(a) The yeast cells fail to multiply in water but they multiply rapidly in sugar solution. Give one reason for it. (b) Why does bread mould grow profusely on a moist slice of bread but not on a dry slice of bread?

(a) Yeast being a non-green plant it cannot prepare its own food. In water, there is no source of energy for yeast to reproduce. In a sugar solution it grows as sugar acts as a source of energy.

(b) A moist slice of a bread provides all the necessary conditions needed by the spores of the bread mould to germinate. Hence, bread mould grow profusely on a moist slice of bread.