A fertile agriculture soil appears dark coloured at the surface as compared to soil one metre down.The reason for colour of top soil is
More moisture
Rich in organic matter
Rich in iron,calcium and magnesium
Recent formation
Sewage drained into water bodies kill fishes because:
Excessive carbon dioxide is added to water.
It gives off a bad smell.
It removes the food eaten fish.
It increases competition with fishes for dissolved oxygen.
Which important green-house gas, other than methane, is being produced from the agricultural fields?
Arsine
Sulphur dioxide
Ammonoa
Nitrous oxide
The transfer of energy from one trophic level to another is governed by the second law of thermodynamics. The average efficiency of energy transfer from herbivores to carnivores is:
5%
10%
25%
50%
Keystone species in an ecosystem are those which:
are present in maximum number.
are most frequent.
attain a large biomass.
contribute to ecosystem properties.
Ultraviolet radiations from sunlight cause a reaction which producess
O3
SO2
CO
CH4
The sum total of the population of the same kind of organisms constitute
Colony
Genus
Community
Species
Which of the following is free - living, aerobic, non- photosynthetic nitrogen-fixing bacterium?
Rhizobium
Acetobacter
Nostoc
Azospirillum
Most hazardous metal pollutant of automobiles exhausts is
Mercury
Cadmium
Lead
Copper
Fish die in water bodies polluted by sewage due to
Pathogens
Clogging of gills by silt
Reduction in oxygen
Fuel smell
