NCERT Solutions for Class 9 Science Chapter 13 Why do we fall ill

The drugs which are obtained from micro-organism and used to kill or suppress the multiplication of micro-organism are called antibiotics, e.g. tetracycline, penicillin, chloramphenicol, streptomycin, etc.

It will provides nutrition to all parts of the body which is essential for their proper functioning, e.g. lack of vitamin A leads to night blindness, vitamin C deficiency leads to scurvy, vitamin D deficiency leads to rickets.

If surrounding are not clean chances of infections are high, House fly spreads many diseases.

On stagnant water mosquito breads which spreads malaria.

Good economic condition help to get proper and regular meal. Social harmony leads to peace and happiness. Social disharmony leads to stress, hypertension and depression.

When an infected person sneeze or cough, little droplets are thrown in air which enter body of a healthy person who gets infection. Poorly ventilated areas do not get fresh air and lack of oxygen may cause breathing problems.

It is because virus use host machinery and do not have their biological processes.

Syndrome is a group of symptoms, or signs, physical and biological which have common causes. It reduces immunity of the body to fight against infections. HIV that causes AIDS damages T4 helper cells. As a result, small cold leads to pneumonia.

(i) Remain away from specific and particular cause for discomfort or disease. For which personal and public cleanliness and good physical environment are necessary. (ii) Proper and sufficient food necessary for functioning of cells and tissues of the body.

Infectious disease show a lack of success of the immune system of the body. For the functioning of immune system properly, sufficient nourishment and easily digestible food is necessary for a sick person.

Infection causing microbes travel from patient to person through: (i) Air: Sneezing or coughing since little droplets are thrown which they reach another person through air. Example, common Cole, pneumonia etc. (ii) Water: contaminated water carries disease causing microbes which cause infection on its usage. Example, diseases such as cholera. (iii) Sexual contact: Diseases such as syphilis or AIDS are transmitted by sexual contact from one person to the other. (iv) Animals: These are intermediaries, called vectors, transmitting diseases from a patient to the host. Example, mosquitoes (Female Anopheles mosquito) cause spread of malaria.