Importance of Water

7 July 2016

Water is a very small molecule, consisting of two hydrogen atoms covalently bonded to an oxygen atom. However the electrons shared are not done so equally, oxygen is more electronegative and has a firmer hold on the electrons and pulls them slightly towards its nucleus. Due to this, the charge across the molecule of water is not equally distributed, and the oxygen atom has a partial negative charge whereas the two hydrogen atoms have a partial positive charge, this makes water a polar molecule. The partial charge of oxygen in a water molecule attracts the opposite partial charge in another water molecule which is the positive hydrogen.

This constitutes a hydrogen bond which is defined as being a weak interaction between a slightly negatively charged atom and a slightly positively charged hydrogen. Hydrogen bonding is strong enough however to have an effect on physical properties of water and the hydrogen bonding gives water some of its useful properties. Water’s polarity means it is used as a solvent, a substance capable of dissolving other substances, and is specifically good for other polar molecules. The electrostatic attraction between polar water molecules and ions of the opposite charge means that the ions become completely surrounded by water molecules and dissolve.

Importance of Water Essay Example

This is the basis for hydrophobic and hydrophilic molecules, polar molecules can interact and are known as hydrophilic, molecules seen as hydrophobic, the non-polar molecules, arrange themselves to expose as little as possible surface area to the water and do not readily dissolve. This enables water to be a good solvent to polar molecules and as most biological reactions take place in solution and as most metabolic processes rely on this factor to enable chemicals to react together, water is seen as being pretty essential. Hence why cytoplasm is primarily water.

A prime example of the use of dissolved chemicals reacting in living organisms is the processes of respiration in both plants and animals and photosynthesis in just plants. In both, energy is produced that enables other reactions and processes to commence that ultimately keeps them alive. It also means living organisms can take in useful substances such as mineral ions that may be essential to is functioning. The solvent properties combined with its liquid state at room temperature also mean water can act as a transport medium for polar solutes.

Examples of this include; the transport around multicellular animals via the blood and lymph, the removal of metabolic wastes such as urea and ammonia in urine and in the vascular tissues in plants. Water has a high specific heat capacity which is the amount of energy needed to heat 1 Kg of water by 1 Most of the heat required is to overcome and break the hydrogen bonds that hold the water molecules together. The hydrogen bonds can themselves absorb a lot of energy, which in turn means there is less heat energy available to actually increase the temperature of the water.

This allows organisms to avoid rapid temperature changes, meaning they are very thermostable, they are less prone to heat damage by changes in environmental temperatures. Water also possesses a high latent heat of evaporation, the latent heat is the heat energy required to change a substance from one state to another. Water only evaporates when the hydrogen bonds holding water molecules together are broken. This allows the molecules on the surface of the water to evaporate and escape into the air as gas.

The hydrogen bonds however are attracting the water molecules to each other and make it more difficult for the molecules to escape as vapour. A high input of energy is needed to break the hydrogen bonds. This is used extensively by living organisms as a cooling mechanism as the body can be considerably cooled with a minimal loss of water; some animals pant, some sweat and plants use it to cool transpiring leaves. The evaporating water carries away with it some heat energy as it leaves a surface, which cools the surface and helps to lower the temperature. Both factors help in the thermoregulation of living things.

The weakness of individual hydrogen bonds mean that individual water molecules continually jostle one another, and are continually forming and breaking hydrogen bonds as they do so. This enables water molecules to move easily relative to one another and allows osmosis to take place which is vital to all living organisms for uptake of water and the movement of water. However as the temperature of the water begins to reach the freezing point the kinetic energy of the water molecules falls. The water molecules slow down enough so that each one can form its maximum number of hydrogen bonds.

In order for this to happen the water molecules must be held further apart from each other to give sufficient room for all four hydrogen bonds to fit. As the water molecules are held further apart in solid form than in liquid form, ice is less dense. And explains why ice floats on the water’s surface. This is useful to living organisms especially in cold environments as the ice on the surface of the water acts as an insulator and prevents the water underneath from freezing. This can protect aquatic ecosystems even during freezing conditions.

The water underneath also means that when temperatures return to normal the ice thaws rapidly. The changes in density also maintain circulation in large bodies of water and help the cycling of nutrients. The floating ice also provides transport routes and hunting grounds for the likes of polar bears and penguins. Water is also very cohesive, which is the tendency for water molecules to stick together which is all due to the hydrogen bonds. This aids the flowing of water and makes it a better transport medium and also plays a role in the transpiration stream.

The continuous column of water is able to move up the xylem vessel because of the cohesive forces between water molecules and the adhesion between the water and the walls of the vessel. Without which the plant would be unable to function. At the surface of the water cohesion also results in surface tension. Insects are able to ‘walk on water’ because of the surface tension but they are really walking on a ‘raft’ of hydrogen bonds. Both the cohesive and adhesive properties enable water to be a useful lubricant in biological systems as it is very viscous.

For example; synovial fluid lubricates many joints, pleural fluid minimizes friction between lungs and the ribs during breathing and mucus aids egestion. The cohesive forces between water molecules also means that it is not easily compressed and is excellent for support mediums such as; turgor pressure in plant cells, amniotic fluid that protects and supports the foetus, and as a general support such as for the huge whales. Water is essential for living organisms as it can both directly and indirectly affect other functions the organisms must carry out in order to survive.

The physical state of water either as ice or water provide environments in which different organisms can live and thrive. Without water and its many properties life on Earth would be very different and it is easy to say would probably not exist at all. Even the fact that water is transparent permits photosynthesis to occur in aquatic environments if it is relatively shallow. Water is used directly in metabolic processes in photosynthesis and in digestion, without either one humans would be unable to survive and neither would many other species.

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