Water
Water has 2 very important roles! But anyway, without water no life would
exist on earth, it is the most important biochemical of all. Three quarters
of the earth is covered with water.
1.Role
70-95% percent of a cell contains water. The human body for example contains about 60% water.
2.Role
An environment for all organisms, which live in water.
Such a small molecule would exist as a gas at normal Earth temperatures were it not for its special property of hydrogen bonding to other water
molecules.
In water (used as a medium) molecules and ions can mix in and hence a
medium. In this medium life could envolve.
Hydrogen Bonds are hard to break and hard to convert from liquid standard to
a gas. Therefore a lot of energy is needed. Because of this qualitys, it is
difficult to separate the water molecules and to affect the physical
properties of water.
Important other roles
Water as a solvent
Water is a solvent for ions and polar molecules. Water has the quality,
that its molecules are attracted to ions and polar molecules and can collect
around and separate them.
Chemicals can move free and react with other chemicals in water. Most
processes in living organisms take place in solution in this way. As soon as
a chemical dissolves in water, the watermolecules start doing the mentioned
process.
But, water is not a solvent for non-polar molecules and lipids. In contrast,
the water molecules start pushing them together, until the water molecules
are attracted to each other. Because of this, the structures are more
stabile and it is important in hydrophobic interactions in protein and membrane structure.
Water as a transport medium
The fact that water is an solvent is very important in other areas, too. In
animals it is needed, to transport things in the blood, in the lymphatic, in
the excretory and in the digestive systems. In plant cells it is needed as a
tranport medium in the vascular tissues.