Chapter 3 — Health: The Ultimate Treasure

Chapter 3, 'Health: The Ultimate Treasure', covers the WHO definition of health (complete physical, mental, and social well-being), the difference between communicable and non-communicable diseases, how pathogens spread, how the immune system and vaccines work, and the responsible use of antibiotics.

According to the World Health Organization (WHO), health is defined as 'a state of complete physical, mental, and social well-being, and not merely the absence of disease'.

A symptom is what we feel — such as pain or tiredness. A sign is something that can be seen or measured, such as fever, rash, high blood pressure, or swelling. Both help doctors understand what might be making a person unwell.

Communicable diseases are caused by pathogens (bacteria, viruses, fungi, worms, protozoa) and can spread from one person to another — examples include typhoid, dengue, flu, chickenpox, and COVID-19. Non-communicable diseases such as cancer, diabetes, and asthma are not caused by pathogens and do not spread between people; they are linked to lifestyle, diet, and/or environment.

Pathogens are disease-causing organisms. Examples include bacteria (e.g., cause of tuberculosis, cholera, typhoid), viruses (e.g., cause of common cold, chickenpox, measles, dengue), fungi, worms (e.g., roundworms causing ascariasis), and protozoa — single-celled organisms such as those that cause malaria.

Communicable diseases spread through the air when an infected person coughs or sneezes, through direct contact (e.g., handshaking) or indirect contact (sharing personal items), through contaminated food or water, and through insect vectors such as mosquitoes and houseflies.

Immunity is the natural ability of our body to fight diseases, carried out by the immune system. Vaccines train the immune system by using dead, weakened, or harmless parts of a pathogen — or instructions to make a harmless part — so it can recognise and attack the real germ, providing acquired immunity. Vaccines are preventive, not curative; they reduce the chance of getting the disease but do not treat someone already ill.

English doctor Edward Jenner discovered the first vaccine in the late 1700s. He observed that people who had cowpox did not get smallpox, hypothesised that cowpox pus protected against smallpox, and tested this by injecting cowpox sap into a boy who later showed no illness when exposed to smallpox. Mass vaccination eventually helped eradicate smallpox worldwide by 1979.

No. Antibiotics kill bacteria by targeting parts of bacterial cells that are different from human cells. They do not work against viruses or diseases caused by protozoa. Taking antibiotics for a viral infection like cold, cough, or flu is therefore ineffective and contributes to antibiotic resistance.

Antibiotic resistance is a phenomenon where bacteria that were earlier killed by a given antibiotic survive and multiply despite treatment with that antibiotic. This happens when antibiotics are used indiscriminately — taking them when not needed or not completing the full dose. It makes common infections harder to treat and increases the risk of complications, prolonged illness, and even death. To prevent it, antibiotics should only be taken when prescribed by a doctor, in the correct dose, and for the right duration.

Non-communicable diseases (NCDs) such as diabetes, heart disease, and cancer are linked to lifestyle, diet, and environment — not pathogens. They are the most common cause of death in India. They have become more common due to changes in how people live, such as eating more processed food, getting less exercise, and living longer lives. Diseases like scurvy, anaemia, and goitre — caused by nutritional deficiencies — are also classified as non-communicable deficiency diseases.

Key preventive steps include keeping yourself and your surroundings clean, washing hands with soap and water, covering your mouth and nose when coughing or sneezing, wearing a mask in crowded places, avoiding sharing personal items like towels, keeping food and water clean, staying home when unwell, and getting vaccinated against diseases such as polio, measles, tetanus, and hepatitis.

Yes, the NCERT Class 8 Science Chapter 3 PDF is available free on cbseprepmaster.com with no sign-up or account required.