Parkinson's disease occurs when nerve cells in part of the brain die, resulting in less secretion of a neurotransmitter called dopamine. Dopamine is involved in the control of muscle movement and in emotional responses. As a result, common symptoms of Parkinson's disease are muscle twitching and stiff muscles. Other symptoms can include depression, memory loss and problems with sleeping. The disease is progressive, so over time the symptoms become worse.

1. (a)(i)Scientists collected data on the number of males and females with Parkinson's disease in specific age groups in the USA. Fig. 2.1 shows these data presented as number of people with Parkinson's disease per 100 000. [Figure 2.1] State what conclusions can be made from Fig. 2.1 about Parkinson's disease in the USA.[3]
2. (a)(ii)A student suggested that the Spearman's rank correlation could be used to test the relationship between age and the occurrence of Parkinson's disease. Give a reason why it is possible to use the Spearman's rank correlation to analyse the data shown in Fig. 2.1.[1]
3. (a)(iii)State a null hypothesis for this test.[1]
4. (b)(i)There is currently no cure for Parkinson's disease although a range of treatments can be used to relieve the symptoms. Drugs are given that are absorbed by brain cells and converted to dopamine. As the disease progresses, more brain cells die and so less of the drug is absorbed. As a result, the effectiveness of these drugs decreases. Research into the use of neural stem cells (NSC) as a more effective treatment for Parkinson's disease is being carried out. One study was carried out to test the hypothesis that: The use of a Chinese herbal drug increases the differentiation of NSC into neurones that produce dopamine. In this study, 48 healthy male rats of similar mass were randomly divided into four groups. Each rat was kept in a separate cage and supplied with food and water. Fig. 2.2 shows the experimental design of the study. [Figure 2.2] Identify two variables that have been standardised in this study.[2]
5. (b)(ii)Suggest one variable that should have been standardised in this study but for which there is no information about how this was done.[1]
6. (c)At 7, 14 and 28 days after the start of the study, a sample of four rats from each group was tested to find the dopamine concentration in the brain. The results are shown in Table 2.1. [Table 2.1] State two advantages of calculating standard deviations (s) in studies of this type.[2]
7. (d)The researchers concluded that, in rats, the use of a Chinese herbal drug increases the differentiation of NSC into neurones that produce dopamine. With reference to all the information about this study, give one piece of evidence that supports this conclusion and one piece of evidence that suggests this conclusion is not valid. evidence that supports this conclusion evidence that suggests this conclusion is not valid[2]

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