Yeast cells can respire in anaerobic conditions. Bioethanol is a type of biofuel produced from maize starch on an industrial scale. In the high temperature method, heating to 120°C is used to break apart starch molecules. The enzymes α-amylase and glucoamylase are added to the resulting starch suspension once it has cooled down. These enzymes hydrolyse the starch to glucose. Yeast cells are then added and maintained in anaerobic conditions to produce ethanol. The high temperature method is expensive to carry out, so a new method has been developed which heats starch to a lower temperature of 80°C. In the lower temperature method, enzymes catalysing the hydrolysis of starch do not need to be added to the starch suspension. A genetically modified (GM) strain of the same yeast species is used. The GM strain of yeast has genes that allow the cell to produce α-amylase and glucoamylase and to attach these enzymes to the external surface of the cell surface membrane. The GM yeast cells are added to the starch that was heated to 80 °C and are maintained in anaerobic conditions to produce ethanol. An investigation was carried out to compare the GM strain of yeast with the yeast that had not been genetically modified (non-GM strain). In this investigation, the starch suspension produced after heating to 80°C was allowed to cool to 30°C before adding yeast cells. The results are shown in Fig. 2.1. [Figure 2.1]