Tell a hypothesis, a theory and a law apart
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Read this first
Notebook
Notes on a vitamin C study (classmate's notebook), 4 lines. Columns: line, entry. Line 1: 200 volunteers chose whether to take vitamin C daily; 100 did and 100 did not. Line 2: Colds lasted 5.0 days for the vitamin C group and 6.0 days for the others. Line 3: The vitamin C group also reported exercising more often. Line 4: So vitamin C shortens colds.
Ari reads a classmate's notebook about a vitamin C study. Which line has the mistake?
- Line 4: volunteers chose their group and exercised more, so random assignment is missing
- Line 1: 200 volunteers is too few for any conclusion about colds
- Line 3: exercise cannot matter, since colds are caused by viruses and not by habits of the people
- Line 2: a difference of 1 day is too small to count as a result
Notebook
Notes on swan-neck flasks (classmate's notebook), 4 lines. Columns: line, entry. Line 1: Boiled broth in a swan-neck flask stayed clear for a year. Line 2: When the neck was broken off, the broth turned cloudy in two days. Line 3: So life has not arisen from non-living matter at any time in history. Line 4: So the microbes in broth come from cells carried in the air.
Bo reads a classmate's notebook about swan-neck flasks. Which line has the mistake?
- Line 4: air cannot carry microbes, since the swan neck stayed open to the air
- Line 3: the flasks rule out microbes arising in broth, not every origin of life
- Line 1: boiled broth is not clear, since boiling makes it cloudy
- Line 2: a broken neck cannot change what is in the broth, so the cloud is a mistake
Three hypotheses for DNA copying and what each predicts after one copying (example data)
hypothesis prediction after one copying conservative one heavy band and one light band semiconservative one band of in-between density dispersive one band of in-between density Bacteria with heavy-nitrogen DNA copied it once in light nitrogen. Jun sees one band of in-between density. Which hypothesis does this rule out?
- No hypothesis: one result cannot rule out an idea, however well it fits
- Conservative: it predicts a heavy band and a light band, and only one in-between band appeared
- Semiconservative: it predicts a light band, so a lone in-between band rules it out
- Dispersive: it predicts a heavy band, so a lone in-between band rules it out
Predictions after two copyings (example data)
hypothesis prediction after two copyings semiconservative half in-between density, half light dispersive one band, lighter than in-between After a second copying, Kira sees equal amounts of in-between and light DNA. Semiconservative and dispersive both fit round one. What does round two show?
- It favors dispersive, since lighter DNA appeared after the second copying
- It favors semiconservative, which predicts two bands, and counts against dispersive
- It brings back conservative, since a light band appeared
- It settles semiconservative for good, so no later result from any lab could ever change that
Luz reads that Schleiden thought new cells formed like crystals, while Virchow said cells come from cells. Which observation favors Virchow?
- Finding cells in many species of plants and animals
- Watching one cell under a microscope divide into two cells over time
- Seeing cells in a thin slice of plant tissue under a microscope
- Counting millions of cells in one sample of animal tissue
Milo tests: "DNA, not protein, enters bacteria and carries the virus's genes." Viruses carried 35S (in protein) and 32P (in DNA). Which result would falsify it?
- Most 32P DNA label found inside the bacteria and most 35S label outside
- Most 35S protein label found inside the bacteria and little 32P label
- Most 35S protein label found outside the bacteria after the shaking step
- No result could falsify it, since viruses are too small to test
Two field experiments (example data)
experiment how plots got fertilizer X plots experiment 1 applied to the sunny south edge, none on the shady north edge 10 experiment 2 assigned at random to 5 of 10 plots 10 Noah tests: "Fertilizer X raises corn yield." Which of the two field experiments tests it better?
- Neither: crop yield cannot be tested outdoors where weather varies
- Experiment 2: random assignment spreads sun and soil differences across both groups
- Experiment 1: sunny plots give bigger yields, so any effect is easier to see
- Both test it equally, since each has 10 plots and one fertilizer
Mendel's flower color counts (real data, Mendel 1866)
measure value violet flowers 705 white flowers 224 total 929 Ren's friend says Mendel's 705 : 224 is not exactly 3 : 1, so the law of segregation is disproved. Which reply is best?
- Disproved: 705 is more than 697, so the law fails for violet flowers
- Not disproved: 3:1 predicts about 697 and 232, and chance explains the gap to 705 and 224
- Supported exactly: 705 ÷ 224 equals 3, so the ratio is perfect
- Disproved: a law must match its ratio exactly, and 705 : 224 is not exactly the same as 3 : 1, so the law fails
Use the table
A prediction about fish and four-legged animals (real data, Daeschler et al. 2006)
step detail prediction a fish with limb-like fins should be found in rocks about 375 million years old search a team explored rocks of that age on Ellesmere Island, Canada found Tiktaalik, in 2004, with a neck and wrist-like fin bones Tala's friend says evolution is just a guess about the past. Which reply uses the Tiktaalik record best?
- One fossil settles evolution for good, so no further evidence is needed
- It is a law now, since a fossil matched and enough matches promote a theory
- Not a guess: the theory pointed to rocks about 375 million years old, and the fossil was there
- It is a guess, since no one watched the past and a fossil cannot be used to test an idea about it
Bacteria on antibiotic plates (example data)
day resistant cells (%) 0 1 2 12 5 60 Zee's friend says natural selection cannot be tested because it happened long ago. Which reply fits the data?
- Agree: a theory is just a guess about the past, so it cannot be tested
- Disagree: the data show selection is true for good, with no more tests needed
- Agree: a theory cannot make predictions that can be tested, because it just describes what has happened before
- Disagree: selection predicts resistant cells will spread under antibiotics, and tests can show it