descrive the biological importance of water

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Making up between 70 and 95% of the mass of a cell, and covering over three quarters of the planets surface, water is one of the most important compounds on this planet.

A single water molecule is made up of one oxygen atom covalently bonded to two hydrogen atoms. Covalent bonds are formed by sharing electrons between the outer shells of the oxygen and hydrogen atoms. However, what makes water so unique is the fact that it remains a liquid at room temperature. Many similar sized molecules (ammonia has a molecular mass equal to that of water-18) remain in their gaseous form at this temperature. The reasons for this unique thermal property are hydrogen bonds.

The nucleus of an oxygen atom is larger and therefore contains many more protons that that of a hydrogen atom. Therefore, the electrons shared in the covalent bond between the oxygen and hydrogen atoms have a greater affinity for the oxygen atom than either hydrogen atom. This pulls the electrons closer to the oxygen atom and away from the hydrogen atoms resulting in the oxygen atom having a slightly negative charge and the hydrogen atoms developing slightly positive charges.

These slight charges mean that when water molecules are close together, positively charged hydrogen atoms are attracted to the negatively charged oxygen atoms of a different water molecule. These attractions are known as hydrogen bonds and although they are weak individually, together they are very strong and result in water remaining a liquid at room temperature.

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Water is a polar molecule- the oxygen has a negative charge and the hydrogen has a positive charge. Water can therefore dissolve polar or ionic substances and keep them in solution. Substances that dissolve in water are known as hydrophilic substances. Ionic substances such as sodium chloride, NaCl, are made up of both positive and negative ions. Sodium chloride is held in it’s structure by the strong attraction between it’s positive sodium ions and negative chloride ions. Normally these ionic attractions require a large amount of energy to break, but when put into water, the negative oxygen side of ...

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Punctuation, grammar and spelling all done to a very high level. Format and tone of the essay are also well done

Their introduction is good, but it really should expand to include some of the aspects they are going to talk about in the essay as well as stating basic facts about the importance of water. The candidate starts by outlining well the chemical properties of water and how this relates to its function and this continues in depth across a number of examples. Their conclusion is adequate based on the information they have discussed and it ties up loose ends well.

A very well done essay. The candidate can clearly relate biological function to deeper chemical aspects of water in great depth. This shows great scientific understanding. They also discuss a wide variety of factors that make water a very important substance in good scientific depth and in a concise and clear way.