Concise Selina Solutions for Class 9 Biology Chapter 16 Diseases: Causes and Control

The definitions are as follows: Infection - It is the transmission of diseases from one person to another. Pathogen - A pathogen is a disease-causing micro-organism. Incubation period - It is the period between the entry of germs and appearance of the first symptoms of the disease. Diseases - Cause and Control discuss the various aspects of diseases. It provides a brief introduction to communicable and non-communicable diseases (infectious and non-infectious diseases) the different modes of transmission of diseases (water, air, food, insect-borne) endemic, pandemic and sporadic diseases.

Different diseases are caused by different pathogens such as protozoans, bacteria (tuberculosis, cholera, and typhoid), viruses (AIDS, chickenpox, hepatitis, etc.). It is a well-known fact that cell is the fundamental unit of living beings and there is constant activity in the cells and the organs in the body like beating action of the heart, filtering action of kidneys, breathing action of lungs, etc. Anything that disrupts the normal functioning of these organs will lead to improper functioning of the body.