Water

• water is a polar molecule, consisting of two slightly positive hydrogen atoms and one slightly negative oxygen atom.
• the polarity of water means that it can dissolve ionic compounds
• water's ability to form hydrogen bonds allow for it to have many properties. the slightly negative charge of the oxygen attracts the slightly positively charged hydrogen atom. Numerous of these bonds create a lattice structure.
• cohesion of water is due to hydrogen bonds between water molecules. this helps in transpiration as the forces holding the molecules together allow water to go against gravity, travelling upwards in a long, thin column.
• cohesion also results in surface tension which allows small invertebrates to walk on water.
• water's solid form (ice) is less dense than its liquid form as the hydrogen bonds grow further apart, causing ice to expand. this is necessary for the survival of aquatic organisms at freezing temperatures as it allows them to move in the water habitat while a layer of ice acts as thermal insulation at the water surface.
• water has high specific heat capacity - takes a lot of energy to change temperature by 1 degree celsius. this makes it useful for regulating body temperature in animals.
• water has low viscosity - easy to flow through narrow spaces such as blood vessels or xylem tubes making it an excellent transport medium.
• water has high latent heat of vaporisation - requires a large amount of energy to evaporate from a liquid state into gas. this is important for cooling down an animal's body when sweating.
• water as the universal solvent - when a hydrophilic solute is placed in water, water molecules cluster around the charged part of the solute keeping the solute molecules apart, allowing it to dissolve. Most metabolic reactions take place in the cytoplasm due to the presence of water.