NCERT Solutions for Class 9 Science Chapter 13 Why Do We Fall Ill

Short Note:

• Health: Defined by the WHO as a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.

• Significance of Health: Good health allows an individual to perform their daily tasks efficiently and interact properly with their community.

• Personal and Community Issues: Human beings live in societies. Therefore, public cleanliness, good economic conditions, social equality, and harmony are essential for individual health.

• Healthy vs. Disease-Free: Being disease-free means lacking a specific sickness, but it does not automatically mean a person is healthy (which includes mental and social well-being).

Short Note:

• Acute Diseases: Diseases that last for only a very short period of time and do not cause long-term bad effects on general health (e.g., common cold, cough).

• Chronic Diseases: Diseases that last for a long time, even as much as a lifetime, causing drastic long-term effects on human health (e.g., elephantiasis, tuberculosis, diabetes).

• Causes of Diseases: Diseases can be caused by immediate factors (like pathogens) or contributory causes (like poor nourishment, genetic abnormalities, or lack of public services).

• Infectious vs. Non-Infectious:

  - Infectious: Caused by microbes/pathogens and can spread from one person to another (e.g., malaria, COVID-19).

  - Non-Infectious: Not caused by infectious agents and do not spread (e.g., cancer, high blood pressure).

Short Note:

• Infectious Agents:

  - Viruses: Cause common cold, influenza, dengue fever, AIDS.

  - Bacteria: Cause typhoid, cholera, tuberculosis, anthrax.

  - Fungi: Cause many common skin infections (e.g., ringworm).

  - Protozoa: Cause malaria, kala-azar.

  - Worms: Cause intestinal infections, elephantiasis.

• Means of Spread (Transmission):

  - Air-borne: Droplets spread by coughing/sneezing (e.g., TB, pneumonia).

  - Water-borne: Contaminated water containing excreta (e.g., cholera).

  - Vectors: Animals or insects that carry pathogens (e.g., mosquitoes carrying malaria).

  - Physical Contact: Direct contact or sexual contact (e.g., syphilis, AIDS).

Short Note:

• Principles of Treatment: Involves two steps:

  1. Reduce the effects: Using medicines to bring down fever, pain, or loose motions (symptom-directed treatment) and taking bed rest.

  2. Kill the cause: Using specific drugs like antibiotics (for bacteria) or antivirals to kill the infectious microbes.

• Principles of Prevention: Prevention is always better than cure because curing a disease takes time, causes suffering, and allows the patient to become a source of further infection.

  - General ways: Preventing exposure (e.g., clean air, safe drinking water, proper sanitation) and ensuring a properly functioning immune system through a balanced diet.

  - Specific ways (Immunization): Using vaccines to introduce weakened pathogens into the body, memory cells are created by the immune system to fight off future severe infections (e.g., vaccines for polio, tetanus, measles).