AIIMS 2003 Botany Industrial Use of Microbes Assertion Reason Question

Explanation of the Question

Assertion: Yeasts such as Saccharomyces cerevisiae are used in the baking industry.

Reason: Carbon dioxide produced during fermentation causes bread dough to rise by thermal expansion.

Analysis of the Assertion and Reason

1. Assertion Validity: The assertion is true. Saccharomyces cerevisiae is a species of yeast widely used in the baking industry. It plays a crucial role in the fermentation process, converting sugars into alcohol and carbon dioxide through anaerobic respiration. The carbon dioxide produced during this process is what causes bread dough to rise, giving bread its airy texture.

2. Reason Validity: The reason is also true, but it is important to clarify the mechanism. When yeast ferments sugars, it produces carbon dioxide. This gas gets trapped within the dough, leading to the formation of bubbles. As the dough is baked, the heat causes the gas to expand, which contributes to the rising of the dough. However, the primary reason for rising is not solely thermal expansion; it is mainly due to the increase in gas volume as the temperature rises, which is a direct effect of the fermentation process itself.

Correct Answer

The correct answer is C: Assertion is true but Reason is false.

Justification for the Correct Answer

• The assertion is correct because yeasts like Saccharomyces cerevisiae are indeed used in baking, facilitating the fermentation process.
• The reason is misleading because while carbon dioxide does cause the dough to rise, the assertion that it rises due to "thermal expansion" alone is not entirely accurate. The rise is primarily due to the production of gas during fermentation, not just the expansion of gas when heated.

Clarification of Incorrect Options

• Option A: Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

  • Incorrect because, while both the assertion and reason are true, the reason does not correctly explain why the dough rises; it oversimplifies the fermentation process.

• Option B: Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

  • Incorrect because the reason, while true, incorrectly attributes the rising of dough solely to thermal expansion rather than the overall fermentation process.

• Option D: Both Assertion and Reason are false.

  • Incorrect as both the assertion and reason are true, although the reason is not a complete explanation.

Key Concepts

1. Fermentation Process: The process of fermentation in yeasts involves the conversion of sugars (e.g., glucose) to ethanol and carbon dioxide through the following simplified reaction:

   $$\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2 \text{C}_2\text{H}_5\text{OH} + 2 \text{CO}_2$$

   This reaction is crucial for bread-making as it produces the gas that causes the dough to rise.

2. Gas Expansion: The gas produced during fermentation expands when heated, contributing to the rise of the dough. This expansion is not solely due to thermal expansion but involves the accumulation of gas during the fermentation stage.

Conclusion

In summary, while both statements in the question are true, the reasoning provided is not an accurate representation of how bread dough rises. Understanding the fermentation process and the role of carbon dioxide is essential in grasping the applications of yeasts in the baking industry.