Many small had not become part of any . They were floating free in the waters of the . This was the food which the first cells ate and used both as building materials and as an energy source.
Living cells get chemical from food when it is broken down into smaller molecules such as or . This process is called fermentation. The small molecules were sent out of the cell as waste products.
Fermentation is still important on Earth today, and is used by people in several ways. Our cells use fermentation as the first step in breaking down sugars. Normally the end result of fermentation, such as lactic acid, is further broken down by the process of respiration to produce carbon dioxide and water. However, if we exert ourselves for example by running, lactic acid builds up in our muscles and causes pain.
We use the fermentation of other cells in various ways. Yeast breaks down sugars into alcohol, and we use this to make beers, wines and spirits. Fermentation releases carbon dioxide and we use this to cause bubbles in bread. Lactic acid producing bacteria are also used in the cheese making process, as well as making buttermilk, sour cream and yoghurt.
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