71% of the earth is covered in water. Life originated from the depths of the ocean and now most of the organisms on our planet have adapted to reside in the vital compound of H2O. Water is the main constituent of all organisms and it has five main roles in living organisms. It acts as a solvent, a temperature buffer, a metabolite and as a living environment.
Water is made up of two Hydrogen atoms and one oxygen atom giving it the formula of H2O. The molecule of water is dipolar meaning it has a separation of positive and negative charges within the molecule. The Oxygen atom has a slight negative charge, whilst the two Hydrogen atoms have a slight positive charge this is due to Oxygen’s high electronegativity (δ-) in comparison to Hydrogen (δ+). Overall this creates a dipole each water molecule. The polar qualities of the water molecule mean that water molecules are attracted to each other and other polar molecules, as the relatively positive areas are attracted to the relatively negative areas. The attraction between the molecules is called Hydrogen bonding. Hydrogen bonding is the strongest type of intermolecular force however it is still weak in comparison to the covalent bonding within the water molecule itself. These Hydrogen bonds require a lot of energy to overcome so give water a high latent heat of vaporisation. This property allows water to remain in its liquid states at the earth’s conditions which is vital for life to thrive.
All living organisms are made up of cells. Within cells, chemical reactions, such as respiration, occur in order to allow to organisms to live. Many of these chemical reactions are catalysed by globular proteins called as enzymes. Enzymes have an optimum temperature and pH so the internal conditions of the body must be maintained allowing the enzymes to work at their maximum capacity. Water acts as a temperature buffer, keeping the temperature of the body controlled in homeostasis. Water, due to its hydrogen bonding, has a high specific heat capacity which helps limits changes in body temperature in a warm or cold environment, for example, this allows artic fish to remain alive when the water freezes over them at the surface of the sea. This allows the organisms to maintain optimum temperature for enzymes to catalyze metabolic reactions. Water is also used to lower the body temperature via sweating due too its high latent heat of vaporisation. When the body's temperature is too high the body sweats releasing water onto the surface of the skin. When the water evaporates away from the skin it takes thermal energy away with it effectively cooling down the body maintaining homeostasis.
Water is used as a solvent for many biochemical solutions and it enables the transport of nutrients, removal of waste products and secretion of substances. Water as a polar molecule regularly dissolves charged ions and other polar substances. Glucose is also a polar molecule. Once carbohydrates, like starch, are hydrolysed α glucose molecules are absorbed by water. It is in this way that glucose is transported around the bloodstream in the plasma because the polar water molecules are attracted to the polar glucose molecules. Glucose is vital for mitochondria in cells to release energy from ATP because glucose is a key reactant in aerobic respiration (C6O6H12 + 6O2 ---> energy from ATP + 6H2O + 6CO2). Similarly to glucose, amino acids and electrolytes are also polar molecules so dissolve into water and are transported through the blood in the plasma. Water is also essential for many other metabolic reactions like photosynthesis in plants (6CO2 + 6H2O -----> C6H12O6 + 6O2) and hydrolysis reactions. Not just useful molecules but waste products are transported by water around the blood as well. Urea and sodium chloride are waste products from the body and because they are soluble in water are also transported in the blood until excretion. It is very important that we excrete waste products from our bodies as they can be toxic and cause many negative effects should they build up in excess. Whilst water transports toxins to the kidneys or lungs, where they’re expelled from the body, it also breaks toxins down. Water is used in hydrolysis reactions. A hydrolysis reaction is the breakdown of a molecule with the addition of a water molecule or an OH- ion. Hydrolysis is a vital reaction and occurs in many situations like DNA replication and digesting large food molecules into smaller soluble molecules that can be absorbed into the bloodstream. This enables the body to break down various waste products so they can be excreted or utilised. For example in the deamination of Cytosine, water is added and breaks cytosine down into uracil, releasing ammonia in the process. Deamination is the removal of an amino group from excess amino acids which occurs via a hydrolysis reaction. The ammonia produced is then converted into urea or uric acid by enzymes through the addition of CO2 molecules. The urea is then added to water in the kidneys during filtration and excreted in urination.
As water occupies around 60% of our body, but it doesn't just play a role in our biochemistry it also provides a lot of support and structure. Our body uses water in all our cells, tissues and organs. It is also responsible for keeping our bones healthy as calcium and magnesium, essential "bone making" materials are carried by water. Water doesn't just aid our structure and support animals, it also is very important for plants to remain upright. Because water is not easily compressed due to the intermolecular forces. In plants, water is responsible for keeping herbaceous plants upright. It does this by creating a pressure between the protoplast and the cell wall resulting in turgor as the cells take up water bringing with it nutrients and minerals. The intermolecular hydrogen bonds also induce cohesive forces between the water molecules, causing a high specific tension allowing small aquatic insects like pond skaters and water bugs (also known as Jesus bugs) to walk on the surface of the water. Likewise, due to the strong cohesive forces between the lighen (surface of the xylem) and the water molecules, it allows water to be pulled through the xylem so it can reach the leaves to be used for photosynthesis. This is known as adhesion. Water is also responsible for the hydrostatic skeletons of coelenterates, annelids and molluscs.
Water is a very unusual compound. It is the only compound which is denser in a liquid form than its solid form: ice floats on water. The reason behind this is waters hydrogen bonding. Hydrogen bonds are the intermolecular forces holding two water molecules together. As water cools to below 4° the Hydrogen bonds adjust to hold the negatively charged Oxygen atoms apart. This adjustment produces a crystalline lattice known as ice. Ice floats because it roughly takes up 9% more space than liquid water so it is 9% less dense. It is this property of water which provides buoyancy to many animals such a cetaceans. When an animal as great a size as a blue whale can float on water, this is because the upward force exerted on the animal is equal to the weight of the animal applying pressure down. Water has a density of 1g/cm3 and for an object to sink it must have a higher density than that of water. This property is vital for the mammals living in the ocean as they must rely on floating to access the Oxygen in the air above.
In conclusion, water is incredibly significant to living organisms as it provides biological stability, chemically and physically enabling the organisms to survive. Water is a vital and unique compound which provides living organisms with life in many different ways.
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