Class 9 Science Ch13 Why Do We Fall Ill Notes PDF

The chapter “Why Do We Fall Ill” in Class 9 Science Syllabus explains the basic reasons behind illness and how our body stays healthy. It helps students understand the meaning of health, the causes of diseases, and the difference between infectious and non-infectious diseases. These important notes from cbse syllabus class 9 science give a clear and simple overview of the chapter and are useful for quick revision and exam preparation. Let’s dive in and learn this chapter step by step!

Class 9 Why do We Fall ill Important Notes 

These Class 9 Why Do We Fall Ill Important Notes are prepared to help students understand the chapter in a simple and clear way. They cover all key concepts, definitions, and points needed for quick revision and exam preparation. So, download the notes from below and make your study easier and more effective.

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Chapter 13 Science Class 9 Notes

This chapter teaches us about health and disease, including what it means to be healthy and the various factors that affect our health. You will also understand the causes of diseases, with a clear distinction between infectious and non-infectious diseases.

It introduces pathogens such as bacteria, viruses, fungi and protozoans, which are responsible for causing different diseases. You will learn about the transmission of diseases, including how they spread through air, water, food and vectors.

Additionally, the chapter covers prevention and treatment methods, such as vaccination, medicines, maintaining hygiene and adopting healthy lifestyle measures. 

1. Key Terms for Chapter 13 Science class 9

Let us first learn the following key terms.

• Health: Health is the state of an individual where his  physical, mental and social health are well-being.
• Disease: when the human body suffers internal distribution that disturbs the normal functioning of the human  body.
• Healthy Person:A person who can Can work normally, perform Daily tasks efficiently and is mentally and socially well are considered as a health person 

Distinctions

• Health ≠ Disease-free: Many people think that a disease-free person is automatically healthy. However, being free from disease does not always mean a person is truly healthy, because hidden or latent diseases may exist in the body and affect health over time.‍
• Example: A person may appear physically well and not show any illness, but they can still experience poor mental or social health issues.

2. Causes of Diseases

Diseases can arise due to multiple factors, including microorganisms and lifestyle-related conditions.

• Immediate cause: The microorganism or foreign agents in the environment can cause disease by entering the human body through the nose or mouth.‍
• Contributory cause: Some diseases are directly linked to an individual’s lifestyle. Poor diet, poverty and unhygienic conditions increase the risk of disease and lack of proper nutrition can also lead to illness.

3. Types of Diseases

Diseases can be classified based on their duration and impact on the human body.

a) Acute Disease: Acute diseases are those that last for a short duration. They usually appear suddenly and may resolve quickly with or without treatment. ‍

Example: Cough and cold.

b) Chronic Disease: Chronic diseases are those that persist for a long time and negatively affect the body’s functions. These diseases can cause long-term damage to organs and, in severe cases, increase the risk of death. ‍

Example: Tuberculosis, diabetes, cancer.

4. Classification of Diseases

Diseases can be classified into infectious and non-infectious types based on their causes.

a) Infectious Diseases: These diseases are caused by microorganisms that live in our environment. They enter the body through the mouth or nose and multiply by destroying human cells, using the body to produce more microorganisms. 

Infectious diseases can spread from person to person, usually through physical contact, so it is important to avoid close contact with affected individuals.

Example: Flu, Tuberculosis, COVID-19.

b) Non-infectious Diseases: These diseases are not caused by pathogens. They usually result from poor lifestyle choices, such as unhealthy eating habits or lack of exercise. Non-infectious diseases cannot spread from one person to another. 

Example: Diabetes, Cancer.

c) Organ and Tissue Specificity - All different diseases affect different organs of the human body.

Example- Jaundice affects liver, TB affects lungs and cancer can affect every part of the human body.

5. Infectious Agents and Their Examples

Different types of microorganisms cause infectious diseases, each with specific examples.

• Virus: Causes diseases like AIDS and Common Cold.
• Bacteria: Causes diseases like Typhoid and Tuberculosis (TB).
• Fungi: Causes skin infections.
• Protozoa: Causes diseases like Malaria and Amoebiasis.‍
• Worms: Cause intestinal infections.

