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Why Do We Fall Ill? – CBSE NCERT Study Resources

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Why Do We Fall Ill?

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9th

9th - Science

Why Do We Fall Ill?

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Chapter: Why Do We Fall Ill?

Overview

This chapter explores the various factors that contribute to human illness, including the causes, types, and prevention of diseases. It emphasizes the importance of health, the difference between being healthy and disease-free, and the role of immunity and vaccination in maintaining well-being.

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

Health and Its Significance

Health is a crucial aspect of life that affects an individual's ability to function effectively. Good health depends on factors such as a balanced diet, personal hygiene, clean surroundings, and mental well-being.

Diseases and Their Causes

Diseases can be classified into two main categories:

  • Acute Diseases: Short-term illnesses that occur suddenly and last for a brief period (e.g., common cold).
  • Chronic Diseases: Long-lasting conditions that may persist for years (e.g., diabetes).

Disease: A condition that impairs normal functioning of the body, caused by pathogens, genetic disorders, or environmental factors.

Types of Diseases

Infectious Diseases

Caused by pathogens like bacteria, viruses, fungi, and parasites. Examples include malaria, tuberculosis, and dengue.

Non-Infectious Diseases

Not caused by pathogens but by factors like genetic abnormalities, malnutrition, or lifestyle choices. Examples include cancer and heart disease.

Means of Spread of Infectious Diseases

Infectious diseases can spread through:

  • Air: Via droplets from coughing or sneezing (e.g., flu).
  • Water: Contaminated water sources (e.g., cholera).
  • Vectors: Organisms like mosquitoes (e.g., malaria).
  • Direct Contact: Physical touch or sharing personal items (e.g., skin infections).

Prevention of Diseases

Preventive measures include:

  • Maintaining personal and public hygiene.
  • Vaccination to build immunity.
  • Proper sanitation and clean drinking water.
  • Healthy lifestyle choices like balanced diet and exercise.

Vaccination: The process of administering a vaccine to stimulate the immune system and provide immunity against a specific disease.

Principles of Treatment

Treatment depends on the type of disease:

  • Infectious Diseases: Antibiotics, antiviral, or antifungal medications.
  • Non-Infectious Diseases: Lifestyle changes, surgery, or long-term medication.

Immunity and Its Types

Immunity is the body's ability to resist infections. It can be:

  • Innate Immunity: Present from birth (e.g., skin barrier).
  • Acquired Immunity: Developed after exposure to pathogens (e.g., through vaccination).

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
Define health.
Answer:

Health is a state of complete physical, mental, and social well-being.

Question 2:
Name two communicable diseases.
Answer:
  • Common cold
  • Tuberculosis
Question 3:
What causes malaria?
Answer:

Malaria is caused by Plasmodium parasite.

Question 4:
How is dengue transmitted?
Answer:

Dengue spreads through Aedes mosquito bites.

Question 5:
What is immunity?
Answer:

Immunity is the body's ability to fight diseases.

Question 6:
Name a vaccine-preventable disease.
Answer:

Polio is a vaccine-preventable disease.

Question 7:
What is the role of antibiotics?
Answer:

Antibiotics kill or inhibit bacterial growth.

Question 8:
Give an example of a vector-borne disease.
Answer:

Malaria is a vector-borne disease.

Question 9:
What is HIV/AIDS?
Answer:

HIV/AIDS weakens the immune system.

Question 10:
Name a non-communicable disease.
Answer:

Diabetes is a non-communicable disease.

Question 11:
How does vaccination work?
Answer:

Vaccination boosts immunity against specific diseases.

Question 12:
What is hygiene?
Answer:

Hygiene refers to practices maintaining health.

Question 13:
Name a waterborne disease.
Answer:

Cholera is a waterborne disease.

Question 14:
What is PEM?
Answer:

PEM stands for Protein-Energy Malnutrition.

Question 15:
What is the primary cause of infectious diseases?
Answer:

The primary cause of infectious diseases is the invasion of harmful microorganisms such as bacteria, viruses, fungi, or parasites into the body.

Question 16:
Name two vector-borne diseases and their carriers.
Answer:
  • Malaria – transmitted by female Anopheles mosquito
  • Dengue – transmitted by Aedes mosquito
Question 17:
What is the role of vaccination in preventing diseases?
Answer:

Vaccination helps the body develop immunity against specific diseases by stimulating the production of antibodies without causing the actual illness.

Question 18:
Differentiate between acute and chronic diseases with an example of each.
Answer:
  • Acute diseases last for a short duration (e.g., common cold).
  • Chronic diseases persist for a long time (e.g., tuberculosis).
Question 19:
Why is public hygiene important in disease prevention?
Answer:

Public hygiene reduces the spread of pathogens by maintaining cleanliness in surroundings, water, and food, thus preventing infections.

Question 20:
What are antibiotics? Give one example.
Answer:

Antibiotics are medicines that kill or inhibit the growth of bacteria. Example: Penicillin.

Question 21:
How does HIV weaken the immune system?
Answer:

HIV attacks and destroys white blood cells (WBCs), particularly CD4 cells, weakening the body's ability to fight infections.

