Water, chemical molecule H2O, is a component of the hydrosphere present in the three physical states of matter in constant change: solid, ice (with solidification / melting at 0 ° C), liquid (at room temperature, between 21 and 23 ° C ) and gaseous, water vapor (usually occurring with evaporation).
The cycle of this substance is extremely important for the maintenance of the biosphere, establishing means and conditions fundamental to the metabolism of living beings and contributing to the structural transformations of the environment, for example, the erosive and sedimentary processes of the lithosphere.
The cyclic renewal of this abiotic resource can be considered according to two aspects: from a short cyclic process (small cycle) or by a long cyclic process (large cycle).
In the small cycle, with purely temporal implications (temperature, humidity and pressure zones), the rain periodicity (rains) stands out, subjecting the water contained in aquatic environments (lakes, rivers, oceans and glaciers) to processes of evaporation. The vapor, reaching the highest layers of the atmosphere, condenses to form clouds. As a result of condensation, it returns to the Earth’s surface (percolation) in the form of droplets, snowflakes or hail particles.
In the great cycle, much more complex, the collaboration of both animals and plants is considered. Mechanisms of hydration (water absorption), transpiration (secretion) and respiration (obtaining energy) from organisms, generate relative concentrations depending on the amplitude of an ecosystem, causing considerable water deficit or increase.
The transpiration that occurs in the leaves of the plants (stomatal transpiration), in addition to providing suction pressure in the capillaries of the xylem (raw sap conductive vessel), affecting the absorption of water from the soil, due to the absorptive capacity of the radicle, simultaneously performs photosynthesis.
In animals, the acquisition of a water content favorable to organic reactions, is established through the direct ingestion of water or indirect in the composition of food, gradually returning to the medium, as necessary, physiological excretion, either through urine, by the act defecation (in feces) or sweating (sweating).