Reaction time required practical

Slower, longer-lasting reactions to changes in the internal and external environment are controlled by hormones, while faster reactions are controlled by the nervous system. The speed of reactions controlled by the nervous system are often limited by the speed that impulses are passed across synapses. Drugs can affect synapses and so speed up or slow down reaction time. To test the effect of caffeine on reaction time:

1. Randomly divide a group of twenty people into two groups of 10 - large numbers of people make the results more representative of the whole population

2. Measure the initial reaction time of all twenty people by holding a ruler so that the top of their thumb and forefinger are level with the 0 cm mark and 1 cm away from the ruler. Release the ruler at a random time (approximately 3 - 5 seconds after setting up the experiment). Give the person three practice runs and then record the measurement at the top of the forefinger on the ruler on the 4th run

3. Use a measuring cylinder to measure out 100 cm3 of caffeine free diet coke into 10 cups and 100 cm3 of caffeinated diet coke into 10 cups 

4. Tell the first person in the first group to drink a cup of caffeine free diet coke but don't tell them which drink it is (i.e. a blind trial) - this helps avoid bias in their response

5. Re-measure the reaction time of this person 30 minutes later by giving them three practice runs and recording the 4th run

6. Repeat steps 4 and 5 for everyone in the first group and then everyone in the second group using the caffeinated drink

7. Calculate the mean average initial reaction distance and final reaction distance for each group. Then calculate a percentage change in reaction distance using the formula:

((Final distance - start distance) / start distance) x 100

Experimental setup