NCERT Solutions Class 9 Science Chapter 13

NCERT Solutions For Class 9 Science Chapter 13- Why Do We Fall Ill

Understanding the human body is very important. Especially when it comes to knowing about health and diseases, these concepts are quite complex with several interconnected issues. Throughout our bodies, various specialised activities are going on. The kidney filters urine, the heart beats, the lungs breathe, and the brain thinks. All of these activities are linked together. All of these interrelated operations require energy and raw materials. Food is necessary for the proper functioning of cells and tissues. A lack of adequate activity in the body will result from anything that stops cells and tissues from working properly. Students will study health and diseases from this context. The students will be able to understand all these challenging ideas with the aid of NCERT Solutions For Class 9 Science Chapter 13.

A thorough understanding of Extramarks NCERT Solutions For Class 9 Science Chapter 13 on Why Do We Fall Ill is very important for students. It will help students take a closer look at the various concepts related to health and diseases. They will understand in detail health and its failure, diseases and their causes, infectious diseases and the different concepts that come under these topics. It becomes crucial to understand these concepts to learn about one’s health and various kinds of diseases that are caused by a variety of issues. Although it might look difficult initially, with the easy-to-understand solutions provided by Extramarks, students will become well-versed in all the topics.

Students are generally advised to read the NCERT Solutions for each chapter to increase their knowledge and clarity of the topic. Extramarks has created NCERT Solutions For Class 9 Science Chapter 13 to assist students in understanding, structuring and revising their answers with the help of solutions. Extramarks NCERT Solutions For Class 9 Science Chapter 13 were created by subject matter experts who followed the most recent CBSE guidelines while meeting all students’ requirements, regardless of their ability. Students gain in-depth subject knowledge, which improves their overall academic performance.

The Extramarks website has much more to offer students than just NCERT Solutions Class 9 Science Chapter 13. By registering on the Extramarks website, students may quickly access materials such as NCERT books, CBSE study guides, practice tests, exam papers of previous years and more. Using these study aids can assist students in better understanding and practising the topics covered in different chapters.

Key Topics Covered in NCERT Solutions For Class 9 Science Chapter 13

Class 9 Science Chapter 13 Question Answer list by Extramarks introduces students to various new topics. For Class 9 Science Students, it is important to understand how multiple diseases spread and how one can prevent and treat them. The fundamental concepts are made easier with the help of the NCERT Solutions For Class 9 Science Chapter 13. Students can quickly review all the important concepts taught in class, which will ultimately help them perform better in their examinations.

The main topics included in the NCERT Solutions For Class 9 Science Chapter 13 are given below

  • Health and its significance
  • Difference between health and disease
  • Disease and Its Causes
  • Acute and Chronic Diseases
  • Causes of Diseases
  • Infectious and Non-Infectious Causes
  • Infectious Agents
  • Means of Spreading of Infectious Diseases
  • Organ-Specific and Tissue-Specific Manifestations
  • Principles of Treatment
  • Principles of Prevention
  • Immunisation

A detailed description of the topics as given in Extramarks NCERT Solutions For Class 9 Science Chapter 13 is mentioned below:

Health and its significance

  • Health: A person’s health is the state of complete physical, mental and social well-being. Anything that interferes with the appropriate functioning of cells and tissues will result in a lack of proper body functioning. Health is affected by both individual and societal factors.
  • Health is not something we can acquire on our own. Every living thing on this planet depends on other living things or the environment for better health.
  • All creatures’ health is affected by their surroundings or environment. The physical environment is part of the environment. Our social environment, public sanitation, excellent financial conditions and jobs, social equality and agreement all define an individual’s health.

Difference between health and disease

  • The term “disease” means “uncomfortable.” A diseased person’s internal organ systems will not operate properly. A disease is a physical or mental suffering that the body endures. Either external or internal elements might cause an infection.
  • A healthy state is one in which a person is fit and well in all aspects, including physical, mental, psychological and emotional well-being. Besides, being healthy means being free of all diseases.
  • However, being disease-free does not imply being healthy; for example, a disease-free individual may not be as mentally stable as a healthy person.
  • Poor health can exist in people even when there isn’t a clear-cut sickness to blame. It is why we consider societies and communities when we think about health. When we think about disease though, we focus on individual patients.

Disease and Its Causes

  • When a person becomes ill, the functioning or the look of the body’s systems begins to deteriorate.
  • These variations will result in symptoms and indicators of the disease. Symptoms of disease are defined as unusual changes experienced by the individual.
  • Headache, cough, diarrhoea and pus-filled wounds are some of the symptoms that may arise throughout the diseased condition. These symptoms suggest the presence of an illness but not the condition’s cause.
  • These imply that there may be an illness, but they do not specify the condition. A headache, for example, could be due to exam stress, or in rare cases, meningitis or could also be a dozen other disorders.
  • Physicians will check for illness signs based on the symptoms. Signs will provide a more definitive indication of the presence of a specific disease. Physicians will also order laboratory testing to help them better understand the condition.

