The Importance of Water.

        Water has a very high heat capacity (heat capacity is defined as the amount of heat required to raise the temperature of I gram by 1°C) then many other liquids. This is highly important because it can retain its heat for longer in say, cooler temperatures. This is significant because animals and plants cannot tolerate wide variation with temperature. Another biochemical importance of this is that the temperature range in witch chemical reactions can take place is very narrow. The high heat capacity of water makes it ideal for keeping the temperature constant, thus making it ideal for plants and animals. A good use of this would be found in the womb where babies are kept at a constant temperature with the help of water encasing it. If it weren’t for waters high heat capacity, for a substance of low relative molecular mass, it would most probably have been lost to outer space.

        Surface tension is the force that causes the surface if a liquid to contract so that it occupies the least possible area. It is caused by the inward-acting cohesive forces between the molecules at the surface, this being caused by the polarity of water which I will explain later. Water has the highest surface tension of any known liquid except mercury and this is of great biological importance. Molecules dissolved in water lower its surface tension and tend to collect at the interface between it liquid phase and other phases. This may have been important in the developing of the cell surface membrane, and certainly plays an important part in the way molecules move across it. The high surface tension of water a long with the high cohesion forces which exist between the molecules also plays a part in the movement of water through capillary like vessels and tracheids in the stems of plants. It also allows a sort of ‘film’ around the water to allow certain animals to live on it.

Waters properties as a solvent depend on the fact that it is a polar molecule. This means that the distribution of electric charge is permanently such that the centre of positive and negative charge is separated by a short distance. This is because of the configuration of a water molecule; instead of being arranged in a straight line the hydrogen and oxygen atoms are situated asymmetrically to each other as shown in the diagram above. (☺)

The hydrogen atoms are situated like this because oxygen has 2 more free electron pairs which still contribute to the bond angle of the different atoms which are not shown on the diagram.

The oxygen part of the molecule has a net negative charge and the hydrogen charge has a net positive charge. Thus the molecule as a whole shows polarity. Now consider what happens if a crystal of sodium chloride is placed in water. In the crystal the sodium and chloride atoms are held together because they are strongly attracted to each other. In the presence of water this attraction is greatly reduced, with the result that the ions part company and go into solution. Water effectively weakens the attraction between ions of opposite charge because, having a positive and negative charge itself, it attracts both. Furthermore the ions are prevented from rejoining because by water molecules clustering around them. Water is therefore a good solvent because ionic solids and polar molecules readily dissolve init. This is of great biological importance because all chemical reactions that take place in cells are done so in aqueous solutions. Also the polarity of the molecule also plays another significant role. The negative charge of the hydrogen has an attraction with the positive charge of the oxygen from different molecules, this is known as weak-hydrogen-bonding. This has great significant in the shape of biological molecules such as enzymes and proteins. Without this polarity they would not be able to form complex 3d structures such as hemoglobin.