Why Do We Fall Ill Class 9 Notes | Comprehensive


Why Do We Fall Ill Class 9 Notes – Health refers to a condition where an individual experiences overall well-being in terms of physical, mental, and social aspects.

The Immune System

The immune system is an essential component of the body’s defence against diseases, poisons, and other harmful substances. It has specialised cells like lymphocytes and macrophages that eradicate the harmful microorganisms and control their population. While a weak immune system raises the danger of illness, a strong immune system reduces it. The immune system has a strong memory of previous illnesses, which helps to stop them from recurring. Based on this memory, vaccination introduces vulnerable microbes into the body to produce immunity and halt the spread of disease. A good diet is essential for the immune system to work effectively and combat illnesses.

Basic conditions for good health

  • Regular physical activity and exercise
  • Eating a balanced and nutritious diet
  • Getting enough sleep each night
  • Avoiding harmful habits such as smoking and excessive alcohol consumption.
  • Maintaining good hygiene by washing hands frequently and maintaining a clean living environment.
  • Managing stress and practicing good mental health habits
  • Regular medical check-ups


Disease is a condition or disorder that affects the body’s organs or tissues’ normal function and can cause discomfort or malfunction on the physical, mental, and/or emotional levels. Infections, genetic anomalies, environmental pollutants, inadequate nutrition, lifestyle choices, or a mix of these may all be contributing causes. Infections, autoimmune conditions, malignancies, metabolic, cardiovascular, and neurological illnesses are a few examples of common diseases.

Acute disease

Acute diseases are those that appear quickly and last for only short period of time, typically from a few days to a few weeks. Some acute diseases are Appendicitis, influenza, pneumonia, strep throat.

Chronic disease

A chronic disease is a disorder that affects a person’s health for a longer length of time, typically more than three months and sometimes for the rest of their lives. It is brought on by a confluence of many genetic, environmental, and lifestyle variables. Asthma, diabetes, heart disease, rheumatoid arthritis, and several cancers are a few examples of chronic illnesses.

Causes of diseases

There are numerous potential causes for diseases, such as:

  1. Microorganisms like bacteria, viruses, fungus, and parasites are the main cause of infections.
  2. Genetic mutations or hereditary traits can lead to some diseases.
  3. Exposure to poisons, pollution, radiation, or other dangerous substances is one example of an environmental factor.
  4. A variety of diseases can be caused by poor diet, inactivity, substance misuse, and other lifestyle choices.
  5. These are illnesses like lupus and multiple sclerosis that develop when the immune system of the body assaults its own healthy tissues.
  6. As we get older, our bodies are more prone to being sick.
  7. Unknown causes: A illness may occasionally have an unknown cause.
Different types of Causes of Disease

Pathogens such as viruses or bacteria can be responsible for causing diseases, while genetic mutations and other internal factors can also contribute to the development of certain illnesses. In other words, diseases can arise from either external factors, such as infectious agents, or internal factors, such as genetic abnormalities.

Infectious Diseases

Pathogens like viruses, bacteria, fungus, or parasites cause infectious diseases, which can transmit from one person to another through a variety of channels such contact with human fluids, contaminated surfaces, or airborne droplets. Colds, flu, measles, TB, malaria, HIV/AIDS, COVID-19, and other contagious illnesses are a few examples.

Non-infectious diseases

Diseases classified as non-infectious are those that cannot be passed from one person to another and are frequently not brought on by microorganisms. Diabetes and hypertension are examples of non-infectious diseases. These conditions are brought on by a range of internal and external causes, including genetics, way of living, and environmental variables.


Pathogens are agents that come from outside an organism and that can harm or afflict it. It is possible for pathogens to be dangerous germs like bacteria, viruses, fungus, or protozoa that can lead to a variety of diseases and infections. In other words, pathogens might include a wide range of microorganisms that have the potential to cause disease or infection. They are exterior agents that can enter and harm living things.


Living things called vectors are capable of spreading infections from one host to another. Mosquitoes, rats, and mice are a few examples of vectors. They can carry a variety of infectious diseases and spread them from an infected host to a susceptible recipient. Otherwise put, vectors are living things that serve as carriers for infections and are crucial in the spread and transmission of numerous infectious diseases.


Bacteria are a type of microorganism that can be found in nearly all environments. While not all bacteria are pathogenic, some can cause harm to humans and other organisms. However, many bacteria are actually beneficial and play important roles in human life. For example, bacteria are essential for processes such as digestion, the production of antibiotics, and nitrogen fixation.


A virus is a type of microorganism that is inherently pathogenic, meaning it has the potential to cause disease in its host. Unlike bacteria, viruses lack the molecular machinery to replicate on their own and must rely on a host cell to reproduce. Once a virus enters a host cell, it hijacks the host’s cellular machinery to replicate itself and produce more virus particles, which can ultimately lead to the destruction of the host cell. Many common diseases are caused by viruses, including the common cold, influenza, dengue fever, AIDS, and many others.


