NOTES Chapter 13: "Why Do We Fall Ill?" from Class 9 Science CBSE NCER T:

Chapter 13: "Why Do We Fall Ill?" from Class 9 Science CBSE NCER T:

1. Introduction to Health and Disease

  • Health is a state of physical, mental, and social well-being, where a person is free from illness, injury, and discomfort.
  • Disease is a condition in which the normal functioning of the body or any part of the body is disturbed. It leads to a loss of health.
  • Diseases can be caused by:
    1. Infectious agents (like bacteria, viruses, fungi).
    2. Non-infectious causes (like genetic disorders, malnutrition).

2. Types of Diseases

Diseases are mainly classified into two broad categories:

  • Infectious Diseases:

    • These diseases are caused by harmful microorganisms like bacteria, viruses, fungi, or protozoa.
    • They spread from one person to another, either directly or indirectly.
    • Examples: Malaria, Tuberculosis, Influenza, Chickenpox, etc.

  • Non-Infectious Diseases:

    • These diseases are not caused by microorganisms and cannot be spread from one person to another.
    • They are caused due to genetic factors, lifestyle choices, or environmental factors.
    • Examples: Diabetes, Heart disease, Cancer, Asthma, etc.

3. What Causes Infectious Diseases?

Infectious diseases are caused by microorganisms that enter the body and multiply, leading to symptoms of illness. These pathogens can spread through:

  • Direct Contact: Physical touch, kissing, etc.

    • Example: Common cold, flu.

  • Indirect Contact: Through contaminated objects or surfaces.

    • Example: Touching doorknobs with germs, using unclean water.

  • Airborne Transmission: Pathogens are spread through the air via droplets when an infected person coughs, sneezes, or talks.

    • Example: Tuberculosis, Influenza.

  • Vector-borne Transmission: Transmission via vectors (organisms that carry the disease-causing pathogens).

    • Example: Malaria (transmitted by mosquitoes), Dengue.

  • Water-borne Diseases: Caused by consuming contaminated water.

    • Example: Cholera, Typhoid.

4. How Do Infectious Diseases Spread?

Infectious diseases spread by:

  • Pathogens entering through different portals such as mouth, nose, skin, etc.
  • Contaminated air, food, or water can carry pathogens into the body.
  • Vectors like mosquitoes, flies, and fleas can transfer pathogens to humans.

5. Disease-Causing Microorganisms

  • Bacteria: Single-celled organisms that can multiply rapidly. Some bacteria are harmful and cause diseases by releasing toxins in the body.

    • Example: Tuberculosis, Strep throat.

  • Viruses: Extremely small infectious agents that need a host to multiply. They cause diseases by invading body cells.

    • Example: Influenza, HIV/AIDS, Chickenpox.

  • Fungi: These are organisms that can cause diseases in the skin or inside the body.

    • Example: Athlete’s foot, ringworm.

  • Protozoa: Single-celled organisms that can cause diseases in humans, especially in tropical areas.

    • Example: Malaria, Amoebic dysentery.

6. Non-Infectious Diseases

These diseases are caused by:

  • Genetic factors (inherited from parents).
  • Environmental factors (pollution, radiation).
  • Lifestyle factors (diet, exercise, smoking).

Examples of non-infectious diseases include:

  • Diabetes: Caused by problems in insulin production or its use.
  • Cancer: Abnormal and uncontrolled cell growth.
  • Asthma: A condition in which the airways in the lungs become inflamed.

7. Prevention and Control of Diseases

  • Hygiene: Maintaining personal hygiene, like washing hands regularly, bathing, and brushing teeth, helps prevent infections.
  • Vaccination: Vaccines help the body develop immunity to certain infectious diseases.
    • Example: Polio vaccine, Measles vaccine.
  • Proper Sanitation: Clean water, proper sewage systems, and good sanitation practices reduce water-borne diseases.
  • Vector Control: Using nets, insect repellents, and eliminating breeding grounds for mosquitoes can prevent diseases like malaria and dengue.
  • Balanced Diet: Eating a healthy, balanced diet boosts the immune system, helping to prevent both infectious and non-infectious diseases.

8. The Importance of Immunity

  • Immunity is the body’s ability to resist infections through defense mechanisms.
  • Types of Immunity:
    1. Innate Immunity: The natural defense mechanism present at birth (e.g., skin, mucus).
    2. Acquired Immunity: Immunity gained after exposure to a pathogen, either by infection or vaccination.
  • Active Immunity: When the body produces antibodies after infection or vaccination.
  • Passive Immunity: When antibodies are passed from one individual to another (e.g., from mother to baby through breast milk).

9. Role of Vaccination

  • Vaccines contain weakened or killed microorganisms or their components. When injected into the body, they stimulate the immune system to produce antibodies without causing disease.
  • Example: The BCG vaccine for tuberculosis, Hepatitis B vaccine, and Measles vaccine.

10. Health Care and Treatment

  • Health care involves the prevention, diagnosis, treatment, and recovery from diseases.
  • Treatment can be in the form of medications (like antibiotics for bacterial infections), surgery, or other therapies.
  • Antibiotics are used to treat bacterial infections, but they do not work against viral infections.
  • Antiviral medicines are used to treat viral infections (like HIV).

11. How to Stay Healthy?

  • Exercise regularly to keep the body fit.
  • Eat a balanced diet rich in vitamins, minerals, proteins, and fiber.
  • Avoid smoking and drinking alcohol.
  • Stay hydrated by drinking plenty of water.
  • Get enough sleep to help the body recover and function properly.

Key Takeaways

  1. Health is not just the absence of disease but also involves physical, mental, and social well-being.
  2. Diseases can be classified into infectious (caused by microorganisms) and non-infectious (caused by genetic, environmental, or lifestyle factors).
  3. Infectious diseases are spread by pathogens (bacteria, viruses, fungi, protozoa) through direct contact, airborne transmission, vectors, and contaminated food or water.
  4. Vaccination, good hygiene, proper sanitation, and vector control are important for preventing diseases.
  5. Immunity helps the body resist infections, and we can improve immunity through proper care, vaccination, and a healthy lifestyle.
  6. Health care involves diagnosis, treatment, and prevention of diseases, with different approaches for infectious and non-infectious diseases.

Important Terms

  • Pathogen: Disease-causing microorganisms like bacteria, viruses, etc.
  • Immunity: The body’s defense mechanism to fight off infections.
  • Vaccination: The process of getting vaccinated to build immunity.
  • Infectious Diseases: Diseases caused by pathogens that can be transmitted from one person to another.
  • Non-Infectious Diseases: Diseases that cannot be transmitted between individuals, like diabetes and cancer.

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