The gas responsible for puffing-up appearance of dough comes from -

Options

A. aerobic respiration.
B. fermentation
C. photosynthesis
D. photorespiration

Answer

### Step-by-Step Solution:

1. **Understanding the Dough Composition**:
- Dough typically contains flour, water, and sugar. The sugar is crucial for the fermentation process.

2. **Fermentation Process**:
- When dough is prepared, yeast (specifically Saccharomyces cerevisiae) is added. This yeast ferments the sugar present in the dough.

3. **Products of Fermentation**:
- During fermentation, the yeast converts the sugar into two main products: ethanol and carbon dioxide (CO2).

4. **Role of Carbon Dioxide**:
- The carbon dioxide produced during fermentation gets trapped in the dough. As CO2 gas forms, it creates bubbles that cause the dough to rise, giving it a puffed-up appearance.

5. **Evaporation of Ethanol**:
- While ethanol is also produced, it evaporates during baking, leaving behind the carbon dioxide that has helped to raise the dough.

6. **Conclusion**:
- The gas responsible for the puffing-up appearance of dough is carbon dioxide (CO2), which is a byproduct of the fermentation process carried out by yeast.

### Final Answer:
The gas responsible for the puffing-up appearance of dough comes from the fermentation process, specifically carbon dioxide (CO2) produced by yeast.

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