The changes that occur as a result of ageing may be categorised as physiological or pathological.

A physiological change due to ageing is one that will occur in all individuals. A pathological change is one that is not inevitable; it is caused by disease or ill health.

State why each of the following changes is a physiological change due to ageing.

reduced muscle power ______________

reduced immunity ______________

Scientists investigated the effect of two types of dietary protein on the ability of old men to produce body proteins.

Table 2 shows information about the two types of dietary protein investigated.

Figure 4 shows the percentage of protein absorbed that becomes body protein in old men following a meal of casein or whey.

A statistical test confirmed that the difference between the results shown in Figure 4 was significant.

Suggest which type of dietary protein would be better for old men to eat to cause a net gain of body proteins. Use the information provided to explain your answer.