body
- The immune system recognises the pathogen as foreign
- Antibodies are produced to fight it
- Memory cells are created — they 'remember' the pathogen
- If the real pathogen attacks later, the immune system responds rapidly
'This is called ACTIVE IMMUNITY — the body produces its own antibodies. There is also PASSIVE IMMUNITY (antibodies given directly, e.g., mother to baby through breast milk).'
Important Vaccines in India
| Vaccine | Protects Against | Given At |
|---|---|---|
| BCG | Tuberculosis (TB) | Birth |
| Polio (OPV/IPV) | Poliomyelitis | Birth, 6, 10, 14 weeks |
| DPT | Diphtheria, Pertussis (whooping cough), Tetanus | 6, 10, 14 weeks |
| Measles | Measles | 9–12 months |
| Hepatitis B | Hepatitis B (liver infection) | Birth, 6, 10, 14 weeks |
| COVID-19 | COVID-19 | Adults and children 12+ |
'AP Board Focus: The Universal Immunisation Programme (UIP) in India provides free vaccines to all children. Pulse Polio Programme eradicated polio from India in 2014.'
6. Antibiotics
What are Antibiotics?
Antibiotics are chemical substances produced by microorganisms (bacteria, fungi) that kill or stop the growth of other microorganisms — specifically bacteria.
| Antibiotic | Source | Used For |
|---|---|---|
| Penicillin | Penicillium notatum (fungus) | Ear, throat, skin infections |
| Streptomycin | Streptomyces griseus (bacterium) | Tuberculosis |
| Tetracycline | Streptomyces species | Acne, respiratory infections, cholera |
Important Facts About Antibiotics
| Fact | Explanation |
|---|---|
| Only for bacteria | Antibiotics do NOT work on viruses (common cold, flu, COVID-19) |
| Antibiotic resistance | Overuse and misuse of antibiotics causes bacteria to evolve resistance |
| Finish the course | Always complete the full course even if you feel better — stopping early can leave resistant bacteria |
| Not painkillers | Antibiotics are NOT painkillers — they don't reduce fever directly |
'Critical Point: Antibiotic resistance is a global health crisis. Overusing antibiotics — including in livestock feed — is making bacteria 'superbugs' that no antibiotic can kill.'
7. AP Public Health Initiatives
AP State Public Health Initiatives
| Initiative | Description |
|---|---|
| YSR Aarogya Sri | Health insurance scheme — free treatment up to Rs. 5 lakh for below-poverty-line families in AP |
| 108 Ambulance Service | Emergency ambulance service — free for all AP residents |
| Village Health Clinics | Primary health centres in every gram panchayat |
| Pulse Polio in AP | Active polio vaccination drives — AP is polio-free |
| Anaemia control | Iron + Folic Acid tablets distributed in schools for adolescent girls |
| Malaria control | Distribution of mosquito nets, fogging in rural areas |
| Godavari water quality monitoring | Regular checks on drinking water quality in Godavari delta districts |
Common Public Health Challenges in AP
| Challenge | Details |
|---|---|
| Malaria in tribal areas | Visakhapatnam Agency area, Srikakulam — tribal populations at higher risk |
| Dengue outbreaks | Urban areas — Vijayawada, Visakhapatnam — during monsoon season |
| Anaemia | High prevalence among women and adolescent girls |
| Tuberculosis | AP has a robust TB control programme under National TB Elimination Programme |
| Waterborne diseases | Diarrhoea, cholera — especially in flood-prone coastal districts |
'AP Context: The 'Agency area' (tribal regions of Visakhapatnam, Vizianagaram, and Srikakulam) faces unique health challenges — limited access to healthcare, higher prevalence of malaria and malnutrition.'
8. Worked Examples
Example 1: Identify the Disease Type
Question: A patient has had a cough with blood in sputum for over 3 months, along with weight loss and night sweats. Is this acute or chronic?
Answer: Chronic — the symptoms have persisted for months and indicate Tuberculosis (TB).
Example 2: Pathogen Identification
Question: A child develops a high fever with chills every 48 hours. Which disease is suspected and what causes it?
Answer: Malaria — caused by Plasmodium (protozoan), transmitted by female Anopheles mosquito.
Example 3: Vaccination
Question: Why does a vaccine protect you from a disease for years, while a medicine only works while you take it?
