Read a biology experiment: variables, controls, repeated trials

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   Two data sets on plant food (example data)

   data set	plants per group	unfed mean (cm)	fed mean (cm)
   school archive, five years	100	15.1	16.8
   own test	6	15.6	15.9

2. 1.

   Ari compares an archive with a small test. How should the two data sets be read together?

   • Average the two gaps to get 1.0 cm, and report that as the effect size
   • The small test overturns the archive, since it found almost no gap between its groups
   • They agree in direction, and the 100 plants in the archive make its 1.7 cm gap firmer
   • The archive is wrong, because it is older than the new test is, and so out of date

3. Two plant food studies (example data)

   study	unfed mean (cm)	fed mean (cm)
   tomato	10.0	12.0
   bean	20.0	22.4

4. 2.

   Bo compares the two studies. Which gives the larger effect in relative terms?

   • The bean study, since its fed mean of 22.4 cm is the larger of the two
   • The bean study, since its 2.4 cm gap is larger than the tomato gap of 2.0 cm
   • Both are the same, since each gap is about 2 cm
   • Tomato: +20 percent against +12 percent, though the bean gap is larger in cm

5. Two classes grew the same plant (example data)

   class	plants	mean height (cm)
   A	8	18
   B	24	14

6. 3.

   Esme combines the two classes into one data set. What is the mean height of all the plants?

   • 16 cm
   • 15 cm
   • 32 cm
   • 14 cm

7. Four trays (example data)

   tray	treatment	mean height (cm)
   A	plant food	18
   B	plant food	15
   C	no plant food	14
   D	no plant food	12

8. 4.

   Kira had two trays for each treatment. What do the means show about a tray effect?

   • Fed plants are clearly taller on average: 16.5 cm against 13 cm
   • Trays given the same treatment differ by 2 to 3 cm, so plant food is unclear
   • Trays A and D show the effect clearly: 18 cm against 12 cm, a 6 cm gap
   • Tray effects do not matter, since each tray held many plants to average

9. Six lakes (model data)

   lake	phosphorus (µg per L)	algae, as chlorophyll (µg per L)
   1	10	3
   2	20	6
   3	35	9
   4	50	14
   5	70	20
   6	90	27

10. 5.

    Luz sees both numbers rise together across lakes. Does this show phosphorus causes more algae?

    • No: six lakes are too few to show any pattern in the data
    • No: sunlight or warmth could drive both; adding phosphorus would test it
    • Yes: the pattern is almost a straight line, so one must cause the other one
    • Yes: the algae rise as phosphorus rises in each of the six lakes studied
11. 6.

    The first 10 minutes gave 3 mL per minute. Milo predicted 90 mL at 30 minutes from the first 10 minutes. The reading was 62 mL. What does this show?

    • The 62 mL reading must be a measuring error, since the model said 90 mL
    • The straight-line model fits the early readings, but the rate slowed later
    • The model is right, since gas is still rising at 30 minutes, just as it predicted
    • The yeast stopped making gas at minute 10, when the rate was highest
12. 7.

    Seedling A, height = 4 + 1.5 × day; seedling B, height = 1 + 2.5 × day. Pia wants to know when seedling B is as tall as seedling A. On which day are they the same height?

    • Day 2, since 4 − 1 = 3 and 3 ÷ 1.5 = 2
    • Day 3, when both are 8.5 cm tall
    • At no point, since seedling A starts taller than seedling B
    • Day 1.2, since 3 ÷ 2.5 = 1.2

13. Bean seeds sprouted of 50 per dish after 7 days (example data)

    salt (g per L)	seeds sprouted
    0	46
    2	40
    4	21

14. 8.

    Ren writes up the results. Which claim, evidence and reasoning is best?

    • Salt at 2 g helps. Evidence: 40 sprouted at 2 g, which is many. Reasoning: seeds need minerals to sprout.
    • Salt ruins seeds. Evidence: 21 of 50 sprouted at 4 g. Reasoning: seeds need water, and salt is a chemical.
    • Salt lowers sprouting. Evidence: 46, 40, then 21 of 50 as salt rose. Reasoning: salt pulls water out of seeds.
    • Salt lowers sprouting. Evidence: seeds are alive. Reasoning: living things dislike salt and avoid it.
15. 9.

    Working explanation: warmer water speeds up the yeast. Tala wants new data to test the explanation. Which new result would most challenge it?

    • Less gas at 50 °C than at 40 °C, which would show that heat can harm yeast
    • More gas at 35 °C than at 30 °C, which would fit the pattern in the table
    • Three bottles at 40 °C giving 21, 22 and 23 mL, close to the mean
    • Bubbles forming faster at 50 °C, which would fit the pattern

16. Two yeast studies (example data)

    study	bottles per temperature	yeast batches	how gas was measured
    A	4	1	syringe volume
    B	1	3	bubbles counted by eye

17. 10.

    Both studies found more gas at 40 °C. Zee compares them. Which statement is best?

    • They are equally strong, since both found more gas at the same temperature
    • B is stronger, since counting bubbles is a more direct measure of gas
    • A is stronger: replicates, one yeast batch and a measured volume cut chance
    • B is stronger, since it used three yeast batches against one for A