GES:They are used in preparation of curd,bread,cake etc. (e. g)the bacterium Lactobacillus promotes the formation of curd from milk.The bacterium Renin is used in cheese PRODUCTION.Yeast( saccharomyces cerevisiae) is used for the purpose of baking bread. Since, it is also known as ‘baker’s yeast’.2 . They are used in the production of alcohol from :Sugar or starchWine from fruit juiceBy the process called fermentation.3. In the cleaning of the ENVIRONMENT by breaking down the organic waste into HARMLESS and usable substances.(e. g)Anaerobic bacteria degrade the animal dung into biogas and the left-over slurry can be used as manure.4. Many microorganisms (bacteria, fungi and moulds) produce certain chemicals which inhibit the growth of some other microorganisms. Such chemical compounds are known as antibiotics. PENICILLIN, Streptomycin,Tetracycline, Erythromycin and Gramicidine are some common antibiotics which is used to cure many microbacterial diseases.DISADVANTAGES:It causes many types of diseases in humans.Clostridium tetani is a pathogenic bacterium that causes tetanus.AIDS that is caused by HIV virus.Maleria is caused by parasite plasmodium.TUBERCULOSIS is caused by a bacterium-called Mycobacterium tuberculosis.