Class 9 Science Notes Chapter 13 (Chapter 13) – Examplar Problem (English) Book

Alright class, let's get straight into Chapter 13, "Why Do We Fall Ill?". This is a crucial chapter, not just for your exams but for understanding our own health. Pay close attention, as concepts from here often appear in various government exams.

Chapter 13: Why Do We Fall Ill? - Detailed Notes for Exam Preparation

1. Health and Its Significance

• Definition: Health is a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity (WHO definition).
• Significance:
  • Personal: Enables us to function efficiently, cope with stress, enjoy life.
  • Community: Healthy individuals contribute to a productive society. Community health depends on factors like clean environment, sanitation, availability of food and healthcare.
• Factors Affecting Health:
  • Personal Hygiene: Maintaining cleanliness.
  • Balanced Diet: Proper nutrition.
  • Clean Environment: Access to clean drinking water, sanitation, clean air.
  • Social Equality & Harmony: Reduces stress, promotes mental well-being.
  • Economic Conditions: Affects access to nutrition, housing, healthcare.

2. Distinction between 'Healthy' and 'Disease-Free'

• Disease-Free: Absence of any specific disease or discomfort. A person might be disease-free but not necessarily healthy (e.g., stressed, unfit).
• Healthy: Encompasses physical fitness, mental alertness, and social comfort. It's a broader concept than just being disease-free.

3. Disease: Meaning and Causes

• Definition: Any condition that impairs the normal functioning of the body or mind, causing discomfort, distress, or dysfunction. Literally means "disturbed ease".
• Symptoms vs. Signs:
  • Symptoms: Subjective indications of disease felt by the patient (e.g., headache, nausea).
  • Signs: Objective indications that can be observed or measured by others (e.g., fever, rash, high blood pressure).
• Types of Diseases:
  • Acute Diseases: Last for a short duration, effects are often severe initially but don't usually cause long-term damage (e.g., common cold, typhoid).
  • Chronic Diseases: Last for a long time, even a lifetime. Develop gradually and cause long-term effects on health (e.g., diabetes, tuberculosis, elephantiasis, arthritis). Chronic diseases have drastic long-term effects on health compared to acute diseases.
• Causes of Diseases:
  • Immediate Causes: The primary factors directly causing the disease (e.g., microorganisms like viruses, bacteria).
  • Contributory Causes: Factors that make an individual more susceptible to the disease (e.g., poor nutrition, genetic predisposition, lack of public services, poverty).
  • Levels of Causes:
    • First level: Pathogen (e.g., virus causing diarrhoea).
    • Second level: Lack of resistance due to malnutrition, contaminated water (why the pathogen entered).
    • Third level: Poverty, lack of public services (why there was malnutrition or contaminated water).

4. Infectious and Non-Infectious Diseases

• Infectious Diseases (Communicable Diseases):
  • Caused by external agents called pathogens (microorganisms like viruses, bacteria, fungi, protozoa, worms).
  • Can spread from an infected person to a healthy person.
  • Examples: Common cold, Influenza, Tuberculosis (TB), Cholera, Typhoid, Malaria, AIDS, Ringworm.
• Non-Infectious Diseases (Non-Communicable Diseases):
  • Not caused by infectious agents.
  • Cannot spread from person to person.
  • Causes include: Genetic factors, lifestyle factors, nutritional deficiencies, environmental factors, organ degeneration.
  • Examples: Cancer, Diabetes, High Blood Pressure (Hypertension), Arthritis, Heart diseases, Scurvy (Vitamin C deficiency), Goitre (Iodine deficiency).