Question 22:
Name two water-borne diseases and their causative agents.
Answer:
  • Cholera – caused by Vibrio cholerae
  • Typhoid – caused by Salmonella typhi
Question 23:
What is the difference between symptoms and signs of a disease?
Answer:
  • Symptoms are felt by the patient (e.g., headache).
  • Signs are observed by others (e.g., fever).
Question 24:
Why are airborne diseases highly contagious?
Answer:

Airborne diseases spread easily through airborne droplets (e.g., sneezing/coughing), allowing pathogens to infect multiple people quickly.

Question 25:
What is immunity? Name its two types.
Answer:

Immunity is the body's ability to resist infections. Two types: innate immunity (present from birth) and acquired immunity (developed after exposure).

Question 26:
How does a balanced diet help in maintaining good health?
Answer:

A balanced diet provides essential nutrients, strengthens the immune system, and helps the body fight diseases effectively.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
Define health according to the WHO.
Answer:

Health, as defined by the World Health Organization (WHO), is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.

Question 2:
What are communicable diseases? Give one example.
Answer:

Communicable diseases are illnesses caused by infectious agents that can spread from one person to another or through vectors.
Example: Common cold caused by rhinovirus.

Question 3:
Name two diseases caused by bacteria.
Answer:
  • Tuberculosis (caused by Mycobacterium tuberculosis)
  • Cholera (caused by Vibrio cholerae)
Question 4:
Differentiate between acute and chronic diseases.
Answer:
  • Acute diseases: Short-term, severe symptoms (e.g., flu)
  • Chronic diseases: Long-lasting, develop slowly (e.g., diabetes)
Question 5:
Why is balanced diet important for good health?
Answer:

A balanced diet provides essential nutrients like proteins, carbohydrates, and vitamins to:
1. Maintain body functions
2. Strengthen immunity
3. Prevent deficiency diseases

Question 6:
List two vector-borne diseases and their carriers.
Answer:
  • Malaria – Spread by female Anopheles mosquito
  • Dengue – Spread by Aedes mosquito
Question 7:
How does personal hygiene help in disease prevention?
Answer:

Personal hygiene (e.g., handwashing, clean surroundings) reduces exposure to pathogens by:
1. Removing germs
2. Blocking transmission routes
3. Preventing contamination

Question 8:
What are antibiotics? Name one commonly used antibiotic.
Answer:

Antibiotics are medicines that kill or inhibit bacterial growth.
Example: Penicillin, derived from the fungus Penicillium.

Question 9:
Explain how airborne diseases spread with an example.
Answer:

Airborne diseases spread via tiny droplets containing pathogens released during coughing/sneezing.
Example: Tuberculosis bacteria (Mycobacterium) travel through air.

Question 10:
Why is community health essential for individual well-being?
Answer:

Community health ensures:
1. Clean water and sanitation
2. Disease surveillance
3. Vaccination programs
This reduces infection risks for everyone.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Explain the difference between acute and chronic diseases with examples.
Answer:

Acute diseases are short-term illnesses that occur suddenly and last for a brief period. They often resolve on their own or with minimal treatment. Example: Common cold, flu.

Chronic diseases are long-lasting conditions that develop gradually and may persist for months or years. They often require ongoing medical care. Example: Diabetes, hypertension.

Key difference: Acute diseases are temporary, while chronic diseases are prolonged and may lead to complications if untreated.

Question 2:
How does vaccination help in preventing diseases?
Answer:

Vaccination introduces a weakened or inactive form of a pathogen into the body, stimulating the immune system to produce antibodies.

  • Creates memory cells that recognize the pathogen in future infections.
  • Provides immunity without causing the actual disease.
  • Helps in herd immunity, reducing disease spread in communities.

Example: Polio vaccine prevents poliomyelitis by triggering antibody production against the poliovirus.

Question 3:
Describe two ways in which communicable diseases can spread.
Answer:

Communicable diseases spread through:

  • Direct contact: Physical touch with an infected person (e.g., skin contact in scabies).
  • Airborne transmission: Inhaling droplets from coughs/sneezes (e.g., tuberculosis, COVID-19).

Other modes include contaminated food/water (cholera) and vectors like mosquitoes (malaria). Preventive measures like hygiene and sanitation reduce transmission.

Question 4:
Why is AIDS considered a syndrome and not a disease?
Answer:

AIDS (Acquired Immunodeficiency Syndrome) is a syndrome because it is a collection of symptoms and infections caused by the HIV virus weakening the immune system.

  • It doesn’t have a single symptom but leads to multiple opportunistic infections (e.g., tuberculosis, pneumonia).
  • Unlike a disease, which has a specific cause and effect, a syndrome encompasses broader health deterioration.
Question 5:
List three general preventive measures to avoid infections.
Answer:

Three key preventive measures are:

  • Personal hygiene: Regular handwashing with soap to kill pathogens.
  • Vaccination: Immunization to build immunity against specific diseases.
  • Clean surroundings: Proper sanitation and waste disposal to prevent vector breeding (e.g., mosquitoes).

Additional measures include eating a balanced diet and avoiding close contact with infected individuals.

