A student used the internet to find information about caffeine and the possible effects it has on the body. The student decided to test the hypothesis that: Caffeine decreases the reaction time and increases the heart rate. Table 1.1 shows the results of the student's research into the caffeine content of drinks. Table 1.1 drink cup of coffee cup of tea 100 cm³ energy drink 350 cm³ cola caffeine content/mg 80 40 30 45 The student also found that it takes about 45 minutes before caffeine from a drink is fully absorbed into the blood and about 4 to 5 hours for the effect to wear off. After further research, the student decided: • test subjects should not know whether they are having a drink with caffeine or without caffeine • drinks with caffeine and without caffeine should look identical • to measure the subject's reaction time using a computer programme that flashes a coloured light at random intervals. The subject presses a switch as soon as they see the light • to measure the heart rate using a pulse meter attached to the first finger.

1. (a)Suggest why it is important that the test subjects should not know whether they are having a drink with caffeine or without caffeine.[1]
2. (b)(i)State the independent variable and the two dependent variables in this investigation. independent variable ................................................................................................................................. dependent variables ...................................................................................................................................[2]
3. (b)(ii)Use the information given to describe a method by which the student could test their hypothesis using one of the drinks. Your method should be detailed enough for another person to follow.[8]
4. (c)(i)State why Pearson's linear correlation test is suitable for the data.[1]
5. (c)(ii)The results of the statistical test gave Pearson's linear correlation, r = −0.722. State what this value indicates about the relationship between the concentration of caffeine and the mean reaction time.[1]
6. (c)(iii)Describe how the student calculated the degrees of freedom.[1]
7. (c)(iv)Describe how the student used the probability table to find out if the value for r = 0.722 is significant.[3]
8. (d)Suggest two reasons why the method used for the investigation into the effect of caffeine concentration may have given results that are not reliable.[2]
9. (e)Effects of caffeine in the body include the promotion of acetylcholine release and the inhibition of acetylcholinesterase. Suggest how this could account for the results in Table 1.2.[1]

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