In order to gain nutrition, fungi, which are eukaryotic creatures, saprophytically break down organic substances in their surroundings. They can exist as single-celled or multicellular creatures and can be found in a variety of habitats. Certain fungus, including ringworm and nail infections, can infect people and other living things and cause infections and disorders. Fungi are diverse, significant organisms, but some of them can be harmful to people’s health.


A parasite is a type of organism that cannot survive on its own and instead lives in or on another organism, known as the host. The parasite benefits by taking resources from the host, such as nutrients, blood, or shelter, and in doing so, it often causes harm or disease to the host. The parasite relies entirely on the host for its survival, as it cannot live or reproduce without it.


Microorganisms such as bacteria, viruses, fungi, and parasites invading and multiplying within a host organism is what causes an infection. These microbes have the potential to harm the host by destroying cells, tissues, and organs, which can result in a variety of symptoms and diseases. Direct touch, ingestion, inhalation, or by vectors like insects are just a few of the ways that infections can spread.


AIDS, which stands for Acquired Immunodeficiency Syndrome, is a condition that results from infection with the Human Immunodeficiency Virus (HIV). HIV attacks and gradually destroys the immune system of the infected individual, leaving them susceptible to a variety of infections and diseases.

Prevention of Disease


Antibiotics are drugs produced by other organisms, such as specific fungi and bacteria, and they are used to treat illnesses brought on by dangerous pathogens. These antibiotics function by interfering with the pathogen’s capacity to proliferate and expand, which ultimately aids the body’s immune system in battling the illness.

  • Inhibition Antimetabolite Activity.
  • Alteration of Cell Membranes.
  • Inhibiting of Cell Wall Synthesis
  • Inhibition of Nucleic Acid Synthesis.
  • Inhibition of Protein Synthesis
Principles of treatment

Depending on the particular ailment and characteristics specific to each patient, different diseases may require different treatment philosophies. Nonetheless, a few widespread therapeutic tenets are as follows:

  • Correct diagnosis: The right treatment depends on an accurate identification of the ailment. This could entail a thorough medical history review, physical exams, and tests.
  • Targeted therapy: The disease and its underlying causes should be the focus of the treatment. This could entail taking medicine, having surgery, altering one’s lifestyle, or a combination of these.
  • Personalized care: Care should be provided according to the needs of each patient, taking into account their age, general health, and any additional medical issues they might be suffering from.
  • Monitoring and follow-up: To evaluate the efficacy of treatment and make any necessary adjustments to the treatment plan, routine monitoring and follow-up visits are crucial.
  • Complications management: The goal of treatment should be to prevent or control any consequences brought on by the illness, such as infections or organ damage.
  • Patient education: Patients should get information about their illness, available treatments, and any lifestyle modifications that might be required to effectively manage the condition.
  • Multidisciplinary approach: In some situations, it may be required to provide complete care with the help of a multidisciplinary team that includes experts in many different medical specialties, including cardiology, endocrinology, and oncology.
Preventive Measures

Infection can be prevented and good health can be maintained by taking a variety of preventive actions. Among the most popular actions are:

  • Treating and storing drinking water safely: Safe drinking water treatment and storage can help reduce exposure to pathogenic bacteria that can lead to diseases.
  • Hand hygiene: Maintaining good hand hygiene can help stop the transmission of infectious diseases by washing hands with soap before eating and after urinating.
  • Food covering: Food covering can help stop flies from contaminating it and spreading infections.
  • Cleaning fruits and veggies: Fruits and vegetables can be cleaned effectively to get rid of pollutants and harmful microorganisms.
  • Avoiding open defecation: Open defecation should be avoided as it can promote the transmission of diseases.
  • Proper waste disposal: Maintaining a sound drainage system and disposing of trash properly can both assist stop the spread of infectious diseases.
  • Having a healthy, balanced diet: Consuming a nutritious diet can strengthen the immune system and make it more resistant to infections.
  • Regular exercise: Frequent exercise can also strengthen the immune system and lower the chance of infection.
  • Immunization: Immunizations are safe and effective for people of all ages in protecting against a range of infectious diseases.

Immunization is a technique that makes people resistant to or immune to the sickness, assisting in protecting them from infectious diseases. Vaccination is the most used method of immunization.

Immune system cells use specific proteins called antigens that are present on the surface of the pathogen to recognize and react to them during the vaccination process. Inactivated or compromised versions of the pathogen or its antigens are present in vaccines. When these antigens are brought into the body, the immune system reacts by making antibodies against them, which can aid in battling the illness.

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