MS-LS4-4: How Inherited Variation Changes the Odds of Surviving and Reproducing
In plain English: MS-LS4-4 is the NGSS middle school performance expectation that asks students to construct an explanation, based on evidence, of how inherited differences in a trait give some individuals a better chance of surviving and reproducing in a specific environment. Students use simple probability statements and proportional reasoning. It is usually taught in grade 7 or 8 life science.
Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals' probability of surviving and reproducing in a specific environment.
Clarification Statement: Emphasis is on using simple probability statements and proportional reasoning to construct explanations.
Next Generation Science Standards · Disciplinary Core Idea: Biological Evolution: Unity and Diversity · Official standard
Students construct explanations, backed by evidence, of how genetic variation (inherited differences among individuals of one species) gives some individuals a higher probability of surviving and reproducing in a particular environment. They turn counts into probabilities, compare the probabilities with ratios such as "about twice as likely", and see that the same trait can help in one place and not in another. Cases include stick insects on two kinds of shrubs, coneflowers on a windy hill, voles in a cold winter, thistles in grazed pastures, frog tadpoles in drying pools and a paper model of winged seeds. All data sets on this page are invented for teaching; where a pattern comes from real field studies, the page says so.
The NGSS Clarification Statement says: "Emphasis is on using simple probability statements and proportional reasoning to construct explanations." MS-LS4-4 has no official Assessment Boundary. The lesson stays at the level of traits and counts: it does not ask how genes work inside cells, and it treats the long-term change of a whole population over many generations as the next standard, MS-LS4-6. Students do the practice of constructing explanations: they analyze data, write probability statements and build a claim, evidence and reasoning paragraph.
Learning Objectives
By the end of this lesson, students will be able to:
Tell inherited variations of a trait apart from features an organism picks up during its life
Calculate probabilities of surviving or reproducing from counts, and compare them with ratios
Explain why the same inherited trait can raise the probability of surviving in one environment and lower it in another
Construct an explanation, with a claim, evidence and reasoning, of how a trait affects the chance of surviving and reproducing
Prior Knowledge Required
Students should already be comfortable with:
Differences among individuals of a species can give advantages in surviving, finding mates and reproducing 3-LS4-2
Offspring inherit traits from their parents, and traits vary within a group 3-LS3-1
A probability is a number from 0 to 1 that describes how likely an event is 7.SP.C.5
Using ratios and rates to compare quantities 6.RP.A.3
Show a photo or drawing of a green caterpillar on a green leaf and the same kind of caterpillar on a brown twig. Tell students that caterpillars of this kind vary in color, and that the color is passed from parents to offspring.
Warm-Up Prompt
"A bird is hunting on this plant. Which caterpillar is more likely to be eaten? Does that mean it will be eaten for sure? What would change if the caterpillars lived on brown twigs instead?"
Write student words such as "more likely", "less likely" and "for sure" on the board. Point out that scientists describe chances with numbers called probabilities, and that the answer to the last question depends on the environment.
Direct Instruction15-20 minutes
Key words. A population is a group of organisms of one species living in the same area. A trait is a feature of an organism, such as body color or fur thickness. Genetic variation means that individuals in a population inherit different versions of a trait from their parents. A trait an organism picks up during its life, such as a scar, is not inherited and is not genetic variation. The environment is everything around the organism: weather, plants, predators (animals that hunt and eat other animals) and so on. Surviving means staying alive, and reproducing means producing offspring (young or seeds).
Probability. A probability is a number from 0 to 1 that tells how likely something is: 0 means it cannot happen, 1 means it is certain. From data, probability of surviving = number that survived ÷ number at the start. A probability of 0.7 means about 7 out of every 10 individuals like this are expected to survive, not that each one is safe. To compare two probabilities, divide one by the other: 0.6 ÷ 0.3 = 2 means "twice as likely". All numbers in these examples are invented for teaching.
Survival in one environment: stick insects on chamise
Timema stick insects live on shrubs in California. Some inherit a white stripe down the back and some are plain green. Chamise, one of their food shrubs, has thin, needle-like leaves. In a field test (invented counts, based on a pattern found in real studies), 120 striped and 120 plain insects were placed on chamise where birds hunt. After 3 weeks, 84 striped and 36 plain insects were found alive.
Result: Striped: 84 ÷ 120 = 0.70. Plain: 36 ÷ 120 = 0.30. 0.70 ÷ 0.30 ≈ 2.3, so on chamise a striped insect was a bit more than twice as likely to survive. The stripe blends in with the thin leaves.
The same trait in a different environment: stick insects on ceanothus
Ceanothus, another food shrub, has broad, flat leaves. In the same kind of test on ceanothus, 42 of 120 striped and 90 of 120 plain insects survived 3 weeks (invented counts). See Diagram 1.