Question 6:
How do antibiotics work against bacterial infections but not viral infections?
Answer:

Antibiotics target specific structures or processes in bacteria, such as cell wall synthesis or protein production, to kill or inhibit their growth.

  • Viruses lack these structures and instead hijack host cells to replicate, making antibiotics ineffective.
  • Antiviral drugs are designed to block viral replication mechanisms.

Example: Penicillin works on bacterial cell walls but has no effect on viruses like the flu.

Question 7:
Describe how vectors contribute to the spread of diseases. Give two examples.
Answer:

Vectors are organisms (usually insects) that transmit pathogens from an infected host to a healthy one. They act as carriers without getting sick themselves.

  • Mosquitoes spread malaria (through Plasmodium) and dengue (through dengue virus).
  • Houseflies transmit typhoid and cholera by contaminating food with pathogens.

Prevention includes controlling vector populations and maintaining hygiene.

Question 8:
Why is immunization important in preventing diseases? Explain with an example.
Answer:

Immunization strengthens the immune system by introducing weakened or dead pathogens, triggering antibody production without causing illness. This provides long-term protection.

Example: The BCG vaccine prevents tuberculosis by preparing the body to fight Mycobacterium tuberculosis.

Benefits:
1. Reduces disease spread.
2. Eradicates deadly infections (e.g., smallpox).
3. Cost-effective compared to treatment.

Question 9:
List three symptoms of viral fever and suggest two preventive measures.
Answer:

Symptoms of viral fever:
1. High body temperature (fever).
2. Body aches and fatigue.
3. Headache and sore throat.

Preventive measures:
1. Maintain personal hygiene (e.g., frequent handwashing).
2. Avoid close contact with infected individuals.

Note: Viral fevers are self-limiting but hydration and rest aid recovery.

Question 10:
How does poor sanitation lead to waterborne diseases? Name two such diseases.
Answer:

Poor sanitation contaminates water sources with pathogens from human/animal waste. Consuming or using this polluted water causes infections.

Examples:
1. Cholera (caused by Vibrio cholerae) leads to severe dehydration.
2. Hepatitis A (viral infection) damages the liver.

Solution: Proper sewage disposal and access to clean drinking water prevent outbreaks.

Question 11:
What are antibiotics? Why are they ineffective against viral infections?
Answer:

Antibiotics are medicines that kill or inhibit bacteria by targeting their cell walls or metabolic processes.

They don’t work against viruses because:
1. Viruses lack cell structures (e.g., cell walls) that antibiotics target.
2. They replicate inside host cells, making drug action difficult.

Example: Penicillin treats bacterial pneumonia but not influenza (viral).

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the difference between acute and chronic diseases with examples. How do they impact health differently?
Answer:
Concept Overview

Acute diseases last for a short time (e.g., common cold), while chronic diseases persist longer (e.g., diabetes).

Process Explanation
  • Acute diseases show sudden symptoms but recover quickly.
  • Chronic diseases develop slowly and may last a lifetime.
Real-world Application

Our textbook shows tuberculosis as a chronic disease, requiring long-term treatment, unlike flu which resolves in days.

Question 2:
Describe how vaccination helps prevent diseases. Give one NCERT example.
Answer:
Concept Overview

Vaccination introduces weakened pathogens to trigger immunity.

Process Explanation
  • White blood cells produce antibodies against the pathogen.
  • Memory cells provide long-term protection.
Real-world Application

Our textbook mentions the polio vaccine, which eradicated polio in India by strengthening immunity.

Question 3:
What are communicable diseases? Explain with an NCERT example and a prevention method.
Answer:
Concept Overview

Diseases spread through pathogens (e.g., viruses, bacteria) are communicable.

Process Explanation
  • Transmission occurs via air, water, or vectors.
  • Example: Malaria (NCERT) spreads through mosquito bites.
Real-world Application

Using mosquito nets prevents malaria, as studied in our textbook.

Question 4:
How does poor sanitation contribute to disease spread? Link it to a disease from NCERT.
Answer:
Concept Overview

Poor sanitation breeds pathogens in contaminated water or food.

Process Explanation
  • Open defecation pollutes water sources.
  • Leads to diseases like cholera (NCERT example).
Real-world Application

Building toilets, as in Swachh Bharat, reduces cholera cases.

Question 5:
Explain the role of antibiotics in treating bacterial infections. Why are they ineffective against viruses?
Answer:
Concept Overview

Antibiotics kill or inhibit bacteria (e.g., penicillin).

Process Explanation
  • They target bacterial cell walls or metabolic processes.
  • Viruses lack these structures, making antibiotics useless.
Real-world Application

Our textbook shows antibiotics treat typhoid but not viral flu.

Question 6:
Explain the difference between infectious and non-infectious diseases with examples.
Answer:
Concept Overview

Infectious diseases spread from person to person, caused by pathogens like bacteria or viruses. Non-infectious diseases do not spread and arise from internal factors like genetics.

Process Explanation
  • Infectious: Example—Malaria (mosquito-borne).
  • Non-infectious: Example—Diabetes (lifestyle disorder).
Real-world Application

Our textbook shows how vaccination prevents infectious diseases, while balanced diets reduce non-infectious risks.

