Health and its failure.


→ ‘Health’ is a state of being well enough to function well physically, mentally and socially.

Disease: Any disturbance in the structure or function of any organ or part of body.
→ The various causes of diseases are pathogens (virus, bacteria), lack of nutritious diet/balanced
diet and lack of public health services.
→ Acute diseases occur suddenly and lasts for a short duration while chronic diseases develop
slowly and lasts for long period of time.
→ The diseases/infections can be prevented by life style (exercise, proper sleep, enough relaxatio
modification, taking balanced diet, good personal health and hygiene and also maintaining a cle
and healthy surrounding.
→ Treatment involves killing of the microbes/pathogens.


→ Health is a state of physical, mental and social well-being.

• The conditions necessary for good health are:
(i) Good physical and social environment.
(ii) Good economic conditions.
→ Good physical and social environment includes clean surroundings, good sanitation, proper
garbage disposal and clean drinking water.
→ Good economic conditions includes job opportunities for earning to have nutritious food and to
lead a healthy life.
→ Personal and Community Issues Both Matter for Health
→ All those activities which people do both individually and in groups for the development of their
society, constitute the community health.
→ Personal and community health are supplementary to each other.
→ We protect ourselves by keeping our body clean.
→ For this, we also require a good and healthy environment in our surroundings.
→ We can have this only by the means of community health and development.
→ So, both personal and community health are inter-related.
Differences between Being Healthy and Disease-free
Being Healthy Being Disease-free
It is a state of being well enough to function well
physically, mentally and socially.
It is a state of absence from diseases.
It refers to the individual, physical and social environment.
It refers only to the individual.
The individual has good health. The individual may have good health or poor health.
Disease and Its Causes

What does disease look like?
→ When a person is affected by a disease either the functioning or the appearance of one or mor
systems of the body will change for the worse.
→ These changes give rise to symptoms and signs of disease.
→ On the basis of the symptoms the physicians look for the signs of a particular disease and
conduct tests to confirm the disease.

Types of Diseases

(i) Acute Diseases: Acute diseases which last for only very short period of time and affect body
suddenly and quickly. Example: Cold, cough, typhoid etc.
(ii) Chronic Diseases: The diseases which last for a long time, even as much as a life time, are cal
chronic diseases. Example: Diabetes, tuberculosis, elephantiasis etc.
Causes of Diseases
• Diseases are caused by:
→ Pathogens like virus, bacteria, fungi, protozoans or worms.
→ Poor health and under nourishment.
→ Hereditary and genetic disorder.
→ Lack of proper treatment of immunization.
→ Environmental pollution (air, water etc.)


Infectious and Non-infectious diseases, their causes and manifestation

Infectious and Non-infectious Diseases

(i) Infectious Diseases: The diseases which spread due to infection by micro-organisms are called
infectious diseases.
→ It is communicated from diseased person to healthy person, caused by some biological
agents/pathogens like viruses, bacteria, fungi, protozoans, fungi worms.

(ii) Non-infectious Diseases: The disease which does not spread by contact between infected and
healthy person through air and water, is called non-infectious disease.
Example: Arthritis, heart disease.

Different Micro-organisms
SARS Viruses

→ SARS viruses are coming out of the surface of an infected cell (see the arrows for example).
→ 500 nanometer = 0.5 micrometer = 0.001 millimeter.
→ Trypanosoma is a protozoan organism.
→ It causes sleeping sickness.
→ The saucer-shaped substance lying next tothe protozoa, is a red blood cell.
Staphylococcus bacteria
→ The Staphylococcus bacteria causes acne.
→ The scale is indicated at the line at the top left of the picture. It is 5 micrometers long.
Adult roundworm
→ Adult roundworm is found in the small intestine.
→ Its technical name is Ascaris Lumbricoides.
→ The ruler next to it shows 4 centimeter to give an idea of the scale.
→ Leishmania, the protozoan organism causes kala-azar.
→ The organisms are oval-shaped, and each has one long whip-like structure.
→ The immune cell is about ten micrometres in diameter.


→ Antibiotics blocks biochemical pathways important for bacteria. Hence, they are effective against
them. Example: Penicillin, tetracycline.
→ Many bacteria make a cell wall to protect themselves, the antibiotics (Penicillin) blocks the
bacterial process that builds cell wall.
→ Antibiotics works only against the bacteria and not against the viruses.

Means of Spread of Infectious Diseases


→ Infectious diseases spread from an infected person to a healthy person through air, water, food,
vectors, physical contact and sexual contact.
• Through air: By sneezing and coughing, the microbes spread into air and enter into the body of
healthy person, like common cold, tuberculosis, pneumonia etc.
• Through water : The microbes enter into our body by drinking/eating polluted and contaminate
water/food, like cholera, amoebic dysentery etc.
• Vectors: Some organisms like female anopheles mosquito also work as a vector of disease, like
malaria, dengue, yellow fever etc.
• Through sexual contact: Syphilus, AIDS spread by sexual contact with infected person. AIDS virus
can also spread through blood transfusion and from the mother to her child during pregnancy an
through breast feeding.

Diseases caused by microbes (Virus, Bacteria and protozoans) and their prevention

Revision Notes for Science Chapter 13 - Why do we fall ill (Class 9th) |  askIITians

Principles of treatment and prevention

Principles of Treatment

→ The treatment of infectious diseases consists of two steps. They are to reduce the effects of the
disease (symptoms) and to kill the microbes which caused disease.
(i) To reduce the effects of the disease: This can be done by taking medicines to bring down the
effects of the disease like fever, pain or loose motions etc. and by taking bed rest to conserve our
(ii) To kill the microbes: This can be done by taking suitable antibiotics and drugs which kills the
microbes and the disease is cured.

