Hydrogen bonds are formed between the oxygen of 1 water molecule and the hydrogen of another – as a result this H2O has an attraction called cohesion. Cohesion is responsible for surface tension, which enables aquatic insects such as pond skaters to walk on pond surfaces and also aids capillarity, the way in which plants pull up water through xylem vessels from the roots to the leaves, this is also called the transpiration stream.
H2O has a high specific heat capacity, it takes 4.2 joules of energy to raise 1 gram of water by 1°C, and therefore it takes a lot of heat energy to raise the temp of water significantly, but once warm, it cools slowly. This is essential to life where internal body temperature has to be maintained at a constant temperature as fluctuations can result in the breakdown of essential processes.
Due to the large number of H bonds holding water molecules together, it takes 2kj per gram of water to separate the bonds and turn H2O in vapour. Water is therefore described as having a high latent heat of evaporation. Animals use this property of water by using excess body heat to evaporate water from their surfaces, resulting them transferring a lot of energy into the environment but losing only a little water. Sweating and panting are based on this principle.
H2O also has a high latent heat of fusion from solid to liquid. It requires 300J per gram of ice to melt it to water; this means that water stays liquid. This is vital for cytoplasm in cell, which is made of a high percentage of water – once frozen, irreparable damage would be caused.
As H2O cools its density increases and becomes more latticed. Ice is able to float on water, which has a higher density. Water is most dense at 4°C – this means that a layer of ice insulates the water below which stays at 4°C, so aquatic life can continue.
Water is a medium for many reactions, especially those that occur in cells. Water is key in condensation reactions where water is removed from molecules to bond the together, this occurs with many sugars and carbohydrates.
Water is also used to split molecules in a process called hydrolysis. This is essential to animals and plants because this process allows them to utilise their stored foods.
Respiration produces water as a by-product, a large amount of energy is produced by oxidising hydrogen. Photosynthesis uses water as a source of hydrogen atoms, which are needed to produce glucose, which is the stored in the plant cells as starch or used for respiration. Without water these 2 essential reactions would not occur and life would not be able to continue on earth. Water allows cells to become turgid and due to its incompressibility plants can support themselves.
In conclusion waters unique properties make it the most biologically important substance on the planet. No other substance share similar properties to water in the way one single molecule can possess such varied and essential characters.
