A food stall owner was preparing dough for making bhaturas. He added a pinch of yeast and sugar to the dough and left it in a warm place. After a few hours, the dough had risen. There was a sour smell too. (a) Why did the dough rise? (b) Why did the dough smell sour? (c) Why was sugar added to the dough? (d) What would have happened if the dough was kept in the refrigerator, soon after it was prepared?
ScienceClass 7CBSEAnswered 27 Mar 2026
Answer
Soln:
a) CO2 produced by yeast during respiration makes the dough rise
b) During anaerobic respiration yeast produces alcohol. This gives sour smell to the dough.
c) Sugar acts as food for yeast
d) If kept in the refrigerator, yeast will not respire and multiply and the dough will not rise and will not produce a sour smell.
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