• Health = state of being well to function properly physically, mentally and socially
  1. Physical health – proper functioning of your whole body without difficulty
  2. Social health – clean and hygienic society with proper access to natural resources
  3. Mental health – having a positive attitude to interact with others (social equality) and to face any difficulty in life (harmony)
  • Living organisms are surrounded by nature or environment. So, their health depends upon the environment they live in.
  • Sometimes, physical health is dependent on social health. So, to be healthy one should have proper physical, social and mental health.
  • Disease = state of discomfort and having problem in the normal state that disturbs the proper functioning of the organism

A disease can be diagnosed by analyzing some signs which are unique features observed in the human having the disease and these signs are called symptoms.

  • Disease can be an effect of
  1. Intrinsic or Internal factors = disease causing factors which are present inside the human body

Organic or metabolic diseases = diseases caused by intrinsic factors

The intrinsic factors are

(a) Improper functioning of one or more body parts

Example : Cardiac failure (Heart attack)

Normal : Heart pumps blood in and out of it and helps in circulating food and oxygen to different organs of the body

Abnormal : Gradual decrease in heart beat and sudden stopping of the heart beat

(b) Genetic disorder which are passing onto the child by their parent(s)

Example : Haemophilia

Normal : Blood clotting in an area of cut or wound to stop excess blood loss

Abnormal : Blood do not clot in and area of cut or wound which results into excess blood loss

(c) Hormonal Imbalances which may result in hyposecretion (less secretion than the normal amount) or hypersecretion (more secretion than the normal amount) of a hormone secreted by an endocrine gland

Example : Diabetes mellitus

Normal : Pancreas secrete insulin hormone

Abnormal : Pancreas secrete less amount of insulin hormone (hyposecretion)

(d) Improper functioning of the immune system which consist of immune cells which protect the body from any foreign harmful object

Example : Auto-immune diseases

Normal : The immune system indicates foreign organisms (bacteria or virus) and respond to them to destroy them and protect the body

Abnormal : The immune system indicates its own cells (tissues or organs) as foreign object and respond by destroying the body’s own cells

2. Extrinsic or External factors = disease causing factors present outside the body which enter into the body

  • The extrinsic factors are

(a) Pathogens (disease causing microorganisms) such as virus, bacteria, fungi, protozoa etc. enter the human body through air, water, soil, physical contact, food, other animals and sexual contact.

(b) Insufficient or unbalanced diet can make a person unhealthy as there is a lack of proper nutritional food which lead to many deficiency disorders.

(c) Environmental pollutants such as gases (CFC, Carbon monoxide, etc.), industrial waste, heavy metals (mercury, arsenic, etc.), pesticides etc. can affect a healthy person.

(d) Tobacco, alcohol and narcotic drugs can harm a healthy person if consumed in excess.

Diseases can be classified based on

  • Span of occurrence – Acute diseases & Chronic diseases
  • Based on birth – Congenital diseases & Acquired diseases

Acute diseases – diseases that remain for very short period of time

Example : Cough and Cold remains for very short time and the person gets cured within few weeks

Chronic diseases – diseases that remain for very long period of time

Example : Tuberculosis of the lungs remains for over many years and the person losses weight and feels tired all the time

Congenital diseases – diseases present from birth

may be caused due to genetic disorder, metabolic disorders, problem in any organ, improper development of fetus

are permanent, not easily curable and are transferred from parents to children

Acquired diseases – diseases developed after birth

can be classified into

  1. Infectious or Communicable diseases – disease caused by pathogens or living microorganisms
  • can be rapidly spread from a diseased person to a healthy person by different methods (communicable)

Example : Bacteria Staphylococcus causes acne on skin

2. Non-infectious or Non-communicable diseases – diseases caused by improper metabolism or improper interaction between cells and tissues

  • does not get spread from unhealthy person to healthy person (non-communicable)
  • only restricted to an individual facing the problem

Example : Cancer is a genetic abnormality which results into uncontrolled division of cells

