Question

Whether micro-organisms are useful and harmful. How explain.(

SCERT Class 8 Telangana, Biology Chapter 3 Story of Microorganisms

Answer 1

micro organisms , though a large number can cause diseases in plants and animals , including humans . But all microbes arent harmful.
a number of microbes are very useful, particularly in industries , agriculture and medicine. In fact, their beneficial effects are far more than the harm they cause. 
1)- lactobacillus acidophilus is a bacteria which converts milk in  to curd
2)-the dough that is used to make dosa and idli ( south indian dishes ) is fermented by bacteria , streptococcus species 
3)- saccharomyces cerevisiae , bakers yeast or simply called yeast is used as a raising agent in bread making and in bakery
4)-alcoholic drinks are made using fermentation 
5)- preparation of antibiotics 
6)-used in sewage treatment
7)- microbes are used in the production of biogas
8)-they are used as the biocontrol agents
9)-microbes are used as bio fertilisers 

Answer 2

Answer:

micro organisms are harmful and useful as well the lactobacillus bacteria helps to turn milk into curd and some micro organisms when enter our body causes diseases