Result: Striped: 42 ÷ 120 = 0.35. Plain: 90 ÷ 120 = 0.75. Now the plain form is about 0.75 ÷ 0.35 ≈ 2.1 times as likely to survive. The trait is the same; the environment decides whether it helps.
Reproducing: tall and short flower stalks on a windy hill
In a population of purple coneflowers, stalk height is inherited. Bees visit tall stalks more, so an unbroken tall stalk makes about 140 seeds and a short one about 90 (invented). On a windy hilltop, 20 of 40 tall stalks and 2 of 40 short stalks snapped before their seeds ripened. In a sheltered valley, none snapped.
Result: Hilltop: tall 20 ÷ 40 = 0.5 stay standing, and 0.5 × 140 = 70 seeds per plant on average; short 38 ÷ 40 = 0.95, and 0.95 × 90 = 85.5 seeds. Valley: tall 140 against short 90. Short stalks have the advantage on the hill, tall ones in the valley.
Surviving, then reproducing: fur thickness in a cold winter
A model population of meadow voles (small rodents) has 50 females with thick fur and 50 with thin fur, a trait passed from parents to young (invented). In a very cold winter, 30 thick-fur and 15 thin-fur females survive. In spring each survivor raises a first litter of 4 young. In a mild winter, 42 thick-fur and 40 thin-fur females survive.
Result: Cold winter: 30 ÷ 50 = 0.6 and 15 ÷ 50 = 0.3, so thick fur doubles the chance of surviving. Young: 30 × 4 = 120 and 15 × 4 = 60, so 120 of 180, or 2/3, of the young have thick-fur mothers. Mild winter: 0.84 against 0.80, almost no advantage. See Diagram 2.
After each example, ask three questions: "Is the trait inherited? In this environment, which form has the higher probability? Why does the trait change the chance of surviving or reproducing here?" Stress that a higher probability is not a guarantee: some plain stick insects survived on chamise, and some striped ones died.
Guided Practice10-15 minutes
Pairs analyze invented data on a wild thistle whose plants inherit either many spines or few spines. Cattle graze one pasture and avoid eating spiny plants; the other pasture has no grazing animals. Making spines uses some of the plant's energy, so a surviving few-spine plant makes more seeds. Each group started with 60 young plants.
Guided practice data (invented): wild thistle plants after one summer
Pasture
Many spines: survived
Few spines: survived
Seeds per surviving plant
Grazed by cattle
48 of 60
18 of 60
many spines 200, few spines 240
No grazing animals
51 of 60
54 of 60
many spines 200, few spines 240
Find the probability of surviving for each kind of plant in each pasture.
In the grazed pasture, how many times as likely is a spiny plant to survive as a few-spine plant?
Multiply each probability by the seeds per surviving plant to find the expected seeds per young plant. Which kind leaves more seeds in each pasture?
Write an explanation: "In the ___ pasture, plants with ___ have a higher probability of surviving and reproducing. Evidence: ___. Reasoning: ___."
Independent Practice10-15 minutes
Each student writes an explanation from a new invented data set. Wood frogs lay their eggs in spring pools that can dry up in summer, and a tadpole must turn into a froglet before its pool dries. In this population, some tadpoles inherit a faster rate of development than others. Researchers followed 60 fast and 60 slow developers in a dry year, when the pools dried early, and in a wet year, when they stayed full.
Independent practice data (invented): tadpoles that became froglets
Year
Fast developers
Slow developers
Dry year
45 of 60
15 of 60
Wet year
48 of 60
51 of 60
Students find all four probabilities, write one probability statement for each year (for example, "In a dry year, a fast developer is ___ times as likely to become a froglet"), and write a claim, evidence and reasoning paragraph about how development rate affects survival in each kind of year. Ask them to name one thing besides development rate that could differ between the two years.
Closure5 minutes
Exit ticket: "Choose one example from today. Name the inherited trait, the environment, and the two probabilities. Then finish this sentence: The trait increases the probability of ___ because ___." Return to the warm-up caterpillars and ask students to rewrite "will be eaten" as a probability statement.
Differentiation Strategies
For Struggling Students
Give a three-row organizer for each data set: "Number at start", "Number that survived", "Survived ÷ start"
Let students write probabilities as fractions first (36 out of 120) before turning them into decimals
Provide the frame: "In ___, individuals with ___ are ___ times as likely to ___ because ___."
