The Role of Water in Living Organisms

596 Words2 Pages

Water is one of the most abundant substances on the planet. It can be

found naturally in all three states; solid (ice), liquid (water), and

gas (steam). However, chemically it is very unusual. For example,

water molecules are slightly polar i.e. they have a positive and

negative end. Due to this difference in electro-negativity the

slightly positive charge on the hydrogen atom is attracted to the

slightly negative charge on the oxygen atom in another molecule. This

bond is called a hydrogen bond and is what causes the water to have

its unusual properties. For example, other molecules of the same size

of water (H2O) are all gases at room temperature and pressure (R.T.P).

Without the hydrogen bonds, water too would be a gas at RTP and would

have a boiling point of -120°C.

Because it is polar, water also has uses as a solvent. Other polar

substance are dissolved by water as the electrostatic attractions

between the water molecules and the ions are greater that the

attraction between the anion and cation. The water molecules surround

the ions and thus the ions become hydrated. Polar substances that

dissolve in water are said to be hydrophilic or "water-loving". The

ability of water to be a solvent has uses in organisms. For reactions

within the body to take place, they usually have to be in solution.

Therefore, using water as the solvent enables more reactions to take

place as more compounds may be dissolved. It is not only human that

use water as a solvent, plants are only able to take up mineral salts

in solution and so use water. Also, organisms that live in marine

environments still need oxygen to respire. The only reason they

survive is because oxygen is dissolved in the water. This would not be

possible if the water molecule was non-polar.

As I have said, water is the most abundant molecule on the planet, but

is also the most abundant molecule organisms. The lowest percentage

composition is 20% in seeds, with the highest being 99% in jelly fish.

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