Biological Oxygen Demand (BOD) is a standard criterion for:
- (a)Measuring O₂ level in blood
- (b)Pollution assay in aquatic ecosystems
- (c)Assaying O₂ level in high altitude regions
- (d)Computing O₂ level in forest ecosystems
Correct — B, Pollution assay in aquatic ecosystems. BOD is the amount of dissolved oxygen that aerobic microorganisms consume to break down the organic matter in a water sample over a set period (typically 5 days at 20°C). The more organic pollution (sewage, effluent) a water body carries, the more oxygen the microbes use up — so a HIGH BOD indicates heavy organic pollution. BOD is therefore a standard yardstick for organic pollution / water quality in aquatic ecosystems.
- (a)Measuring O₂ level in blood — Oxygen in blood is measured by blood-gas analysis or pulse oximetry (as SpO₂/PaO₂), which has nothing to do with BOD.
- (c)Assaying O₂ level in high altitude regions — Atmospheric oxygen at altitude is a matter of air pressure, not BOD; BOD is a water-quality parameter.
- (d)Computing O₂ level in forest ecosystems — BOD applies to organic pollution in water, not to oxygen in terrestrial/forest ecosystems.
BOD measures how much dissolved oxygen aerobic microbes need to decompose the biodegradable organic matter in water. It is an indirect but standard indicator of organic pollution: clean water has a low BOD, while sewage- or effluent-laden water has a high BOD because more organics feed more oxygen-hungry microbes.
The correct option is the only one about water; the others distract with 'oxygen' in unrelated settings (blood, altitude, forests). BOD is often paired with COD (Chemical Oxygen Demand) and dissolved oxygen (DO) — a high BOD usually goes with a low DO.
- BOD = dissolved oxygen used by microbes to decompose organic matter in water.
- Standard test: 5 days at 20°C (BOD₅).
- High BOD → heavy organic pollution → typically low dissolved oxygen (DO).
- Related parameters: COD (chemical oxygen demand) and DO (dissolved oxygen).
BOD indexes organic pollution: more organic load means more oxygen consumed by microbes.
- Being distracted by 'oxygen' in blood/altitude/forest options — BOD is only about water
- Confusing BOD with COD (COD includes chemically oxidisable, non-biodegradable matter too)
Both UPPSC and UPSC ask BOD as a direct 'what does it measure' question or pair it with COD/DO in water-pollution sets.
Biological Oxygen Demand (BOD) is a standard criterion for
- (a) Measuring oxygen levels in blood
- (b) Computing oxygen levels in forest ecosystems
- (c) Pollution assay in aquatic ecosystems
- (d) Assessing oxygen levels in high altitude regions
Answer(c) Pollution assay in aquatic ecosystems — BOD indexes organic pollution in water.
Near-identical question — UPSC 2017 asked the very same 'BOD is a standard criterion for' item, answer 'pollution assay in aquatic ecosystems'.
- practice — not a real PYQ
A high BOD value in a river sample most directly indicates:
- (a)Very clean water
- (b)Heavy organic pollution
- (c)High mineral content
- (d)Low temperature
Answer(b) Heavy organic pollution — more organic load means microbes consume more oxygen.
- practice — not a real PYQ
Which parameter measures both biodegradable and chemically oxidisable matter in water?
- (a)BOD
- (b)COD
- (c)DO
- (d)pH
Answer(b) COD (Chemical Oxygen Demand) — it captures more than just the biodegradable fraction measured by BOD.