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Class 9 Science Revision Notes for Chapter 13 Why Do We Fall Ill are created by experts at askIITians to help you understand the causes and cure of various diseases. This chapter helps you understand how important it is for you to take care of your health. It is an interesting chapter with topics like the difference between being healthy and being disease-free, acute and chronic diseases, causes of diseases, infectious and non-infectious diseases, means of spread of diseases, principles of prevention, principles of treatment, and immunisation.
The revision notes for CBSE Class 9 Science Chapter 13 Why Do We Fall Ill are available for free on our website. These notes will be extremely helpful for every student because they include short, concise yet clear explanations for all the topics of the chapter. The notes are based on the latest syllabus and hence will help you prepare well for the exams. You can find pointwise explanations for every concept of the chapter which makes our notes easier to read. You can use these revision notes to revise the whole chapter before exams in just 20 minutes or less!
At askIITians, we provide a plethora of study resources to the students for Class 9 Science. These include mind maps, flashcards, NCERT Solutions, NCERT Exemplar solutions, important questions, extra questions, and more. We also provide class 6, 7, 8, 9, 10, 11, 12 notes for Science and Maths to the students.
Online Revision Notes for Class 9 Chapter 13 Why do we Fall Ill
The activities performed inside our body by the internal organs are all interconnected. For instance, the heart always forms the blood in the body, the brain always thinks, the kidney filters out waste from our body and so on. If any of these activities stop, this would affect the whole functionality of our body.
It is a state of being well so that one can perform physical, social and mental functions properly. For Example, we say a person is healthy if they can perform their day to day tasks very well.
Figure 1: What is health?
Yes, we cannot achieve health solely on our own. Every organism in this world depends upon another or the environment for its better health.
Figure 2: Healthy and Disease-Free
We can stay disease-free by maintaining good health that is,
Acute Disease
Chronic Disease
Acute diseases last for only a short period of time.
Chronic diseases last for a long period of time
It is caused randomly.
It is caused in due course of time.
It does not cause a major effect on general health.
Example: Cough, dysentery.
It causes a major effect on general health.
Example: Elephantiasis, heart disease, tuberculosis.
We know that diseases can be caused by two factors:
Internal factors in our body such as
External factors such as
Based on the following there are two broad categories of causes of diseases –
Immediate Causes
Contributory Causes
These are the actual causes that are responsible for a disease. These causes can be infectious as well as non-infectious.
These are not the direct causes but factors that contribute to causing disease.
For Example, Bacteria, Fungi, Viruses, Germs etc.
For Example Poor diet, Unhealthy lifestyle, Polluted environment etc.
Congenital diseases are present since birth. For eg hole in heart of an infant. Acquired Diseases occur after birth. Based on their ability to spread from one individual to another, Acquired diseases are of two types:
Infectious Causes
Non-infectious Causes
These are the extrinsic or external disease-causing factors.
These are the intrinsic or internal disease-causing factors.
They lead to infectious diseases and can affect the whole community as they are transferable from one person to another.
They lead to non-infectious diseases and do not affect the whole community as they are non-transferable from one person to another.
Infectious or Communicable Diseases
Non-infectious or Non-Communicable Diseases
They are caused by an attack of pathogens.
They are not caused by pathogens.
The diseases are brought about by extrinsic or external factors.
The diseases are mostly bought by intrinsic or internal factors.
Infectious diseases can pass from a diseased person to a healthy person.
Non-infectious diseases cannot pass from one person to another.
Transmission of infection occurs through direct contact or some medium (air, water, vectors).
Transmission is absent, However, hereditary diseases are transmitted from parent to offspring.
Community hygiene can reduce the incidence of infections diseases
Community hygiene is ineffective in reducing the incidence of non-infectious diseases.
Example: Cholera, Tuberculosis (TB), Pneumonia, Chickenpox.
Example: High blood pressure, Heart, Disease, Cancer.
The pathogens or microbes that cause infectious diseases are also called Infectious Agents.
Figure 3: Infectious Agents
If we understand the characteristics we can treat the diseases caused by them in a better way. We can find out which medicine would work on which infectious agent. Some common characteristics of infectious agents are:
Antibiotics are generally used to block the growth of bacteria. The bacteria cells grow by creating a cell wall that protects them. Penicillin is an antibiotic that prevents the growth of the cell wall and hence bacteria die easily. Penicillin is used for fighting against different kinds of bacteria.
Based on the means of spread of a disease, we can classify it into different categories:
Type of Disease
Causing Factor
Examples
Airborne diseases
They are caused by germs, bacteria or virus in the air
Common cold, tuberculosis
Foodborne diseases
They are caused by germs (bacteria, toxins, viruses, fungi) present in the food
Food poisoning, Typhoid
Waterborne diseases
They are caused by drinking contaminated water
Cholera, Amoebiasis
Lifestyle diseases
They occur because of poor or unhealthy lifestyle
Heart disease, Diabetes
Vector-borne Diseases
they are caused due to animals that carry infectious agents from a sick person to another person
Malaria, Dengue Fever
These animals that act as an intermediate between disease-causing germs and people are called vectors.
Sexually transmitted diseases
They are caused due to sexual contact from one person to another
AIDS, Syphilis
Figure 4: Principles of Treatment
We may treat infectious disease in two ways:
We can reduce the symptoms in the following ways:
We can kill the infectious agents in our body in the following way:
Antibiotics commonly work by blocking the biochemical pathways that are important for bacteria. Thus these inhibit the growth of bacteria, hamper their metabolism and kill them. Antibiotics do not work on viruses because viruses do not use the biochemical path and use host cell machinery for making proteins.
However, the most effective way to treat viral infections and disease is vaccination as it can prevent a person from getting the disease in the first place.
Are there any limitations of treating infectious agents via medicines?
Yes, there are three limitations:
Therefore, we should find out ways to prevent these diseases in the first place. There are two ways to prevent diseases:
A peptic ulcer is a sore that occurs on the inner lining of the stomach. In 2005, Barry J. Marshall and J. Robin Warren received a Nobel Prize for discovering that Helicobacter Pylori bacteria are a cause of such ulcers. Before that, it was believed that stress and lifestyle are major causes of such ulcers. The Helicobacter Pylori bacteria weakens the mucous lining of the stomach which lets the acid present inside the stomach get through the inner sensitive lining. The acid and bacteria together irritate the lining and cause a sore or ulcer.
Figure 5: List of Diseases
Chapter 13 Why Do We Fall Ill helps you understand the meaning of living a healthy life or being healthy. It gives information about various diseases, their causes, prevention and cures. It also helps you understand why public hygiene is important and sheds light on immunisation. This chapter is important in daily life as well as in advanced studies.
You can join askIITians online coaching for Class 9 Science where we teach every concept in detail. There are live, interactive classes, doubt removal sessions, discussions and tests to help you master every concept of Class 9 Science. Along with this, we provide a plethora of study materials like revision notes, NCERT Solutions, NCERT Exemplar Solutions, important questions and more to help you prepare every topic for exams.
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