Answer: A vaccine triggers the immune system to produce memory cells that 'remember' the pathogen. When the real pathogen attacks, the body responds quickly. Medicines kill pathogens directly but do not create memory.
Example 4: Antibiotics
Question: Why won't antibiotics help a patient with the common cold?
Answer: The common cold is caused by a virus. Antibiotics work ONLY against bacteria, not viruses.
Example 5: Mode of Spread
Question: A village reports many cases of cholera after flooding. What is the most likely mode of spread?
Answer: Waterborne — flood water mixes with sewage, contaminating drinking water sources with Vibrio cholerae bacteria.
9. Common Mistakes
| Mistake | Fix |
|---|---|
| Calling all diseases infectious | Many diseases are non-infectious (diabetes, cancer, heart disease) — they do not spread |
| Thinking antibiotics cure everything | Antibiotics only work against BACTERIA — not viruses, fungi, or protozoa |
| Skipping the full antibiotic course | Stopping antibiotics early creates RESISTANT bacteria — always finish the course |
| Confusing vector and pathogen | Vector = mosquito that CARRIES the pathogen; Pathogen = Plasmodium (the actual disease-causing agent) |
| Saying 'vaccine cures disease' | Vaccines PREVENT disease by building immunity — they do not cure an existing infection |
| Believing a healthy person cannot get sick | Anyone can get infected regardless of health — though healthier people recover faster |
| Not knowing AP health initiatives | Remember Aarogya Sri, 108 ambulance, village health clinics for AP-specific questions |
10. Exam Focus (AP Board BSEAP Class 8)
| Topic | Marks | Question Type |
|---|---|---|
| Health — definition and factors | 2 | Short answer |
| Acute vs Chronic disease | 2 | Table / Short answer |
| Infectious vs Non-infectious | 2 | Classification table |
| Pathogen types and diseases (table) | 4 | Table completion |
| Means of disease spread | 2–4 | Short answer / List |
| Vaccination and immunisation | 2–4 | Short answer / Explanation |
| Antibiotics — uses and limitations | 2 | Short answer |
| AP public health initiatives | 2–4 | Short answer (AP-specific) |
| Specific diseases — Malaria, TB, Cholera | 2 | Very short / Short answer |
11. Quick Self-Test
Q1. What is the WHO definition of health? A1. A state of complete physical, mental, and social well-being — not just absence of disease.
Q2. What is the difference between acute and chronic disease? A2. Acute = short duration (days), sudden onset. Chronic = long duration (months/years), gradual onset.
Q3. Name one bacterial and one viral disease. A3. Bacterial: Cholera / Typhoid / TB. Viral: Common cold / COVID-19 / Polio.
Q4. How does malaria spread? A4. Through the bite of an infected female Anopheles mosquito.
Q5. What is a vaccine? A5. A preparation of weakened or dead pathogens that stimulates the body to produce antibodies.
Q6. Do antibiotics work on viruses? A6. No — antibiotics work only against bacteria.
Q7. What is antibiotic resistance? A7. When bacteria evolve to survive antibiotics — caused by overuse and misuse of antibiotics.
Q8. Name one AP public health initiative. A8. YSR Aarogya Sri (health insurance for BPL families) or 108 Ambulance Service.
Q9. What is the difference between a vector and a pathogen? A9. Vector = organism that TRANSMITS the disease (e.g., mosquito). Pathogen = organism that CAUSES the disease (e.g., Plasmodium).
Q10. Why is polio considered eradicated from India? A10. Due to the Pulse Polio vaccination programme that vaccinated all children under 5 years — no polio case has been reported in India since 2011.
12. Summary
- Health = physical + mental + social well-being
- Acute diseases = short duration (cold, diarrhoea). Chronic = long duration (TB, diabetes)
- Infectious diseases: Caused by pathogens — bacteria, virus, protozoa, fungi, helminths
- Non-infectious: Diabetes, cancer, heart disease — do not spread
- Transmission: Airborne, waterborne, foodborne, vector-borne, contact, blood
- Prevention: Hygiene, safe water, mosquito control, isolation, vaccination
- Vaccines build immunity by creating memory cells
- Antibiotics kill bacteria — do NOT work on viruses. Overuse causes resistance
- AP Public Health: Aarogya Sri, 108 ambulance, village clinics, malaria/dengue control, anaemia programme
'The best medicine is prevention. A healthy diet, clean environment, regular exercise, and timely vaccination are your strongest defence against disease.'
