Water is the most abundant component of all living beings. It is present inside the cell as intracellular water and outside the cell as extracellular water.
Tissue water exists both in free form (94-95%) and also as bound forms (4-5%) loosely held to proteins and other molecules. The water content of living cell varies from 60 to 95%.
provides the physical environment for support to life and the whole range of physical and chemical events within and around the cell. It stabilizes the structural organization of living matter and maintains conformations of bio molecules.
The oxygen atom being more electronegative than the hydrogen atom attracts electrons more strongly than the hydrogen nuclei; as a result the shared electrons are nearer to oxygen atom. Due to this asymmetrical or unequal distribution of charges, the water molecule has electrical polarity and acts as dipole: + with ‘sticky ends’. Each of water’s two covalent bonds has a partial charge at each end 5~ (delta minus) at oxygen and 5+ at hydrogen end.
The most stable arrangement of these charges is a tetrahedron where the two negative and two positive charges are approximately equidistant from each other. The oxygen atom lies at the centre of the tetrahedron, the hydrogen atoms occupy two of the apices, and the partial negative charges occupy the other two apices.
Water is an inorganic molecule, technically known as double hydride of oxygen or hydrogen oxide or hydride of oxygen. The atoms of the two elements are in the ratio of 2:1 (H20). The two hydrogen atoms are linked with oxygen atom by polar covalent bonds and both the hydrogen atoms stay to one side of oxygen atom. The angle between the two hydrogen atoms is 104.50.
This polarity of hydrogen 1 molecules result in the formation of hydrogen bonds between the slightly negative charged oxygen atoms of one molecule with slightly positively charged hydrogen atom of another molecule.
Hydrogen bond is a weak bond formed between an electronegative atom of one molecule and a covalently held hydrogen atom of another molecule. Because of the formation of hydrogen bonds, water molecules have high cohesive and adhesive properties.
The high cohesive forces make water a liquid while other molecules with similar or larger molecular weight than water are gases. The cohesion of liquid water is also responsible for its high surface tension.
Water is said to have a high specific heat (the amount of heat that must be absorbed or lost by 1 gm of a substance to change its temperature by 1°C). So water heats up more slowly and this property helps organisms with high water content to maintain a relatively constant internal temperature (it acts as a temperature buffer). The high specific heat of water is attributed to hydrogen bonding.
Water has high heat of vaporization (586 calories). A considerable amount of heat is absorbed for transition of liquid water to vapor as a large number of hydrogen bonds are required to be broken. Many organisms thus dispose body heat by evaporating cooling.
When temperature is lowered the water molecules are locked in three dimensional crystal-like lattices. Lattice formation increases with further lowering of temperature, forming solid, called ice at 0°C. Interestingly ice is less dense than water and as a result it floats in water.
This is helpful in maintaining aquatic ecosystem. If ice were heavier than liquid water, it would sink to the bottom of water bodies. In the deep sea, for example, ice formation would start from the bottom to the top and once frozen, would be difficult to melt.
Under such a situation no aquatic life would survive. As ice floats in water, the water beds would not solidify from the bottom to the top. Water has maximum density at 4°C.
Pure water is colorless, odorless, transparent liquid and a bad conductor of electric current. It is a powerful solvent. Any substance bearing electric charge, if put in water, then the water molecules gather closely around it in a cloud, forming hydration shell and preventing it from associating with other molecules. Hydration shell is formed around ions as well as polar molecules.
1. Water is the principal constituent of the cell.
2. Water is a universal solvent.
3. Water, because of its high specific heat, acts as a temperature buffer and It helps in maintaining body temperature.
4. It brings about the cooling effect as organisms dispose off excess heat by evaporating cooling.
5. It helps stabilize the conformation of bimolecular and provide a medium for the physical and biochemical events in the cell.
6. Water is incompressible and thereby, helps maintain the turgidity of the tissue.
7. Because of high cohesive force, water moves up through the conducting elements in plants.
8. Water helps in the movement of plants, plant parts and several other organisms.