Question 7:
Describe how vaccination helps in preventing diseases.
Answer:
Concept Overview

Vaccines introduce weakened pathogens to trigger immunity without causing disease.

Process Explanation
  • Body produces antibodies.
  • Memory cells fight future infections.
Real-world Application

Our textbook cites polio eradication in India due to vaccination. Similarly, COVID-19 vaccines reduced severe illness.

Question 8:
What are vectors? Explain with an NCERT example.
Answer:
Concept Overview

Vectors are organisms transmitting pathogens without getting sick themselves.

Process Explanation
  • Example: Anopheles mosquito carries Plasmodium (malaria parasite).
Real-world Application

Our textbook highlights how using mosquito nets prevents malaria. Similarly, clean water stops Aedes (dengue vector).

Question 9:
How does poor sanitation contribute to disease spread?
Answer:
Concept Overview

Poor sanitation breeds pathogens in contaminated water or food.

Process Explanation
  • Example: Cholera spreads via dirty water.
Real-world Application

Our textbook shows Swachh Bharat reduced diarrhea cases. Proper waste disposal also prevents fly-borne diseases.

Question 10:
Explain antibiotics with their limitations.
Answer:
Concept Overview

Antibiotics kill or inhibit bacteria but not viruses.

Process Explanation
  • Example: Penicillin treats bacterial infections.
  • Limitation: Overuse causes resistance.
Real-world Application

Our textbook warns against misuse for colds (viral). Doctors now prescribe antibiotics cautiously.

Question 11:
Explain the role of vaccination in preventing diseases. Discuss how it helps in building immunity with an example.
Answer:

Vaccination is a medical process that helps the body develop immunity against specific diseases without causing the actual illness. It involves introducing a weakened or inactive form of a pathogen (like a virus or bacteria) into the body. This stimulates the immune system to produce antibodies and remember the pathogen, providing long-term protection.


Here’s how vaccination works:

  • The vaccine contains antigens that mimic the disease-causing pathogen.
  • The immune system recognizes these antigens as foreign and produces antibodies to fight them.
  • Memory cells are created, allowing the body to respond faster if exposed to the actual pathogen in the future.

Example: The polio vaccine contains an inactive polio virus. When administered, it trains the immune system to recognize and combat the virus, preventing polio infection.


Value-added point: Vaccination not only protects individuals but also contributes to herd immunity, reducing the spread of diseases in communities.

Question 12:
Explain the difference between infectious and non-infectious diseases with suitable examples. Also, discuss how the mode of transmission differs in infectious diseases.
Answer:

Infectious diseases are caused by pathogens like bacteria, viruses, fungi, or parasites and can spread from one person to another. Examples include malaria (caused by a parasite) and tuberculosis (caused by bacteria). Non-infectious diseases, on the other hand, are not caused by pathogens and do not spread. Examples include diabetes (due to insulin imbalance) and cancer (due to uncontrolled cell growth).

The mode of transmission in infectious diseases varies:

  • Airborne transmission: Pathogens spread through air (e.g., common cold via droplets).
  • Waterborne transmission: Pathogens spread through contaminated water (e.g., cholera).
  • Vector-borne transmission: Pathogens spread via organisms like mosquitoes (e.g., dengue).
  • Direct contact: Spread through touch or bodily fluids (e.g., HIV).

Understanding these differences helps in prevention and treatment strategies.

Question 13:
Explain the differences between infectious and non-infectious diseases with suitable examples. How can the spread of infectious diseases be prevented?
Answer:

Infectious diseases are caused by pathogens like bacteria, viruses, fungi, or parasites and can spread from one person to another. Examples include malaria (caused by a parasite) and tuberculosis (caused by bacteria). Non-infectious diseases, on the other hand, are not caused by pathogens and do not spread. Examples include diabetes (due to insulin deficiency) and cancer (due to uncontrolled cell growth).


To prevent the spread of infectious diseases, the following measures can be taken:

  • Personal hygiene: Washing hands regularly, covering mouth while sneezing/coughing.
  • Vaccination: Immunization against diseases like polio and measles.
  • Clean surroundings: Proper sanitation and waste disposal to avoid breeding of disease-causing organisms.
  • Vector control: Using mosquito nets and insecticides to prevent diseases like malaria.

Understanding these differences helps in adopting the right preventive measures and maintaining public health.

Question 14:
Explain the differences between infectious and non-infectious diseases with suitable examples. How can personal and community hygiene help prevent infectious diseases?
Answer:

Infectious diseases are caused by pathogens like bacteria, viruses, fungi, or parasites and can spread from one person to another. Examples include common cold, tuberculosis, and malaria. On the other hand, non-infectious diseases are not caused by pathogens and cannot be transmitted. Examples include diabetes, cancer, and hypertension.


Personal hygiene like regular handwashing, proper sanitation, and maintaining cleanliness can prevent the spread of infectious diseases. Community hygiene involves clean water supply, waste disposal, and vaccination programs to reduce disease transmission.


By following these practices, we can minimize the risk of infections and promote overall health in society.

