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The Water Molecule.

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The Water Molecule The simple molecule of H20 has many interesting physical and chemical properties which contribute to its importance. It is the only substance which can be found naturally in all three states solid- ice, liquid and gas- water vapour. Water is the most abundant component of any organism. Humans are 60% water and most organisms are 60%-90%. The lowest water content is 20% which can be found in plant seeds and the highest in jellyfish at 99% and this is because of their transparency. The water is found mainly in the protoplasm and plays vital roles in many functions such as metabolism in all organisms and photosynthesis and support in plants. A water molecule is formed when two atoms of hydrogen bond covalently with an atom of oxygen. The oxygen atom attracts the electrons more strongly than the hydrogen this gives water an unbalanced distribution of charge and molecules that have ends with partial negative and positive charges are known as polar molecules. ...read more.


In mammals the alveoli in the lungs are moist and in plants their leaves have moist surfaces for the gas exchange to occur. Many organisms living in water spend much or all of their time under the surface so they need oxygen gas to respire and as water is such a good solvent the required oxygen gas is dissolved in the water. As water has a high specific heat capacity, this means that to raise the temperature of a certain amount of water by as little as 1oc a large amount of energy is needed therefore the temperature of water is not easily changed. This then shows that bodies composed largely of water are very thermo stable and less prone to heat damage by changes in environmental temperatures. This leads on to why mammals sweat. Mammals sweat when their body temperature is too high and the large amount of energy required to evaporate the sweat from the surface of the organisms is taken from the organism, this giving a large cooling effect. ...read more.


There are many other fluids which act as lubricants- Synovial fluid- lubricates many vertebrate joints Pleural fluid- minimises friction between lungs and the rib cage during breathing. Mucus- allows food to pass more easily through the gut. As water cools towards its freezing point the individual molecules slows down sufficiently for each one to form its maximum number of hydrogen bonds. For this to happen the water molecule are widely separated, while in liquid form they are closer together although less tightly bonded. Therefore the water expands, and as it freezes it becomes less dense than liquid water and is able to float upon its surface. As the ice forms on the surface of ponds and lakes it insulates organisms in the water and below it. The floating ice also gives penguins and polar bears somewhere to stand. From this we can see that water is the most useful substance on earth, without it, there would be no life. Water in biological terms has great importance both inside cells and externally. ...read more.

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