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Q59 (IAS/2017) Environment & Ecology › Pollution & Conservation › Water pollution indicators Official Key

Biological Oxygen Demand (BOD) is a standard criterion for

Result
Your answer: —  ·  Correct: C
Explanation

The correct answer is option C. Biological oxygen demand (BOD) is a proxy measure that captures the outcome of a host of pollutants that affect dissolved oxygen[2] in water bodies. The biological oxygen demand (BOD) is already 6.4 mg per liter in the river water instead of 3 mg per liter which is normal and safe for bathing[3], demonstrating its use as a pollution assessment criterion in aquatic ecosystems. Presence of organic and inorganic wastes in water decreases the dissolved Oxygen (DO) content of the water. Water having DO content below 8.0 mg/L may be considered as contaminated. Water having DO content below 4.0 mg/L is considered to be highly polluted.[4] BOD is specifically used for water quality monitoring and pollution assessment, not for measuring oxygen in blood (which involves haemoglobin), forest ecosystems, or high-altitude regions. It is a standard water quality parameter used to classify waters that receive effluents and assess the level of organic pollution in aquatic systems.

Sources
  1. [1] https://documents1.worldbank.org/curated/en/537481566459193718/pdf/Quality-Unknown-The-Invisible-Water-Crisis.pdf
  2. [2] https://documents1.worldbank.org/curated/en/537481566459193718/pdf/Quality-Unknown-The-Invisible-Water-Crisis.pdf
  3. [3] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > Five Confluences in the upper reaches of Ganga > p. 13
  4. [4] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > DO, BOD, COD > p. 76
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. Biological Oxygen Demand (BOD) is a standard criterion for [A] Measuring oxygen levels in blood [B] Computing oxygen levels in forest e…
At a glance
Origin: Mixed / unclear origin Fairness: Moderate fairness Books / CA: 5/10 · 0/10
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This is a classic 'Sitter' from the static Environment module. It tests a fundamental definition found in every standard text (Shankar IAS, NCERT Science). The strategy is simple: Master the basic definitions of pollution metrics (BOD, COD, PM2.5) before diving into complex current affairs.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Is Biological Oxygen Demand (BOD) a standard criterion for measuring oxygen levels in blood?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > Five Confluences in the upper reaches of Ganga > p. 13
Presence: 5/5
“According to the Central Pollution Board, the Ganga is one of the most polluted rivers of the world. The water at Hardwar District fails almost all parameters of safety. According to official sources, nearly one lakh devotees bathe at the over 20 Ghats (bathing sites) of Hardwar every day. The biological oxygen demand (BOD) is already 6.4 mg per liter in the river water instead of 3 mg per liter which is normal and safe for bathing. In India rivers are highly revered, but with rapid industrialization and urbanization, rivers have increasignly become depositories of urban waste and industrial effluents.”
Why this source?
  • Explicitly uses 'biological oxygen demand (BOD)' with mg/L values to describe river water pollution and bathing safety.
  • Shows BOD as a water-quality metric applied to rivers, not to physiological blood measurements.
Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Do You Know? > p. 90
Presence: 4/5
“When the body size of animals is large, the diffusion pressure alone cannot take care of oxygen delivery to all parts of the body. Instead, respiratory pigments take up oxygen from the air in the lungs and carry it to tissues which are deficient in oxygen before releasing it. In human beings, the respiratory pigment is haemoglobin which has a very high affinity for oxygen. This pigment is present in the red blood corpuscles. Carbon dioxide is more soluble in water than oxygen is and hence is mostly transported in the dissolved form in our blood.”
Why this source?
  • Explains that haemoglobin in red blood corpuscles is the respiratory pigment that takes up and carries oxygen in human blood.
  • Indicates that blood-oxygen status is fundamentally about haemoglobin-mediated transport, a physiological concept distinct from BOD.
Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.7 > p. 91
Presence: 4/5
“We have seen in previous sections that blood transports food, oxygen and waste materials in our bodies. In Class IX, we learnt about blood being a fluid connective tissue. Blood consists of a fluid medium called plasma in which the cells are suspended. Plasma transports food, carbon dioxide and nitrogenous wastes in dissolved form. Oxygen is carried by the red blood corpuscles. Many other substances like salts, are also transported by the blood. We thus need a pumping organ to push blood around the body, a network of tubes to reach all the tissues and a system in place to ensure that this network can be repaired if damaged.”
Why this source?
  • States that oxygen is carried by red blood corpuscles and that plasma transports dissolved gases and wastes.
  • Reinforces that oxygen measurement in blood relates to cellular/physiological carriers (RBCs/plasma), not environmental BOD measures.
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