Principles of Prevention

• There are two ways of prevention of infectious diseases. They are general ways and specific way
(i) General ways of prevention: Public hygiene is most important for prevention of infectious
diseases. Proper and sufficient food for everyone will make people healthy to resist the infection.
→ Air borne diseases can be prevented by living in conditions that are not crowded. Water borne
diseases can be prevented by providing safe drinking water.
→ Vector borne diseases can be prevented by providing clean environment.

(ii) Specific ways of prevention: There are disease specific measures which are used to fight them
It is done by Immunisation.
→ This is the process of introducing a weakened pathogen inside the body of the host to fool his/h
immune system to produce antibodies against that particular disease.
→ Not only does our immune system fight the disease (feeble pathogen), but also keeps a memo
of the incident by keeping those antibodies in blood.
→ Thus, next time even if the disease will strike the host’s body with full vigor, the body will be able
protect itself with the help of these antibodies.
→ This is also the basic law followed by vaccination programmes done for infants.

Classification of infectious diseases based on their causative agents.... |  Download Scientific Diagram

Pulse Polio programmes.

Pulse polio programme-

Pulse polio immunization programme forms the largest single day public health project. Pulse means a dose of a substance (here polio vaccine) especially when applied for a short period of time. It was conducted for the first time in 1995. The program uses oral polio vaccine or OPV. As per the national immunization Schedule (NIS), a dose of 3 drops is given orally to the child, i.e. one dose each at 1.5, 2.5 and 3.5 months age. Finally a booster dose si given at the age of 1.5 years. After oral administration. Virus particles in the vaccine begin to live in the intestine of the human body and multiply. It leads to production of protective molecules in the intestine and the blood.

1. Introduction

Why do we fall ill


Health is a state of complete physical, mental and social well-being.

Basic conditions for good health:

•    Proper balanced and nutritious diet.
•    Personal hygiene.
•    Clean environment and surroundings.
•    Healthy air, no pollution in the surrounding.
•    Regular exercise.
•    Proper rest.
•    Good standard of living and economic status.

Disease: 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.

Disease is classified as Acute and Chronic.

Acute disease: Diseases that last for only short period of time, e.g., headache, common cold etc.
Chronic disease: Diseases that last for long time,’ are called chronic diseases, e.g., elephantiasis, tuberculosis, etc.

Causes of diseases: Immediate cause and contributory cause.

Immediate cause: The organisms that enter our body and causes disease is called immediate cause. For example, virus, bacteria, protozoa etc.

Contributory cause: The secondary factors which led these organisms enter our body are called as contributory cause. For example, dirty water, unclear
surroundings, contaminated food, improper nourishment, poverty, poor standard of living etc.
Diseases may be due to infectious and non-infectious causes.

(a) Infectious causes: Diseases where microbes are the immediate causes are called infectious diseases. The infection spreads from one person to another.

(b) Non-infectious causes: Some diseases that do not spread in the community, but remains internal are called non-infectious diseases. Example, cancer, genetic abnormalities, high blood pressure etc.

2. Types of Diseases

Infectious diseases (Communicable diseases): When a disease-causing organism enters our body it causes infection, it multiplies and grows in the body called host and micro-organisms multiplies in the host body.
Non-Infectious diseases (Non communicable diseases): Diseases that are not contagious are called non-infectious or non-communicable diseases because they can't be spread from one person to another. So, there's no vector for them to move from one host to another, no virus, no bacteria, no pathogen.
Instead, these diseases are caused by other factors, such as genetics, environment, and lifestyle behaviours.

3. Mode of Transmission of Diseases

Infectious diseases spread through:

•    Air: Causes air-borne diseases due to bacteria, virus e.g., common cold, influenza, measles, tuberculosis.
Food and water: Is caused due to contaminated food and water that contains bacteria, virus, worm etc. Example, cholera, typhoid and hepatitis.
Contact: Many diseases spread by contact of infected person with the healthy person. Examples, fungal infection, scabies etc.
AIDS and syphilis spread due to sexual contact.
Body fluids: Body fluids like blood, semen, mother milk when infected can also cause disease. Example, AIDS.


4. Symptons and Signs, Prevention of Diseases

Antibiotics: These are the chemicals (medicine, drugs) that block biochemical pathways important for bacteria. They are used for diseases caused by bacteria.

Inflammation: When an active immune system releases many cells to the affected tissue to heat-off the disease-causing microbes it is called inflammation. Local effects caused on body due to inflammation are—swelling, pain, fever and redness.

Principles of treatment

•    To reduce the effects of the diseases.
•    To kill the cause of the disease i.e., to kill the microbes like bacteria fungi, protozoa.

Principles of Prevention

•    General method
•    Specific method

General ways of preventing infections relate to preventing exposure.

Prevention of exposure can be done by following ways:

•    For air borne infections—valid -visiting public place, cover your nose and mouth while coughing.
•    For water borne infections- Drink, clean and boiled drinking water.
•    For vector borne infections Keep the surroundings clean, do not keep any puddle of water open in the surrounding as it allows the breeding of mosquitoes.
•    Self-immune system that can (fight off and kill microbes when it enters our body.
•    Availability of proper and sufficient -food for everyone.

Vaccination & Immunization

•    Vaccination: The use of vaccines to stimulate your immune system to protect you against infection or disease
•    Immunization: The process of making you immune or resistant to an infectious disease, typically via vaccination