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?

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   • The archive is wrong, because it is older than the new test is, and so out of date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

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?

   • 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
   • The bean study, since its 2.4 cm gap is larger than the tomato gap of 2.0 cm
   • The bean study, since its fed mean of 22.4 cm is the larger of the two

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?

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

7. Result (example data)

   The plants given plant food sit by the window, and they are taller, 18 cm against 15 cm. Explanation 1: the plant food helped. Explanation 2: the window light helped.

8. 4.

   Jun reads the result. Which extra test best separates the two explanations?

   • Add a third group with extra plant food by the window
   • Repeat the test with the same positions and many more plants in each
   • Measure the plants by the window more often, to be sure of their heights
   • Put some fed and some unfed plants both by the window and away from it

9. 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

10. 5.

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

    • Trays A and D show the effect clearly: 18 cm against 12 cm, a 6 cm gap
    • 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
    • Tray effects do not matter, since each tray held many plants to average

11. 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

12. 6.

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

    • No: sunlight or warmth could drive both; adding phosphorus would test it
    • Yes: the algae rise as phosphorus rises in each of the six lakes studied
    • Yes: the pattern is almost a straight line, so one must cause the other one
    • No: six lakes are too few to show any pattern in the data
13. 7.

    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 straight-line model fits the early readings, but the rate slowed later
    • The yeast stopped making gas at minute 10, when the rate was highest
    • The model is right, since gas is still rising at 30 minutes, just as it predicted
    • The 62 mL reading must be a measuring error, since the model said 90 mL
14. 8.

    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 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
    • Day 2, since 4 − 1 = 3 and 3 ÷ 1.5 = 2

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

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

16. 9.

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

    • 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.
    • Salt ruins seeds. Evidence: 21 of 50 sprouted at 4 g. Reasoning: seeds need water, and salt is a chemical.
    • Salt at 2 g helps. Evidence: 40 sprouted at 2 g, which is many. Reasoning: seeds need minerals to sprout.

17. 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

18. 10.

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

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