1. Chemical elements and water The most frequently occurring elements in all living things: Carbon (19%) Hydrogen (10%) Oxygen (65%) Nitrogen (3%)

2. Other elements required in small amounts: Sulphur (0.25%) Calcium (1.5%) Phosphorus (1%) Iron (0.7%) Sodium (0.15%)

3. The role of certain elements (S) In certain amino acids (cysteine and methionine), proteins form disulphide bonds (Ca) Found in bones and teeth, also involved in neurotransmitter release in synapses (P) Component of nucleic acids and cell membranes. (Fe) Found in haemoglobin (animals), allowing for oxygen transport (Na) Involved in the generation of nerve impulses in neurons

4. Structure of water molecules Hydrogen is slightly positive Oxygen is slightly negative

5. Hydrogen bonds between water molecules Hydrogen bonds are weak. Give an example of where this is significant.

6. Special properties of water Write 3 or 4 sentences for each of the properties of water: Thermal Properties Cohesive Properties Solvent Properties Other Properties

7. The relationship between the properties of water and its use in living organisms as a coolant, medium for metabolic reactions and transport medium Outline this relationship using the following headings: Coolant Medium for Metabolic Reactions Transport Medium