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The Invisible Living World: Beyond Our Naked Eye — Science STD 8 — Question

Gujarat BoardEnglish MediumSTD 8ScienceThe Invisible Living World: Beyond Our Naked Eye5 Marks
Question
In a school laboratory experiment based on the textbook, three test tubes were prepared:
Image
- Test Tube A contained only sugar solution and water.
- Test Tube B contained sugar solution, water, and a pinch of yeast.
- Test Tube C contained yeast and water only.
All three test tubes were sealed with balloons on top and left undisturbed for 2 days. After the observation period, the balloon on Test Tube B was inflated. When the gas collected from this tube was passed into lime water, it turned milky.
Q.1. What gas caused the balloon on Test Tube B to inflate?
Q.2. Why was there no balloon inflation in Test Tube A and Test Tube C?
Q.3. What chemical reaction caused lime water to turn milky?
Q.4. What is the process called in which yeast converts sugar into alcohol and carbon dioxide?
Q.5. What conclusion can you draw about the role of sugar in this experiment?
✓

Answer

1. Carbon dioxide (CO2)
2. Test Tube A had no yeast to perform fermentation, and Test Tube C had no sugar as food for yeast, so no gas was produced.
3. CO2 reacted with lime water (calcium hydroxide) to form calcium carbonate, a white precipitate, making it milky.
4. Fermentation
5. Sugar is essential as an energy source for yeast to carry out fermentation and produce CO2.

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