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The Biological Importance of Water

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Introduction

Watery World Water, water, everywhere, Nor any drop to drink. As said by Samuel Coleridge in "The Rhyme of the Ancient Mariner" water is everywhere. Our planet's name - Earth - cannot be taken for face value because in reality the "Earth" is covered by more than 70% water. To be exact there is approximately 326 million cubic miles of water on Earth. In order to appreciate and envisage such an enormous amount you have to put it into perspective. Out of all the water on Earth, only 0.3% of it is usable by humans. The other 99.7% is unusable in oceans, seas, ice and the atmosphere. And even out of that 0.3%, most of it is out of our reach. But what is water? Water is a substance whose molecule is made from two 1hydrogen atoms and one 16oxygen atom (H20) and that is in a liquid state at room temperature. It boils at 100�C and melts at 0�C. Water is probably the fundamental reason for sustenance of life on Earth. Every living thing depends on it to survive which is why water is so important. As well as being essential to life, water also has many other uses. Some of these include being a very good solvent, for washing or even as habitats and environments. Water's abundance and requirements towards life already make it special but there are even more properties of water as a result of the hydrogen bonds between water molecules that make water an ideal constituent of living things. The structure of water molecules is unique. ...read more.

Middle

As a result if ice is formed then it will float on water. This is seen on lakes etc. where there may be a layer of ice on top and however thick it may be, there will be liquid water under it. This unusual density pattern is very useful in creating habitats for animals. If there is a sheet of ice on top of a lake then the water under it becomes insulated so preventing the whole body of water from freezing into a solid mass. This allows sea creatures to remain in the water all through the year without risk of being turned into novelty ice cubes (providing there is sufficient food and oxygen available). Also since the ice floats, it allows mammalian life to live on top of the ice. Again the example of a polar bear can be used which lives on glaciers and icecaps all year. There is a natural tendency for water molecules to dissociate into ions. When this happens protons and negative hydroxide ions are produced. The protons become attached to the oxygen atom of another molecule creating oxonium (H30) ions. At 25�C the concentration of oxonium ions in pure water is 10-7 mol dm-3 and this is given the value of 7 on the pH scale. The pH within most cells is within 6.5 - 8.0. This value remains fairly constant because substances within the cell act as buffers so do not considerably change their pH. ...read more.

Conclusion

Water is quite viscous which makes it a useful lubricant so easing movement in creatures. Lubricating fluids which are largely water constituted include mucus to aid movement in animals; synovial fluid for movement in many vertebrate joints; pleural fluid for movement of lungs during breathing; pericardial fluid for heart movement; perivisceral fluid for movement of other internal organs. Water simply being a liquid means that it cannot be compressed much under pressure unlike gases. Therefore water is used a lot in structural support. Examples include hydrostatic skeletons in animals such as the earthworm which are supported by the pressure of the aqueous medium within them; turgor pressure in herbaceous plants etc where support is provided by the osmotic influx of water into their cells; the shape of the eye in vertebrates is maintained by the aqueous and vitreous humours within them; amniotic fluid supports and protects the mammalian foetus; a medium in which to live because it supports the weight of very large organisms e.g. the blue whale which wouldn't be able to move on land because of its sheer size. One last biological significance of water can be in the aid of hearing and balance. The watery endolymph and perilymph play a role in hearing and balance. If you count up all the many ways in which water is significant to life on Earth as I have listed them (and these are but a few) then you can realise the value of this most abundant liquid which we call water - the basis of life itself. ?? ?? ?? ?? - 1 - Biology - Milan Shah - 12E ...read more.

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