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Why is Water such an important substance in biology

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Why is Water such an important substance in biology? Water plays a major role in all living things. It makes up between 65 and 95% by mass of most plants and animals. About 80% of an individual human cell is water. Water has a simple molecular structure. It is composed of one oxygen atom and two hydrogen atoms. Each hydrogen atom is covalently bonded to the oxygen, by a pair of shared electrons. Thus there are 4 pairs of electrons surrounding the oxygen atom, two pairs involved in covalent bonds with hydrogen, and two unshared pairs on the opposite side of the oxygen atom. Oxygen is an 'electronegative' or electron 'loving' atom compared with hydrogen. ...read more.


Water has a high heat capacity; that is, a great deal of heat is required to raise the temperature of water. This, again, is due to the hydrogen bonds. Most of the energy is used to break these bonds, restricting the mobility of the molecules. As a result, water takes a long time to heat and cool. This specific heat capacity is the highest of any known substance. This is significant because it means aquatic environments are slow to change temperature. It also means bulky organisms have a stable temperature in the face of fluctuating external temperatures. The heat energy needed to melt ice, known as the latent heat (enthalpy) of fusion, is unusually high, as is the latent heat of vaporisation (energy needed to vaporise water). ...read more.


This is useful in the sea, lakes and ponds because it means any ice that forms in cold weather will float. The ice insulates the water below and so it less likely for the whole area to freeze over. As water is colourless, it also enables plants to photosynthesise well in deep water. In humans, the low viscosity, or runniness of water is essential, as it lets water flow easily through capillaries. Certain small animals rely on water to land on and to move across. This is because at the surface of water, the molecules are positioned so that the hydrogen bonds point inwards, giving water a very high surface tension. This enables the lighter creatures to move on top of the water surface. All these properties and uses of water show that it an unusual and incredibly important substance in biology. Life as we know it depends on these properties. ...read more.

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