6. Means of Spread

Diseases can spread in different ways dependin g on the source and medium.

a) Airborne: Sneezing or coughing by a person can spread viruses through the air and infect several people.
Example: Cold, TB

b) Waterborne: Diseases can spread through contaminated water that is unsafe to drink. Harmful bacteria in water can cause serious illnesses, as water is a good medium for microorganisms to spread.
Example: Typhoid, Cholera, Jaundice

c) Contact: Direct contact with a person suffering from a disease can transmit it.
Example: Skin infections

d) Vectors: Animals like mosquitoes can transmit diseases like malaria and dengue by biting humans. Precautions should be taken to avoid mosquito bites.Example: Malaria, Dengue

7. Principles of Treatment

Treatment of diseases focuses on targeting the root cause of infection and supporting the body to recover.

• After Microorganism enters into your body doctors treat you with medicine to kill the root cause of your disease. 
• Firstly the doctor prescribed antibiotics, an antiviral drug to Kill the infectious microbe in our human body. So the microorganisms can’t able to produce in human body
• It reduces the symptoms and effects  the disease to destroy all the clones of a microorganism and after some time the person will be disease free.

8. Principles of Prevention

General measures to keep the human body healthy include the following:

• Clean Environment: Keep your house and surroundings clean to reduce the growth of microorganisms and insects. A clean environment lowers the risk of diseases and promotes overall health.
• Safe Drinking Water: Always drink clean and safe water. Clean water reduces the workload on the kidneys and helps prevent kidney-related problems in the future. Using methods like RO (Reverse Osmosis) filtration ensures water is free from harmful impurities.
• Proper Nutrition: Consume a balanced diet that provides all essential nutrients, including proteins, carbohydrates, fats, vitamins and minerals. Proper nutrition supports growth, development and overall immunity. Supplements can be used if dietary intake is insufficient.‍
• Good Hygiene and Sanitation: Maintain personal hygiene, such as regular bathing, handwashing and keeping clothes and surroundings clean. This reduces the chances of infections and disease.

9. Specific Measures

Following are some specific measures to keep yourself safe and harmless from diseases.

1. Vaccination: Take vaccines for diseases like polio, measles, COVID-19, hepatitis and tetanus to prevent infections and reduce future medical expenses. Adults should ensure that children receive all recommended vaccinations so they remain healthy and protected against serious illnesses.
2. Regular Health Check-ups: Visit a doctor periodically for routine check-ups. Early detection of diseases helps in timely treatment and prevents complications.
3. Use of Mosquito Nets and Insect Repellents: Protect yourself from vector-borne diseases like malaria, dengue and chikungunya by using mosquito nets, repellents and eliminating stagnant water around your home.
4. Safe Food Practices: Eat freshly cooked food, wash fruits and vegetables thoroughly and avoid stale or contaminated food to prevent foodborne illnesses.
5. Physical Activity and Exercise: Regular exercise strengthens immunity, improves overall health and reduces the risk of lifestyle-related diseases like diabetes, obesity and heart problems.

This chapter teaches us how to maintain good health and prevent diseases. Knowing the causes of illnesses, both infectious and non-infectious, helps us take timely action. 

Treatment with medicines like antibiotics and antivirals targets the root cause, while preventive measures such as clean surroundings, proper hygiene, safe water, balanced nutrition, vaccinations, regular check-ups and physical activity protect us from falling ill. 

FAQs

Q1. What is the difference between health and being disease-free?

Ans: Health is the overall physical, mental and social well-being of a person, while being disease-free only means not showing symptoms of illness. A person can be disease-free but still have poor health due to hidden conditions or mental and social issues.

Q2. What are infectious and non-infectious diseases?

Ans: Infectious diseases are caused by microorganisms and can spread from person to person (e.g., flu, tuberculosis). Non-infectious diseases are not caused by pathogens and cannot spread (e.g., diabetes, cancer).

Q3. How do diseases spread in the body?

Ans: Diseases can spread through air (sneezing, coughing), water (contaminated water), direct contact and vectors like mosquitoes.

Q4. What are the principles of treatment for diseases?

Ans: Treatment targets the root cause using antibiotics, antivirals or other medicines and is supported by rest, hydration and proper nutrition to restore health.

Q5. How can diseases be prevented?

Ans: Prevention includes maintaining hygiene, drinking safe water, eating balanced nutrition, taking vaccinations, regular check-ups, using mosquito nets and exercising to strengthen immunity.