5. Infectious Agents (Pathogens)

• Viruses: Cause diseases like Common Cold, Influenza, Dengue fever, AIDS (HIV), Measles, Mumps, Polio, COVID-19. (Note: Viruses live inside host cells; antibiotics don't work on them).
• Bacteria: Cause diseases like Typhoid fever (Salmonella typhi), Cholera (Vibrio cholerae), Tuberculosis (Mycobacterium tuberculosis), Anthrax, Tetanus, Diphtheria, Whooping cough. (Antibiotics are effective).
• Fungi: Cause skin infections like Ringworm, Athlete's foot.
• Protozoa: Cause diseases like Malaria (Plasmodium, spread by female Anopheles mosquito), Kala-azar (Leishmania, spread by sandfly), Amoebic dysentery (Entamoeba histolytica), Sleeping sickness (Trypanosoma, spread by tsetse fly).
• Worms (Helminths): Cause diseases like Elephantiasis or Filariasis (Filarial worms, spread by Culex mosquito), Ascariasis (Ascaris - roundworm), Tapeworm infections.

Why classify pathogens? Understanding the category helps in deciding the type of treatment (e.g., antibiotics work on bacteria but not viruses).

6. Means of Spread (Modes of Transmission)

• Air-borne: Pathogens transmitted through droplets expelled during coughing, sneezing, talking (e.g., Common cold, Pneumonia, Tuberculosis).
• Water-borne: Pathogens transmitted through contaminated drinking water (e.g., Cholera, Amoebic dysentery, Typhoid).
• Food-borne: Pathogens transmitted through contaminated food.
• Vector-borne: Diseases transmitted by animals, called vectors, that carry the pathogen from an infected person to a healthy person.
  • Mosquitoes: Female Anopheles (Malaria), Aedes (Dengue, Chikungunya), Culex (Filariasis/Elephantiasis).
  • Flies: Houseflies (Cholera, Typhoid - mechanical carriers), Sandfly (Kala-azar), Tsetse fly (Sleeping sickness).
• Physical Contact:
  • Direct skin contact (e.g., Ringworm, Scabies).
  • Contact with contaminated articles (fomites) like clothes, utensils (e.g., Ringworm).
• Sexual Contact: Diseases transmitted through sexual intercourse (Sexually Transmitted Diseases - STDs) (e.g., Syphilis, Gonorrhoea, AIDS). AIDS can also spread through blood transfusion and from infected mother to child during pregnancy or breastfeeding.

7. Organ-Specific and Tissue-Specific Manifestations

• Pathogens enter the body through different routes (nose, mouth, skin breaks, etc.) and often target specific organs or tissues.
• Entry Point Determines Target:
  • Air (via nose): Lungs (e.g., Tuberculosis bacteria).
  • Mouth (via food/water): Gut lining (e.g., Typhoid bacteria) or Liver (e.g., Hepatitis viruses).
• Spread via Blood: Some pathogens enter via one route (e.g., mosquito bite for Plasmodium) but travel via blood to target specific organs (e.g., Liver, then Red Blood Cells for Malaria; Brain for Japanese Encephalitis virus). HIV enters via sexual organs or blood but spreads to lymph nodes and damages the immune system.
• Manifestations: The signs and symptoms depend on the tissue or organ targeted.
  • Lungs targeted: Cough, breathlessness.
  • Liver targeted: Jaundice.
  • Brain targeted: Headaches, vomiting, fits, unconsciousness.
• General Effects: Besides tissue-specific effects, there are common effects like fever, inflammation (swelling, pain), and general feeling of illness, which are part of the body's immune response.

8. Principles of Treatment

• Two Strategies:
  1. Symptomatic Treatment: Reduce the effects/symptoms of the disease (e.g., medicine for fever, pain, loose motions). This provides relief but doesn't cure the underlying cause (the microbe). Bed rest is advised to conserve energy.
  2. Causal Treatment: Kill the cause of the disease (the microbe). This involves using medicines that target the specific pathogen group.
     • Antibiotics: Target bacteria by blocking essential biochemical pathways (e.g., cell wall synthesis). They don't work on viruses because viruses use the host's machinery. Examples: Penicillin.
     • Antiviral drugs: Difficult to make because viruses have few biochemical mechanisms of their own. However, some exist (e.g., drugs for HIV).
     • Antifungal drugs: Target fungal pathways.
     • Antiprotozoal drugs: Target protozoan pathways.
     • Antihelminthic drugs: Target worms.