Acute and Chronic Diseases

As mentioned in the Extramarks NCERT Solutions For Class 9 Science Chapter 13, based on duration, diseases can be classified into two:

  1. Acute Diseases: Acute diseases typically last for a brief length of time without causing harm to the body. Consider the common cold, which is the best example of acute disease.
  2. Chronic Diseases: Chronic diseases can endure for an extended length of time and have serious consequences for one’s health. Diabetes is an example of chronic disease. Chronic diseases, as opposed to acute infections, have more severe long-term effects on a person’s health.

Any sickness that impairs the functioning of any portion of the body impacts our health. It is so because maintaining good health depends on all bodily functions.

Causes of Diseases

Two factors can cause diseases, as mentioned in the Extramarks NCERT Solutions For Class 9 Science Chapter 13, namely,

  1. Internal Factors: these include hormonal imbalance, allergic reactions, genetic disorders, malfunctioning of body organs, etc.
  2. External Factors: these include unhealthy diet, disease-causing germs (bacteria, viruses, fungi), pollution in the environment, unhealthy lifestyle, etc.

Infectious and Non-Infectious Causes

Based on its origin, transmission and duration, a disease may be classified in the following ways as mentioned in the NCERT Solutions For Class 9 Science Chapter 13:

  1. Infectious: Infectious diseases are caused by microorganisms, including bacteria, viruses, fungi and protozoa. These can be carried from one person to another via numerous mediums, such as air, food and water.
  2. Non-Infectious: Non-infectious diseases are caused by genetic defects. They are sometimes called non-communicable diseases because they do not transfer from person to person. Cancer is an example of a non-infectious disease.

Different diseases have different means of spreading and being treated and prevented at the community level. It would be heavily influenced by whether the immediate causes are infectious or non-infectious.

Infectious Agents

  • Infectious agents are organisms that cause diseases. The host organism serves as its food source. Some examples include bacteria, viruses, fungi, protozoa and helminths.
  • Bacterial and ulcer-caused diseases include typhoid, cholera, tuberculosis, anthrax, pimples and peptic ulcers.
  • The common cold, influenza, dengue fever, SARS and AIDS are viral illnesses.
  • Fungi are responsible for skin illnesses.
  • Malaria, kala-azar and sleeping sickness are all caused by Protozoa.
  • Helminthic worms cause intestinal infections also known as elephantiasis.

We can better treat diseases caused by them if we understand their properties. We can determine which medication would be effective against which infectious agent. Infectious agents have the following features in common:

  1. Viruses dwell in the body of their host.
  2. Bacteria do not normally reside within the host body.
  3. Fungi, bacteria and viruses multiply rapidly.
  4. Worms are slow to reproduce.

Means of Spreading of Infectious Diseases

Infectious diseases are transferred by microbial organisms when an infected individual comes into touch with a healthy person. Consequently, they are also known as communicable diseases. Microorganisms are also spread through physical contact, air, water and vectors.

  1. Airborne diseases: Diseases transferred through the air in the form of droplets. Some airborne diseases are the common cold, pneumonia and tuberculosis.
  2. Waterborne diseases: Diseases spread by the effluent of someone with an infectious disease. For example, cholera can contaminate the drinking water of surrounding residents.
  3. Physical touch: Diseases spread through direct contact. AIDS is spread by various routes, including blood-to-blood contact with infected individuals, transfer from an infected mother to her child during pregnancy and intimate contact between partners.
  4. Vectors: Also referred to as carriers. Female mosquitoes, dogs, hens and other vectors are responsible for transmitting pathogens from one person to another. The rabies virus is spread through dog and cat bites.

Organ-Specific and Tissue-Specific Manifestations

  • Microorganisms target a specific site in the body. Symptoms are indications of the organ/s being infected.
  • Malaria-causing microbes enter the human body through a mosquito bite, reach the liver and start destroying red blood cells.
  • The signs and symptoms of the disease depend on the target tissue or organ. If the liver is targeted, it will lead to jaundice. If the brain is targeted, headaches, vomiting, fits or unconsciousness will occur.
  • An active immune system instructs many cells to reach the affected tissue and kill the disease-causing microorganism. This recruitment process is known as inflammation.
  • It is also vital to remember that the severity of disease manifestation is determined by the number of microorganisms in the body. If the number of microorganisms is relatively small, illness signs may be minimal or unrecognised. However, if there is a great number of the same germ, the sickness can be severe enough to be fatal.
  • The immune system plays a vital role in determining the number of microbes surviving inside the body.

Principles of Treatment

An infectious disease can be treated in several ways:

  1. The first is to lessen the effects of the disease. Antibiotics are medicines that are used to treat diseases caused by bacteria, fungi and protozoans. An antimicrobial medication is a penicillin. Antiviral medications are used to treat viral illnesses. In comparison to antibacterial medications, these drugs are relatively complex to manufacture. Despite this limitation, there are currently effective antiviral medications, such as those used to treat an HIV infection.
  2. The second is to eliminate the source of the disease. One method is to utilise antimicrobial medications. They are classified as viruses, bacteria, fungi or protozoa. Each organism category will have some key biochemical life mechanism unique to that group and not shared by the others. These processes could be mechanisms for creating new substances or pathways for respiration. Our cells can produce new chemicals using a mechanism distinct from bacteria. We need to identify a medication that inhibits bacterial synthesis while not interfering with our own. It is what the antibiotics we are all familiar with accomplish. Similarly, some drugs kill protozoa, such as the malarial parasite.

