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Environmental Issues — BIOLOGY STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYEnvironmental Issues5 Marks
Question
Is it true that if the dissolved oxygen level drops to zero, the water will become septic. Give an example which could lower the dissolved oxygen content of an aquatic body.
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Answer

It is true that if dissolved oxygen level drops to zero, the water will become septic. Absence of oxygen in water means the water will no longer be able to sustain living beings because aquatic plants and animals use dissolved oxygen for respiration.
When sewage is discharged into water body, microorganisms feed on organic impurities. In this process, they consume most of the oxygen present in water. This reduced the level of dissolved oxygen to negligible level.

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