Which step is important for continuity of glycolysis in anaerobic respiration ?

Options

A. Oxidation of PGAL
B. Substrate level phosphorylation
C. Oxidation of NADN
D. Formation pyruvic acid.

Answer

To determine which step is important for the continuity of glycolysis in anaerobic respiration, we can analyze the options provided:

1. **Oxidation of phosphoglyceraldehydes**
2. **Substrate level phosphorylation**
3. **Oxidation of NAD**
4. **Formation of pyruvic acid**

### Step-by-Step Solution:

1. **Understanding Glycolysis**: Glycolysis is the metabolic pathway that converts glucose into pyruvic acid, producing a small amount of ATP in the process. This pathway occurs in both aerobic and anaerobic conditions.

2. **Anaerobic Conditions**: In the absence of oxygen (anaerobic conditions), the pyruvic acid produced from glycolysis cannot enter the aerobic respiration pathway (Krebs cycle and oxidative phosphorylation). Instead, it must be converted into other products to regenerate NAD+.

3. **Role of NAD+**: During glycolysis, NAD+ is reduced to NADH. For glycolysis to continue, NAD+ must be regenerated. In aerobic respiration, NADH is oxidized back to NAD+ in the electron transport chain. However, in anaerobic respiration, this process cannot occur.

4. **Conversion of Pyruvic Acid**: In anaerobic respiration, pyruvic acid is converted into lactic acid (in animals) or ethanol and carbon dioxide (in yeast and some bacteria). This conversion involves the oxidation of NADH back to NAD+.

5. **Identifying the Key Step**: The oxidation of NADH to NAD+ is crucial because it allows glycolysis to continue by providing the necessary NAD+ for the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate in the glycolytic pathway.

6. **Conclusion**: Therefore, the step that is important for the continuity of glycolysis in anaerobic respiration is the **oxidation of NAD**.

### Final Answer:
The correct answer is **oxidation of NAD**.