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Write a short note on:

(i) Useful micro-organisms.

(ii) Harmful micro-organisms.

Answer:

(i) Useful micro-organisms:

(a) Friendly micro-organisms: They are used for various purposes. They are used in making curd (Lactobacillus bacteria) and bread. They are ingredients of Idli, Dhoklas and Bhaturas.

(b) Commercial uses: Micro-organisms are used for the large scale production of alcohol and wine.

Yeast is grown on natural sugars present in grains such as barley, wheat, rice, fruit juices for this purpose.

(c) Medicinal uses: A very useful medicine group ?antibiotics? is prepared from micro-organisms.

Commonly-used antibiotics are formed by fungi and bacteria. Vaccines also protect us from microbes.

(d) Increasing soil fertility: Some bacteria and blue-green algae are able to fix nitrogen from atmosphere and form nitrogen compounds which increase the soil fertility.

(e) Decomposers: They decompose the dead organic substances into their constituents and clean the environment.

(ii) Harmful micro-organisms:

(a) Pathogens: Disease causing micro-organisms are called pathogens.

Diseases such as dysentery and malaria are caused by protozoa. Typhoid and tuberculosis are bacterial diseases. Virus causes common ailments such as cold, influenza and coughs.

(b) Food spoilage: Some micro-organisms spoil food, clothing and leather. Fungus developed in moisture on leather and some food articles spoils them.