UPSC Prelims 2017 · GS Paper I

Question 59: Environment and Ecology

Biological Oxygen Demand (BOD) is a standard criterion for

aMeasuring oxygen levels in blood

bComputing oxygen levels in forest ecosystems

cPollution assay in aquatic ecosystems

dAssessing oxygen levels in high altitude regions

AnswerUPSC’s answer is (c).

Biological Oxygen Demand is the amount of dissolved oxygen that microorganisms need to break down the organic matter in a water sample over a set period, usually five days at 20 degrees Celsius. The more organic pollution in the water, the higher the BOD. It is therefore a standard criterion for assaying pollution in aquatic ecosystems, and not for oxygen in blood, forests or high-altitude air. Remember: high BOD means heavily polluted water.

Why each option is right or wrong

(a) Wrong: blood oxygen is measured differently, for example with oximetry.
(b) Wrong: BOD does not compute oxygen in forest ecosystems.
(c) Right: BOD measures organic pollution in water.
(d) Wrong: BOD does not assess oxygen in high-altitude air.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2017, General Studies Paper I, Series A. The paper on upsc.gov.in.