What are 2 ways that organisms get energy when no oxygen is present? List and describe each type of fermentation.
When no oxygen is present, organisms can obtain energy through two types of fermentation: alcoholic fermentation and lactic acid fermentation.
1. Alcoholic fermentation: This type of fermentation is carried out by certain microorganisms, including yeast. During alcoholic fermentation, glucose is converted into ethanol (alcohol) and carbon dioxide. It is often used in the brewing and winemaking industries. The process involves the following steps:
- Glycolysis: Glucose is broken down into two molecules of pyruvate. This step occurs in the cytoplasm of the cell.
- Decarboxylation: Each pyruvate molecule is decarboxylated, which means a carbon dioxide molecule is removed, resulting in the formation of acetaldehyde.
- Reduction: Acetaldehyde is then reduced by NADH to form ethanol, while NADH is oxidized back to NAD+ to be used again in glycolysis. This step regenerates the molecule needed to continue the process.
2. Lactic acid fermentation: This type of fermentation occurs in some bacteria and in certain cells of muscle tissues. During lactic acid fermentation, glucose is converted into lactic acid. The process goes as follows:
- Glycolysis: Glucose is broken down into two molecules of pyruvate.
- Reduction: In the absence of oxygen, pyruvate is reduced directly by NADH to form lactic acid. This conversion regenerates NAD+ for further use in glycolysis.
Both alcoholic and lactic acid fermentation are forms of anaerobic respiration, allowing organisms to generate some ATP (energy) without oxygen.