Question 15:
Explain the difference between acute and chronic diseases with suitable examples. How do these diseases impact an individual's health differently?
Answer:

Acute diseases are those that occur suddenly and last for a short duration, usually a few days to weeks. They often have severe symptoms but can be treated effectively. Examples include common cold, flu, or fever. On the other hand, chronic diseases develop slowly and persist for a long time, often for months or even a lifetime. Examples include diabetes, heart disease, and arthritis.


The impact of these diseases on health differs significantly:

  • Acute diseases cause sudden discomfort but usually do not cause long-term damage if treated properly. They may weaken the body temporarily but recovery is quick.
  • Chronic diseases, however, lead to prolonged suffering and can cause permanent damage to organs or bodily functions. They often require lifelong management and can reduce the overall quality of life.

For example, a person with flu (acute) may recover in a week with rest and medication, while a person with diabetes (chronic) must monitor their diet and take medication regularly to avoid complications like nerve damage or kidney failure.

Question 16:
Explain the difference between infectious and non-infectious diseases with suitable examples. How can personal and community hygiene help prevent the spread of infectious diseases? (5 marks)
Answer:

Infectious diseases are caused by pathogens like bacteria, viruses, fungi, or parasites and can spread from one person to another. Examples include common cold, tuberculosis, and malaria. On the other hand, non-infectious diseases are not caused by pathogens and do not spread. Examples include diabetes, cancer, and hypertension.


Personal hygiene practices like regular handwashing, proper sanitation, and maintaining cleanliness can prevent the entry of pathogens into the body. Community hygiene measures such as clean drinking water, waste disposal, and vaccination programs help reduce the spread of infectious diseases at a larger scale.


By following these practices, we can minimize the risk of infections and promote overall public health.

Question 17:
Explain the role of vaccination in preventing diseases. How does it help in building immunity? Support your answer with an example.
Answer:

Vaccination is a medical process that helps the body develop immunity against specific diseases by introducing a weakened or inactive form of a pathogen (like a virus or bacteria). This stimulates the immune system to produce antibodies without causing the actual disease.


When a person is vaccinated, their immune system recognizes the pathogen as a foreign invader and creates memory cells. If the person is exposed to the actual disease later, these memory cells quickly produce antibodies to fight it, preventing illness.


Example: The polio vaccine contains an inactivated poliovirus. When administered, it trains the immune system to recognize and combat the virus, leading to near-eradication of polio in many countries.


Benefits of Vaccination:

  • Prevents deadly diseases like smallpox, measles, and tetanus.
  • Reduces the spread of infections (herd immunity).
  • Cost-effective compared to treating diseases.
Question 18:
Explain the difference between infectious and non-infectious diseases with suitable examples. How can personal and community hygiene help prevent infectious diseases?
Answer:

Infectious diseases are caused by pathogens like bacteria, viruses, fungi, or parasites and can spread from one person to another. Examples include common cold, tuberculosis, and malaria. On the other hand, non-infectious diseases are not caused by pathogens and do not spread. Examples include diabetes, cancer, and hypertension.


Personal and community hygiene play a crucial role in preventing infectious diseases:

  • Personal Hygiene: Regular handwashing, maintaining cleanliness, and avoiding contact with infected individuals reduce the risk of infections.
  • Community Hygiene: Proper waste disposal, clean water supply, and vaccination programs help control the spread of diseases at a larger scale.

By adopting these practices, we can minimize the transmission of pathogens and protect public health.

Question 19:
Explain the differences between infectious and non-infectious diseases with suitable examples. How can public health measures help in preventing the spread of infectious diseases?
Answer:

Infectious diseases are caused by pathogens like bacteria, viruses, fungi, or parasites and can spread from one person to another. Examples include malaria (caused by Plasmodium parasite) and tuberculosis (caused by Mycobacterium tuberculosis). On the other hand, non-infectious diseases are not caused by pathogens and do not spread. Examples include diabetes (due to insulin deficiency) and cancer (due to uncontrolled cell growth).


Public health measures to prevent infectious diseases include:

  • Vaccination: Immunization programs help build immunity against diseases like polio and measles.
  • Sanitation: Proper waste disposal and clean drinking water reduce the risk of waterborne diseases like cholera.
  • Hygiene practices: Regular handwashing and use of masks prevent the spread of airborne diseases like COVID-19.
  • Vector control: Eliminating mosquito breeding sites helps prevent malaria and dengue.

These measures are essential for community health and reducing disease outbreaks.

Question 20:
Explain the role of vaccination in preventing diseases, highlighting how it strengthens the immune system. Provide examples of diseases that can be prevented through vaccination.
Answer:

Vaccination is a medical process that introduces a weakened or inactive form of a pathogen into the body to stimulate the immune system to produce antibodies. This helps the body recognize and fight the actual pathogen if encountered in the future.


The process works as follows:

  • The vaccine contains antigens (harmless parts of the pathogen).
  • The immune system identifies these antigens as foreign invaders.
  • It produces antibodies and memory cells to combat them.
  • If the real pathogen attacks later, the immune system responds faster and more effectively.

