Read a biology experiment: variables, controls, repeated trials
Grade 9 Science Worksheet - Building Confidence
Circle the best answer.
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 Bo reads the same results. Which bottle is the positive control, and what does it show?
- Bottle 3: glucose feeds yeast, so it shows the setup can detect gas
- Bottle 2: it has the sweetener that the test is about
- Bottle 1: it shows the setup gives no gas without sugar
- Neither control matters; the sweetener bottle answers the question by itself
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 Esme gets these results on another day. What should Esme conclude about the sweetener?
- Nothing yet: the glucose bottle made no gas, so the test itself failed
- The sweetener does not work, since bottle 2 made little gas
- Yeast cannot use any sugar, so the sweetener fails too
- The sweetener works as well as glucose does
Bean seedlings after 14 days (example data)
group mean height (cm) without plant food 12 with plant food 15 Jun compares the two groups. By what percent are the fed seedlings taller than the unfed ones?
- 125 percent
- 20 percent
- 25 percent
- 3 percent
Gas from yeast (example data)
time (min) gas (mL) 0 0 4 12 10 36 Kira reads the gas table. What is the mean rate of gas production between minute 4 and minute 10?
- 24 mL per minute
- 4 mL per minute
- 6 mL per minute
- 3.6 mL per minute
Seeds sprouted after 7 days, 20 seeds per dish (example data)
dish seeds sprouted control 12 treated 17 In the treated dish, Luz counts how many seeds sprouted. By how many percentage points is sprouting higher than in the control?
- 5 percentage points
- 42 percentage points
- 25 percentage points
- 85 percentage points
Gas from three yeast batches (mL in 10 minutes) (example data)
batch trial 1 trial 2 trial 3 A 14 15 16 B 10 15 20 C 13 15 17 All three batches have a mean of 15 mL. Milo asks which batch's trials agree best.
- Batch C, because its range is the middle one
- Batch B, because its trials cover the most values
- The three agree equally, because their means match
- Batch A, with the smallest range, 2 mL
One seedling (example data)
day height (cm) 3 2 9 14 Noah measures one seedling twice. What is its mean growth rate between day 3 and day 9?
- 1.6 cm per day
- 12 cm per day
- 4.7 cm per day
- 2 cm per day
Batch A, four trials (mL in 10 minutes) (example data)
trial gas (mL) 1 14 2 15 3 16 4 31 One bottle in batch A was shaken before it was read. Pia wants a summary of a typical trial. Which summary is best?
- The median, 15.5 mL, which the extreme trial does not pull up
- The largest trial, 31 mL, since it shows what the yeast can do
- The range, 17 mL, since it uses the extreme trials
- The mean, 19 mL, since it uses each trial
Bean seeds sprouted of 50 per dish (example data)
salt (g per L) seeds sprouted 0 46 4 21 Tala tested bean seeds only. A poster says salt lowers sprouting in all seeds. What is the best reply?
- Supported: beans are seeds, so all seeds must behave alike
- Not supported: 50 seeds per dish is too few for beans
- Supported for beans only; other seeds were not tested
- Supported: 25 fewer seeds sprouted, which is enough for each kind
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 removes the chance errors, because each count becomes the same
- It adds more chance errors, because more trials add more counts
- It changes nothing, because each count is already right
- It shrinks the chance errors, because high and low counts balance out
