In a classic experiment carried out by the biologist Hop
dic 20 century, 20 young rats were divided into two groups.
One group was fed on a diet of pure carbohydrate, lipid and
protein; the other was fed the same diet. but with some added
milk. The rats were weighed every day. After 18 days the diets
of the two groups were swapped over.
A)Name two types of nutrient that were missing from the diet of only one of the groups.
B) Suggest why Hopkins used young rats rather than adult rats, for his investigation.
C) Explain the importance of switching the diets of the two groups after 18 days.
D) suggest some important control variables that Hopkins kept constant during his investigation.