So, acquired diseases may or may not be permanent and curable

Significance of classification of diseases

  1. Every disease has its unique mechanism of occurrence and means of spreading
  2. Curable diseases require treatment which are different for different diseases
  3. Diseases which are not curable can be managed to extend the lifespan of an individual
  4. Congenital diseases can be prevented from being inherited with proper counseling and selection of partner for marriage
  5. Acquired diseases can be prevented or maintained with proper diet and medication

Infectious Diseases

Infectious Agents

The world is filled with living organisms which are diverse from each other and based on their unique characteristics they are classified into different groups. Some living organisms survive and reproduce inside human (host) body by taking control over the host cells and utilize its nutrition and cellular pathways. These living organisms are called infectious agents.

Means of Spread

Infectious diseases are also called communicable diseases because they can be communicated by getting transferred from an infected person to a healthy person. So, diseases can be transferred by the following methods :

  1. Air-borne diseases – disease-causing microbes spread through the air
  • Microbes can spread through little droplets thrown out by talking, coughing and sneezing by an infected person.

Examples – Tuberculosis, Pneumonia and Common cold

2. Water-borne diseases – disease-causing microbes spread through the water

  • Microbes can spread through excretory products such as stool and urine from an infected person, suffering from any metabolic disease, which get mixed in the water of nearby locality which are used for drinking and cleaning food.

Examples – Cholera and Amoebiasis

3. Sexually-transmitted diseases – disease-causing microbes spread through only sexual contact

  • Microbes can spread through sexual contact between a healthy person and an infected person on not using any protection. These diseases cannot be spread by physical contacts such as handshakes, hugs or any kind of touch which are done socially.

Examples – Syphilis and AIDS

AIDS (Acquired Immunodeficiency Syndrome) is a sexually-transmitted diseases and the HIV (virus causing AIDS) can also spread through blood-to-blood contact with an infected person or from an infected mother to its offspring during pregnancy or through breast-feeding.

4. Direct contact – disease-causing microbes spread through direct contact

  • Microbes can spread through direct physical contact, such as handshake, kiss and hug, with an infected person.

5. Indirect contact – disease-causing microbes spread through indirect contact

  • Microbes can spread through indirect contact with an infected person. Articles which come in contact with an infected person can be a source of infection.

6. Vectors – disease-causing microbes spread through other animals

  • Microbes can spread through vectors which are other animals which live in the same environment as ours. Vectors are an intermediate carrier which carries the infectious agent from an infected person to a healthy person, which can be potential host.

Example – Malaria is transmitted by female mosquitoes (Anopheles sp.)

  • Female Mosquitoes require high nutritious food in the form of blood to lay mature eggs. So, they feed on warm-blooded animals including humans. In this process, they can transmit the protozoan received by biting an infected person to a healthy person which she bites next.

Symptoms of Disease

Human body have an organ-level organization which makes it bigger compared to the microbes. So, microbes target some specific organs or tissues to grow and reproduce. Microbes have evolved with time to be able to invade inside a body and attack specific targets.

Based on the microbe target, symptoms are visible in the form of any structural and functional changes in the body or body parts which are evidence for understanding the disease.

Based on the symptoms, doctors can predict the specific clues or signs of the disease. They use certain instruments or conduct laboratory analysis to understand the cause.

On understanding the cause, the doctors come to the conclusion about the disease.

  • The following illustration explain the above detection process with an example of the malaria disease. Mosquito, carrying the protozoan causing malaria, bites a healthy person. The protozoan enters the liver and then to the red blood cells. The red blood cells carry the protozoan to the whole body and cause the disease.

Principle of Treatment

  • Making Anti-viral medicines is harder than making Anti-bacterial medicines
  1. Viruses have very few biochemical pathways of their own and mostly they depend on the mechanisms of its host for their life processes.
  2. Viruses undergo vigorous amount of mutation (changes) in their genome which makes them uneasy to understand.

On the other hand,

  1. Bacteria have many unique biochemical pathways of their own and do not totally depend on the host for their life processes.
  2. Bacteria undergo mutation (change) in their genome very rarely which makes them easy to understand.