9. Principles of Prevention

• "Prevention is better than cure." Why?
  • Disease causes suffering and body damage, which may not be fully reversible.
  • Treatment takes time and resources, and may have side effects.
  • Infected persons can act as sources of further spread.
• Two Approaches:
  1. General Ways (Preventing Exposure): Applicable to all infectious diseases.
     • For Airborne microbes: Avoid overcrowded places, cover mouth/nose when coughing/sneezing.
     • For Waterborne microbes: Ensure safe drinking water (treatment, boiling). Proper sewage disposal.
     • For Vector-borne microbes: Provide clean environment, prevent mosquito breeding (no stagnant water), use mosquito nets/repellents. Control vector populations.
     • Public Hygiene: Sanitation, garbage disposal, clean surroundings are crucial. Availability of proper, sufficient food for everyone (boosts immunity).
  2. Specific Ways (Boosting Immune System): Relates to the immune system's ability to fight off specific microbes.
     • Immune System: Body's defense mechanism. Fights microbes upon first encounter and develops 'memory' for subsequent encounters, responding faster and stronger.
     • Immunization / Vaccination: Introducing weakened or killed microbes (or their parts) into the body (vaccine). This 'fools' the immune system into developing memory against the actual pathogen without causing the disease. Provides immunity against specific diseases.
     • Examples: Vaccines for Tetanus, Diphtheria, Whooping Cough (DPT), Measles (MMR), Polio (OPV), Hepatitis B, Tuberculosis (BCG), Smallpox (eradicated due to vaccination - pioneered by Edward Jenner).

Key Terms for Exams: Health, Disease (Acute/Chronic), Pathogen, Vector, Infectious/Non-infectious, Antibiotics, Vaccination, Immunization, Epidemic, Endemic, Pandemic, Symptoms, Signs, Inflammation.

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on the chapter:

1. Which of the following statements correctly defines 'Health' according to WHO?
   a) Absence of disease
   b) Physical fitness only
   c) A state of complete physical, mental, and social well-being
   d) Ability to perform daily tasks efficiently

2. Which of these is a chronic disease?
   a) Common cold
   b) Influenza
   c) Elephantiasis
   d) Cholera

3. Antibiotics are generally effective against diseases caused by:
   a) Viruses
   b) Bacteria
   c) Protozoa
   d) Fungi

4. Malaria is caused by a ____ and spread by the vector ____.
   a) Virus, Aedes mosquito
   b) Bacterium, Housefly
   c) Protozoan (Plasmodium), Female Anopheles mosquito
   d) Worm, Culex mosquito

5. Which of the following is NOT a mode of transmission for the Human Immunodeficiency Virus (HIV)?
   a) Sexual contact
   b) Sharing meals
   c) Blood transfusion
   d) From infected mother to child during pregnancy

6. Vaccination helps prevent diseases by:
   a) Killing existing pathogens in the body
   b) Providing symptomatic relief
   c) Strengthening the body's immune system to recognize and fight specific pathogens
   d) Preventing exposure to pathogens

7. Kala-azar is caused by Leishmania, which is a type of:
   a) Bacterium
   b) Virus
   c) Fungus
   d) Protozoan

8. Which of the following is a non-infectious disease?
   a) Tuberculosis
   b) Diabetes
   c) Measles
   d) Typhoid

9. The principle of treatment that aims to reduce the severity of symptoms like fever or pain is called:
   a) Causal treatment
   b) Symptomatic treatment
   c) Preventive treatment
   d) Immunization

10. Providing a clean environment and preventing stagnation of water helps in controlling the spread of diseases transmitted by:
    a) Air
    b) Direct contact
    c) Vectors like mosquitoes
    d) Contaminated food

Answer Key:

1. c
2. c
3. b
4. c
5. b
6. c
7. d
8. b
9. b
10. c

Revise these notes thoroughly. Focus on the definitions, classifications, examples of diseases with their causative agents and modes of spread, and the principles of treatment and prevention. Good luck with your preparation!