The Role of Water in the Lives of Organisms

Water (Hydrogen Oxide - H2O), is a compound that is found everywhere

on the planet. It can occur as solid, liquid and gas. It forms as much

as 2/3 of the Earth's surface and is vital to all varieties of life.

Water has importance inside cells and externally. This may be because

it has interesting chemical and physical properties; it can be found

naturally in all three of its states. However its molecules are bonded

together by hydrogen bonds, this rises its melting and boiling points,

i.e. its boiling point would be -120ºC rather than 100ºC. Also because

it contains slightly negatively charged oxygen atoms and slightly

positively charged hydrogen atoms making it polar.

Water is called a universal solvent because of it polarity. This means

it can easily ionise substances, many compounds, whether ionic, polar

or covalent will dissolve in it, therefore more reactions take place

while in solution with water. Often in organisms substances must be in

solution and water is the solvent. For example plants can only obtain

mineral salts in solution and human digestion will only dissolve

soluble foods, meaning large starch molecules must be broken down into

soluble sugars. Also many organisms living in water spend most of

their time underwater, yet they require oxygen to respire, and as

water is such a good solvent that the required oxygen gas is dissolved

in the water.

Water is the most abundant component in any organism, the lowest is

20% in seeds, while jellyfish are 99% (hence the transparency). It

plays vital roles in the metabolism of all cells and in photosynthesis

(providing raw materials) in plant cells. In all cells water is used

for; hydrolysis, the breakdown of a substance by water, e.g.

polysaccharides to monosaccharides, it is also a medium for chemical

reactions, due to its properties as a solvent; the diffusion and

osmosis of substances, e.g. gaseous exchange, where there needs to be

moist lung wall linings as the exchange takes place in solution,

therefore there is water in the lungs or in.