UPSC Prelims 2017 Q59: Environment & Ecology – Pollution

UPSC Prelims 2017, General Studies Paper I · Environment & Ecology

Biological Oxygen Demand (BOD) is a standard criterion for

Answer: (c) Pollution assay in aquatic ecosystems

Explanation

Biological Oxygen Demand (BOD)

BOD is the amount of dissolved oxygen that micro-organisms need to break down organic matter in water.

It is a standard test for water pollution.

BOD value	Meaning
Low	Little organic waste; clean water
High	Much organic waste (sewage); polluted water; fish may die for lack of oxygen

BOD and COD compared:

Feature	BOD	COD
Full form	Biological Oxygen Demand	Chemical Oxygen Demand
Measures	Biodegradable organic matter	All oxidisable matter
Test time	5 days at 20 degrees Celsius	A few hours

It has nothing to do with oxygen in blood, forest ecosystems or high altitude regions.

Answer: (c) Pollution assay in aquatic ecosystems.

(a) Incorrect. Oxygen levels in blood are measured by oximetry, not by BOD.
(b) Incorrect. BOD is a test of water, not of oxygen in forest ecosystems.
(c) CORRECT. BOD is the standard criterion for pollution assay in aquatic ecosystems.
(d) Incorrect. Oxygen at high altitude regions depends on air pressure, not BOD.

BOD = dissolved oxygen needed by microbes to decompose organic matter in water; higher BOD means more polluted water.

BOD measures organic pollution in water.

Thinking high BOD means more oxygen and cleaner water; it means the opposite.
Confusing BOD with dissolved oxygen (DO) itself.
Mixing up BOD with COD, which also counts non-biodegradable matter.

High BOD = high pollution = low dissolved oxygen.

NCERT Class XII — Biology (Environmental Issues: water pollution and its control)
Central Pollution Control Board — Water Quality Criteria