Principles of Prevention

  • There are two approaches: a generic one and one that is particular to each disease. The most general methods of infection prevention involve avoiding exposure.
  • By considering the infectious bacterial dissemination methods, we can prevent exposure to them.
  • We can prevent exposure to airborne germs and those carried by droplets by establishing living conditions that are not overcrowded, maintaining proper physical distance, wearing appropriate masks, practising hand cleanliness and so on.
  • We can reduce exposure to waterborne microorganisms by providing safe drinking water. Authorities can accomplish it by treating the water to eliminate any microbial contamination.
  • We can create clean conditions to prevent vector-borne diseases. For example, it would not allow mosquito breeding. In other words, public hygiene is a critical component of infectious disease prevention.
  • Like any other system in our body, the immune system will not work properly if correct and adequate nourishment and nutrients are unavailable. As a result, providing sufficient food for all is the second basic principle of infectious disease prevention.

To understand more about diseases, their causes, types and prevention, students must study the NCERT Solutions For Class 9 Science Chapter 13.


Immunisation is the process of becoming immune or resistant to an infectious disease. The most prevalent method of immunising people is through vaccines.

The process of immunisation depends on immune system cells preserving the memory of a pathogen. The vaccination comprises an inactivated or weakened pathogen or its antigen (protein). When these antigens are introduced into the body, our immune system generates antibodies that neutralise the infection. The immune system also remembers the specific illness, and when infected again, it responds with increased vigour to eradicate pathogens or related species faster.


Antibiotics are antimicrobial medications created by other species, such as bacteria and fungi, and are used to treat others from hazardous infections caused by harmful microbes or pathogens. How antibiotics work is as follows:

  1. Modifications to cell membranes
  2. Blocking the activity of antimetabolites.
  3. Reduction in the production of nucleic acids.
  4. Preventing the synthesis of cell walls.
  5. A decline in the production of proteins.

NCERT Solutions For Class 9 Science Chapter 13: Exercise and Solutions

Extramarks offers students authentic, practical and dependable study materials. Our NCERT Solutions For Class 9 Science Chapter 13 comprises multiple-choice (MCQ), short-answer and long-answer questions. Students can use them to ace examinations and improve their grades.

Students can view NCERT Solutions For Class 9 Science Chapter 13 by clicking on the links below:

Class 9 Science Chapter 13: Very Short Answer Type Questions

Class 9 Science Chapter 13: Short Answer Type Questions

Class 9 Science Chapter 13: Long Answer Type Questions

Students may access NCERT Solutions For Class 9 Science Chapter 13 and other chapters by clicking on the links below. In addition, students can also explore NCERT Solutions for other classes below.

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Key Features of NCERT Solutions For Class 9 Science Chapter 13

Extramarks NCERT Solutions For Class 9 Science Chapter 13 make it simple and easy to understand the chapter’s central concepts. Students can use this resource to quickly study all the essential concepts taught in class, which will help them do well on their examinations.

The following are some of the essential aspects of Extramarks NCERT Solutions For Class 9 Science Chapter 13 on How Do We Fall Ill:

  • Students can handle end-text problems using the Extramarks solutions, which provide comprehensive answers to the chapter questions and example test questions to help them become well-versed in their subject areas.
  • Our NCERT Solutions For Class 9 Science Chapter 13 is created by highly qualified and experienced experts who meticulously follow the most recent NCERT textbooks to give students with authentic and dependable study materials.
  • Extramarks regularly updates its NCERT solutions following the CBSE Board. Students can usefully apply these useful notes because most of the questions on CBSE board exam question papers are solely drawn from the NCERT.
  • By summarising the chapter’s core concepts, the NCERT Solutions For Class 9 Science Chapter 13 provides a foundation for students to resolve queries and problems.

FAQs (Frequently Asked Questions)

1. What are the many ways in which diseases spread?

The following are the main ways that infectious diseases are spread: air, water, bodily fluids and sexual contacts (cough droplets, sperm, etc.), pests and direct contact with an infected individual. These vectors or routes of contact are how disease-causing microorganisms are passed from one person to another.

2. What is the immune system?

Our bodies are shielded from disease by an intricate network of cells, tissues and organs known as the immune system. Our body’s defence mechanism is known as the immune system.

The immune system detects and destroys disease-causing bacteria in our bodies with the help of special cells known as white blood cells. Because these cells are present in circulation, they circulate throughout the body and monitor it.

Antigens are microorganisms or any foreign substance that penetrates our body. When the immune system recognises these antigens, it produces antibodies that bind to them and subsequently destroy them with the assistance of other cells. Immunity refers to a body’s ability to resist disease through antibodies.