Question

If BOD of river is high, it means that the river
A) Is not polluted
B) Is very polluted
C) Does not have green plants
D) Get least amount of light

Answer 1

A high level of BOD means low levels of dissolved oxygen available to other marine organisms, such as fish. The dissolved oxygen is used by the aerobic microorganisms to split down the organic pollutants present in the river.

Complete answer:
To answer this question, first we should know about BOD. Biological Oxygen Demand is characterized as the amount of dissolved oxygen that aerobic microorganisms need to split down the organic materials in a water sample at a given temperature.
Now, let us find the solution from the given options-
BOD measures the level of organic compounds present in the water.It is the amount of oxygen required by the aerobic microorganisms to degrade the organic material present in the water. If the water is not polluted then the level of oxygen is high and thus, the BOD is low. So, the option A cannot be the correct option. Thus, the river is not polluted.
BOD measures the level of organic compounds present in the water. The flow with a high BOD level indicates high levels of pollutants in the system because the dissolved oxygen present in the water is consumed by the bacteria, resulting in less food available to fish and other marine organisms. So, option B is the correct option. Thus, the river is very polluted is the correct answer.
The bacteria use the dissolved oxygen in the water, which leads to less oxygen available to aquatic plants. Thus, there will be a smaller number of green plants. So, option C cannot be the correct answer. Thus, the river does not have green plants is an incorrect answer.
The impact of pollutants on a water body is by no means simple and involves analysis of other aspects not included in determining BOD, such as the natural water body temperature, sunlight, oxygen concentrations, biological organisms and the influence of deposits at the bottom. So, option D cannot be the correct option. Thus, the river that gets the least amount of light is an incorrect answer.

Thus, the right answer is, option D. i.e. All of these.

Note: Biological demand for oxygen can be used as a measure of pollution levels. For example, the higher the organic matter amounts, the higher the BOD. Therefore a high level of BOD means that the amount of dissolved oxygen accessible for other marine organisms is low.