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 Ari uses the mean rate from the first to the last reading to predict gas at 7 minutes. What is the prediction?
- 18 mL, the 6 minute reading
- 2.3 mL
- 21 mL
- 26 mL, the 8 minute reading
Bo reads the table. In which 2 minute interval was the rate highest?
- 2 to 4 minutes, at 3.5 mL per minute
- 0 to 2 minutes, where the yeast starts
- 8 to 10 minutes, where the reading is largest
- 6 to 8 minutes, at 4 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 needs 3 minutes before it starts making gas
- The bottle held 3 mL of gas at the start
- The yeast made 3 mL of gas in total
- Each minute, about 3 more mL of gas is made
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?
- Assign the seedlings to the two groups at random
- Give both groups the same light
- Use just the 20 tallest seedlings to make the test stronger
- Measure the plant-food group more often
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?
- Measure each seedling twice and keep the larger of the two values
- Add 20 more seedlings to each group
- Have a helper who does not know the groups do the measuring
- Switch to a ruler with finer marks
a balance reads 0.3 g with nothing on it. Noah weighs seedlings on the balance. How should the readings be treated?
- Average many readings, which will remove the 0.3 g from the final result
- 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
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?
- Neither: the readings differ from each other a lot
- Accurate but not precise: the readings sit near 5.0 g
- Precise but not accurate: the readings agree but sit far from 5.0 g
- Both accurate and precise: the readings agree with each other
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 works, since the fed mean is higher
- Plant food adds 2 cm to each seedling
- Plant food has no effect, since the ranges are not the same
Tala reads these group summaries. Which statement do the data best support?
- The 12 cm and 21 cm extremes show the effect varies too much
- No conclusion is possible, since means alone cannot show a cause
- Plant food will add 5.5 cm to any plant
- The ranges do not overlap, so the 5.5 cm gap is likely real here
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
- Not supported: no plant food should give the tallest plants
- Supported: 18 cm at 4 g is the tallest, so more must be better
- Supported: 2 g and 4 g were taller than 0 g