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 some useful substances.
Bacteria are used to increase the fertility of the soil in the agricultural sector,  and preparation of medicines in the pharma industry, respectively.
Yeast is a bacteria used in the baking industries.
(Try this at home)
Take half kilogram of maida, add sugar and mix with warm water. Add a small amount of yeast powder and knead to a soft dough. You can find the dough rising after 2 to 3 hours.
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. In bakeries, yeast is used extensively for this pupose.
We will discuss some of the disease causing microorganisms in detail in the next material.