Biological Oxygen Demand (BOD) is a standard criterion for
Contents9
- AMeasuring oxygen levels in blood
- BComputing oxygen levels in forest ecosystems
- CPollution assay in aquatic ecosystems
- DAssessing oxygen levels in high altitude regions
Show answer
Answer: (C) Pollution assay in aquatic ecosystems
Biological Oxygen Demand (BOD) is the amount of dissolved oxygen needed (demanded) by aerobic biological organisms (mainly bacteria) to break down organic material present in a given water sample at a certain temperature over a specific time period.
It is one of the most important indicators of water pollution in aquatic ecosystems.
A high BOD value means there is a lot of organic matter in the water, which in turn means the water is highly polluted — because more oxygen is being consumed by microorganisms to decompose this organic matter, leaving less oxygen for fish and other aquatic life.
Option (a) is wrong — BOD has nothing to do with blood oxygen levels.
Option (b) is wrong — it is not used for forest ecosystems.
Option (d) is wrong — it has nothing to do with high altitude regions.
This is a basic concept from NCERT Class 12 Biology, Chapter 16 (Environmental Issues).
(Source: NCERT)
BOD measures how much oxygen bacteria need to decompose organic waste in water - higher BOD means more pollution and less oxygen for fish.
Water pollution assessment became more prominent in UPSC after initiatives like Namami Gange and National Water Mission gained focus in the mid-2010s.
The question tests whether students can distinguish BOD from general oxygen measurement - it's specifically about decomposition by bacteria, not just oxygen presence.
Biological Oxygen Demand (BOD)
Environment Biological Oxygen Demand BOD
BOD: Key Water Pollution Indicator & UPSC Applications
BOD measures oxygen needed by bacteria to decompose organic matter in water
High BOD = high pollution (more organic waste to decompose)
Standard criterion for pollution assay in aquatic ecosystems
Measured at specific temperature over specific time period
What is BOD
BOD is the amount of dissolved oxygen that aerobic bacteria need to break down organic material in water. It directly indicates water pollution levels — cleaner water has low BOD, polluted water has high BOD.
How BOD Works
Organic waste enters water (sewage, food waste, dead plants)
Aerobic bacteria consume this waste using dissolved oxygen
More waste = more oxygen consumption = higher BOD value
Less oxygen remains for fish and aquatic life
BOD test measures oxygen consumed over 5 days at 20°C
BOD vs Other Water Quality Parameters
Parameter | What It Measures | Use |
|---|---|---|
BOD | Oxygen demand by bacteria for organic waste | Organic pollution indicator |
COD (Chemical Oxygen Demand) | Oxygen needed to chemically oxidize all pollutants | Total pollution (organic + inorganic) |
DO (Dissolved Oxygen) | Current oxygen level in water | Water health status |
pH | Acidity/alkalinity of water | Chemical pollution indicator |
Question Context
This question tests the specific application of BOD. The correct answer is pollution assay in aquatic ecosystems — BOD is exclusively used to measure water pollution, not blood oxygen, forest oxygen, or high-altitude oxygen.
Trap: Options A and D use 'oxygen levels' — BOD measures oxygen demand, not oxygen levels
Trap: Forest ecosystems (Option B) — BOD only applies to water bodies, not terrestrial ecosystems
Memory aid: BOD = Bacteria Oxygen Demand in water
Water Pollution Assessment Methods
Environment pollution assay aquatic ecosystems
Water Pollution Indicators: BOD, COD & Key Parameters
Multiple indicators assess different types of water pollution
BOD for organic pollution, COD for total pollution
Physical, chemical, biological parameters all matter
Major Water Quality Indicators
Indicator | Measures | Normal Range | High Value Indicates |
|---|---|---|---|
BOD | Oxygen demand by bacteria | 1-2 mg/L (clean water) | High organic pollution |
COD | Total oxygen demand | < 10 mg/L (clean water) | Chemical + organic pollution |
Dissolved Oxygen | Available oxygen for aquatic life | 6-8 mg/L (healthy) | Water health status |
Coliform Count | Bacterial contamination | 0 per 100ml (drinking) | Sewage contamination |
pH | Acidity/alkalinity | 6.5-8.5 (normal) | Industrial pollution |
Water Quality Assessment Process
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Sample Collection**
Water samples from different depths/locations`"]
s2["`**Physical Tests**
Color, odor, turbidity, temperature`"]
s3["`**Chemical Tests**
BOD, COD, pH, dissolved oxygen, heavy metals`"]
s4["`**Biological Tests**
Coliform count, presence of indicator species`"]
s5["`**Assessment**
Compare with standards (WHO, BIS, pollution boards)`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5India's Water Quality Standards
Central Pollution Control Board (CPCB) sets national standards
Bureau of Indian Standards (BIS 10500) for drinking water
Different standards for drinking, bathing, irrigation, industrial use
Ganga Action Plan uses BOD as key monitoring parameter