Theory:

Microorganisms play a very important role in our lives. They are friendly as well as harmful.
 
They are also used in cleaning up the environment, especially the organic wastes (vegetable peels, feces, remains of animals, plants, etc.) that are broken down into harmful and useful substances by bacteria.
 
Bacteria are used in increasing the soil fertility for agricultural purposes and also in the preparation of medicines.
 
Yeast is a bacteria used in the baking industries.
 
Activity:
(Try this at home)
Take half kilogram of maida, add sugar and mix with warm water. Add small amount of yeast powder and knead to a soft dough. You can find the dough rising after 2 to 3 hours.
 
maida.PNG
 
How did that happen?
 
The yeast mixed in the dough reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. For this purpose, in bakeries yeast is used extensively.
 
We will discuss some of the disease causing microorganisms in detail in the next material.