Water

• The importance of water: 

  • Water is a metabolite in a lot of important metabolic reactions such as condensation and hydrolysis
  • Water is a solvent which mean substances can dissolve in it, where most metabolic reaction take place in a solution
  • Water helps with temperature control as it has a high latent heat of vapourisation and a specific high capacity.
  • Water molecules are very cohesive, helping water transport in plants as well as transport in other organisms.
• Structure of water:

  • A molecule of water is one atom of oxygen joined to two atoms of hydrogen by shared electrons. Because the shared negative hydrogen electrons are pulled towards the oxygen a lot the other side of each hydrogen atom is left with a partially positive charge. The unshared negative electrons on oxygen atoms leaves it to be partially negative. This makes water a polar molecule, it has a partial negative charge on one side and a partial positive charge on the other.
• Hydrogen bonding

   bonds between a partially positive hydrogen atom in one molecule and slightly negatively charged atom in another molecule. E.g hydrogen bonding form in water because the partially negatively charged oxygen atoms of water attract the partially positively charged hydrogen atoms of other water molecules
• Water as a metabolite

  • Important metabolite: 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.
• Water as a good solvent

  • because water is polar, the partially positively charged end of a molecule will be attracted to the negative ion, and the partially negatively charged end of a water molecule will be attracted to the positive ion = ions will be completely surrounded by water molecules meaning they will dissolve. So organisms can take up useful substances e.g mineral ions dissolved in water can be transported around the organisms body.
• Water has a high latent heat of vaporisation

  water evaporates when hydrogen bonds holding water together are broken, this allows water molecules on the surface of the water to escape into the air as a gas. It takes a lot of energy to break the hydrogen bonds between molecules so a lot of energy is used up when water evaporates this mean water has a high latent heat of evaporation.
• why is a high latent heat good for organisms

  • they can use water loss through evaporation to cool down without losing too much water. When water evaporates, it carries heat energy away from a surface cooling the surface lowering temperature.
• Can buffer/resist change in temperature:

  •  Hydrogen bonds give water a high specific heat capacity ( energy needed to raise the temperature of 1 gram of a substance by 1 degree) when water is heated a lot of heat energy is used to break the hydrogen bonds between water molecules, so there is less heat energy to increase temperature of the water, so water has a high specific heat capacity - it takes a lot of energy to heavy it up. - useful for living organisms as water doesn't experience rapid temperature changes, maintains internal body temperature, making water a good habitat.
• water as Very cohesive:

  cohesion is the attraction between molecules of the same time. Water molecules are very cohesive because they are polar. Strong cohesion helps water to flow, good for transporting substances. Strong cohesion means that water has a high surface tension when in contact with air = why sweat forms droplets which evaporate from skin to cool an organism down.