Examples of vaccine-preventable diseases include:

  • Polio (oral polio vaccine)
  • Tetanus (DPT vaccine)
  • Hepatitis B (Hep-B vaccine)
  • Measles (MMR vaccine)

Vaccination not only protects individuals but also contributes to herd immunity, reducing disease spread in communities.

Question 21:
Differentiate between acute and chronic diseases with suitable examples. How do these diseases impact an individual's health in the long term?
Answer:

Acute diseases are short-term illnesses that occur suddenly and last for a brief period, whereas chronic diseases develop slowly and persist for a long time, often for a lifetime.


Differences:

  • Duration: Acute diseases (e.g., common cold, flu) last for days or weeks, while chronic diseases (e.g., diabetes, hypertension) last for years or a lifetime.
  • Severity: Acute diseases may be severe but recover fully, while chronic diseases often worsen over time.
  • Treatment: Acute diseases usually require short-term medication, whereas chronic diseases need long-term management.

Long-term impact:

  • Chronic diseases weaken the immune system, making the body prone to other infections.
  • They reduce overall productivity due to prolonged illness.
  • They may lead to organ damage (e.g., heart disease from hypertension).
  • Acute diseases, if untreated, can sometimes turn chronic (e.g., untreated infections leading to tuberculosis).

Preventive measures like a balanced diet, exercise, and regular health check-ups can reduce the risk of chronic diseases.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A village reported several typhoid cases due to contaminated water.
Case Summary: Poor sanitation led to bacterial spread.
Q1. Identify the causative agent and suggest two preventive measures.
Answer:
Case Summary: Salmonella typhi bacteria causes typhoid.
Scientific Principle: Contaminated water/food spreads pathogens (NCERT Example: Chapter 13).
Solution Approach:
  • Boil drinking water (kills bacteria)
  • Vaccination (like Typbar-TCV in India)

Our textbook shows vaccines prevent diseases. Real-world: Clean water projects reduce outbreaks.

Question 2:
Rahul had high fever and rashes. Doctor diagnosed chickenpox.
Case Summary: Symptoms matched viral infection.
Q2. Explain why antibiotics won’t work and name the transmission mode.
Answer:
Case Summary: Chickenpox is caused by Varicella-zoster virus.
Scientific Principle: Antibiotics target bacteria, not viruses (NCERT Example: Page 178).
Solution Approach:
  • Transmission: Airborne droplets (real-world: school outbreaks)
  • Rest/isolation prevents spread

We studied viruses need antivirals, not antibiotics.

Question 3:
A school campaign promoted handwashing to curb diarrhea.
Case Summary: Hygiene reduced disease incidence.
Q3. Link hygiene to disease prevention with one NCERT and one real example.
Answer:
Case Summary: Handwashing removes pathogens.
Scientific Principle: NCERT states poor hygiene spreads microbes (Chapter 13).
Solution Approach:
  • NCERT: Clean toilets prevent cholera
  • Real-world: COVID-19 showed soap destroys viruses

Our textbook and pandemic proved hygiene breaks infection chains.

Question 4:
Malaria cases spiked post-monsoon in a city.
Case Summary: Stagnant water bred mosquitoes.
Q4. Name the vector and describe two community-level controls.
Answer:
Case Summary: Anopheles mosquito transmits malaria.
Scientific Principle: Vectors need stagnant water (NCERT Example: Page 180).
Solution Approach:
  • Drain waterlogged areas
  • Use mosquito nets (real-world: Govt. distributes nets)

We studied eliminating breeding sites controls vectors effectively.

Question 5:
A student got food poisoning after eating street food.
Case Summary: Name two bacteria causing this. What first-aid steps should be taken?
Answer:
Case Summary: Common bacteria are Salmonella and E.coli.
Scientific Principle: They enter through contaminated food/water (NCERT example).
Solution Approach:
  • Drink ORS to prevent dehydration
  • Avoid solid food initially
  • Consult doctor if symptoms persist
Question 6:
Riya observed her friend coughing frequently and having a fever. The doctor diagnosed it as tuberculosis.
Case Summary: Identify the causative agent and mode of transmission. How can Riya prevent its spread?
Answer:
Case Summary: Tuberculosis is caused by Mycobacterium tuberculosis.
Scientific Principle: It spreads through airborne droplets when the infected person coughs. Our textbook shows it affects lungs.
Solution Approach: Riya can prevent spread by:
  • Encouraging her friend to wear a mask
  • Maintaining hygiene and ventilation
  • Avoiding close contact till recovery
Question 7:
A village reported several cases of malaria after monsoon.
Case Summary: Name the vector and preventive measures. How does stagnant water contribute?
Answer:
Case Summary: Malaria is spread by female Anopheles mosquito.
Scientific Principle: Stagnant water acts as breeding ground. NCERT mentions this in Why Do We Fall Ill?.
Solution Approach:
  • Use mosquito nets/repellents
  • Cover water containers
  • Spray insecticides
Question 8:
During a health camp, many children showed vitamin A deficiency symptoms like night blindness.
Case Summary: What is the dietary solution? How does deficiency weaken immunity?
Answer:
Case Summary: Lack of vitamin A causes weakened immunity.
Scientific Principle: NCERT states it’s essential for mucous membrane health.
Solution Approach:
  • Include carrots, spinach in diet
  • Government provides supplements
  • Regular health check-ups
Question 9:
Rahul observed his friend coughing frequently and having a fever. The doctor diagnosed it as tuberculosis. Explain the mode of transmission and preventive measures for such diseases.
Answer:
Case Summary

Rahul's friend has tuberculosis, a bacterial infection.

