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?
- 26 mL, the 8 minute reading
- 18 mL, the 6 minute reading
- 21 mL
- 2.3 mL
Bo reads the table. In which 2 minute interval was the rate highest?
- 2 to 4 minutes, at 3.5 mL per minute
- 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
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
- Measure the plant-food group more often
- Give both groups the same light
- Use just the 20 tallest seedlings to make the test stronger
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
Plan (example data)
10 plants with plant food sit in tray A, by the window. 10 plants without plant food sit in tray B, in the middle of the room.
Luz reads the plan. Which change best separates plant food from tray effects?
- Water tray B more often
- Measure just the plants in tray A
- Use several trays for each treatment, in mixed positions
- Put 20 plants in each tray instead of 10 plants in each tray
a balance reads 0.3 g with nothing on it. Noah weighs seedlings on the balance. How should the readings be treated?
- 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
- Ignore it, since a small error cancels out
- Subtract 0.3 g from each reading, since the error is the same each time
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?
- Precise but not accurate: the readings agree but sit far from 5.0 g
- Both accurate and precise: the readings agree with each other
- Neither: the readings differ from each other a lot
- Accurate but not precise: the readings sit near 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?
- Plant food has no effect, since the ranges are not the same
- Plant food works, since the fed mean is higher
- The 2 cm gap may be chance: the ranges overlap from 14 to 18 cm
- Plant food adds 2 cm to each seedling
Tala reads these group summaries. Which statement do the data best support?
- The ranges do not overlap, so the 5.5 cm gap is likely real here
- Plant food will add 5.5 cm to any plant
- No conclusion is possible, since means alone cannot show a cause
- The 12 cm and 21 cm extremes show the effect varies too much
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: 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
- Not supported: 8 g gave 14 cm, below the 15 cm with no plant food