Substances in organisms often need to be transported to other parts, like organs. In humans our main transport system is our blood. It supplies our bodies with food, hormones, oxygen, waste and much more. Plants version of this is their sap. Both these mediums for transport of nutrients and such consists of mainly water and the products dissolved within. Blood allows oxygen to be transported to tissues and hormones to various organs to control them.
Many reactions occur in organisms catalysed by enzymes. Water being an excellent solvent lets these reactions occur as they often need ionising. However water does not always just provide a place for reactions to take place and can itself be a reactant in a reaction, for example photosynthesis. Substances can only be absorbed in the gut when they are in a solution. Without water this would not be able to take place. When large macro-molecules of starch are broken down into simple sugars such as glucose it uses a process called condensation were water is a released product of the reaction. The reverse of this is carried out in digestion, were water molecules must be supplied. This is called hydrolysis, and is an important process were water is needed as a reactant.
Also a certain measure of water is needed in cells to provide sufficient strength but prevent lysis were cells become over turgid and burst due to the excess of water through osmosis.
Bones meet at joints, and at these points lubrication must be provided to make sure the bones do not scrape one another and cause pain, and possible damage. The lubrication enables free easy movement, and less friction at the joints thanks to synovial fluid, the lubricant consisting of water. Many internal organs have a watery fluid surrounding them for protection and lubrication. Most importantly the brain is surrounded with cerebro-spinal fluid acting as a protection to impacts amongst other purposes. The gut has its own mucus to allow food to pass easily.
Water is essential in fertilisation, when the male sperm is released, it is carried in semen to aid its journey to the ovum to fuse and form a zygote.
Sweating is an important bodily function to keep our body temperatures consistent, like it is important for plants to transpire so the roots can carry out more active uptake. The high water content of cells gives them insulation, and protects them from rapid temperature changes, thus helping to keep cells at a fairly constant optimum temperature
So although water is the most abundant molecule in cells, whole organisms and on earth it is the most important to every living organism. Lack of water causes illness, weakness, poor health and slow collapse of organs, and none causes death. It is absolutely essential to any organism in the world and without water there would be nothing, it is as vital, if not more, than the sun.
Bibliography
Almost everything there is to know-Hunkin
Software Toolworks Multimedia Encyclopaedia
letts key stage three classbook, Science. Terry Hudson-1998
