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 1: 200 volunteers is too few for any conclusion about colds
- Line 4: volunteers chose their group and exercised more, so random assignment is missing
- Line 2: a difference of 1 day is too small to count as a result
- Line 3: exercise cannot matter, since colds are caused by viruses and not by habits of the people
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 3: the flasks rule out microbes arising in broth, not every origin of life
- Line 4: air cannot carry microbes, since the swan neck stayed open to the air
- Line 2: a broken neck cannot change what is in the broth, so the cloud is a mistake
- Line 1: boiled broth is not clear, since boiling makes it cloudy
Notebook
Notes on a law and a theory (classmate's notebook), 4 lines. Columns: line, entry. Line 1: The law of segregation describes the 3 : 1 counts in Mendel's crosses. Line 2: Chromosome theory explains why: paired chromosomes separate when eggs and pollen form. Line 3: The theory explains the law, so the theory is just a more certain law. Line 4: Both can be revised if new evidence shows exceptions.
Esme reads a classmate's notebook about Mendel. Which line has the mistake?
- Line 4: a law or a theory is fixed and cannot be revised, whatever new evidence arrives later on
- Line 3: explaining a pattern is a different job from describing it, so neither ranks higher
- Line 2: chromosome theory is a hypothesis until more tests promote it to a law
- Line 1: segregation is a theory, since it covers the counts from many crosses
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 settles semiconservative for good, so no later result from any lab could ever change that
- It favors dispersive, since lighter DNA appeared after the second copying
- It brings back conservative, since a light band appeared
- It favors semiconservative, which predicts two bands, and counts against dispersive
Luz reads that Schleiden thought new cells formed like crystals, while Virchow said cells come from cells. Which observation favors Virchow?
- Seeing cells in a thin slice of plant tissue under a microscope
- Counting millions of cells in one sample of animal tissue
- Finding cells in many species of plants and animals
- Watching one cell under a microscope divide into two cells over time
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
Two hypotheses about a warm bottle's balloon (example data)
hypothesis reason given H1 warmth speeds up living yeast, so more gas forms H2 warm water simply releases dissolved gas, with or without yeast Two hypotheses both predict a warm bottle fills its balloon more. Pia adds a test to tell them apart. Which test does that?
- Measure just the foam height in the warm bottle, which both predict
- Repeat the warm and cool test again with new bottles, new yeast and the same two temperatures
- Warm sugar water with boiled yeast: a filling balloon favors H2, a flat one favors H1
- Use a larger balloon on each bottle so the sizes are easier to read
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
- Disproved: a law must match its ratio exactly, and 705 : 224 is not exactly the same as 3 : 1, so the law fails
- Supported exactly: 705 ÷ 224 equals 3, so the ratio is perfect
- Not disproved: 3:1 predicts about 697 and 232, and chance explains the gap to 705 and 224
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
- Not a guess: the theory pointed to rocks about 375 million years old, and the fossil was there
- It is a law now, since a fossil matched and enough matches promote a theory
- 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
- Disagree: selection predicts resistant cells will spread under antibiotics, and tests can show it
- Agree: a theory cannot make predictions that can be tested, because it just describes what has happened before