The Biological Importance of Water and Its Role in Living Organisms

The biological importance of water and its role in living organisms

What is water?

Water (from the Old English word water) is a colourless, tasteless, and odourless substance that is essential to all known forms of life and is known also as the most universal solvent.

Water has a very simple atomic structure, the structure consist of two hydrogen atoms bonded to an oxygen atom, which can also be related to as hydrogen oxide. At least 70% of the mass of living organisms is water, and almost all of chemical reaction of life takes place in an aqueous solution. The other chemical that makes up living things are organic macro molecules that belong to the 4 groups Lipids, proteins, nucleic acids, and carbohydrates. Without water, life on earth would not be possible and we as humans are made from approximately 80% water by mass and some amphibians Jellyfish being a primary example are made up of up to 96% water. Water also provides a place for organism to live in, 75% of the earths surface is also covered by water.

The molecular structure of water

A water molecule is formed by a covalent bond; Covalent bonds are formed by sharing electrons in the outer orbits of the quantum shells. Water molecules are charged with the hydrogen atom being slightly positive and the oxygen slightly negative, this opposite that transpires cause an attraction forming hydrogen bonds in the process. This slight charge that occurs means that when water molecules are close together the positively charge hydrogen bond catch the attention of the slightly negatively charged oxygen atom of another water molecule that forms a weak, long distanced hydrogen bond but, the sheer number of them have significant strength to keep the molecules together.

In this diagram the red lines are covalent bonds that hold oxygen that is represented by red and hydrogen (blue) atoms together in the water molecule.

Water has a number of important properties that is essential in making life possible many of the properties listed below are due to hydrogen bonds in water.

* Solvent

* Specific heat capacity

* Latent heat of evaporation

* Density

* Cohesion

* Ionisation

* PH

Water as a solvent.

A solvent is a liquid that dissloves solid, liquid or gaseous solute resulting in a solution.The most common example of a solvent is water, The ploarity of water enables it to be an excellent solvent for other polar molecules.Charged or polar molecules such as salt, sugar and amino acid dissolve readily in water and therefore are given the name hydrophillic ( water loving), non polar molecules such as fats and oils are hydrophobic.

Water cannot dissolve hydrophobic substances such as fats and oils, these are used by organisms as cell membranes to separate cells and also as waterproofing as they prevent water from entering the organism if it is covered in hydrophobic substance.Non- Polar molecules arrange themselves to exposure the minimum possible surface to the water molecules.

The solvent properties also allow water to act as a transport medium for polar solutes for example; movements of minerals to lakes and seas; transport via blood and lymph in multicellular animals and the removal of metabolic wastes such as urea and ammonia

Water having a high specific heat capacity.

The specific heat capacity of water is very high much of the heat absorbed is used to break the hydrogen bonds which hold the water molecule together. It takes 4.2 joules of energy to raise 1 gram of water to 1Ñ" centigrade. It takes 2 kJ per gram of water which is a considerable amount of energy to separate the 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, resulting in them transferring a lot of energy into the environment but only losing a little water. Sweating and panting are based on this principle.

Water having a high latent heat of fusion

Water has a very high latent of heat fusion from solid to liquid; it requires 300 Joules of energy per gram of ice to melt it to water. This is vital in the case of cytoplasm in cells which is made of a high percentage of water because once frozen the cell would be irreparably damaged. The freezing point of water is also lowered by solutes because the soluble molecules disrupt the hydrogen bonds making the water freeze at a lower temperature and it easier to melt ice.

Water and its density

Water is unique in that the solid state (ice) is less dense that the liquid state, so ice floats on water. As the air temperature cools, bodies of water freeze from the surface, forming a layer of ice with liquid water underneath. This allows aquatic ecosystems to exist even in sub-zero temperatures

Water having cohesion and surface tension

Hydrogen bonding causes water molecules

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