SSC Ecology And Environment Sample Paper NCERT Sample Paper-5

  • question_answer
    A lake with an inflow of domestic sewage rich in organic waste may result in:

    A)  Drying of the lake very soon due to algal bloom.

    B)  An increased production offish due to lot of nutrients

    C)  Death of fish due to lack of oxygen

    D)  Increased population of aquatic food web organisms

    Correct Answer: C

    Solution :

    [c] Organic pollution occurs when large quantities of organic compounds, which act as substrates for microorganisms, are released into watercourses. During the decomposition process the dissolved oxygen in the receiving water may be used up at a greater rate than it can be replenished, causing oxygen depletion and having severe consequences for the stream biota. Organic effluents also frequently contain large quantities of suspended solids which reduce the light available to photosynthetic organisms and, on settling out, alter the characteristics of the river bed, rendering it an unsuitable habitat for many invertebrates. Toxic ammonia is often present. Organic pollutants consist of proteins, carbohydrates, fats and nucleic acids in a multiplicity of combinations. Organic pollutants originate from domestic sewage (raw or treated), urban run-off, industrial (trade) effluents and farm wastes. Sewage effluents is the greatest source of organic materials discharged to freshwaters.

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