Principles of Prevention of Disease

  • Limitations of treatment
  1. Some chronic diseases can cause permanent damage to the body structurally and functionally.
  2. Treatment is time-taking and the patient is so weak that they require continuous rest.
  3. The patient suffering from infectious diseases can spread infection to healthy individuals which can increase the problem in the last points by many folds.

So, we should try to prevent ourselves from diseases by certain ways and try not to get infected and undergo a disease condition.

  • General ways
  • Some people suffer from a disease and some do not

Some people are weak and easily get infected, while others do not. It is because, their body do not get enough nutrition for the proper functioning of the immune system. If the body lacks a proper immune system, the person is highly prone to getting infected very often.

With a proper immune system working, a person does not have to suffer from a disease and gets prevented from any disease. The immune system has cells (White Blood Cells) which are specialized to destroy any foreign microbe entering the body.

  •      Specific ways
  1. Natural method

The same type of microbe can enter a person more than once. But every time the immune system does not react the same way. The first encounter (primary infection) is always special and requires more energy.

  • The immune cells have a unique property of keeping a memory of the microbe they have once reacted against.
  • So, when a microbe type enters a body for the second time (secondary infection) the immune system destroys it quickly and requires less energy compared to the first time.

Therefore, the body react specifically against a particular type of microbe and some specific cells (T- and B-cells) get involved which keep the memory after primary infection.

2. Artificial method

The artificial method is based on the natural method. This method is called vaccination or immunization. The word vaccination was derived by an English physician, Edward Jenner (1749 – 1823).

  • The body is injected with a microbe against which the body requires immunity.
  • The microbe lacks the ability to cause the disease (vaccine), but still the body cells can detect the microbe.
  • The immune system prepares the body to fight against the microbe and reacts against it.
  • On reacting, some immune cells (T- and B-cells) keep the memory of the reaction.
  • When an actual disease-causing microbe of the same type enters the body, the immune system destroys it quickly and prevent the disease to occur.

Example of vaccines : tetanus, diphtheria, polio etc.


Q.1.   State any two conditions essential for good health.

Ans.   Two conditions essential for good health are

(i)       proper sanitation or clean environment, and

(ii)     availability of sufficient and nutritious food.

Q.2.   State any two conditions essential for being free of disease.

Ans.   Two conditions essential for being free of disease

(i)       Maintaining proper and clean diet

(ii)     Taking vaccines against common infectious disease

Q.3.   Are the answers to the above questions necessarily the same or different? Why?

Ans.   Answers of above questions (1,2) are interconnected but different. It is because being disease free does not mean is healthy.

Q.4.   List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present would you still go to the doctor? Why or why not?

Ans. The following three symptoms indicate that we are sick and need to go to the doctor :

(i)       Have headache, shivering and high body temperature

(ii)     Have diarrhoea (loose-motions), and

(iii)    Have a wound with pus

If any one of the symptoms are present, we still should consult the doctor. This is because all the three symptoms make us feel uncomfortable and need bed rest for sometimes as a indications for disease.

Q.5.   In which of the following cases do you think the long-term effects on your health are likely to be most unpleasant?

(a)      If you get jaundice;

(b)     If you get lice;

(c)      If you get acne. Why?

Ans.   Jaundice has long-term effects on the body. It is a symptom of the disease hepatitis, which is caused by a virus. The liver gets effected and requires long time to cure the disease by taking proper treatment under the doctor’s supervision.

Lice can be removed easily with short treatment and acne get cured quickly. None of these produce long-term effects on the body.

Q.6.   Why we are normally advised to take bland and nourishing food when we are sick?

Ans.   When we fall sick, one or more organ-systems do not function normally and the immune system need to function properly. Sickness makes the body very weak. To provide the body with sufficient energy to work properly, it is advised to take bland and nourishing food. Such foods are easily digestible and restores the lost vitamins, minerals and other nutrients along with energy.

Q.7.   What are the different means by which infectious diseases are spread?

