All this means that water has several very useful properties which help living organisms to survive.
The polarity allows the molecules attract to each other and although these hydrogen bonds are only 1/20th of the strength of a covalent bond, collectively they still make the water molecules ‘stick together’ strongly and give them a high surface tension (they are cohesive). This is shown when drips from a tap do not drip straight away they try and ‘hold on to the tap’ due to its cohesion. It is this cohesion that allows water to travel up tree trunks to the highest branches on trees, if the cohesion was weaker the water would simply flow back down the xylem vessels due to gravity, therefore without this property of water tall trees and plants would die.
This cohesion of the water creates a surface tension on the surface of water in for example, a pond. In a pond small insects such as pond skaters which are relatively dense can float on the water and live on the surface of the water. Without the tension such organisms would have no habitat and would die.
Water also acts as a good temperature buffer to stabilise experiments within cells. Due to the hydrogen bonds produced bonds between the water molecules water is given the following properties relating to heat and temperature :-
1. Relatively high heat capacity
2. Relatively large latent heat of vaporisation
3. Relatively large latent heat of fusion
These three properties are very similar and basically mean that a relatively large amount of energy required to change the temperature or state of water. The specific heat capacity of water is 4184J/kg, over 40 times that of sodium chloride. This means that a lot of energy is required to change the temperature of water and it is that fact that makes this property very useful in enzyme action. Enzymes in cells only work well in certain temperature ranges and if their temperature increases too much they become denatured and they won’t work. The enzymes are very important as they control the reactions in a cell so if they are damaged cells will die.
This property also maintains a stable environment for organisms living in or on the surface of water. This is very important as animals may not be able to adapt if temperature change is too much and they won’t be able to compete as well for food and against predators and therefore may die.
Another property of water is that it is a very good solvent. Polar molecules attract water, they are hydrophilic and dissolve in water easily as they join onto water molecules by a hydrogen bond because they too are polar and have slightly charged positive and negative poles. So without the polarity feature of water it wouldn’t be as good a solvent. The biological significance of this is that substances can diffuse through membranes much more easily if they in solution. This means energy is not wasn’t moving ions across a membrane by active transport or endo-cytosis. As well as this, chemical reactions in cells occur much quicker if the reactants are in solution, so in effect water speeds up the rate of a reaction by providing the reactant in solution. This makes the cell more efficient which is important.
When water freezes it becomes ice. Most substances become denser when they become a solid but water is at its densest state at 4°C. When it freezes it expands and becomes less dense. In Biology, this provides many arctic animals with a safe habitat under the ice which floats on the surface of the water because it is less dense. Under the ice the animals are protected from some predators and the environment is kept constant and insulated which helps them maintain a constant body temperature. The ice floats on the surface tension of the water and provides other animals with a place to live. If the ice sank to the bottom then the water would freeze from the bottom and eventually there would be no water left and many animals would die.
In conclusion, water is very important to human life and all other organisms as it is evident that without it many would become extinct. It is the fact that water is polar and has hydrogen bonds that give it the properties described and it is these properties that make water so indispensable to life as we know it.
