Why is it important to cut the two potato pieces in roughly equal size and measure their initial weight before placing them in different liquids?
[Pg. No. 14]

It is important to cut the two potato pieces in roughly equal size so that both pieces have nearly the same surface area and volume exposed to the liquids. This makes the comparison fair because the rate of osmosis depends on the exposed surface area. Their initial weight is measured to provide a starting value. After keeping them in different liquids, any increase or decrease in weight can be compared with the initial weight to find how much water has entered or left the potato cells by osmosis. Thus, equal size and initial weighing help ensure that the observed change is mainly due to the difference in concentration of the liquids, not because of unequal potato pieces.