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Health: The Ultimate Treasure

NCERT Class 8 · Science Based on NCERT Class 8 Science textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explores the true meaning of health as defined by WHO — a state of complete physical, mental, and social well-being, not merely the absence of disease. It explains the causes, types, and prevention of both communicable and non-communicable diseases, emphasizing the role of lifestyle, environment, immunity, and vaccines. The one big idea a student must walk away with is that health is a treasure we must actively protect through healthy habits, cleanliness, vaccination, and wise use of medicines like antibiotics.
Key Concepts (16)
Health
A state of complete physical, mental, and social well-being, and not merely the absence of disease.
e.g. A student who eats well, exercises, has friends, and feels happy is truly healthy, even if they never fall sick.
Disease
A condition that affects the normal working of the body or mind, caused when one or more organs or organ systems stop functioning properly.
e.g. When a person has fever and cough due to a cold, their respiratory system is not working normally.
Symptom
What a patient feels, such as pain, tiredness, or dizziness.
e.g. Feeling a headache or body ache when you have the flu is a symptom.
Sign
Something that can be seen or measured, such as fever, rash, high blood pressure, or swelling.
e.g. A doctor measuring a body temperature of 101°F with a thermometer is observing a sign of fever.
Pathogen
Disease-causing organisms such as bacteria, viruses, fungi, worms, or protozoa.
e.g. The virus that causes the common cold is a pathogen.
Communicable disease
A disease caused by pathogens that can spread from one person to another through air, water, food, direct contact, or vectors.
e.g. Chickenpox, flu, and COVID-19 are communicable diseases.
Non-communicable disease (NCD)
A disease not caused by pathogens and not spread from person to person; usually linked to lifestyle, diet, and/or environment.
e.g. Diabetes, heart disease, asthma, and cancer are non-communicable diseases.
Vector
An insect that spreads pathogens from one host to another, such as mosquitoes and houseflies.
e.g. The female Anopheles mosquito is a vector that spreads malaria.
Immunity
The natural ability of the body to fight diseases, provided by the immune system.
e.g. Some people rarely catch colds because their immune system is strong.
Vaccine
A preparation that helps the body fight certain diseases by training the immune system to recognise and attack harmful germs, providing acquired immunity.
e.g. The polio vaccine given to babies protects them from polio infection.
Acquired immunity
Protection developed after exposure to a pathogen or a vaccine.
e.g. After getting a tetanus shot, the body learns to fight tetanus bacteria.
Antibiotic
A medicine that kills bacteria or stops their growth; effective only against bacterial infections, not viruses or protozoa.
e.g. Penicillin is an antibiotic used to treat bacterial infections like strep throat.
Antibiotic resistance
A phenomenon where bacteria that were earlier killed by a given antibiotic survive and multiply despite treatment with that antibiotic.
e.g. Taking antibiotics without a prescription or not completing the full course can lead to antibiotic resistance.
Deficiency disease
A non-communicable disease caused by a lack of specific nutrients in the diet.
e.g. Scurvy is caused by a lack of Vitamin C, and goitre is caused by iodine deficiency.
Chronic disease
A disease that persists for a long time, usually more than 3 months.
e.g. Diabetes and asthma are chronic diseases that require ongoing management.
Parasite
An organism that lives in or on another living being and feeds on its nutrients.
e.g. Roundworms that live in the human intestine and cause ascariasis are parasites.
How It Works
Transmission of communicable diseases
  1. Step 1: A pathogen (e.g., virus, bacteria) enters the body of a healthy person through air, contaminated food/water, direct contact, or a vector bite.
  2. Step 2: The pathogen multiplies inside the body and causes infection.
  3. Step 3: The infected person may show symptoms like fever, cough, or rash.
  4. Step 4: The pathogen can spread to other healthy people through coughing/sneezing, sharing items, or via vectors like mosquitoes.
💡 Students often forget that vectors like mosquitoes are not the disease themselves — they only carry and spread the pathogen.
How vaccines work
  1. Step 1: A vaccine containing a weakened, dead, or harmless part of a pathogen is introduced into the body.
  2. Step 2: The immune system recognises the harmless germ as foreign and produces antibodies against it.
  3. Step 3: The immune system 'remembers' the pathogen.
  4. Step 4: If the real pathogen enters the body later, the immune system quickly attacks and destroys it, preventing disease.
💡 Vaccines are preventive, not curative — they do not treat an existing disease, they prevent it from happening.
Development of antibiotic resistance
  1. Step 1: A person takes antibiotics unnecessarily or does not complete the full course.
  2. Step 2: Some bacteria survive because they have a natural resistance or develop it through mutation.
