What is the biological importance of Water?

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What is the biological importance of H20. Describe with examples how the physical properties of water allow it to perform these roles. Include: Density when solid and liquid boiling point, melting point, hydrogen bonding, surface tension/cohesion (plants), Specific Heat Capacity, Latent Heat of Vaporisation.

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  • Created on: 31-01-12 15:07
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What is the biological importance of H20. Describe with examples how the physical properties of water
allow it to perform these roles. Include: Density when solid and liquid boiling point, melting point, hydrogen
bonding, surface tension/cohesion (plants), Specific Heat Capacity, Latent Heat of Vaporisation.
The water molecule is formed from two hydrogen atoms and one oxygen atom covalently bonded. It Is a
very small molecule. The bond angle in the hydrogen's is almost 105 degrees rather than 180 degrees which
would make the molecule symmetrical. The shared electrons are not shared evenly; the oxygen atom is
capable of pulling the shared electrons towards it and so away from the hydrogen atom. This causes the
molecule to be polar and having a positive and negative side, the hydrogen being positive and oxygen being
negative. This slight charge can allow hydrogen bonds (a weak attraction that can occur wherever molecules
contain slightly negative charged atom to a slightly positive charged hydrogen) to be formed with other
molecules. This makes water tend to stick together. The hydrogen bonds make it more difficult for
molecules to `escape' the liquid to become gas, which is explains waters
high boiling point at 100 degrees Celsius. Molecules such as hydrogen
sulphide which are similar in size to water are gas at room temperatures.
It can be found in all three states, solid (ice), liquid (water) and gas (water
vapour/steam). Water is a very good solvent due to the hydrogen bonding
being able to break up the electrical attraction of atoms of solids and
therefore dissolves them. In ice the water molecules are widely
separated, while in liquid form they are closer together although less
tightly bound. As temperature is reduced there is less kinetic energy more hydrogen bonds form but little is
broken, as water becomes solid they hydrogen bonds formed hold the semi-crystalline structure being less
dense than water. Therefore ice is bulkier and less dense and floats on water; this also insulates the water
below. This allows living organisms to survive the winter, and even to live under
the ice.
The evaporation of water takes up a lot of energy, this means that water
`removes' heat from the surfaces, so heat energy is used in evaporation. This is
how sweating in our bodies helps cool us down due to the heat energy being
used up. A drop of water on a waxy surface can look almost spherical and
hardly wets the surface at all. This is due to the hydrogen bonds pulling water
molecules in at the surface; this property is called cohesion and also results in
the surface tension seen at the surface of a body of water.
Water can be used as a solvent commonly. Metabolic processes in all organisms rely on chemicals being
able to react together in solution; this is a key use of water. Water can also be used as a liquid to move
materials around organisms both in cells and on a large scale in multicellular organisms require a liquid
transport medium; water is used in vascular tissues in water. Water also has thermal stability, large bodies of
water have fairly constant temperatures due to the vast amounts of energy needed to break hydrogen
bonds, and this means the heat capacity of water is high compared to other common materials.

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