Q49 of 54 Page 352

State one way in which the air pollution caused by the burning of fossil fuels in transport and industry can kill the fish living in a lake and one way in which the water pollution caused by an agricultural activity can kill fish living in the same lake.

Fossil fuels burn in the air to produce gases such as Sulphur dioxide and nitrogen dioxide. Sulphur dioxide and nitrogen dioxide which reacts with water vapors in the atmosphere to form sulphuric acid and nitric acid. These acids combine with rain and makes the rain water acidic. This is called Acid rain. Acid rain caused by the burning of fossil fuels makes the lake water too much acidic which kills the fish.

The fertilizers act as nutrients for the algae to grow. When these algae die, they act as a nutrient for decomposers like bacteria. As a result of this process, a lot of oxygen in the water gets used up and leads to the deficiency of Oxygen in the water. This may kill the aquatic organisms including fish.


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46

The farmers use large amounts of a substance P in the fields to increase the crop yield. The excess of P dissolves in water and runs into a lake. The substance P causes rapid growth of tiny green water plants Q in the lake which cover the whole lake like a green sheet. When the plants Q die, the organisms called R decompose them by utilizing S dissolved in lake water. The amount of dissolved Sin water decreases too much due to which the fish living in lake suffocate and die. What are P, Q, R and S?

 47

At many places the wastewater containing human excreta from homes and carried in big underground pipes is dumped into a river as such which pollutes the river water.

(a) What is the common name of such wastewater?


(b) Name five types of harmful organisms contained in it.


(c) Name any five human diseases caused by drinking river water contaminated with such wastewater.

 48

Match the items given in column I with one or more items given in column II:
































Column I



Column. II



(i) Prevents photosynthesis



(a) Sewage dumped in river



(ii)Damage ozone layer



(b) Excess fertilizer in fields



(iii) Produce acid rain



(c) Carbon dioxide in air



(iv) Kill fish by deoxygenating water



(d) Dust in air



(v) Causes water borne diseases



(e) CFCs



(vi) Leads to global warming in air



(j) Sulphur dioxide



 50

The incomplete combustion of firewood in homes produces a very poisonous gas X. When inhaled, gas X combines with the substance Y present in blood and reduces the capacity of blood to carry gas Z causing respiratory problems and suffocation. What are X, Y and Z?