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 3: exercise cannot matter, since colds are caused by viruses and not by habits of the people
- 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 2: a difference of 1 day is too small to count as a result
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 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
- 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
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?
- 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
- Conservative: it predicts a heavy band and a light band, and only one in-between band appeared
- No hypothesis: one result cannot rule out an idea, however well it fits
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 semiconservative, which predicts two bands, and counts against dispersive
- It brings back conservative, since a light band appeared
- It favors dispersive, since lighter DNA appeared after the second copying
- 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?
- Watching one cell under a microscope divide into two cells over time
- Seeing cells in a thin slice of plant tissue under a microscope
- Finding cells in many species of plants and animals
- 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 35S protein label found inside the bacteria and little 32P label
- Most 32P DNA label found inside the bacteria and most 35S label outside
- No result could falsify it, since viruses are too small to test
- Most 35S protein label found outside the bacteria after the shaking step
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 1: sunny plots give bigger yields, so any effect is easier to see
- Experiment 2: random assignment spreads sun and soil differences across both groups
- 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?
- 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
- Repeat the warm and cool test again with new bottles, new yeast and the same two temperatures
- Measure just the foam height in the warm bottle, which both predict
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?
- It is a guess, since no one watched the past and a fossil cannot be used to test an idea about it
- 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
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 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
- 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