Read a biology experiment: variables, controls, repeated trials

Grade 9 Science Worksheet

Circle the best answer.

1. 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

2. 1.

   Ari uses the mean rate from the first to the last reading to predict gas at 7 minutes. What is the prediction?

   • 2.3 mL
   • 21 mL
   • 26 mL, the 8 minute reading
   • 18 mL, the 6 minute reading
3. 2.

   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
4. 3.

   Esme draws a best-fit line through the origin with a slope of about 3 mL per minute. What does the slope mean?

   • The bottle held 3 mL of gas at the start
   • The yeast needs 3 minutes before it starts making gas
   • The yeast made 3 mL of gas in total
   • Each minute, about 3 more mL of gas is made

5. Plan (example data)

   The student who set up the groups measures every seedling and writes down its height, knowing which group it is in.

6. 4.

   Kira reads the plan. Which change best reduces measurement bias?

   • Switch to a ruler with finer marks
   • Have a helper who does not know the groups do the measuring
   • Add 20 more seedlings to each group
   • Measure each seedling twice and keep the larger of the two values

7. 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.

8. 5.

   Luz reads the plan. Which change best separates plant food from tray effects?

   • Put 20 plants in each tray instead of 10 plants in each tray
   • Water tray B more often
   • Use several trays for each treatment, in mixed positions
   • Measure just the plants in tray A
9. 6.

   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?

   • It averages out over the 10 trials, so the final mean will be right again
   • Nothing: every reading is off the same way, so the mean is off too
   • It doubles the error with each added trial
   • It removes the error, because more trials are better
10. 7.

    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
    • Ignore it, since a small error cancels out
    • Subtract 0.3 g from each reading, since the error is the same each time
    • Average many readings, which will remove the 0.3 g from the final result

11. 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

12. 8.

    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
13. 9.

    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
    • No conclusion is possible, since means alone cannot show a cause
    • The 12 cm and 21 cm extremes show the effect varies too much
    • Plant food will add 5.5 cm to any plant

14. 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

15. 10.

    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: 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: no plant food should give the tallest plants