Question

Pollution of lakes and rivers affects aquatic life. Fish cannot live in water that has oxygen less than 4 milligrams per liter. Other freshwater aquatic life (including anaerobic bacteria) also cannot survive without adequate oxygen. 'BOD' stands for:
A.Biological oxygen demand
B.Bacterial oxygen deficit
C.Basic oxygen demand
D.Building oxygen deposits

Answer 1

The statement given deals with the necessity or demand of oxygen for all the organisms including bacteria and other animals that are present in water bodies for decomposing the organic matter.

Complete step by step answer:
Biological oxygen demand is the amount of oxygen that is needed by the biological organism to decompose the organic matters present in water. The biological oxygen demand is commonly expressed in milligrams of oxygen that is consumed by 1 liter of sample during 5 days. BOD works similar to COD that is chemical oxygen demand in both of them the measurement of organic compound is done in water where the latter one is less specific because it includes all the chemical oxidized rather than just biological oxidized matter.
When a high amount of organic matter is present in the water bodies then microorganisms that are bacteria present in water will take more oxygen from water to decompose the organic matter. Organic matter acts as a food for the microorganisms are bacteria and a source of energy for them. Sometime it happens that consumption of oxygen is more than the amount of oxygen being dissolved in water. This causes problems for the other aquatic animals in water because the deficiency of oxygen occurs in water due to these microorganisms. Hence fish and other aquatic insects died because of less availability of oxygen.

Hence option A is correct.

Note:
The growth of this microorganism suppresses due to the presence of some chemicals which leads to the lower value of biological oxygen demand. The sources of these chemicals are industrial waste medical waste chlorination disinfectants etc.