the biological importance of water
Water, the most abundant compound on the planet, is a material which is essential for all living organisms. Its uses in all living things cover a huge variety of everyday functions which are immeasurably important to the continuity of the organism. The fact that water makes up between 60 and 95 percent of all living organisms speaks for itself on the incredible biological importance of this compound.
One of the major functions of water in living organism is its use as a solvent. Because water is slightly ionised, other polar molecules such as salts, sugars and amino acids will dissolve readily in water. This allows water to be used for the transportation of such substances (notably in the bloodstream of animals and the xylem and phloem vessels found in plants). Water can be used in this way to transport many substances: nutrients, excretory products (eg urea, ammonia), hormones and digestive juices can all be transported by using water as a solvent. Molecules such as starch and glycogen which are hydrophobic are not soluble and therefore are ideal for storage.
In the digestive system many polymers and dimmers need to be broken down into smaller molecules by the process of hydrolysis. Water is used in hydrolysis reactions to separate the larger molecules into smaller ones (eg proteins into amino acids). Water is produced in respiration and this water can be very useful for organisms living in dry habitats. The process of photosynthesis requires water in order to create glucose.
The fact that water has an unusually high specific heat capacity makes it a very useful substance for living organisms. Water does not change temperature very easily and therefore minimizes fluctuations in temperature in cells and creates a remarkably constant sea temperature for aquatic organisms.
Water has a high latent heat of vaporisation which means that when animals sweat and plants transpire water, takes energy from the organism when it evaporates and as a result cools the organism.
Ice is less dense than water and so in cold conditions, ice will float on bodies of water. This insulates the water below and allows aquatic life to live in sub zero conditions.
Because water is a polar molecule, molecules of water stick together with hydrogen bonds. This allows long chains of water molecules to stick together – this is useful both for sucking up water through tall trees by transpiration and for creating surface tension which allows many animals to walk on water.
Water is essential for support in plants. By the process of osmosis, plant cells take water in which causes an increase in the pressure against the rigid cell wall – the cell enters a state of turgor. This allows herbaceous plants to remain upright.
In conclusion, water has uses in all organisms – from plants to animals and can offer a great many things from transport to support. This substance is absolutely essential to the existence of every living organism on this planet.
By Michael Northend
1
doc13257 (1).doc