Biological Importance of Water

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Biological Importance of Water:

Water is a truly incredible molecule, biological life as we know it evolved from the water. It is the main constituent of all organisms and we humans are made up of around 70% of it. In order to understand why the water molecule is so important, we have to examine its structure.

The Structure:

A molecule of water consists of two hydrogen and one oxygen atoms (see diagram left). The atoms are joined covalently and the water molecule formed is very stable.

Water is a polar molecule, and since it has two charges it is dipolar which means that it has negative ends (Oxygen) and positive ends (Hydrogen) as shown in the diagram. This dipolar quality gives an electrostatic, albeit weak, force and allows adjacent molecules to bond together resulting in water having a high boiling point.

Water as a Solvent:

         Water is an exceptional solvent in particular when dissolving salts, simple alcohols and sugars all otherwise known as polar substances. For example an ionic salt such as potassium chloride would dissolve because the charged particles (ions) will dissociate within the water. The positive ions attract to the negative oxygen atom and the negative ions to the positive hydrogen.

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        Substances that are non polar however, for example lipids, do not mix with water and consequently can be easily separated from aqueous solutions. For example, when droplets of oil merge in water they do not mix (they are said to be immiscible) and can easily be drained from the top surface of the water.

Water as a lubricant:

Water’s properties, especially its viscosity, make it a useful lubricant. Water based lubricating fluids within the body include:

  • Mucus – This is used externally to aid movement in animals, such as in snails, or internally on the gut wall to aid ...

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*** The student has thought of most of the main points that should be included in this essay, but some are explained better than others. In most cases he has identified the important property of water, but several times he has not fully understood its biological importance. The essay also lacks a logical structure: it jumps around quite a bit, and includes a little too much information about uses of water (e.g. as a transport medium) rather than important properties.