  3. Step 3: These resistant bacteria multiply and become the dominant population.
  4. Step 4: Resistant bacteria can spread to other people through contact, food, or the environment.
  5. Step 5: The antibiotic becomes ineffective against these bacteria, making infections harder to treat.
💡 Antibiotics do not work against viruses — taking them for a cold or flu contributes to antibiotic resistance.
Edward Jenner's discovery of the smallpox vaccine
  1. Step 1: Jenner observed that milkmaids who had cowpox did not catch smallpox.
  2. Step 2: He hypothesised that the pus from cowpox blisters protected people from smallpox.
  3. Step 3: He tested this by injecting cowpox sap into a boy, who later showed no illness when exposed to smallpox.
  4. Step 4: Mass vaccination eventually helped eradicate smallpox worldwide.
💡 This was the first vaccine ever discovered, and it led to the global eradication of smallpox by 1979.
Exam Traps — Don't Make These Mistakes
⚠ Confusing 'symptom' and 'sign'
✗ Fever is a symptom of infection.
→ Fever can be measured with a thermometer, so it is a sign, not a symptom. A symptom is what the patient feels, like pain or tiredness.
✓ Fever is a sign of infection, while body ache is a symptom.
⚠ Thinking antibiotics work against all infections
✗ Antibiotics can cure the flu and common cold.
→ Antibiotics work only against bacterial infections, not viral infections like flu or cold.
✓ Antibiotics are effective only against bacterial infections; they do not work against viruses.
⚠ Calling all diseases 'infectious'
✗ Diabetes is an infectious disease because it spreads from person to person.
→ Diabetes is a non-communicable disease caused by lifestyle, diet, and hormonal imbalances — it does not spread from person to person.
✓ Diabetes is a non-communicable disease caused by unhealthy eating, lack of exercise, and hormonal imbalances.
⚠ Misunderstanding 'vaccine' as a cure
✗ A vaccine cures a disease after you get it.
→ Vaccines are preventive, not curative. They train the immune system to fight a pathogen before infection occurs.
✓ A vaccine prevents disease by building immunity before exposure; it does not cure an existing illness.
⚠ Confusing 'vector' with 'pathogen'
✗ The mosquito is the pathogen that causes malaria.
→ The mosquito is a vector that carries and transmits the pathogen (Plasmodium protozoa), but the mosquito itself is not the disease-causing organism.
✓ The mosquito is a vector that transmits the malaria-causing protozoan, not the pathogen itself.
Compare & Contrast
Cause and spread
Communicable disease
Non-communicable disease
Communicable diseases are caused by pathogens and spread from person to person; non-communicable diseases are caused by lifestyle, diet, or environment and do not spread.
How they are detected
Symptom
Sign
A symptom is what the patient feels (e.g., pain, tiredness); a sign is what can be seen or measured (e.g., fever, rash, high blood pressure).
Purpose and use
Antibiotic
Vaccine
An antibiotic kills bacteria and treats an existing bacterial infection; a vaccine prevents a disease by training the immune system before infection occurs.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 Very Short Answer (1 mark), 1 Short Answer (3 marks), 1 Long Answer (5 marks) — total approximately 11 marks
Most asked: Definition of health (WHO definition) · Difference between communicable and non-communicable diseases · Examples of diseases spread through air, water, and vectors · Role of vaccines and immunity · Antibiotic resistance and its causes
Don't skip: Differentiate between communicable and non-communicable diseases with examples (3-5 marks); Explain how vaccines work and why they are important (3 marks); List preventive measures for diseases spread through air, water, and vectors (5 marks)
One-Line Revision (read aloud before the exam)
  1. Health is a state of complete physical, mental, and social well-being, not just the absence of disease.
  2. A disease is a condition that affects the normal working of the body or mind.
  3. Symptoms are what a patient feels (pain, tiredness); signs are what can be seen or measured (fever, rash).
  4. Communicable diseases are caused by pathogens and spread from person to person.
  5. Non-communicable diseases are caused by lifestyle, diet, or environment and do not spread.
  6. Pathogens include bacteria, viruses, fungi, worms, and protozoa.
  7. Vectors like mosquitoes and houseflies spread pathogens but are not the disease themselves.
  8. Immunity is the body's natural ability to fight diseases.
  9. Vaccines provide acquired immunity by training the immune system to recognise and attack germs.
  10. Antibiotics kill bacteria and work only against bacterial infections, not viruses.
  11. Antibiotic resistance occurs when bacteria survive and multiply despite treatment with an antibiotic.
  12. Prevention is better than cure — handwashing, clean water, vaccination, and healthy habits reduce disease.
  13. Diabetes, heart disease, and asthma are common non-communicable diseases in India.
  14. Deficiency diseases like scurvy and goitre are caused by lack of specific nutrients.
  15. Edward Jenner discovered the first vaccine for smallpox using cowpox pus.
  16. India is one of the world's largest vaccine producers.

