Water

• Water is a reactant in loads of important chemical reactions, including hydrolysis reactions.
• Water is a solvent, which means some substances dissolve in it. Most biological reactions take place in solution.
• Water transports substances. The fact that it's a liquid and a solvent means it can easily transport all sorts of materials, like glucose and oxygen, around plants and animals.
• Water helps with temperature control because it has a high specific heat capacity and a high latent heat of evaporation.
• Water is a habitat. The fact that it helps with temperature control, is a solvent and becomes less dense when it freezes means that many organisms can survive in it.
• A molecule of water is one atom of oxygen joined to two atoms of hydrogen by shared electrons.
• The shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atoms is left with a slight positive charge.
• The unshared negative electrons in the oxygen atom give it a slight negative charge.
• Water is a polar molecule - it has a partical negative charge on one side and a partial positive charge on the other.
• The attraction from water being a polar molecule is called hydrogen bonding and it gives water some of its useful properties.
• Specific heat capacity is the energy needed to raise the temperature of 1 gram of a substance by 1'C.
• The hydrogen bonds between water molecules can absorb a lot of energy, so water has a high specific heat capacity - it takes a lot of energy to heat up.
• Water doesn't experience rapid temperature changes, which is one of the properties that makes it a good habitat
• It takes a lot of energy to to break the hydrogen bonds between water molecules so water has a high latent heat of vaporisation.
• High latent heat of vaporisation is useful for living organisms because it means water's great for cooling things. This is why some mammals sweat when they're too hot. When sweat evapourates, it cools the surface of the skin.
• A polar covalent is a covalent bond where there is a small charge associated with the molecule. One atom has a greater pull on the electrons than another giving the molecules polarity.
• Polar means that one end of the molecule is slightly more positive and the other is slightly more negative.
• Although water as a whole is electrically neutral the sharing of electrons is uneven between the oxygen and hydrogen atoms
• The oxygen atom attracts the electrons more strongly than the hydrogen atoms, resulting in a weak negatively charged region on the hydrogen atoms.