Which one of the following is not a bioindicator of water pollution?
- Blood-worms
- Stone flies
- Sewage fungus
- Sludge-worms
Answer
(2) Stone flies
Solution
Bioindicators of water pollution are organisms that flourish in water rich in organic matter and poor in dissolved oxygen.
⇒ Blood-worms ( Chironomus larvae, red due to haemoglobin), sludge-worms ( Tubifex) and sewage fungus ( Sphaerotilus, a filamentous bacterium) all thrive in polluted water with high BOD.
⇒ Stone-fly nymphs need clean, cool, well-oxygenated water and disappear as soon as the water gets polluted.
∴ Stone flies indicate clean water and are not a bioindicator of water pollution.
Answer: (2)