ï»¿ A lake near a village suffered heavy mortality of fishes within a few days. Consider the following reasons for this(1) lost of urea and phosphate fertiliser were used in the crops in the vicinity.(2) The area was sprayed with DDT by an aircraft.(3) The lake water turned green and stinky/(4) Phytoplankton populations in the lake declined initially thereby greatly reducingÂ photosynthesis.Which were two of above the main causes of fish mortality in the lake? from Biology Environmental Issues Class 12 Nagaland Board

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A lake near a village suffered heavy mortality of fishes within a few days. Consider the following reasons for this
(1) lost of urea and phosphate fertiliser were used in the crops in the vicinity.
(2) The area was sprayed with DDT by an aircraft.
(3) The lake water turned green and stinky/
(4) Phytoplankton populations in the lake declined initially thereby greatly reducingÂ photosynthesis.
Which were two of above the main causes of fish mortality in the lake?

• 2, 3

• 3, 4

• 1,3

• 1,2

D.

1,2

A lake near a village suffered heavy mortality of fishes within a few days, because lots of urea and phosphate fertilizer were used in the crops in the vicinity and the area was sprayed with DDT by an aircraft, Inorganic phosphorus and nitrogen are responsible for the growth of algae. In polluted water these increase due to which algae increase greatly at the surface of water forming water bloom. Due to death of these algae, their organic matter gets decomposed due to which oxygen gets depleted and aquatic animals die.

A lake near a village suffered heavy mortality of fishes within a few days, because lots of urea and phosphate fertilizer were used in the crops in the vicinity and the area was sprayed with DDT by an aircraft, Inorganic phosphorus and nitrogen are responsible for the growth of algae. In polluted water these increase due to which algae increase greatly at the surface of water forming water bloom. Due to death of these algae, their organic matter gets decomposed due to which oxygen gets depleted and aquatic animals die.

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Which of the following pollutants is not produced by exhaust of motor vehicles ?
• CO
• Hydrocarbon
• Fly-ash
• NO

C.

Fly-ash
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Ozone depletion will cause :
• Forest fire
• Pneumonia
• Increased incidence of skin cancer
• None of these

C.

Increased incidence of skin cancer
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The meaning of BOD is :
• Bacterial oxygen demand
• Biological optimum density
• Biochemical oxygen demand
• Bioorganisation decay

C.

Biochemical oxygen demand
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In the scrubber in the electrostatic precipitator the gases are passed through :
• filter
• lime
• spray of water
• both 2 and 3

D.

both 2 and 3
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What is the term for the inflammation of cornea due to high absorption of UV-B radiation :
• myopia
• snow blindness
• biomagnification
• None of the above

B.

snow blindness
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