(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) Water does not provide any energy to the yeast cells. So, yeast cells fail to multiply in water due to inadequate energy in its cells. Sugar provides energy to them to carry out reproduction by multiplying rapidly.
(b) Moisture is necessary for the growth of bread mould. The moist slice of bread provides both moisture and nutrients due to which bread mould grows profusely. On the other hand, the dry slice of bread provides nutrients but no moisture. So, in the absence of moisture, bread mould does not grow on the dry slice of bread.