Fill in the Blank in the Following Paragraph

Short Answer

Fill in the blank in the following paragraph.
"During intense 'anaerobic' physical exercise, the high energy demand in the muscle cells leads to an accumulation of lactic acid in these cells and their surrounding tissues. Similarly, the yeast Saccharomyces cerevisiae can produce ethanol when grown anaerobically. The lactate or ethanol production takes place in a process called ..."