Oxygen Cycle:
Oxygen cycle refers to the movement of oxygen through the atmosphere (air), biosphere (plants and animals) and the lithosphere (the Earth's crust).
………...cycle
plays very important role in the existence of life on the earth.
a) Nitrogen
b) Carbon
c) Oxygen
Few billions years ago, there was no free molecular ……….in the atmosphere.
a) nitrogen
b) carbon
c) oxygen
Today earth atmosphere contains….% oxygen.
a) 0.03
b) 21
c) 78
d) 0.9
Oxygen is the large product of …….by plants.
a) respiration
b) decomposition
c) photosynthesis
d) all of these
Plants use…….to
make food and release oxygen gas.
a) nitrogen dioxide
b) carbon dioxide
c) sulphur dioxide
d) none of these
