"Now, a living organism is nothing but a wonderful machine endowed with the most marvellous properties and set going by means of the most complex and delicate mechanism." Claude Bernard, An Introduction to the Study of Experimental Medicine (1865). For life to be "set going" and survive, the single unit of life (the cell) must utilise and manage energy. This is as true for a single cell as it is for a multi-cellular organism such as you. The course deals with the way cells manage their energy requirements by reference to the processes of carbohydrate, fat and protein metabolism. Cellular processes that allow the complete breakdown of these food molecules to produce energy will be discussed with reference to glycolysis, the citric acid cycle, the breakdown of fatty acids, the terminal respiration system and oxidative phosphorylation. Mechanisms by which cellular molecules are built from simple precursors will also be explored via the processes of gluconeogenesis, glycogen synthesis, the pentose phosphate pathway and amino acid metabolism. This collection of highly dynamic processes can only take place in a coordinated manner because of enzymes, which allow the processes to occur and also offer points of control, consequently enzyme function and catalysis will be discussed. The course will conclude by examining how the human body can control these processes to efficiently control its energy requirements and expenditure.