A student prepared a test tube containing yeast, glucose, and water. After 24 hours, the test tube was analyzed for the presence of several substances. What substance would the student expect to find if respiration occurred in the test tube?
A. Carbon Dioxide
B. Nitrogen
C. Starch
The correct answer and explanation is :
The correct answer is A. Carbon Dioxide.
Detailed Explanation:
In the experiment described, the student prepared a test tube containing yeast, glucose, and water and allowed it to sit for 24 hours. The goal is to determine what substance would be present if respiration occurred.
Yeast is a microorganism that can perform aerobic (with oxygen) or anaerobic (without oxygen) respiration, depending on the conditions. In the presence of oxygen, yeast performs aerobic respiration, breaking down glucose completely into carbon dioxide and water, and releasing energy. If oxygen is limited, yeast shifts to anaerobic respiration, also known as fermentation. During fermentation, yeast converts glucose into carbon dioxide and ethanol (alcohol).
In either case—whether respiration is aerobic or anaerobic—carbon dioxide (CO₂) is a product. This gas is what you would expect to detect in the test tube after 24 hours if respiration occurred.
Here’s the basic chemical equation for aerobic respiration:
[
\text{Glucose (C₆H₁₂O₆)} + \text{O₂} \rightarrow \text{CO₂} + \text{H₂O} + \text{Energy (ATP)}
]
And for anaerobic fermentation in yeast:
[
\text{Glucose (C₆H₁₂O₆)} \rightarrow \text{CO₂} + \text{Ethanol (C₂H₅OH)}
]
Now, let’s address why the other options are incorrect:
- B. Nitrogen: Nitrogen is abundant in the atmosphere, but it is not a product of yeast respiration. Yeast does not produce nitrogen gas during respiration.
- C. Starch: Starch is a complex carbohydrate made of many glucose molecules linked together. Yeast breaks down glucose; it does not produce starch. In fact, if starch were present, yeast would work to break it down into glucose first for respiration.
Thus, the substance expected to be found as a direct result of yeast respiration is carbon dioxide.