Scientific Principle
  • Transmitted via airborne droplets (NCERT example: TB spreads through cough/sneezes).
  • Weak immune system increases risk.
Solution Approach
  • Prevention: Masks, ventilation (real-world: COVID-19 measures).
  • BCG vaccine (NCERT mentioned).
Question 10:
Priya noticed mosquito breeding in stagnant water near her house. How can this lead to vector-borne diseases? Suggest two control methods.
Answer:
Case Summary

Stagnant water causes mosquito breeding.

Scientific Principle
  • Mosquitoes transmit malaria/dengue (NCERT example: Plasmodium parasite).
Solution Approach
  • Control: Cover water containers (real-world practice).
  • Use larvicides (NCERT mentioned).
Question 11:
A school canteen served contaminated food, causing stomach infections. Identify the type of disease and two hygiene practices to avoid it.
Answer:
Case Summary

Food contamination led to infections.

Scientific Principle
  • Water/food-borne diseases like cholera (NCERT example).
Solution Approach
  • Wash hands before eating (real-world habit).
  • Proper food storage (NCERT guideline).
Question 12:
Ananya recovered from chickenpox but her brother got infected later. Explain immunity and why vaccines are given for such diseases.
Answer:
Case Summary

Chickenpox spread despite recovery.

Scientific Principle
  • Active immunity develops after infection (NCERT).
Solution Approach
  • Vaccines provide artificial immunity (real-world: polio drops).
  • Prevents outbreaks (NCERT example).
Question 13:

Rahul noticed that his younger sister was suffering from frequent cold and cough. His mother suggested increasing the intake of citrus fruits like oranges and lemons. Based on this case:

  • Explain why his mother recommended citrus fruits.
  • Name the micronutrient responsible for boosting immunity in this situation.
Answer:

Rahul's mother recommended citrus fruits because they are rich in Vitamin C, which is essential for strengthening the immune system.


The micronutrient responsible for boosting immunity here is Vitamin C (Ascorbic Acid). It helps in:

  • Enhancing the production of white blood cells (WBCs), which fight infections.
  • Acting as an antioxidant to protect cells from damage.

Additionally, Vitamin C aids in faster recovery from illnesses like colds by reducing inflammation and supporting tissue repair.

Question 14:

In a school health camp, students were advised to maintain personal hygiene and get vaccinated. One student asked, "Why are vaccines important?" Based on this scenario:

  • Explain how vaccines work in the human body.
  • Give an example of a vaccine-preventable disease and its causative agent.
Answer:

Vaccines work by introducing a weakened or inactive form of a pathogen (like a virus or bacteria) into the body. This triggers the immune system to produce antibodies without causing the actual disease.


Steps of vaccine action:

  • The body recognizes the pathogen as a foreign invader.
  • Memory cells are created to remember the pathogen for future encounters.
  • If the real pathogen attacks later, the immune system responds faster and stronger.

An example of a vaccine-preventable disease is Polio, caused by the Poliovirus. Vaccination has nearly eradicated polio globally.

Question 15:

Rahul, a 9th-grade student, noticed that his friend Priya frequently falls ill, especially during the monsoon season. Her symptoms include fever, body aches, and fatigue. The doctor diagnosed her with dengue fever, caused by the Aedes mosquito.

Based on this case, answer the following:

  • What are the two main modes of transmission of diseases like dengue?
  • Suggest two preventive measures to control the spread of such diseases.
Answer:

Two main modes of transmission of diseases like dengue:

  • Vector-borne transmission: Through the bite of an infected Aedes mosquito.
  • Direct transmission: Rarely, through blood transfusion or from an infected mother to her baby during childbirth.

Two preventive measures to control the spread:

  • Eliminate stagnant water where mosquitoes breed, such as in coolers, flower pots, or discarded containers.
  • Use mosquito nets, repellents, and wear full-sleeved clothing to avoid mosquito bites.

Additionally, community awareness campaigns can help in early detection and prevention of such diseases.

Question 16:

In a school health camp, students were screened for various health issues. It was found that many students suffered from vitamin deficiencies, leading to conditions like night blindness (due to lack of Vitamin A) and scurvy (due to lack of Vitamin C).

Based on this case, answer the following:

  • How do deficiencies of vitamins affect our immune system?
  • Name two food sources rich in Vitamin A and Vitamin C each.
Answer:

Effect of vitamin deficiencies on the immune system:

Vitamins play a crucial role in maintaining a healthy immune system. Deficiencies weaken immunity, making the body more susceptible to infections. For example:

  • Vitamin A deficiency reduces the body's ability to fight infections, especially in the eyes and respiratory system.
  • Vitamin C deficiency impairs wound healing and increases the risk of infections like scurvy.

