When a question gives you a table about a drug, you must do three things: calculate any value asked for, say what the pattern shows, and say what the data cannot show. This lesson practises that order using an invented stimulant trial.
It builds on telling a medicine from a mechanism and feeds into explaining changes at a synapse, part of drugs and biological effects.
What does “at curriculum level” mean here?
A stimulant increases activity in the nervous system. You are not expected to know laboratory methods or detailed chemistry. You are expected to read the table, use means and state a sensible conclusion.
A reaction time is the time between a stimulus and the response, measured here in milliseconds (ms). A shorter time means a faster response.
A reliable reading order
- Calculate the mean for each group and each condition.
- Find the change by subtracting before from after.
- Compare with the control group, which shows what changes without the drug.
- State the conclusion using wording such as “supports” or “is consistent with”.
- Name one limit, such as sample size or number of trials.
Worked example
Invented data, for teaching only. In a school investigation, 5 students drank a fizzy drink containing Compound Z (an invented stimulant). 5 other students drank the same drink without it. Reaction time in ms was measured before and after.
| Group | Before (ms) | After (ms) |
|---|---|---|
| Compound Z | 260, 275, 240, 250, 285 | 235, 250, 225, 240, 260 |
| Control | 255, 270, 245, 260, 270 | 250, 265, 240, 255, 265 |
Step 1, means. Compound Z before: (260 + 275 + 240 + 250 + 285) ÷ 5 = 1310 ÷ 5 = 262 ms. After: (235 + 250 + 225 + 240 + 260) ÷ 5 = 1210 ÷ 5 = 242 ms.
Control before: 1300 ÷ 5 = 260 ms. After: 1275 ÷ 5 = 255 ms.
Step 2, change. Compound Z: 242 − 262 = −20 ms. Control: 255 − 260 = −5 ms.
Step 3, compare. Both groups got faster, so some improvement happened without the drug, possibly from practice. The Compound Z group improved by 15 ms more than the control (20 − 5 = 15).
Step 4, conclusion. The results are consistent with Compound Z making reactions faster.
Step 5, limit. Each group had only 5 students and one test, so chance could explain part of the 15 ms gap.
The mistake to watch for
Mistaken answer: “Compound Z made reaction time 20 ms faster, which proves it speeds up reactions.”
There are two errors. The 20 ms figure ignores the control, which improved by 5 ms without the drug. And “proves” is too strong for 5 students and one test.
The correction is to use the control difference (15 ms) and to write “supports” or “is consistent with”, followed by one limit.
Check yourself
1. Reaction times in ms for three students after a stimulant were 300, 280 and 290. Calculate the mean.
Show answer
(300 + 280 + 290) ÷ 3 = 870 ÷ 3 = 290 ms.
2. A second invented group of 4 students had a mean before time of 260 ms. After the stimulant their times were 230, 240, 250 and 260 ms. Find the mean change.
Show answer
After mean = (230 + 240 + 250 + 260) ÷ 4 = 980 ÷ 4 = 245 ms. Change = 245 − 260 = −15 ms, so reactions were 15 ms faster on average.
3. Why is a control group needed in this investigation?
Show answer
It shows how much reaction time changes without the drug, for example through practice. Without it you cannot tell whether the drug caused the change.
Where this leads next
Next, explain how a substance can alter signalling to connect a faster response to what happens at a synapse. The mistake log and retest queue is useful for noting which step of the reading order you skipped.
If your conclusions swing between too bold and too vague, our teachers can help you calibrate them in online one-to-one Biology tuition.