Question 9 โ€” Yeast and lime water setup - Questions at the end of the chapter - Chapter 2 Class 8 - The Invisible Living World: Beyond our (Curiosity)

Last updated at June 7, 2026 by

Q 9
Question

A flask A has warm sugar solution with yeast, joined to test tube B with lime water. (i) What happens in flask A? (ii) What is seen in tube B after four hours, and why? (iii) What if yeast was not added in flask A?

๐Ÿ”— Concept: 2.4.2 Microorganisms and Food

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Yeast ferments the sugar and gives off carbon dioxide, which turns the lime water milky.

Explanation

  • (i) In flask A, yeast feeds on the sugar and ferments it, releasing gas.
  • (ii) After four hours, the lime water in tube B turns milky.
  • This is because the gas given off is carbon dioxide.
  • (iii) Without yeast, no gas forms, so the lime water stays clear.
Yeast makes carbon dioxide that turns lime water milky; with no yeast, nothing happens.
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