Read a biology experiment: variables, controls, repeated trials

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. Read this first

   Yeast test of a new sweetener (example data)

   bottle	added to the yeast and water	gas in 10 minutes (mL)
   1	nothing	2
   2	new sweetener	3
   3	glucose	21

2. 1.

   Ari tests whether yeast can use a new sweetener. Which bottle is the negative control?

   • Bottle 2: the sweetener, since it is the thing being tested
   • Bottle 3: glucose, since yeast is known to respond to it
   • No bottle, since the three have yeast in them
   • Bottle 1: nothing is added, so it shows the background gas
3. 2.

   Bo reads the same results. Which bottle is the positive control, and what does it show?

   • Bottle 2: it has the sweetener that the test is about
   • Bottle 3: glucose feeds yeast, so it shows the setup can detect gas
   • Neither control matters; the sweetener bottle answers the question by itself
   • Bottle 1: it shows the setup gives no gas without sugar

4. The same test on another day (example data)

   bottle	added to the yeast and water	gas in 10 minutes (mL)
   1	nothing	2
   2	new sweetener	3
   3	glucose	2

5. 3.

   Esme gets these results on another day. What should Esme conclude about the sweetener?

   • The sweetener does not work, since bottle 2 made little gas
   • Nothing yet: the glucose bottle made no gas, so the test itself failed
   • Yeast cannot use any sugar, so the sweetener fails too
   • The sweetener works as well as glucose does

6. Bean seedlings after 14 days (example data)

   group	mean height (cm)
   without plant food	12
   with plant food	15

7. 4.

   Jun compares the two groups. By what percent are the fed seedlings taller than the unfed ones?

   • 125 percent
   • 25 percent
   • 20 percent
   • 3 percent

8. Gas from yeast (example data)

   time (min)	gas (mL)
   0	0
   4	12
   10	36

9. 5.

   Kira reads the gas table. What is the mean rate of gas production between minute 4 and minute 10?

   • 3.6 mL per minute
   • 24 mL per minute
   • 4 mL per minute
   • 6 mL per minute

10. Seeds sprouted after 7 days, 20 seeds per dish (example data)

    dish	seeds sprouted
    control	12
    treated	17

11. 6.

    In the treated dish, Luz counts how many seeds sprouted. By how many percentage points is sprouting higher than in the control?

    • 42 percentage points
    • 25 percentage points
    • 5 percentage points
    • 85 percentage points

12. One seedling (example data)

    day	height (cm)
    3	2
    9	14

13. 7.

    Noah measures one seedling twice. What is its mean growth rate between day 3 and day 9?

    • 12 cm per day
    • 1.6 cm per day
    • 4.7 cm per day
    • 2 cm per day

14. Gas from yeast in 10 minutes, mean of 3 bottles (example data)

    water temperature (°C)	mean gas (mL)
    20	8
    30	15
    40	22

15. 8.

    Ren writes: "At 50 °C the yeast will make about 29 mL." What is the best reply?

    • Supported: the pattern adds 7 mL for each 10 °C
    • Not supported: 50 °C was not tested, and heat can slow yeast
    • Supported: warmer water gives more gas at any temperature
    • Not supported: the means are too small to compare

16. Bean seeds sprouted of 50 per dish (example data)

    salt (g per L)	seeds sprouted
    0	46
    4	21

17. 9.

    Tala tested bean seeds only. A poster says salt lowers sprouting in all seeds. What is the best reply?

    • Supported: 25 fewer seeds sprouted, which is enough for each kind
    • Supported for beans only; other seeds were not tested
    • Not supported: 50 seeds per dish is too few for beans
    • Supported: beans are seeds, so all seeds must behave alike
18. 10.

    Example data. Bubbles counted by eye in one bottle: 38, 41, 40, 43 in four trials of equal length. Zee counts bubbles by eye, so the counts differ from trial to trial. What does averaging more trials do?

    • It changes nothing, because each count is already right
    • It shrinks the chance errors, because high and low counts balance out
    • It removes the chance errors, because each count becomes the same
    • It adds more chance errors, because more trials add more counts