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Microbes in Human Welfare

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
Which bacterium is responsible for the formation of curd from milk?

Lactobacillus  (Lactic acid bacteria).

Explain any one biological control of pests with examples.

Bacillus thuringinesis has been used as a biological control of pests. The bacteria Bacillus thuringiensis are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees. These bacteria produce a cry protein which when eaten by insects, release toxin in their gut and the larvae gets killed. The  scientists have been able to introduce B. thuringiensis toxin genes into plants with the help of genetic engineering. Such plants are resistant to attack by insect pests. Bt-cotton is one such example which is being cultivated in some states of our country.



In which food would you find lactic acid bacteria ? Mention some of their useful applications.


Lactic Acid Bacteria (LAB) is found mainly in the curd (yoghurt).

Uses of Lactobacillus.
1. It produces large amount of lactic acid, due to which they are used in the production of fermented food.
2.They also improve the nutritional quality of curd by increasing vitamin B12.
3. Kaffir beer is prepared from Sorghum by Lactobacillus delbreuckii.
4. Yoghurt is prepared from milk by Lactobacillus bulgaricus and Kefir (fermented milk) is prepared from milk by Lactobacillus sp.
5. LAB are also found in human stomach where they prevent the growth and multiplication of certain disease causing microbes.


Cyanobacteria is chiefly used as fertilizer in :
  • Wheat
  • Paddy
  • Mustard
  • Gram



You have been deputed by your school principal to train local villagers in the use of biogas plant. With the help of a labelled sketch explain the various parts of the biogas plant.

Biogas plant.

1. The plant consists of well-like underground tank made of bricks. This tank is called digester.

2. The roof of the digester is dome-shaped made of cement and bricks. The dome of the digester tank acts as a gas holder (or storage tank for biogas). Thus, the gas holder in this type of gas-plant is fixed.

3. There is a gas outlet at the top of dome for the supply of biogas.

4. On the one side of digester tank, there is a slopping inlet tank and on the other side there is a rectangular outlet tank, or overflow tank. Both these tanks are made of cement and bricks.

5. Mixing tank is connected with slopping inlet chamber (or tank) while outflow tank is connected with rectangular outlet chamber (or tank).

6. The inlet-chamber is for introducing fresh dung slurry into the main digester tank whereas the outlet chamber is for taking out spent dung slurry after extraction of biogas.

Biogas plant.
1. The plant consists of well-like underground tan



Describe primary and secondary treatment of domestic sewage before it is released for reuse.

Treatment of domestic Sewage. 

1. Primary Treatment. It includes physical processing, such as sedimentation, floatation, shredding (fragmenting and filtering). These processes remove most of the large debris. The primary sludge obtained when all the solids settle down is sent for secondary treatment.

2. Secondary Treatment. It is a biological method in which micro-organisms are used.

Activated Sludge Method. Sewage, after primary treatment, is pumped into an aeration tank or oxidation pond where it is mixed with air and sludge containing bacteria. Bacteria forms flocs along with fungus . The flocs sediment and form activated sludge. A part of activated sludge is used as an inoculum and pumped back. The remaining sludge is pumped into anaerobic sludge digesters where bacteria decomposes the organic matter and releases a mixture of gases that forms biogas.