Water functions

• Within the water molecule:

  The oxygen atom has a slight negative charge.

  The hydrogen atoms have a slight positive charge.

  It has positive and negative poles making it dipolar.
• The positive pole of one water molecule is attracted to the negative pole of another water molecule. This attractive force is called a hydrogen bond. Without this attraction, water molecules would be unable to bond together and would become a gas.
• Specific heat capacity refers to the quantity of heat absorbed by a material. Water has a high specific heat capacity because a significant amount of energy is needed to break its hydrogen bonds.
• Latent heat of vaporisation is the quantity of heat required to convert some of the liquid at boiling point to a vapour or gas without changing the temperature, just the amount. Water has a high latent heat of vaporisation because a large amount of energy is needed to evaporate water.
• Cohesion is the tendency of water molecules to stick together. Water has strong cohesiveness which allows it to be pulled up through xylem vessels. Cohesion also causes slight surface tension, so it is strong enough to support the weight of small insects.
• Water is a main component of all organisms. Mammals are around 65% water, and many other organisms contain more.
• Water has an important role in metabolism. It is an essential reactant for many reactions including hydrolysis.
• Water is a necessary raw material for photosynthesis.
• Water is an important solvent that easily dissolves other substances including:

  °         Gases such as oxygen and carbon dioxide

  °         Waste products including ammonia and urea.

  °         Inorganic ions and small important molecules including amino acids, monosaccharides and ATP as well as some large molecules including enzymes.
• Water is not easily compressed and can therefore play an important structural role, e.g. in creatures such as jelly fish.
• Water is transparent. This means that aquatic plants can photosynthesise under water and also that light can reach the retina of the eye.
• Some inorganic ions are essential for living processes:

  Iron - Forms haemoglobin

  Magnesium - Forms chlorophyll

  Phosphate - Component of DNA and RNA