Describe and explain the importance of water in living organisms.

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Hashim Shah L5

Describe and explain the importance

of water in living organisms.

        Water is a simple molecule. However, the properties of water, it’s biological importance and molecular structure make it an extremely important substance for life. It is a very abundant material, over 70% of the earth and up to 90% of a cell is water.

        Water is a polar molecule. In the covalent bond, the electron pairs are unequally distributed and are closer to the oxygen atom. So the greater number of protons in the oxygen atom, attract electrons in the covalent bond. Therefore, there is a small negative charge on the oxygen atom and so a small positive charge on the hydrogen atom. Consequently, the opposite charges on the two atoms attract each other. These forces of attraction between the hydrogen and oxygen atoms act upon neighboring molecules which then form a ‘hydrogen bond’.

        Water is called a universal solvent because of its polarity, meaning that it can easily ionise substances. Many compounds, such as ionic substances (eg. Sodium Chloride) or non-ionic substances with polar groups ( eg. (OH) groups in sugars and alcohols) dissolve into the water and therefore many reactions can take place. When a substance dissolves in water, it splits into ions and so the substance is said to be hydrophilic (water-loving). However, lipids (used in the cell membrane) do not dissolve in water and therefore are called hydrophobic (water-hating).

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        This is useful for humans due to the fact that digestion will only dissolve soluble molecules; and so large, insoluble substances have to be broken down into smaller, soluble molecules with water being the solvent. Plants can only obtain their mineral ions in solution. It is also needed in the processes of diffusion and osmosis. For example, during gaseous exchange, the surfaces of the lungs or in mesophyll cells (in plants) need to be moist as the gaseous exchange takes place in solution.  Water can also be used as a medium for transportation in organisms, such as in lymph ...

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