Question

Which one of the following is not a bioindicator of water pollution?
A)Sludge worms
B)Blood worms
C)Stoneflies
D)Sewage fungus

Answer 1

Hint: Any plankton, microbe, plant or animal which can be used to assess the health of an ecosystem is referred to as a bioindicator. In the aquatic ecosystem, the entities capable of responding rapidly to a polluted environment can act as a good biomarker for evaluating the quality of water.

Complete answer:
Bioindicators present in any ecosystem indicate the persistence of pollutants as well as their effects on the environment or bioindicators can be considered as any organism indicating the level of pollution in the aquatic ecosystem.

Stoneflies belonging to class insecta and order plecoptera are often found only in clean habitats, say, streams and lakes. Stoneflies, also known as Plecoptera, are the insects that are known to inhabit water when they are immature, but on attaining the adult stage, they become terrestrial. Stoneflies are sometimes also referred to as the flying insects. They consist of an anal filament with two hooks present in the apical region of each leg. They cannot thrive in the polluted water.

On the other hand, Bloodworms and sludge worms have adapted themselves in the polluted environment and therefore their survival can be observed even in conditions of low oxygen concentrations. Hence, their increase in water body points to the existence of organic matter in the concerned aquatic ecosystem, thus indicating high levels of water pollution in the environment.
Growth of sewage fungus also indicates high levels of pollution in the concerned water body.

Hence, the correct answer is option (C)

Note: Bioindicators are the representative species or the communities with the help of which various physicochemical characteristics indicating the water quality of a particular ecosystem could be assessed.