Read a biology experiment: variables, controls, repeated trials
Grade 9 Science Worksheet
Circle the best answer.
Read this first
Gas from yeast at 30 °C (example data)
time (min) gas (mL) 0 0 2 6 4 13 6 18 8 26 10 30 Bo reads the table. In which 2 minute interval was the rate highest?
- 6 to 8 minutes, at 4 mL per minute
- 8 to 10 minutes, where the reading is largest
- 0 to 2 minutes, where the yeast starts
- 2 to 4 minutes, at 3.5 mL per minute
Esme draws a best-fit line through the origin with a slope of about 3 mL per minute. What does the slope mean?
- The yeast made 3 mL of gas in total
- Each minute, about 3 more mL of gas is made
- The bottle held 3 mL of gas at the start
- The yeast needs 3 minutes before it starts making gas
Plan (example data)
a student has 40 bean seedlings of different heights. The 20 tallest go in the plant-food group and the 20 shortest in the control group. All are measured after 14 days.
Jun reviews the plan. Which change fixes its main problem?
- Use just the 20 tallest seedlings to make the test stronger
- Measure the plant-food group more often
- Assign the seedlings to the two groups at random
- Give both groups the same light
Plan (example data)
The student who set up the groups measures every seedling and writes down its height, knowing which group it is in.
Kira reads the plan. Which change best reduces measurement bias?
- Have a helper who does not know the groups do the measuring
- Add 20 more seedlings to each group
- Switch to a ruler with finer marks
- Measure each seedling twice and keep the larger of the two values
a gas syringe is read at a slant, so every reading comes out 2 mL too high. Milo repeats the test 10 times with the slanted syringe. What does repeating do for this error?
- Nothing: every reading is off the same way, so the mean is off too
- It averages out over the 10 trials, so the final mean will be right again
- It doubles the error with each added trial
- It removes the error, because more trials are better
a balance reads 0.3 g with nothing on it. Noah weighs seedlings on the balance. How should the readings be treated?
- Subtract 0.3 g from each reading, since the error is the same each time
- Ignore it, since a small error cancels out
- Discard the balance, since 0.3 g makes the results invalid
- Average many readings, which will remove the 0.3 g from the final result
Example data
a 5.0 g test mass is weighed four times on a balance. The readings are 3.1, 3.1, 3.2 and 3.1 g.
Pia reads the four readings. Which description fits them?
- Both accurate and precise: the readings agree with each other
- Accurate but not precise: the readings sit near 5.0 g
- Neither: the readings differ from each other a lot
- Precise but not accurate: the readings agree but sit far from 5.0 g
Seedling height after 14 days, 12 plants per group (example data)
group mean (cm) range (cm) control 15.0 12 to 18 plant food 17.0 14 to 20 Ren reads the group summaries. Which statement do the data best support?
- The 2 cm gap may be chance: the ranges overlap from 14 to 18 cm
- Plant food has no effect, since the ranges are not the same
- Plant food works, since the fed mean is higher
- Plant food adds 2 cm to each seedling
Tala reads these group summaries. Which statement do the data best support?
- No conclusion is possible, since means alone cannot show a cause
- The ranges do not overlap, so the 5.5 cm gap is likely real here
- The 12 cm and 21 cm extremes show the effect varies too much
- Plant food will add 5.5 cm to any plant
Mean seedling height after 14 days, 12 plants per dose (example data)
plant food (g) mean height (cm) 0 15 2 17 4 18 8 14 Zee writes: "More plant food always gives taller seedlings." Which reply is best?
- Not supported: 8 g gave 14 cm, below the 15 cm with no plant food
- Supported: 2 g and 4 g were taller than 0 g
- Supported: 18 cm at 4 g is the tallest, so more must be better
- Not supported: no plant food should give the tallest plants