Two food sources for each vitamin:

  • Vitamin A: Carrots and sweet potatoes.
  • Vitamin C: Oranges and amla (Indian gooseberry).

A balanced diet with these nutrients helps strengthen immunity and prevents deficiency-related illnesses.

Question 17:

Rahul noticed that his younger sister was suffering from frequent cold and cough. Their family doctor advised her to take proper rest, consume a balanced diet, and maintain personal hygiene. Based on this case:

  • Identify the type of disease she is suffering from and explain why.
  • List two preventive measures that can help reduce such illnesses.
Answer:

The sister is suffering from an acute disease because cold and cough are short-term illnesses that resolve quickly with proper care.


Preventive measures:

  • Washing hands regularly to avoid the spread of pathogens.
  • Maintaining a balanced diet rich in vitamins and minerals to strengthen the immune system.

Additionally, avoiding close contact with infected individuals and keeping the living space clean can further reduce the risk.

Question 18:

In a village, several people reported symptoms like prolonged fever, weakness, and weight loss. The local health worker diagnosed it as tuberculosis (TB). Answer the following:

  • Name the causative agent of TB and its mode of transmission.
  • Suggest two community-level measures to control its spread.
Answer:

The causative agent of TB is Mycobacterium tuberculosis, a bacterium that spreads through airborne transmission when an infected person coughs or sneezes.


Community-level measures:

  • Creating awareness about early diagnosis and DOTS (Directly Observed Treatment, Short-course) to ensure complete treatment.
  • Improving ventilation in crowded places to reduce the concentration of bacteria in the air.

Vaccination with BCG for children and proper sanitation practices also play a crucial role in prevention.

Question 19:

Rahul, a 9th-grade student, noticed that his friend Rohan frequently falls ill due to infections. Rohan's doctor advised him to maintain proper hygiene and consume a balanced diet. Based on this case:

  • Explain why maintaining hygiene helps prevent infections.
  • How does a balanced diet strengthen the immune system?
Answer:

Hygiene and infection prevention: Maintaining hygiene, such as washing hands regularly, prevents the entry of pathogens (disease-causing microorganisms) into the body.
Clean surroundings reduce the breeding of vectors like mosquitoes, which spread diseases like malaria and dengue.

Balanced diet and immunity: A diet rich in proteins, vitamins, and minerals strengthens the immune system.
Vitamin C (found in citrus fruits) boosts white blood cell production, while proteins help build antibodies that fight infections.

Question 20:

Priya observed that her grandmother was diagnosed with diabetes, a non-communicable disease, while her neighbor suffered from cholera, a communicable disease. Based on this case:

  • Differentiate between communicable and non-communicable diseases with examples.
  • Suggest two preventive measures for each type of disease.
Answer:

Difference: Communicable diseases spread from one person to another through pathogens (e.g., cholera, tuberculosis).
Non-communicable diseases do not spread and are caused by internal factors like genetics or lifestyle (e.g., diabetes, hypertension).

Preventive measures:

  • For communicable diseases:
    1. Maintain sanitation and drink clean water.
    2. Get vaccinated (e.g., for hepatitis).
  • For non-communicable diseases:
    1. Follow a healthy diet and exercise regularly.
    2. Avoid smoking and excessive alcohol consumption.

Question 21:
Rahul noticed that his friend Rohan often falls sick during the monsoon season. Rohan complains of frequent fever, cough, and cold. Rahul advised him to drink boiled water and avoid street food. Based on this scenario, answer the following:
(a) Why does Rohan fall sick frequently during monsoons?
(b) How does drinking boiled water help prevent illnesses?
Answer:

(a) Rohan falls sick frequently during monsoons because the season creates a favorable environment for the growth of pathogens like bacteria and viruses. Stagnant water and humidity promote the breeding of mosquitoes, which can spread diseases like malaria and dengue. Additionally, contaminated water and unhygienic food increase the risk of waterborne diseases such as cholera and typhoid.


(b) Drinking boiled water helps prevent illnesses because boiling kills harmful microorganisms present in water. Pathogens like bacteria, viruses, and parasites cannot survive high temperatures, making the water safe for consumption. This reduces the chances of gastrointestinal infections and other waterborne diseases.

Question 22:
Priya’s grandmother suggested that she should get vaccinated before traveling to a new place. Priya was confused about how vaccines work. Explain the following to her:
(a) What is the principle behind vaccination?
(b) How do vaccines help in building immunity?
Answer:

(a) The principle behind vaccination is based on the concept of immunological memory. Vaccines contain weakened or inactive forms of pathogens (like viruses or bacteria) or their components. When introduced into the body, they stimulate the immune system to produce antibodies without causing the actual disease.


(b) Vaccines help in building immunity by training the immune system to recognize and fight specific pathogens. Here’s how:
1. The vaccine introduces a harmless version of the pathogen.
2. The body’s white blood cells produce antibodies against it.
3. Memory cells are created, which remember the pathogen for future encounters.
4. If the real pathogen attacks later, the immune system responds faster and stronger, preventing illness.

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