Year 11 students investigated the effect of age on reaction time. They used the following method:
Five teachers of different ages were selected.
Each teacher sat at a computer waiting for the letter X to appear on the screen.
When the X appeared, the teacher pressed the space bar.
The time taken for each teacher to react was recorded by the computer.

The results are shown in Graph 4.
Graph 4

State the conclusion that can be made from the results shown in Graph 4.
State two variables that should have been controlled to make this a fair test.
1.
2.
State what the students should do to have more confidence in their results.
(i) State the stimulus being detected in this investigation.
[1]
..........
(ii) State how information travels along neurones.
[1]
..........
(iii) State the two parts of the central nervous system.
[2]
..........
..........
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