Biology 2 Marks Questions

During biological treatment of sewage, the primary effluent is passed into large aeration tanks when it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs. While growing, these microbes consume the major part of the organic matter in the effluent. This significantly reduces the BOD (Biochemical Oxygen Demand) of the effluent, thereby reducing the amount of pollution in the water.

Bio-fertilizers are a type of organisms, which increase the nutritional quality of the soil. The main sources of organic fertilizers are bacteria, fungi and cyanobacteria. The nodules present on the roots of leguminous plants are formed by the symbiotic relationship of Rhizobium bacteria.
These bacteria fix atmospheric nitrogen and convert it into orgánic form and plants use it as nutrients. If the nodules of these plants are destroyed then the plants will not be able to grow due to lack of nutrients and will gradually get destroyed.

The following fermentation conditions are necessary to be maintained during the production of biogas:
(1) Fermentation should be carried out in a completely anaerobic environment and no free oxygen should be present.
(2) The pH inside the fermenter should be maintained at almost neutral level from 6.8 to 7.6. (3) Methanogenic bacteria should be present in fermentation.