Water can also separate covalently bonded molecules such as glucose and sucrose. The polar hydroxyl groups in it’s structure forms hydrogen bonds with the water separating the molecules from each other. Water’s property as a solvent is vital to life as most biochemical reactions such as respiration occur in solution. This is why cell cytoplasm contains about 90% water. Water can also dissolve toxic products in our body and take them out as sweat or urine. Water cannot dissolve non-polar substances such as fats and oils; these are used by organisms as cell membranes to separate cells and also as waterproof to stop water from entering if it was covered in a hydrophobic substance.
In many reactions in cells, water is either used up or produced. For example it is used up in photosynthesis and produced in respiration. Water can also transport many essential nutrients in an organism by osmosis or other methods. In animals, blood and lymph transport many vital things for life. In plants water is vital to the way in which phloem and xylem work. The ability of water molecules to stick together allows a plant to transport water to leaves in the highest parts of the tree.
Water also has various thermal properties as a temperature stabiliser. Water has a boiling point of 100°C and a melting point of 0°C, this is unusual for a molecule of it’s size (Water has a RMM of 18) because other molecules of similar size such as: ammonia, NH4 with RMM the same as water and Carbon dioxide with RMM of 44, are all gases at room temperature whereas water is a liquid at room temperature. This because of the hydrogen bonds which holds the molecules together. The hydrogen bond also lets the water to have a high specific heat capacity. A high amount of energy is needed to heat water. Once water is warm it cools very quickly, this is fundamental to life where internal body temperature has to be maintained at a constant temperature and fluctuations can result in breakdown of vital processes. Large bodies of water will remain at a constant temperature allowing temperature regulations for organisms far more straightforward.
A high energy is also needed to separate hydrogen bonds and turn the liquid to 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. This allows them to cool down as high amount of energy is transferred to evaporate a small amount of water. Sweating is an example of this.
When water-cools its density increases and the hydrogen bonds between the molecules take on a more latticed formation as ice. The reason that ice floats on water is that water has its maximum density at 4°C, which is when the bonds are closest together. When water freezes the lattice arrangement of its structure move apart slightly and it floats on the surface. This insulates the water beneath it and saves aquatic life from freezing to death.
Water is the medium for many reactions, especially those which occur in cells. Water is key in condensation reactions where water is removed from molecules to bond them together, this occurs with numerous sugars and carbohydrates.
Water is also used to split up molecules. This is termed Hydrolysis and is fundamental to animals and plants as it allows them to utilise stored food, which are in long chains by breaking off smaller molecules.
Respiration produces water as a by-product. A large amount of energy is produced by oxidising hydrogen, which contains so much energy it is an explosive gas, into water. Photosynthesis uses water as a source of hydrogen atoms, which are needed to produce glucose, which is then stored in the plant cells as starch or used for respiration. Without water these two essential reactions would not occur and life would not be able to continue on earth. An important property of water is also it's transparency, it allows sunlight to pass through it so aquatic plants can photosynthesis and on a larger scale, allow life on earth to begin, since life started in the oceans with small organisms which relied on sunlight for the reaction photosynthesis to take place.
Water molecules are highly cohesive because of the hydrogen bonds between the molecules. Water forms spherical droplets, which have the maximum inner area and least surface area when in contact with a hydrophobic material. The cohesive properties of water allows plants to pull up water through xylem vessels from the roots to the leaves, this is called the transpiration stream. It also means that the water molecules where the water meets the air will be tightly held together and the water molecules below them to form an elastic film known as surface tension. Small creatures can get stuck in the surface water because they cannot break the water surface tension, creatures like water skaters can move across the surface of the water without sinking as they have hydrophobic feet which stops them from breaking the surface tension.
As water has strong hydrostatic, water is incompressible. This provides support for soft-bodied creatures such as worms, slugs and jellyfish, which therefore do not require a supporting skeletal system. Water allows cells filled with water to become turgid and due to its incompressibility plants can support themselves.