Class Nine Science Chapter 13 Why do we fall ill Questions
Chapter 13: Why do we fall ill?
Points to remember: Questions
When the body is not at ease i.e., comfortable then it is said to have a disease. When there is a disease the functioning or appearance of one or more systems of the body changes.
Types of Disease: Depending on their duration, diseases may be of the two types
(i) Acute Diseases
(ii) Chronic Diseases
(i) Acute Diseases: Diseases that last for only a short period of time, are called acute diseases.
Examples: headache, common cold etc.
(ii) Chronic Diseases: Diseases that last for long, are called chronic diseases. Examples: elephantiasis, tuberculosis etc.
Causes of Disease: Causes of the disease may be immediate or contributory.
(i) Immediate causes: The organisms that enter the body and cause the disease are called the immediate cause. For example viruses, bacteria, protozoa etc.
(ii) Contributory causes: The secondary factors which led these organisms to enter our body are called contributory causes. For example, dirty water, unclear surroundings, contaminated food, improper nourishment, poverty, poor standard of living etc. This can further be of the following types
(i) Poor health due to inadequate diet: It leads to a deficiency of one or more nutrients. Example: Kwashiorkor, a nutritional deficiency disease occurring due to low protein diet.
(ii) Genetic disorders: These present the same birth. Haemophilia is a genetic disease
(iii) Various pollutants present in environment: Pollutants in the air, water and soil also contribute to causing disease, For example, intensive use of nitrate fertiliser cause methemoglobinemia.
(iv) Improper functioning of any body organ: Oron – communicable diseases like diabetes blood pressure and heart diseases are due to malfunctioning of body organs.
(v) Lack of public services or poor economic conditions: It also contributes to the causes of disease.
(a) Based on duration :
Acute disease: Disease that lasts for only a short period of time is called acute disease.
Example: common cold etc.
Chronic disease: Disease that lasts for a long time is called chronic disease.
(b) Based on the cause: Diseases can be grouped as infectious/communicable disease and non-infectious, non-communicable disease.
Infectious diseases: They are caused due to microbes and can spread from one person to another.
Non-infectious disease: These types of diseases do not spread in the community, but remain internal. For example, cancer and genetic abnormalities.
Infectious Diseases: Infectious diseases are those diseases which can be communicated by microbial agents from an affected person to someone else in a variety. Some infectious diseases develop and spread rapidly to many people and are called epidemic diseases.
Infectious Agents: The unicellular or multicellular organisms that cause infection are called infectious agents. Some of the infectious agents are viruses, bacteria, fungi, protozoa, etc.
Infectious diseases are caused by the following
(i) Viruses cause common colds, influenza, dengue, fever and AIDS.
(ii) Bacteria cause diseases like typhoid, tuberculosis, cholera and anthrax.
(iii) Fungi cause diseased skin infections
(iv) Protozoan microbes cause many diseases like amoebiasis, malaria and kala-azar.
(v) Worms cause diseases like elephantiasis.
Antibiotics: These are the chemicals (medicine, drugs) that block biochemical pathways important for bacteria. They are used for diseases caused by bacteria. Antibiotic penicillin blocks
the bacterial process of building cell walls and bacteria becomes unable to make cell walls and dies easily.
Antibiotics do not work against viral infections because the virus does not use the same pathway as that of bacteria. Antibiotics include streptomycin, tetracycline, chloromycetin, chloramphenicol etc.
Means of Spread
Diseases spread through various modes like air, water, sexual contact, vectors etc.
(i) Airborne Diseases: In such diseases, disease-causing microbes spread through the air.
Examples of airborne diseases are common colds, coughs, pneumonia and tuberculosis.
Such diseases spread more in overcrowded areas
(ii) Waterborne diseases: In such diseases, disease-causing microbes spread through water and take nourishment through stagnant water. Examples of water-borne diseases are cholera, typhoid and hepatitis.
(iii) Sexually – transmitted diseases: These are microbial diseases, that are transmitted by sexual contact from one partner to others. Syphilis and AIDS are examples of sexually transmitted diseases.
(iv) Spread of Diseases through Vectors: Many animals living with us carry the infecting agents from one infected person to another potential host. These animals act as intermediaries and are termed vectors of ways.