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Ginger Ale Activity
Fermentation Pathway
FermentationEthanol2.gif

Fermentation:
The two main types of fermentation are based on the products they form. The first type is lactic acid fermentation. This process. Recall that fermentation is an anaerobic process to make ATP. Lactic acid is an organic waste produced by anaerobic fermentation. Instead of forming pyruvic acid, these reactions use NADH from glycolysis to form lactic acid.
People use anaerobic species to produce certain kinds of food, like cheese and yogurt. Their slightly sour flavor is a result of lactic acid.

People are exposed to lactic acid in another way. Human muscle cells use a lot of ATP and oxygen to function. During major physical activity like exercising, muscle cells need more oxygen. If muscle cells do not get enough oxygen, they use lactic acid fermentation to produce ATP. As muscle cells use these anaerobic reactions, lactic acid builds up in the cells as waste. This buildup causes sore muscles.

Some anaerobic species use another type of fermentation called ethyl alcohol fermentation. Ethyl alcohol is a colorless liquid waste product produced by anaerobic fermentation. It is also the main chemical in alcoholic beverages. Ethyl alcohol fermentation breaks down glucose into two products, carbon dioxide and ethyl alcohol.

People rely on ethyl alcohol fermentation when they use yeast to make bread. Yeasts are aerobic bacteria that perform ethyl alcohol fermentation and glycolysis. When yeasts are put into dough, they separate from oxygen. Yeasts break down the sugars in the dough mixture to get fuel. As they ferment the sugars, they produce carbon dioxide. Bubbles of C02 gas are trapped in the dough and cause it to rise. Bakers allow this process to happen so the dough will rise and the taste is right. The white, soft part of bread has many tiny air bubbles trapped inside the crust. The spaces are where C02 bubbles were trapped during baking.

The process of fermentation is show in the diagram. Fermentation starts with glucose being turned into pyruvate by glycolysis. Glycolysis produces 2 ATP, but it also must turn two NAD+ into NADH. Fermentation turns pyruvate into ethanol releasing carbon dioxide and turns NADH back into NAD+. This keeps NAD+ available so glycolysis can continue. Glycolysis would stop with out the recycling of NAD+. In fermentation, the carbon dioxide and ethanol are waste products produced by yeast making ATP from sugars.

Copy and fill in the blank.
1. The two main types of fermentation are ...
2. Fermentation is an anaerobic process for ...
3. .............. give cheese is slightly sour flavor.
4. When muscle cells lack oxygen, they use ............... to produce ATP.
5. Alcohol fermentation breaks down glucose into the two waste products ......... and .......... .
6. Yeast are aerobic bacteria that ...
7. As yeast ferment sugars, they produce ...
8. Dough rises because CO2 ............ are trapped in it.
9. The many tiny spaces in bread are caused by ...
10. Fermentation starts with the substance ................ .
11. Fermentation produces 2 ATP using the process of ............... .
12. Glycolysis produces 2 ATP molecules and two .............. molecules.
13. Fermentation turns NADH back into .............. .
14. Glycolysis requires ............... to breakdown glucose and will stop with out it.
15. The waste products of fermentation are ...