12th Class Biology Organisms and population Biosphere

All the thousands of ecosystems together constitute the biosphere, which exists as a thin envelope around the earth’s surface. The global environment consists of three main sub division :

(1) Hydrosphere : All the water (liquid) component of the oceans, seas, rivers and other island water bodies.

(2) Lithosphere : The solid components of the earth crust, rocks, soil and minerals.

(3) Atmosphere : The gaseous cover which envelops the hydrosphere and the lithosphere and the atmosphere. The entire inhabited part of the earth and its atmosphere (including the living and the non-living components) forms the biosphere.

As a result of manipulation by man, the biosphere has become transformed into a human dominated environment of noosphere \[(noo=\]mind).

Role of atmosphere in metabolism : Of much greater significance to metabolism, however, are the biogeochemical cycles of the atmosphere. The air consists mainly of oxygen (20.95 per cent), carbon dioxides (about 0.03 per cent), nitrogen (78.08 per cent), water vapour and minute traces of inert gases. Except the inert gases, all these components of air serve as metabolites; each circulates through a cycle in which the organisms play an important role. As all gases are dissolved in natural waters, the hydrosphere maintains an equilibrium with the atmosphere.