Water

• importance of water

  makes up 80% of cells components and has loads of important functions inside and outside of cells
• water-metabolite

  lots of metabolic reactions including condensation and hydrolysis reactions
• Water-solvent

  some substances can dissolve in it most metabolic reaction reactions take place in a solution e.g. cytoplasm of eukaryotic and prokaryotic cells
• Water-temperature

  helps with temperature control because it has a high latent heat of vaporisation and high specific heat capacity
• Water-cohesive

  water molecules are very cohesive (stick together) which helps water transport in plants as well as transport in other organisms
• Structure of water -Polarity

  a molecule of water H2O is one atom of oxygen joined to two atoms of hydrogen by shared electrons

  because the shared negative hydrogen electrons are pulled toward the oxygen atom the other side of each hydrogen atom is left with a slight positive charge the unshared negative electrons on the oxygen atoms give it a slight negative charge which makes water a polar molecule it has a slight negative charge on one side and slight positive charge on the other
• Structure of water -Hydrogen bonding

  weak bonds between slightly positively charged hydrogen atoms in one molecule and slightly negatively charged atom in another molecule hydrogen bonds form between water molecules because the slightly negatively charges oxygen atoms of water attract the slightly positive charged hydrogen atoms of other water molecules this hydrogen bonding gives water some of its useful properties
• Properties of water -important metabolite

  many metabolic reactions involve a condensation or hydrolysis reaction

  a hydrolysis reaction requires a molecule of water to break a bond

  a condensation reaction releases a molecule of water as a new bond is formed
• Properties of water-Good solvent

  a lot of important substances in biological reactions are ionic which means they're made from one positively charged atom or molecule

  because water is polar the slightly positive-charged end of a water molecule will be attracted to the positive ion and the slightly negative-charged end of a water molecule will be attracted to the positive ion

  this means the ions will get totally surrounded by water molecules in other words they'll dissolve.

  so water polarity makes it useful as a solvent this means living organisms can take up useful substances dissolved in water and these dissolved substances can be transported around the organisms body
• Properties of water -High latent heat of vaporisation

  Water evaporates (vaporises) when the hydrogen bonds holding water molecules together are broken. This allows the water molecules on the surface of the water to escape into the air as a gas. It takes a lot of energy (heat) to break the hydrogen bonds between water molecules, so a lot of energy is used up when water evaporates. This means water has a high latent heat of vaporisation — lots of heat is used to change it from a liquid to a gas.

  This is useful for living organisms because it means they can use water loss through evaporation to cool down without losing too much water.

  When water evaporates it carries away heat energy from a surface, which cools the surface and helps to lower the temperature (e.g. when humans sweat to cool down).
• Properties of water-can buffer changes in temperature

  Hydrogen bonds give water a high specific heat capacity — this is the energy needed to raise the temperature of 1 gram of a substance by 1 °C.

  When water is heated, a lot of the heat energy is used to break the hydrogen bonds between the water molecules. This means there is less heat energy available to actually increase the temperature of the water. So water has a high specific heat capacity — it takes a lot of energy to heat it up.

  This is useful for living organisms because it means that water doesn't experience rapid temperature changes. This makes water a good habitat because the temperature under water is likely to be more stable than on land.

  The water inside organisms also remains at a fairly stable temperature — helping them to maintain a constant internal body temperature.
• Properties of water-Very cohesive

  Cohesion is the attraction between molecules of the same type (e.g. two water molecules). Water molecules are very cohesive (they tend to stick together) because they're polar. Strong cohesion helps water to flow, making it great for transporting substances. For example, it's how water travels in columns up the xylem (tube-like transport cells) in plants Strong cohesion also means that water has a high surface tension when it comes into contact with air. This is the reason why sweat forms droplets, which evaporate from the skin to cool an organism down. It's also the reason that pond skaters, and some other insects, can 'walk' on the surface of a pond.