The conditions for natural selection
Grade 9 Science Worksheet
Circle the best answer.
Read this first
Moths on soot-darkened trees: each survivor leaves 2 young like itself (model data)
moth color generation 1 survived to breed generation 2 dark 20 16 ? light 80 24 ? Ari fills in generation 2 with the model rule in the title. How many dark moths are in generation 2?
- 32 dark moths: 16 survivors leave 2 young each
- 36 dark moths: 20 dark moths plus 16 survivors
- 16 dark moths: the survivors, with no young counted
- 40 dark moths: 20 moths leave 2 young each, whether or not they survived
“Two rounds of an antibiotic on lab plates (model data). Agar plate diagram, zones:” Esme spreads bacteria from the 3 colonies onto a new plate with the same antibiotic. What should Round 2 show, and why?
- Few colonies, since each bacterium turns resistant when touched
- No colonies, since bacteria that grew once cannot grow again
- Many colonies, since the bacteria need resistance and so make it
- Many colonies, since the survivors' young inherit the trait
A model meadow study (model data)
observation result plants in the meadow heights from 20 to 60 cm seeds per tall plant and per short plant 40 and 10 seeds that find room to grow 5 of 100 offspring of tall and of short plants, grown in one soil 30 cm average for both Jun reads a model study. Tall plants leave more seeds, yet generation 2 is not taller. Which condition is missing?
- Inheritance: the height difference is not passed on
- Overproduction: the meadow makes fewer seeds than it has room for
- Variation: the plants do not differ in height
- Differential reproduction: tall and short plants leave equal seeds
A model patch of purple-flowered plants (model data)
observation result petal colors among the plants purple only alleles for petal color the same pair in each plant seedlings that find room 20 of 100 seedlings that match their parent plants 20 of 20 Kira reads a model patch. Natural selection cannot change petal color here. Which condition is missing?
- Overproduction: the patch makes fewer seedlings than it has room for
- Differential survival: white seedlings survive worse than purple ones
- Inheritance: the seedlings do not match their parent plants
- Variation: the plants carry the same alleles, so petal color does not differ
Seedlings by petal color in a model patch (model data)
petal color seedlings made match their parents survived to breed purple 50 48 20 white 50 47 20 Luz reads a model patch. Which condition for natural selection is missing, so petal color will not shift over generations?
- Variation: the patch has one petal color
- Overproduction: the patch makes fewer seedlings than it supports
- Inheritance: seedlings do not match their parents
- Differences in survival: both colors have the same survivors
Model moths on soot-darkened trunks (model data)
moth color moths survived to breed dark 40 28 light 40 4 Where soot darkened tree trunks, dark peppered moths became more common. Milo reads model counts. Which explanation fits?
- Dark moths matched the dark trunks, so a larger share survived and passed on the trait
- Light moths turned dark on the sooty trunks, so each one matched
- Soot made the moths mutate toward dark so they would match
- Dark moths were stronger, so a larger share of them survived
Finches in the 1977 drought on Daphne Major (real pattern from Concepts of Biology)
observation what was found seeds after the drought far fewer; small, soft seeds declined more than large, hard seeds survival the following year large-billed finches survived better than small-billed finches average bill size measured afterward larger inheritance of bill size survivors with large bills tend to have offspring with large bills Noah reads the pattern from the 1977 drought. Which explanation fits the data and the conditions for natural selection?
- The drought made each finch's bill grow deeper, so the average rose
- Large bills are the better trait in any year, so they were favored
- Large-billed finches survived better, and bill size is inherited, so young tended to have larger bills
- The finches needed larger bills, so larger bills appeared in the young
Bacteria carrying a resistance gene, per 10,000 bacteria (model data)
sample carrying the gene before any antibiotic 4 after one round of antibiotic and regrowth 8,200 Pia reads a model sample of bacteria. Which explanation fits the change from 4 to 8,200 per 10,000?
- The gene was already present at a low count, and the antibiotic let those bacteria multiply
- Each bacterium became resistant after it met the antibiotic
- The antibiotic caused new resistance mutations in the bacteria it touched
- The bacteria needed resistance, so more of them mutated to carry it
Finches per 100 on a model island (model data)
trait generation 1 generation 2 generation 3 small-billed 75 60 35 large-billed 25 40 65 Tala compares generations. By how many per 100 did small-billed finches change from generation 1 to generation 3?
- Down by 25, from 60 to 35
- Down by 15, from generation 1 to generation 2
- Up by 40, the change in the large-billed finches
- Down by 40, from 75 to 35
Two plant types in a model patch (model data)
type plants in generation 1 young surviving to breed per plant A 20 6 B 20 2 Zee applies the model rule that young match their parent type. How many type A plants are in generation 2?
- 26, since 20 plants plus 6 young
- 160, since 120 type A and 40 type B
- 20, since the count of type A stays the same
- 120, since 20 plants leave 6 young each