The Importance of Water to Life on Eartha look at the unique structure and behavior of the water molecule—–Water is the most important substance in our evolution and our daily lives. Without water,life as we know it would not have been possible. This essay will examine the water moleculein order to ascertain how it brought about Earth’s thriving ecosystem and how important itis to us today. ==============================______________________________==============================Each water molecule consists of one oxygen atom and two hydrogen atoms. The oxygen atom (orthe apex of the water molecule) bears a slight electronegative charge while hydrogenpossesses a more positive one1 (figure a). Because opposite charges attract, the watermolecules are drawn together. When an oxygen atom is linked to a neighboring molecule’shydrogen atom, a bond called a hydrogen bond is formed2. In an ice crystal the hydrogenbonds govern the shape of the crystal so that the grid of molecules surrounds relativelylarge spaces (imagine figure b in three dimensions). In a liquid form, water has no suchspaces; thus ice is less dense and will float on liquid water. If not for this, great bodiesof water would freeze from the bottom up without the insulation of a top layer of ice andall life in the water would die. The water molecule is a very small one but because of its unique properties it behaves likea larger one. The bonds between water molecules are so strong that water resists changes inits state (Solid, liquid, gas); thus water has a higher melting point and a higher boilingpoint than another molecule of similar size. If water followed the example of othermolecules its size it would have a boiling point of -75*C and a freezing point of -125*C4. This would mean that, on Earth, water would be a gas all of the time and life would not bepossible. When heat is applied to solid water, some hydrogen bonds get so much kinetic energy thatthey break and the ice melts. Liquid water does not necessarily have all four hydrogen bondspresent at all times but it must retain some of them5. For any object to penetrate water, itmust be able to break the hydrogen bonds on the surface of the water. These bonds resistbreaking thus forming a “skin” that allows small insects to walk on the surface of thewater. Without the cohesiveness of water, those insects would not have survived. All plant life on Earth benefits from the ability of water to make a hydrogen bond withanother substance of similar electronegative charge. Cellulose, the substance that makes upcell walls and paper products, is a hydrophilic substance (”water-loving”)6. It interactswith water but, unlike other hydrophilic substances, it will not dissolve in it. Cellulose
can form strong hydrogen bonds with water molecules7. This explains why a paper towel will”wick” water upwards when it comes in contact with it. Each water molecule will make ahydrogen bond with cellulose and pull another water molecule up from down below and so on. Without this feature (capillary action8), plants would find it more difficult to transportwater up their stems to the leaves in order to make food through photosynthesis. Water has a very high heat capacity. Most of the heat introduced to water is used not to setwater molecules in motion (giving them kinetic energy and causing their temperature torise), but to move hydrogen atoms around between neighboring oxygen atoms9. If all of thisheat was used solely to warm the water, living cells would boil in their own heat. Everyaction in a living cell releases some heat. If the heat was not dissipated by the water, allliving things would cook themselves. In order for water to evaporate from the surface of liquid water, a certain amount ofenergy must be expended to break its hydrogen bonds. Because these hydrogen bonds are sostrong, water requires a lot of heat to boil (100*C). When water vaporizes, it takes alongall of the heat energy required to break its bonds thus having a powerful cooling effect onthe original body of water 10. It takes very little water loss to cool water substantially. If humans had no way of perspiring, their body temperatures would rise about 70*C in onesingle day11. Water is very important because it is as close as we can get to a “universal solvent.” Whena crystal of salt is dropped into a glass of water, the water begins to surround the sodiumand chloride atoms in the salt in what is called a hydration sphere12. The atoms interactwith the water molecule and leave the surface of the salt crystal, until the entire crystalis dissolved. This has two effects: the salt is dissolved and the water molecules aredisturbed. When the water molecules are altered in this fashion they can no longer take partin the formation of ice crystals13. This is why oceans, which contain a lot of salt, resistfreezing. In conclusion, it is apparent that water is the most important substance ever to have beencreated because it is so vital to our race. Its unique properties aid all living things tosurvive in the scheme of nature on our planet Earth. 1.Kirk, David L. Biology Today: ThirdEdition p. 225 2.Ibid p. 256 3.Ibid p. 256 4.Ibid p. 257-258 5.Ibid p. 256 6.Ibid p. 2597.Ibid p. 259 8.Ibid p. 259 9.Ibid p. 257 10.Ibid p. 257 11.Ibid p. 257 12.Ibid p. 25913.Ibid p. 259 Bibliography:1)Kirk, David L. Biology Today: Third Edition, Random House Publishers, 1980Biology Today is a comprehensive source of information that contains facts, statistics andopinions from over 200 different sources as well as many different Universities andarchives.