Tell a hypothesis, a theory and a law apart
Grade 9 Science Worksheet
Circle the best answer.
Read this first
Cholera deaths by water company, London 1853 (real data, Snow 1855)
water company houses deaths deaths per 10,000 houses Southwark and Vauxhall 40,046 1,263 315 Lambeth 26,107 98 37 Bo reads John Snow's 1850s London cholera data. Houses on the same streets were mixed between two water companies. Which statement does the table support?
- Southwark and Vauxhall had 1,263 deaths against 98, so it was about 13 times as dangerous
- The table settles water as the cause for good, so no other cause of cholera could exist
- About 8 times the deaths with one company's water, even on shared streets, which points to the water
- The table shows just a link, because counting deaths cannot show a cause in a real city of any size or age
Mendel's seed color counts (real data, Mendel 1866)
seed color seeds counted yellow 6,022 green 2,001 total 8,023 Esme reads Mendel's counts. The law of segregation predicts a 3:1 ratio. Do 2,001 green seeds support it?
- Yes: a 3:1 ratio predicts about 2,006 green seeds, and 2,001 is very close
- No: the law needs exactly 2,006 green seeds, so 2,001 disproves it
- No: a 3:1 ratio predicts about 2,674 green seeds, which is 8,023 ÷ 3, so 2,001 is too few
- Yes: 6,022 ÷ 2,001 is exactly 3, so the match is perfect
Peppered moths released in woods near Birmingham (real data, Kettlewell 1955)
moth color released recaptured dark 154 82 light 64 16 Jun reads Kettlewell's 1955 recapture counts from soot-darkened woods. Why do they show natural selection is more than a guess?
- It predicted dark moths would survive better on dark trees, and 53% against 25% recaptured fits
- 154 dark moths were released against 64 light ones, so dark moths are plainly fitter
- The match upgrades selection from a theory to a law, which is what enough data does
- A theory is a guess, so any numbers would have fitted it; these just happen to agree with it by luck
Predictions of cell theory and what was found (real data, from OpenStax Microbiology)
prediction test result every living tissue is made of cells cork in 1665, plants in 1838, animals in 1839 cells found in each new cells come from existing cells dividing cells watched and described by 1855 cells seen arising from cells Kira reads how cell theory was tested. Why is it more than a guess?
- It fits cork, so it fits every tissue, and one example is enough to settle it
- It is called a theory because not every cell has been seen, so it stays a guess until then
- Predictions about cork, plants, animals and dividing cells could have failed, and none did
- It has been confirmed so many times that it moved up from a theory to a law
Mendel's second-generation counts (real data, Mendel 1866)
trait dominant recessive ratio flower color 705 224 3.15 : 1 seed shape 5,474 1,850 2.96 : 1 seed color 6,022 2,001 3.01 : 1 Statement L: each egg or pollen cell gets one of the two copies of a gene. Statement C: paired chromosomes separate when eggs and pollen form, carrying the copies apart.
Milo reads Mendel's three crosses. Which labels fit statement L, about the copies, and statement C, about chromosomes?
- Both are laws, since both fit the three ratios in the table above equally
- L is the law: it describes the rule behind all three ratios; C is the theory that explains it
- L is the theory and C is the law, because the copies rule explains the counts
- Both are theories, since each covers more than a single cross
Heart rates of three mammals (example data, rounded from typical values)
animal body mass (kg) resting heart rate (beats a minute) mouse 0.02 600 human 70 70 elephant 4,000 30 Statement A: resting heart rate falls as body mass rises. Statement B: a small body loses heat faster for its mass, so its cells need fuel delivered faster.
Noah reads the table and two statements. Which statement describes a pattern, and which explains it?
- B describes the pattern in the table; A is an explanation for the heart rates
- A is a theory, since it covers three different mammals at once
- Both describe patterns, since both mention heart rate or body mass
- A describes the pattern in the table; B is an explanation that more animals could test
Bacteria before one antibiotic dose (example data)
measure value cells 10,000 resistant cells 1% resistant cells that live 90% other cells that live 10% Pia uses natural selection to predict. One dose lets 90% of resistant cells and 10% of other cells live. About what share of survivors is resistant?
- 9%, from 90 survivors out of 1,000 survivors
- 90%, the share of resistant cells that live
- 1%, because a dose does not change which cells are resistant
- About 8%: 90 of the 1,080 survivors are resistant
Two-gene fly cross, 1,000 offspring (example data modeled on Morgan's findings)
offspring type expected if genes assort independently observed parent type 1 250 415 parent type 2 250 415 new mix 1 250 85 new mix 2 250 85 A cross of two genes should give four types equally if the law of independent assortment holds. Ren sees the counts. What should happen to the law?
- It is revised: it still fits genes on different chromosomes; linked genes need a limit
- Nothing changes, since a law that fits most crosses is fixed and cannot be revised by one cross
- It is thrown out, since a single exception ends any law
- It is demoted to a hypothesis, since one cross broke it
Cell theory over time (real data, from OpenStax Microbiology)
year event 1838 Schleiden suggests new cells form like crystals 1839 Schwann finds animals are made of cells too 1855 Virchow states that cells come from existing cells Tala reads a timeline of cell theory. Which conclusion about how ideas change fits it?
- The first idea was a hunch, and the 1855 idea is a proven fact
- The crystal idea was a law that Virchow's evidence had to defeat
- The theory was corrected: cell division evidence replaced the crystal idea
- The theory was not wrong at any stage, since an explanation backed by evidence is fixed
Zee reads a website that says 10,000 more crosses matching 3 : 1 will turn the law of segregation into a theory. What is wrong?
- A theory is just a law that explains the same pattern in simpler words
- More crosses are pointless, since a law is proven the first time it fits
- More crosses strengthen the law as a description; a theory explaining it is a different idea
- Nothing is wrong: a law backed by that much evidence is simply renamed a theory once it has enough