•Water as a solvent
Numerous substances may be dissolved into water, dipolar molecules are attracted to the charges on the molecules of water, so they spread out evenly in the water. Waters great ability to have substances dissolved in it is essential in many areas, for example the blood in animals being predominately water means that substance can be dissolved into it at one point in the body and then transported to another, in a similar way to the watery phloem sap in plants. It is also useful as substances can react together in water easier as in this state they are free to move about which is essential for reactions essential to life such as metabolic reactions. However not all substances dissolve into water, for example those substances with large molecules such as starch or the protein keratin.
• Thermal Properties
Water has a very high specific heat capacity, as it’s molecules are attracted to each other, so it therefore takes a lot of energy to make them move about a lot, this is essential to aquatic organisms as it means that no matter what the temperature of a day, whether hot or cold, the temperature will not change very much from the temperature in which the organism is used to. For example a temperature of 100C must be reached to boil water, so as living organisms contain a very large amount of water, eg. 70% in humans, our cells are protected from damage by dramatic environmental temperature changes, thus helping us as organisms to regulate our body temperature. Also waters latent heat of vaporisation is essential to a mammal as when one becomes too hot it secretes sweat which contains a large amount of water
onto the skin which then absorbs heat from the skin, similar to the way leaves cool themselves by water evaporating from their mesophyll cells.
•Surface Tension
In water the attraction between molecules means that a molecule on top of an amount of water will be pulled down on top of the below others, creating a surface layer much like a skin. This is useful as it allows enough tension for small animals i.e. pond skaters to rest on the upper ‘skin like’ layer.
Water’s high density caused by the hydrogen bonding between individual molecules which creates a close bond means that as most living organisms have a like density, they are able to float in water, which is why aquatic organisms are able to swim in water.
