IX – SCIENCE
1.
2.
ANSWER KEY
Combustion, respiration and in the formation of oxides of nitrogen.
a) Some bacteria are poisoned by elemental oxygen
b) The process of nitrogen- fixing by bacteria.
3.
of earth.
b)
a) Soil:- It is the humus containing and life sustaining weathered uppermost crust
Pedogenesis:- The process of formation of soil is called pedogenesis.
4. Transverse and longitudinal wave.
5. The speed of light is 3X108 m/s, while that of sound of thunder is 330 m/s in air, thus
light reaches earlier than the sound.
6. Sound is a mechanical wave and it need material medium for its propagation. On the
moon there is vacuum i.e. no air, therefore sound can’t propagate on the moon. Thus
the astronauts can not hear each other.
7. Bat produces ultrasonic waves when fly. These waves are received by the ears of bat
after they have been reflected by the object. The ears of the bat are so sensitive and
trained that thay not only get information of distance of the obstacle but also that of the
nature of the reflecting surface.
8. When sound propagate through a medium, it create compression and rarefaction in the
form pressure variation, hence it is known as pressure wave. Due to greater difference
b/w the speed of light and thunder.
9. The water insides the deep reservoir is colder than the water at the surface which gets
heated by the sun. since aquatic organisms are used to a certain range of temperature
in the water body where they live, and a sudden marked change in this temperature
would be dangerous for them or affect their breeding. The eggs and larvae of various
animals are particularly susceptible to temperature changes.
10. a) The nutrient content of the soil.
b) The amount of humus present in the soil.
c) The depth of the soil.
11. i) Nitrogen fixing bacteria eg. Rhizobium, Aztobactor.
ii) Bacteria which convert complex nitrogenous organic compounds (proteins) into
ammonia e.g. Actinomyces.
iii) Dentrifying bacteria.
12. The organisms which decompose the dead remains of plants and animals are called
decomposers.
1) Decomposers help in the cycling of nutrients in the biosphere.
2) Decomposers convert the nutrients available in the usable form.
3) Decomposers help in complete disposal of dead remains of living things.
13. Cause of depletion of ozone layer:1. The use of fluorocarbons in aerosol propellants.
2. The use of CFC’s in air conditioners and refrigerators.
Effects of depletion of ozone layer:1. U.V. rays enter the through the depleted zone of ozone layer and cause skin cancer in
human beings.
2. U.V. rays also affect other organisms and crop plants.
Atmospheric
Oxygen O2
14.
Photosynthesis
Respiration
Organic molecule
C6H12O6
CO2
H2O
Nitrogen in
atmosphere
15.
Denitrification
Nitrogen
Fixation
Protoplasm(animals)
Nitrates
Protoplasm
(Green Plants)
Nitrites
Ammonification
Nitrification
Nitrification
Ammonia
Atmospheric and
industrial fixation
Nitrogen fixation: - Conversion of atmospheric nitrogen gas into nitrogen compounds.
Ammonification:- Conversion of nitrogen containing proteins of dead pants and animals into
ammonia.
Nitrification:- Conversion of ammonia into nitrites and then into nitrates.
Denitrification:- Conversion of nitrate salt into free nitrogen gas.
It is called a perfect cycle because it involves circulation of nitrogen in the biotic
and abiotic component of biosphere as nitrogen is an essential component of amino acids,
proteins, nucleic acids which are essential structural and functional components of living
systems.