MCQs — 10 Questions with Answers

Q1. Which of the following is NOT a component of health according to WHO?

  • A. Physical well-being
  • B. Mental well-being
  • C. Social well-being
  • D. Absence of all exercise ✓

Answer: D — WHO defines health as complete physical, mental, and social well-being; exercise is beneficial, but absence of exercise is not a component of health definition.

Q2. What is the causal agent of chickenpox?

  • A. Bacteria
  • B. Virus ✓
  • C. Fungus
  • D. Protozoa

Answer: B — Chickenpox is caused by a virus that affects the respiratory tract and skin, causing fever, itchy rashes, and blisters.

Q3. Which of the following is a non-communicable disease?

  • A. Influenza
  • B. Typhoid
  • C. Diabetes ✓
  • D. Measles

Answer: C — Diabetes is a non-communicable disease caused by lifestyle and dietary factors, not by pathogens, and does not spread from person to person.

Q4. What is the role of vectors in disease transmission?

  • A. They cure diseases
  • B. They carry and transmit pathogens from infected to healthy persons ✓
  • C. They prevent disease spread
  • D. They strengthen the immune system

Answer: B — Vectors like mosquitoes and houseflies carry and transmit disease-causing pathogens from infected persons to healthy persons.

Q5. A student feels pain in his arm after falling. This pain is a:

  • A. Sign
  • B. Symptom ✓
  • C. Pathogen
  • D. Vector

Answer: B — A symptom is something a person feels, such as pain; a sign is something that can be measured or observed, like swelling.

Q6. During monsoon in India, cases of dengue increase rapidly. Which of the following explains this?

  • A. Increased rainfall directly causes dengue virus
  • B. Mosquitoes breed in stagnant water formed during monsoon, acting as vectors for dengue ✓
  • C. Dengue bacteria become more active in rainy season
  • D. People eat more contaminated food during monsoon

Answer: B — Monsoon creates stagnant water where mosquitoes breed; these mosquitoes act as vectors to transmit dengue virus from infected to healthy persons.

Q7. A person with fast food habits and sedentary lifestyle is at higher risk of which disease?

  • A. Chickenpox
  • B. Tuberculosis
  • C. Type 2 Diabetes ✓
  • D. Measles

Answer: C — Type 2 Diabetes is a non-communicable disease directly linked to poor lifestyle habits like eating processed food high in sugar and oil, plus lack of exercise.

Q8. According to Ayurveda, which practice helps maintain balance of body, mind, and surroundings?

  • A. Eating only fast food
  • B. Following dinacharya (daily routine) and practicing yoga ✓
  • C. Spending maximum time on digital screens
  • D. Avoiding all physical activity

Answer: B — Ayurveda teaches that following daily and seasonal routines, eating fresh wholesome food, regular exercise, yoga, and meditation help maintain complete health balance.

Q9. Which of the following statements correctly distinguishes communicable from non-communicable diseases?

  • A. Both spread from person to person equally
  • B. Communicable diseases spread through pathogens; non-communicable diseases result from lifestyle and environment ✓
  • C. Non-communicable diseases are always caused by bacteria
  • D. Communicable diseases are more common in India than non-communicable diseases

Answer: B — Communicable diseases are caused by pathogens and spread person-to-person; non-communicable diseases like diabetes and heart disease result from poor lifestyle, diet, or environment and do not spread.

Q10. Regular handwashing reduces infection by 50% because:

  • A. Water cures all diseases
  • B. Hands are the only source of pathogens
  • C. Hands touch face and mouth frequently, and washing removes pathogens before they enter the body ✓
  • D. Handwashing increases the size of the immune system

Answer: C — Hands come into contact with pathogens and frequently touch the face, mouth, and eyes; regular handwashing removes these pathogens before they can enter and infect the body.

Flashcards

Define health according to WHO.

Health is a state of complete physical, mental, and social well-being, and not merely the absence of disease.

What is the difference between a symptom and a sign?

A symptom is what a person feels (like pain or tiredness), while a sign is something that can be seen or measured (like fever or a rash).

What are pathogens?

Pathogens are disease-causing organisms such as bacteria, viruses, fungi, worms, or protozoa.

Name two non-communicable diseases.

Diabetes, heart disease, cancer, and asthma are examples of non-communicable diseases.

What is a vector in disease transmission?

A vector is an insect or organism that carries and transmits a pathogen from one person to another, such as mosquitoes for dengue.

List three ways communicable diseases spread.

Communicable diseases spread through air (coughing and sneezing), direct contact (touching), indirect contact (sharing items), contaminated food or water, and vector bites.

What is the Ayurvedic concept of maintaining health?

Ayurveda teaches that true health is a balance of body, mind, and surroundings, achieved through dinacharya (daily routine), ritucharya (seasonal routine), yoga, and meditation.

Name two preventive measures against air-borne communicable diseases.

