We all know that water is essential for life, but how is this substance so vital to living organisms?
Before looking at its actual functions it’s important to first understand more about its structure. A molecule of water, H2O, consists of two hydrogen atoms covalently bonded to an atom of oxygen. As there is a great difference in electronegativity between oxygen and hydrogen, with oxygen being a lot more electronegative, the shared pair of electrons of each covalent bond is more attracted towards the oxygen atom than the hydrogen atoms.
This, therefore, causes the hydrogen atoms to have a slightly positive charge, δ+ (delta positive) and the oxygen atom a slightly negative charge, δ- (delta negative). Due to water being non-symmetrical, a molecule, therefore, has a slightly positively charged side and a slightly negatively charged side, hence causing it to be a polar molecule. The δ- oxygen atom of a water molecule also attracts the δ+ hydrogen atoms of other water molecules, therefore, forming hydrogen bonds between molecules of water.
These structural properties help contribute to why water is so important in that:
● It is a very good solvent (being polar it can dissolve polar solutes- which many crucial substances in biological reactions are- due to there being partial charges of atoms in water and the solute causing there to be attractions between them)
● It is a key metabolite (as metabolic reactions tend to involve a hydrolysis or condensation reaction)
● It is very cohesive (due to the polar nature of water molecules they tend to “stick” together, which makes it easy to transport for example in plants up the xylem as a column)
● It is an effective buffer for temperature changes (as water has a high specific heat capacity due to the hydrogen bonds present, therefore requiring a large change in energy to cause the temperature of 1g of water to vary by 1 degrees Celsius, making it helpful for thermoregulation)
● It is a good coolant (as the hydrogen bonds require a lot of heat energy to break for water to evaporate, meaning that it has a high latent heat of vaporisation so that an organism can remain cool without requiring too much water to be lost as sweat)
So hopefully now you know just why water is such a crucial substance for living organisms.