Why are there several chemical and physical methods for cont

Solution

In the twentieth century, it became quite apparent that micro-organisms were responsible for various diseases- food-borne diseases as well as water borne diseases. So it was essential to develop thorough methods to get rid of the micro-organisms.

Certain physical methods like filtration or pasteurization reduce the number of microbes, but are not able to kill off all the micro-organisms. Then there are certain techniques like ultraviolet treatment which can kill off the microbes by inducing DNA damage.

Chemical methods involve the application of specific chemical agents which inhibit growth or kill microbes on food particles, water or the surface of skin. The selection of an appropriate technique is important, since many physical and chemical agents can cause damage to the cells and tissues of the individual as well as the microbe.