Why Do We Fall Ill — Study Notes

Overview

Health is not just the absence of disease but a state of physical, mental and social well-being. Understanding why we fall ill is crucial for NSO as it connects biology with real-world disease prevention and public health. This topic typically contributes 3–5 questions in the exam, testing your grasp of disease types, causes, transmission modes, prevention strategies and the immune system basics.

You must differentiate between infectious and non-infectious diseases, recognize how pathogens spread, understand the body's defense mechanisms, and apply prevention principles. Questions often present scenarios (crowded slums, contaminated water, vaccination programs) and ask you to identify risk factors, suitable preventive measures, or disease categories. Master the distinction between immediate causes (germs) and contributing factors (poor nutrition, hygiene) — this is a common exam trap.

Key Concepts

• **Health vs Disease**: Health is complete well-being; disease is a condition with specific symptoms disrupting normal functioning. Being healthy means all body systems work efficiently and the person can perform daily activities without discomfort.

• **Immediate Cause vs Contributing Factors**: The immediate cause is the direct agent (bacteria, virus); contributing factors (malnutrition, stress, overcrowding, poverty) make a person more susceptible. Poverty and lack of resources increase disease risk by limiting access to nutrition, clean water and healthcare.

• **Infectious Diseases**: Caused by pathogens (bacteria, viruses, fungi, protozoa, worms) that invade the body. They can spread from person to person or through vectors. Examples: tuberculosis (bacteria), influenza (virus), ringworm (fungus), malaria (protozoa).

• **Non-Infectious Diseases**: Not caused by pathogens; cannot spread from person to person. Causes include genetic defects, nutritional deficiencies, lifestyle factors and environmental toxins. Examples: diabetes, cancer, heart disease, hemophilia, scurvy.

• **Modes of Transmission**: Infectious diseases spread via air (cough/sneeze droplets), water (contaminated drinking water), sexual contact, physical contact, vectors (mosquitoes, flies) and contaminated food. Recognizing transmission mode guides prevention.

• **Acute vs Chronic Diseases**: Acute diseases last short periods with severe symptoms (common cold, cholera). Chronic diseases persist for long durations, sometimes lifelong (diabetes, tuberculosis if untreated, asthma).

• **Immune System**: The body's defense network includes physical barriers (skin, mucus), white blood cells that engulf pathogens, and antibodies that neutralize specific germs. Vaccination trains the immune system by introducing weakened/killed pathogens so it remembers and fights real infections later.