Natural Selection ATLAS Test
ATLAS Practice Exam Grade 8 Science • Life Science
Natural Selection & Population Dynamics
Standards: 8-LS4-4 • 8-LS4-6
Total Points: 20 • 16 Items
Student:
Date:
Period:
Score:
Phenomenon Cluster 1: Fur Color in Desert Rock Pocket Mice Questions 1–4
In the desert of New Mexico, rock pocket mice (Chaetodipus intermedius) inhabit both light granite rocks and dark basalt rock formations created by ancient volcanic lava flows. Biologists collected frequency data across generations following the formation of a dark lava flow surrounded by light granite.
| Substrate Location | Initial Gen. (% Dark Fur) | Gen. 10 (% Dark Fur) | Gen. 30 (% Dark Fur) | Owl Capture Rate (% Dark / % Light) |
|---|
| Dark Basalt Lava Rock | 2% | 38% | 94% | 18% Dark / 82% Light |
| Light Granite Outcrop | 1% | 2% | 1% | 79% Dark / 21% Light |
- [8-LS4-4] Which statement best explains how the dark fur trait first appeared in the rock pocket mouse population prior to the lava flow?
A Mice intentionally mutated their DNA to blend in.
B A random genetic mutation produced variation.
C Dark soot from the basalt permanently stained fur.
D Heat from cooled basalt stimulated melanin genes.
- [8-LS4-6] Based on the table, what was the mathematical percentage-point increase of dark-furred mice on basalt rock between Generation 10 and Generation 30?
A 36 percentage points
B 56 percentage points
C 92 percentage points
D 94 percentage points
Question 3 • Evidence-Based Selected Response [8-LS4-4 • 2 Points]
Part A: Why did the dark fur trait become predominant on basalt rock over time?
A Dark mice survived visual predation and reproduced more.
B Light mice migrated completely away to granite outcrops.
C Dark mice required significantly less caloric food energy.
D Basalt lava altered reproductive mating behavior directly.
Part B: Which piece of mathematical evidence from the table directly supports your answer to Part A?
A Light granite outcrop had 1% dark mice at Generation 30.
B Owls captured 82% light mice versus 18% dark mice on basalt.
C Initial dark fur frequency was 2% on basalt rock.
D Owl capture was 79% dark mice on light granite rock.
- [8-LS4-6] Multi-Select Select TWO mathematical predictions that will occur if a new light sandy deposit completely covers the basalt rock over the next 20 generations.
□ Dark fur frequency will decrease from 94% toward <10%.
□ Owl predation of light mice will increase to over 90%.
□ Light-furred mice will show a higher relative reproductive rate.
□ Both phenotypes will remain at exactly a 50:50 ratio.
Arkansas ATLAS Grade 8 Science • Life Science Performance Assessment Page 1 of 4
Section 2: Quantitative Trait Shift in Daphne Major Finches Standards: 8-LS4-4 • 8-LS4-6
Phenomenon Cluster 2: Galápagos Ground Finches & the 1977 Drought Questions 5–8
Biologists Peter and Rosemary Grant studied medium ground finches (Geospiza fortis) on the island of Daphne Major. In 1977, a severe drought struck the island, drastically reducing the abundance of small, soft seeds. Only large, hard woody seeds from Tribulus cistoides remained available.
Total Population Size
1,200 → 180 birds
85% mortality rate in 1977
Mean Beak Depth (1976)
8.8 mm
Pre-drought parent gen.
Mean Beak Depth (1978)
9.8 mm
+1.0 mm offspring gen.
- [8-LS4-6] Which mathematical statement accurately describes how the distribution of beak depth in the finch population shifted after the drought?
A Mean beak depth increased by approximately 11.4%.
B Mean beak depth decreased by 1.0 mm due to malnutrition.
C The range of beak depth shifted to include birds with 15 mm beaks.
D The total number of surviving finches doubled in 1978.
- [8-LS4-4] A student claims: "Individual finches grew deeper beaks during 1977 because they had to crack hard seeds to survive." Why is this student's claim scientifically inaccurate?
A Birds already had soft seeds in storage and did not need to crack seeds.
B Individual beak anatomy does not grow or change; only population trait averages change through differential survival.
C Beak depth is completely controlled by temperature rather than food type.
D Finches only reproduce during rainy seasons, so natural selection could not act.
Question 7 • Evidence-Based Selected Response [8-LS4-4 • 2 Points]
Part A: What specific environmental pressure caused the change in the beak trait?
A Scarcity of small soft seeds, leaving only tough, large seeds.
B Predator hawks hunting finches with shallower beaks.
C Excessive rainfall flooding low-elevation nesting sites.
D Invasive insect species competing directly for nesting holes.
Part B: Which biological mechanism explains why the 1978 offspring generation had a higher mean beak depth than the 1976 parent generation?
A Surviving birds passed heritable alleles for deeper beaks to offspring.
B Smaller-beaked birds interbred with a different large-beaked species.
C Offspring stretched their beaks during development in the nest.
D Drought caused a high mutation rate in all surviving embryonic eggs.
- [8-LS4-6] In 1983, an El Niño event brought 10 times the normal rainfall, resulting in an explosion of small, soft seeds and vines. Which mathematical model predicts the population response by 1985?
A Mean beak depth decreases back toward ~8.6 mm as smaller beaks gain an efficiency advantage.
B Mean beak depth continues increasing rapidly up to 14.0 mm regardless of seed size.
C The entire finch population dies out because large beaks cannot consume soft seeds.
D Beak sizes become perfectly uniform with zero variation across all individuals.
