The amount of oxygen required to decompose the organic matters of water by microbes is known as?

UPPSC-2021

Microbiology

Easy

Appeared in: UPPSC-2021

Explanation

Biological Oxygen Demand (BOD) is the standard measure for the amount of oxygen consumed by microorganisms (mainly bacteria) while decomposing organic matter in water.
It serves as a key indicator of the level of organic pollution in a water body.
A high BOD value signifies a high concentration of biodegradable organic material, which can deplete the water's oxygen supply as it is consumed by microbes.
The standard test measures the oxygen consumed over 5 days at 20°C (BOD₅).
Untreated domestic sewage typically has a high BOD (around 300 mg/L), while clean river water has a very low BOD (less than 3 mg/L).

Option A: Dissolved oxygen (DO) is the amount of oxygen currently available in the water for aquatic life to use. The question asks for the oxygen required for decomposition, not what is already present.
Option C: Eutrophication is a broader ecological process involving nutrient enrichment that leads to algal blooms. While the decomposition of these blooms does cause a high BOD, eutrophication itself is the process of enrichment, not the measure of oxygen demand.
Option D: Surface flow, or runoff, is a term from hydrology describing how water moves over the land. It has no direct connection to the biochemical measurement of oxygen in water.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Water Quality and Pollution Indicators as background academic context rather than a clinical decision trigger.
Understanding BOD is crucial for community health nurses as it indicates the level of water contamination, particularly from sewage. High BOD suggests a risk of waterborne diseases like cholera, typhoid, and dysentery.
Nurses play a role in health education, teaching communities about safe water sources, the dangers of polluted water, and the importance of proper sanitation to prevent contamination of water bodies.
What if the water source showed a high BOD but still had a high DO level? This could indicate a very recent pollution event where the microbial population has not yet had time to consume the available oxygen. It represents an early warning sign before a major oxygen crash occurs.

How to Approach the Question

First, break down the question stem to identify the core definition being asked. The key phrases are 'oxygen required,' 'decompose organic matters,' and 'by microbes.'
Evaluate each option against this definition. 'Biological oxygen demand' directly relates the biological process (microbes) to the 'demand' for oxygen.
Eliminate 'Dissolved oxygen' because it refers to oxygen that is present, not required or demanded.
Rule out 'Eutrophication' as it is a larger process of nutrient enrichment, not the measurement of oxygen demand itself.
Discard 'Surface flow' as it is an unrelated hydrological term.
Confirm that 'Biological oxygen demand' is the precise term for the definition provided.

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 2 — Subpart B (pp 233-449 of 464) p. 80-82