$ The chief respiratory substrate of a cell is carbohydrate
! Fermentaiton is also called Glycolytic pathway.

Options

A. If both As and R are correct and R is correct explanation of As
B. If both As and R are correct but R is not correct explanation of As
C. If As is correct, R is wrong
D. If both As and R are wrong.

Answer

To solve the question regarding the chief respiratory substrate of a cell and the relationship between fermentation and the glycolytic pathway, we can break down the explanation into clear steps.

### Step-by-Step Solution:

1. **Understanding Chief Respiratory Substrate**:
- The chief respiratory substrate refers to the primary component that is utilized in the process of cellular respiration. In most cells, carbohydrates, particularly glucose, serve as the main substrate for energy production.

2. **Identifying Carbohydrates**:
- Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen. The most common carbohydrate used in cellular respiration is glucose (C6H12O6). This molecule is crucial as it is the primary source of energy for cells.

3. **Role of Oxygen**:
- While carbohydrates are the chief substrate, oxygen is also essential for aerobic respiration. Without oxygen, cells can only perform anaerobic processes like fermentation.

4. **Explaining Fermentation**:
- Fermentation is a metabolic process that converts glucose into energy without the use of oxygen. It primarily occurs when oxygen is scarce. The process begins with glycolysis, where glucose is broken down into pyruvate.

5. **Linking Fermentation to Glycolysis**:
- Glycolysis is the first step in both aerobic respiration and fermentation. In glycolysis, glucose is converted to pyruvate, which can then either enter the Krebs cycle (in the presence of oxygen) or undergo fermentation (in the absence of oxygen).

6. **Conclusion**:
- The assumption that carbohydrates are the chief respiratory substrate is correct. The reason that fermentation is also referred to as the glycolytic pathway is also accurate, as both processes begin with the breakdown of glucose into pyruvate.

### Final Answer:
Both the assumption that the chief respiratory substrate of a cell is carbohydrate and the reason that fermentation is also called the glycolytic pathway are correct. The reason provides a valid explanation for the assumption.

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