IGCSE Biology Paper-2: Specimen Questions with Answers 138 - 138 of 203

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Question 138



Which pollutants of water can lead to eutrophication?


√ Present

× Absent


Choice (4)


Herbicides- × , Insecticides sewage- × , Fertilizer- √


Herbicides- × , Insecticides sewage- × , Fertilizer- ×


Herbicides- √ , Insecticides sewage- √ , Fertilizer- √


Herbicides- √ , Insecticides sewage- × , Fertilizer- √




There is ageing of water bodies in nature, which affect the aquatic ecosystem. Such natural ageing of a water body due to biological enrichment of its water, leading to depletion of species diversity, is called Eutrophication.

  • A young lake has cold and clear water supporting little life.
  • With the time, the streams draining into lake introduce the nutrients like,
  • Nitrogen and Phosphorus, which encourage the growth of aquatic fauna and flora.
  • When the lake fertility increases, the plants, animals and the micro- organisms multiply very fast and organic remains begin to be deposited at the bottom of the lake.
  • Over the centuries, the organic debris and silt pile up and the lake becomes shallower and warmer. The warm water organisms now replace the cold-water organisms.
  • The marsh plants, now, begin to fill the original lake. This later gives the way to large masses of floating plants (Bog) which finally converts the lake into land. The ageing process can however, be accelerated by the transportation of pollutants from homes, agricultural fields and industries due to human activities. Such wastes may poison the whole population of fish and the decomposing- remains further deplete the dissolved oxygen content, and the lake can literally choke to death. This phenomenon of choking of lake is called Cultural or Accelerated Eutrophication.

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