Ans.   The different means by which infectious diseases are spread are through air, through water, through vectors, through sexual contact, through direct physical contact or through indirect contact by touching used articles of an infected person.

Q.8.   What precautions can you take in your school to reduce the incidence of infectious diseases?

Ans.   Precautions can be taken in the school to reduce the incidence of infectious diseases. They can be :

i.        Keeping the whole campus clean and periodical sterilization

ii.       Providing clean and purified drinking water

iii.      Proper education should be provided the different causes of infectious diseases

iv.      Vaccination of students from time to time

v.       Not allowing students undergoing infectious disease to attend school or providing them separate place for studying away from the crowd

Q.9.   What is immunisation?

Ans.   An artificial method based on the natural method of body keeping memory of primary infection of a microbe and on secondary infection of the same type of microbe eliminates it quickly and with less energy than the first time is called immunisation or vaccination. In this method, the body is injected with a dead microbe allowing the body to interact with and react to the microbe and keep a memory of the infection. When the actual disease-causing microbe enter the body, the body is able to get rid of it quickly because of their previous memory of the primary infection.

Q.10. What are the immunisation programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area?

Ans.   At the nearest public health centre in our locality, following childhood immunisation programmes are available :

i.        for preventing polio;

ii.       for preventing tetanus, diphtheria, and whooping cough;

iii.      for preventing measles;

iv.      for preventing tuberculosis.


Q.1.   How many times did you fall ill in the last year? What is the illness?

(a) Think of any change you could make in your habits in order to avoid any of most of the above illnesses.

(b) Think of any change you would wish for in your surrounding in order to avoid any of/ most of the above illnesses.

Ans. I fell ill twice in the last year and I suffered from sore throat and cough.

  1. I stopped consuming cold things and started doing gurgling with hot water
  2. Planted more trees, cleaned my surroundings and regularly disposed the garbage

Q.2.   A doctor/nurse/health-worker is exposed to more sick people than others in the community. Find out how she/he avoids getting sick herself/himself?

Ans.   A doctor/nurse/health-worker is exposed to more sick people than others in the community. They avoid getting sick by :

  1. keeping their place of work sterilized by using phenyl
  2. keeping regularly used equipment sterilized
  3. washing their hands with soap or sanitizers after examining a patient
  4. wearing clean clothes
  5. drinking clean and purified water

Q.3.   Conduct a survey in your neighborhood to find out what the most common diseases are. Suggest three steps that could be taken by your local authorities to bring down the incidence of these diseases.

Ans.   The three most common diseases in the neighbourhood are Diarrhoea, Cold and cough, Typhoid.

Three steps that should be taken by the local authorities are

  1. providing clean water used for drinking and cleaning
  2. providing better sanitization by disposing garbage and cleaning the drainage passing through the locality
  3. arranging vaccination programmes periodically

Q.4.   A baby is not able to tell her/his caretakers that she/he is sick. What would help us to find out

(a) that baby is sick?

(b) what is the sickness?

Ans.   (a) Symptoms indicating sickness in baby are

  1. improper food intake and high body temperature
  2. continuous crying and restlessness in the child
  3. loose motion

(b) The baby is suffering from diarrhoea.

Q.5.   Under which of the following conditions is a person most likely to fall sick?

(a) when she is recovering from malaria

(b) when she has recovered from malaria and is taking care of someone suffering from chicken pox

(c) when she is on a four-day fast after recovering from malaria and is taking care of someone suffering from chicken-pox. Why?

Ans.   (c) Malaria is a disease caused by parasite Plasmodium which can be spread from an infected person to a healthy person through Anopheles mosquito (vector). Malaria causes anaemia and enlargement of liver and spleen.

The lady had suffered from malaria which has made her body weak and she needs some more time to recover completely. Other than that, she is on four days fast which has made her weaker due to lack of sufficient food. So, she is more prone to infections. She is also taking care of someone suffering from chicken-pox which is also an infectious viral disease. She has a possibility of getting infected by chicken-box.

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