Arkansas ATLAS Grade 8 Science • Life Science Performance Assessment Page 2 of 4
Section 3: Mathematical Trends in Peppered Moth Populations Standards: 8-LS4-4 • 8-LS4-6
Phenomenon Cluster 3: Peppered Moths (Biston betularia) & Clean Air Legislation Questions 9–12
Peppered moths exist in two forms: a speckled light morph and a solid dark (melanic) morph. In the 1800s, industrial coal soot killed pale tree lichens and darkened tree bark. Following the 1956 Clean Air Act, sulfur dioxide emissions dropped, allowing pale lichens to regrow on trees. Field researchers tracked moth capture counts across four decades.
| Census Year | Tree Trunk Condition | Light Morph Count | Dark Morph Count | Total Sample |
|---|
| 1960 | Dark & Sooty (0% Lichen) | 50 | 450 | 500 |
| 1975 | Moderate Soot (20% Lichen) | 160 | 340 | 500 |
| 1990 | Mostly Clean (65% Lichen) | 365 | 135 | 500 |
| 2005 | Clean Pale Lichens (90% Lichen) | 460 | 40 | 500 |
- [8-LS4-6] Calculate the relative frequency (%) of the light morph in 1960 and in 2005. Which mathematical statement represents this change?
A Light morph frequency increased from 10% in 1960 to 92% in 2005.
B Light morph frequency decreased by 82 percentage points over the study.
C Dark morph frequency increased from 50% to 90% in 2005.
D Total population decreased by 410 individuals between 1960 and 2005.
- [8-LS4-4] Multi-Select Select TWO factors that directly caused the probability of survival for dark morph moths to decrease after 1960.
□ Lichen regrowth made dark moths more visually conspicuous to predatory birds.
□ Dark moths stopped laying eggs because of cleaner atmospheric air.
□ Higher predation on dark moths reduced their reproductive opportunities.
□ Lichen produced a toxic airborne chemical that killed only dark larvae.
- [8-LS4-4] Why is high survival alone not sufficient for natural selection to change trait frequencies over generations?
A Surviving individuals must also reproduce and pass heritable traits to fertile offspring.
B Predators must eat equal numbers of both morphs to maintain balance.
C Surviving adults must physically change their body color during their lifetime.
D Natural selection only functions when the total population size decreases.
- [8-LS4-6] Which graph description correctly models the relationship between percent lichen coverage (x-axis) and the proportion of light morph moths (y-axis)?
A A positive linear/curvilinear trend: as lichen coverage increases, light morph proportion increases toward 1.0.
B A negative trend: as lichen coverage increases, light morph proportion declines to 0.
C A horizontal flat line indicating that lichen coverage has 0 mathematical effect.
D A parabolic U-curve where light moths exist only at 0% and 100% lichen coverage.
Arkansas ATLAS Grade 8 Science • Life Science Performance Assessment Page 3 of 4
Section 4: Pesticide Resistance & Evidence-Based Explanation Standards: 8-LS4-4 • 8-LS4-6
Phenomenon Cluster 4: Rootworm Resistance to Bt Corn Questions 13–16
Corn rootworms feed on maize roots. Farmers began planting genetically modified corn producing a bacterial protein (Bt toxin) that kills rootworms. Agricultural scientists compared two farming methods over 6 years: Field 1 planted 100% Bt corn; Field 2 planted 80% Bt corn with a 20% "refuge strip" of standard non-Bt corn.
| Agricultural Strategy | Year 1 (% Resistant) | Year 3 (% Resistant) | Year 6 (% Resistant) | Root Damage Rating (1–5 Scale) |
|---|
| Field 1: 100% Bt Corn (No Refuge) | 0.1% | 18.5% | 89.2% | 4.8 (Severe Failure) |
| Field 2: 80% Bt Corn + 20% Non-Bt Refuge | 0.1% | 1.2% | 4.1% | 1.4 (Protected) |
- [8-LS4-4] How did the alleles conferring Bt resistance enter the rootworm population?
A Bt toxin caused beetles to create defense antibodies that became genes.
B Pre-existing rare genetic mutations existed before Bt was introduced.
C Corn plants transferred their Bt genes directly to rootworm chromosomes.
D Beetles learned to avoid toxic plants and passed this habit to larvae.
- [8-LS4-6] Comparing the two fields at Year 6, how many times greater was the frequency of Bt-resistant beetles in Field 1 than in Field 2?
A ~4.5 times
B ~15.2 times
C ~21.8 times
D ~85.1 times
Question 15 • Two-Part Analysis [8-LS4-4 • 8-LS4-6 • 2 Points]
Part A: Why did Field 2's refuge strategy maintain low resistance frequencies for 6 years?
A Susceptible beetles from refuge strips mated with rare resistant beetles, diluting resistant alleles.
B Refuge strips actively emitted airborne chemicals that destroyed beetle eggs.
Part B: What would mathematically occur in Field 2 if the farmer discontinued planting refuge strips after Year 6?
A Resistance frequency would remain static at 4.1% permanently.
B Resistance frequency would rise rapidly toward ~90% due to intense selective pressure.
Constructed Response Question 16 • Claim-Evidence-Reasoning
[8-LS4-4 • 8-LS4-6 • 3 Points]
Using data from Field 1 and Field 2, construct a scientific explanation that describes how natural selection caused the shift in rootworm traits, and justify why agricultural refuge strips mathematically slow the evolution of resistance. Include: (1) A clear claim, (2) quantitative data evidence, and (3) biological reasoning linking survival, reproduction, and allele inheritance.
Claim:
Evidence (Include numerical data from table):
Scientific Reasoning (Connect survival, reproduction, and trait inheritance):
Arkansas ATLAS Grade 8 Science • Life Science Performance Assessment Page 4 of 4
