🧬 Why Do We Fall Ill – Class 9 Biology

Health

A state of complete physical

Disease

Disturbance in the normal functioning of body or mind

Healthy person

Free from infections

Acute disease

Disease lasting for a short duration (e.g.

Chronic disease

Disease lasting for a long time (e.g.

Infectious disease

Disease that spreads from one person to another (e.g.

Non-infectious disease

Disease that does not spread (e.g.

Pathogens

Disease-causing organisms like bacteria

Bacteria

Single-celled microorganisms (e.g.

Virus

Non-cellular pathogens (e.g.

Protozoa

Single-celled eukaryotic organisms (e.g.

Fungi

Cause skin infections (e.g.

Worms

Multicellular parasites (e.g.

Transmission

Mode by which diseases spread (air

Air-borne diseases

Spread through air (e.g.

Water-borne diseases

Spread through contaminated water (e.g.

Vector-borne diseases

Spread by insects (e.g.

Direct contact

Spread by touching or bodily fluids (e.g.

Carrier

Organism that carries pathogen but is not affected (e.g.

Organ-specific diseases

Diseases targeting specific organs (e.g.

Symptoms

Signs that indicate a disease (e.g.

Inflammation

Reaction of body to infection (pain

Immune system

Body’s defense system against infection

Principle of treatment

Kill the cause of disease or reduce its effects

Antibiotics

Medicines that kill bacteria (not viruses)

Antivirals

Medicines that treat viral infections

Principle of prevention

Prevent exposure or boost immunity (vaccines

Vaccination

Injecting a weak/dead microbe to build immunity

Immunization

Developing resistance to a disease by vaccination

Public hygiene

Clean environment to prevent spread of diseases

Personal hygiene

Keeping oneself clean to avoid infections

AIDS

Acquired Immune Deficiency Syndrome – caused by HIV virus

HIV

Human Immunodeficiency Virus – weakens immune system

Diabetes

Non-infectious disease related to insulin imbalance

High blood pressure

Chronic non-infectious disease

Cancer

Uncontrolled division of abnormal cells – non-infectious

Typhoid

Bacterial disease caused by Salmonella typhi

Pneumonia

Lung infection caused by bacteria/virus

Malaria

Protozoan disease caused by Plasmodium

Organism causing malaria

Plasmodium (spread by Anopheles mosquito)

Tuberculosis (TB)

Bacterial disease affecting lungs (caused by Mycobacterium tuberculosis)

Prevention of TB

BCG vaccine

Hepatitis A

Viral infection of liver – spread via water

Ringworm

Fungal skin infection

Dysentery

Bacterial infection causing diarrhoea with blood

Health vs Disease

Health is a state; disease is a condition affecting that state

Community health

Health of a group of people depending on public facilities

Socio-economic impact of disease

Loss of income

Nutrition and health

Good food strengthens immune system and health

Prevention better than cure

Easier and cheaper to prevent than to treat diseases