Wearing masks, washing hands frequently, not sharing personal items, and maintaining good hygiene are preventive measures against air-borne diseases.

Why are non-communicable diseases increasing in India?

Non-communicable diseases are increasing in India due to changes in lifestyle such as eating more processed food, getting less exercise, and living longer lives.

How does a clean environment help us stay healthy?

A clean environment reduces breeding grounds for disease vectors like mosquitoes, ensures clean air and water, and decreases transmission of communicable diseases.

Important Board Questions

Define health according to WHO. [1 mark]

Health = state of complete physical, mental, and social well-being (not just absence of disease). Write the complete WHO definition.

Distinguish between communicable and non-communicable diseases with one example of each. [2 marks]

Communicable diseases spread person-to-person via pathogens (e.g., chickenpox, typhoid); non-communicable diseases do not spread and result from lifestyle/environment (e.g., diabetes, heart disease).

A person shows fever, cough, and body ache during winter. Explain how these could be symptoms of influenza and what preventive measures should be taken to avoid its spread. [3 marks]

Influenza virus infects respiratory tract → causes fever, cough, body ache. Prevention: frequent handwashing, use mask, avoid close contact, don't share personal items, maintain hygiene.

Draw and label a diagram showing four different methods of transmission of communicable diseases from an infected person to a healthy person. Explain how clean environment and personal hygiene help prevent disease spread. [5 marks]

Transmission methods: (1) Air (cough/sneeze), (2) Direct contact (touching), (3) Indirect contact (sharing items), (4) Vector (mosquito), (5) Contaminated food/water. Clean environment reduces vectors and pathogens; hygiene prevents pathogen entry into body. Draw diagram with all routes labeled clearly and explain each.

Assertion-Reason Questions for Health: The Ultimate Treasure

Q1. Assertion (A):

A person living in a clean environment with adequate nutrition but experiencing loneliness and stress may not be considered completely healthy.

Reason (R):

Health includes physical, mental, and social well-being according to WHO definition.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both assertion and reason are true, and the reason correctly explains why the assertion is valid. Mental and social dimensions are integral to the WHO definition of health, not just physical factors.

Q2. Assertion (A):

Excessive screen time in children is directly responsible for causing dry eye disease.

Reason (R):

Screen watching reduces blinking and causes eye strain, leading to dry eye disease in children.

Answer: B — Both A and R are true, but R is NOT the correct explanation of A — Both are true statements. The assertion is supported by the textbook data showing dry eye disease link to screen watching. However, the reason provided (blink reduction and eye strain) is the physiological mechanism, not the reason from the textbook passage itself. The textbook states the correlation but not this specific mechanism.

Q3. Assertion (A):

Diabetes prevalence in South-east Asia is higher than in other regions.

Reason (R):

People in South-east Asia consume more vegetables and whole grains than other populations.

Answer: C — A is true but R is false — The assertion is true (WHO data confirms higher diabetes prevalence in South-east Asia). However, the reason is false—the textbook identifies fast food and unhealthy lifestyle as causes, not vegetable consumption. The reason contradicts the actual cause mentioned in the material.

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Case-Based Questions (CBQ) for Health: The Ultimate Treasure

Case Study:

A research study in India tracked health outcomes in two communities over one year. Community A had access to safe drinking water, a clean waste management system, and regular health education on handwashing (reaching 80% of residents). Community B lacked safe water access and had minimal hygiene awareness. At the start, both communities had similar populations of 10,000 people. After one year, Community A reported only 500 cases of water-borne diseases, while Community B reported 2,500 cases. Community A also had lower rates of vector-borne diseases like dengue and malaria.

Q1. What was the primary factor contributing to the lower disease burden in Community A?

  • A. Community A had younger population demographics
  • B. Community A's access to safe water and hygiene education reduced infections ✓
  • C. Community A had better hospital facilities than Community B
  • D. Community A's residents were naturally immune to diseases

Answer: B

Q2. Based on the data, if handwashing reduces infection by 50%, approximately how many cases might have been prevented in Community B through handwashing alone?

  • A. Approximately 250 cases
  • B. Approximately 500 cases
  • C. Approximately 1,250 cases ✓
  • D. Approximately 2,000 cases

Answer: C

Q3. Why did Community A also show lower rates of vector-borne diseases like dengue and malaria?

  • A. Good waste management and clean environment reduce mosquito breeding sites ✓
  • B. Vector-borne diseases are unrelated to environmental cleanliness
  • C. Community A residents used more insecticides
  • D. Weather patterns naturally prevented mosquitos in Community A

Answer: A

Q4. Which health principle does this study BEST demonstrate?

  • A. Diseases only spread during monsoon season
  • B. Health depends on both environmental conditions and personal hygiene practices ✓
  • C. Only antibiotics can prevent infectious diseases
  • D. Population size determines disease rates

Answer: B

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