CBSE Class 9 Science Revision Notes Chapter 13

CBSE Class 9 Science Revision Notes Chapter 13 – Why Do We Fall ill?

In the Class 9 Science Chapter 13 Notes, you will learn about different diseases and their appearance in our bodies. The Chapter 13 Science Class 9 Notes will familiarise you with the illnesses and reasons why one falls ill due to several factors in one’s diet, environment, or both. Furthermore, Class 9 Chapter 13 Science Notes will also help you learn about different treatments for various diseases. These notes are prepared by our team of experienced Science teachers from NCERT books keeping in mind the latest CBSE syllabus. You can download CBSE revision notes in PDF format from the Extramarks website for quick revision before the exams.

Extramarks also provides CBSE past years’ question papers and CBSE sample papers to assist students in practising crucial questions from an exam perspective. Students can better understand the concepts and perform well in exams by practising important questions and CBSE extra questions.

CBSE Class 9 Science Chapter 13 – Why Do We Fall ill Revision Notes 

Access Class 9 Science Chapter 13 – Why do we fall Ill Notes

Notes of Chapter Why Do We Fall ill

A disease is known as any physical or mental condition that causes pain, discomfort, or abnormal behaviour. One can fall ill for many reasons that might be internal or external.  Some of the factors that contribute to an illness are listed below:

  • Consumption of contaminated or polluted food and water.
  • When normal flora relocates from its native place to another part of the body.
  • Lack of a sound immune system.
  • Changes in environmental and weather conditions.
  • Inhalation of polluted air.
  • The influence of a person’s mental health on their overall health.
  • Lack of nutrition due to poor diet.

Class 9 Chapter 13 Science Notes: Diseases and Their Types

How can we tell if we are ill when our body is functioning normally? We are capable of sensing that something is wrong with our bodies. The organism has multiple organ systems that contain tissues, and tissues contain cells that help our body perform several functions. Our body begins to behave abnormally when we have any sickness, which results in several symptoms like coughing, fever, the flu, headaches, and more, and it tells us that it’s time to see a doctor. Class 9 Science Notes Chapter 13 tells us that diseases can be of two types: 

  • Chronic Diseases:

Chronic diseases are serious conditions that affect a patient’s body for a long time and, in some circumstances, permanently. These diseases may be the result of a poor lifestyle or hereditary, and there is no cure for them. Examples: asthma, diabetes, cancer, arthritis, etc. 

  • Acute Diseases:

These temporary diseases only last a few days or even a few weeks in some circumstances. They are often curable and do not affect the patient for the rest of their life. Examples: typhoid, food poisoning, chickenpox, etc.

Notes of Ch 13 Science Class 9: Different Types of Causes of Diseases

Pathogens like bacteria and viruses cause diseases. Other causes of sickness include internal and genetic factors.

  • Infectious Diseases

Diseases that are caused by pathogens and can spread to other people in the community are called infectious diseases. For example, the common cold, smallpox, malaria, HIV, etc.

  • Non-infectious Diseases

Non-infectious diseases are those that cannot be spread from one person to another. These diseases are typically not brought on by a pathogen. For example, diabetes and high blood pressure.

  • Pathogen

Pathogens are external agents that cause illnesses or diseases in their host. They include harmful microbes or microorganisms, such as viruses, fungi, protozoa, or bacteria. 

Science Chapter 13 Class 9 Notes: Prevention of Diseases

Infectious diseases can be treated in the following ways:

The first step is to reduce the effects of the disease, and the second step is to kill the cause of the disease. Antibiotic medications are used to treat diseases caused by bacteria, fungi, and protozoans, for example, Penicillin. Antiviral medications are used to treat diseases caused by viruses. Compared to antibacterial drugs, these medications are far more challenging to manufacture. Despite this restriction, the market currently offers powerful antiviral medications, including those used to manage HIV infection.

The primary focus of all prevention efforts should be on avoiding getting infections in the first place. Improvements in living conditions away from congested areas can help limit the spread of air-borne germs. A clean environment and access to safe drinking water can help to reduce water-borne illnesses. Diseases transmitted by vectors can be prevented by maintaining a clean environment. Public hygiene is one of the fundamental steps in preventing infectious diseases. 

Infectious diseases can also be avoided with proper and sufficient nutrition, and it is necessary to get immunised promptly. Vaccines are a specialised method of disease prevention that has proven to be effective against a wide range of diseases, including tetanus, diphtheria, whooping cough, measles, and polio, among others.

Antimicrobial drugs, commonly known as antibiotics, are produced by multiple other organisms, like bacteria and fungi. They are used for treating harmful infections caused by microorganisms or pathogens. Antibiotics function by:

  1. Altering cell membranes
  2. Inhibiting antimetabolite activity
  3. Inhibiting nucleic acid synthesis
  4. Inhibiting cell wall synthesis 
  5. Inhibiting protein synthesis 

Class 9 Science Why Do We Fall Ill Notes: Preventive Measures

Several preventive measures can avoid infections. To avoid diseases, one should always practise good hygiene. People should drink pure and filtered water. Immunisation is one of the most crucial preventative measures. It is the procedure by which a person becomes resistant to or immune to a particular infectious disease, and immunisation causes the body to become more resistant. 

FAQs (Frequently Asked Questions)

1. List three reasons why a person would think that he or she is sick and should see a doctor. Would you still go to the doctor if only one of these symptoms were present? Why or why not?

 Given below are three reasons for feeling sick and visiting a doctor:

(1) having a headache

(2) having a cold, flu, and cough

(3) having loose motions

It is still advisable to visit a doctor even if just one of these symptoms is present because the doctor can identify the illness based solely on the symptoms. Additionally, the doctor will prescribe laboratory testing to help identify the disease.

2. Why are we usually advised to take bland and nourishing food when we are sick?

During sickness, our body becomes weak, and the digestive system does not function properly. Therefore, it is advised to take bland and healthy foods, which can be easily digested by our body and speed our recovery. It is advised to avoid spicy foods, which make digestion faster and prevents the release of acids in the body that could interfere with the treatment and recovery.

3. What are the various means through which infectious diseases are spread?

Infectious diseases can spread in a variety of ways:

(i) Through air: These illnesses are referred to as air-borne diseases. The air carries microorganisms, such as bacteria and viruses. Examples: common cold, influenza, tuberculosis, etc.

(ii) Through food and water: Whenever someone consumes contaminated food or water that carries bacteria, viruses, worms, etc., it can be the cause of diseases such as cholera, typhoid, and hepatitis.

(iii) Through contact: Many diseases, such as fungal infections, skin conditions, scabies, etc., are transferred through contact between an infected person and a healthy person.

(iv) By sexual contact: Sexual interaction between two people can result in the transmission of a number of diseases known as sexually transmitted diseases (STDs). Examples: Syphilis and AIDS.

(v) By body fluids: Infected bodily fluids, such as blood, semen, and mother’s milk, can also spread diseases. For example, AIDS.

(f) Vectors: Organisms that transmit diseases by transporting pathogens from one location to another are referred to as vectors. For example, mosquitoes are vectors that carry pathogens such as protozoa.


4. What precautions can you take as a student at your school to reduce your chances of contracting an infectious disease?

You can take the following precautions to decrease the chances of infectious diseases:

  • Use a handkerchief while coughing or sneezing.
  • Wash your hands before eating lunch or snacks.
  • Choose to stay at home if someone in the class has an infectious disease.
  • Timely vaccinations before the infection begins.
  • Keep the school’s surroundings clean.

5. What is immunisation?

Immunisation is the procedure by which the body develops the ability to combat any disease with the use of a vaccine.