For Advanced Students
Ask students to combine surviving and reproducing in one number, expected offspring per individual, for the coneflower or thistle data
Have students explain why a 3 of 4 survival count is weaker evidence than 75 of 100, even though both give 0.75
Ask students to predict what share of the next generation of voles would have thick fur after two cold winters in a row
Assessment Guidance
What to Look For
Check that students divide survivors by the starting number, not by the other group, and that they compare probabilities with a ratio or a difference and say which one they used. Look for explanations that name the environment and say how the trait works there (it hides the insect, it keeps the vole warm). Listen for students who say an animal "grew" a trait because it needed it, or who treat a probability as a guarantee.
02
Classroom Activities
3 Activities
1
Paper Spinner Seeds: Wing Length in Wind and Calm
25 minutesGroups of 3
Many trees, such as maples, make winged seeds that spin as they fall. Wing length varies from tree to tree and is inherited. A seed that lands far from its parent tree is less likely to grow up in the parent's shade. Groups build paper models of seeds with three wing lengths and find the probability that each lands beyond a line 1 m away, with and without wind.
Procedure
Cut three strips of copy paper 3 cm wide. Make spinners with wings 5 cm, 8 cm and 11 cm long: cut each strip down the middle to make two wings, fold the wings in opposite directions and clip one small paper clip to the bottom as the seed.
Tape a start mark on the floor and a line 1 m away from it. Place a desk fan on low at the start mark, pointing toward the line.
One student stands at the start mark, holds the spinner at shoulder height and lets go. Drop each spinner 10 times and count how many drops land past the line.
Repeat with the fan off.
Safety: keep fingers and paper away from the fan blades, stand on the floor (no chairs) and handle scissors with care.
Sample Data (invented)
Drops that landed past the 1 m line, out of 10. Fan on: 5 cm, 2; 8 cm, 5; 11 cm, 8. Fan off: 5 cm, 0; 8 cm, 1; 11 cm, 1.
Discussion Questions
With the fan on, which wing length had the highest probability of landing past the line? How many times as likely was it as the 5 cm wing?
With the fan off, no wing length landed past the line more than 1 time in 10. What does that tell you about the environment the advantage depends on?
Wing length is inherited. Use your data to explain why trees with longer-winged seeds might have more offspring in a windy, open field.
Challenge Variation
Groups predict, then test, whether doubling the paper clips (a heavier seed) changes the probability for the 11 cm wing. They write one sentence about why a heavier seed might still be an advantage in a different environment, for example where seedlings need stored food.
2
Same Trait, Different Place: Data Card Pairs
20 minutesGroups of 4
Each group gets 8 cards that form 4 pairs. Both cards in a pair show the same inherited trait in two environments (all counts invented). Groups match the pairs, compute the probabilities and write one probability statement for each card.
The Four Card Pairs
Sulphur butterflies, dark or pale wings. Dark wings warm up faster in sunlight. Cold mountain meadow: females that laid eggs, dark 32 of 40, pale 20 of 40. Warm lowland: dark 26 of 40, pale 34 of 40.
Young pine trees, thick or thin bark. Forest with frequent ground fires: survived 10 years, thick 54 of 60, thin 21 of 60. Forest without fires: thick 50 of 60, thin 52 of 60.
Dune plant, large or small seeds. Dunes where blowing sand buries seeds deeply: seedlings that came up, large 33 of 50, small 9 of 50. Firm soil with no sand burial: large 40 of 50, small 43 of 50.
Wild mustard, hairy or smooth leaves. Field with leaf-eating beetles: plants that made seeds, hairy 42 of 60, smooth 24 of 60. Field without the beetles: hairy 48 of 60, smooth 54 of 60.
Discussion Questions
In every pair, the form with the higher probability in one environment had the lower probability in the other. Check this with your numbers.
In which card does one form have the largest advantage, measured as times as likely? What about the environment makes the advantage so large?
Pick one pair and explain how the trait works in each environment: what does it protect the organism from, or help it do?
Modification for Mixed Groups
Give each student one card of a pair. Partners must find each other by matching the trait, then compare their probabilities before writing the group statement.
3
Critique Corner: Which Explanation Is Strongest?
15 minutesPairs, then whole class
Arctic foxes come in two inherited coat colors: white in winter, or a dark "blue" coat all year. Pairs read invented data and three sample explanations, rank them and rewrite the weakest one.
Data (invented)
Adult foxes that raised pups in one year. Rocky coast with little winter snow: blue 18 of 30, white 9 of 20. Snowy inland highlands: blue 6 of 20, white 15 of 30.
Sample Explanations
Explanation A: "Blue foxes are better than white foxes."
Explanation B: "Foxes on the coast turn blue because they need to hide on dark rocks, and then their pups are blue too."
Explanation C: "Coat color is inherited. On the coast, 0.6 of blue foxes raised pups compared with 0.45 of white foxes, and inland 0.5 of white foxes did compared with 0.3 of blue foxes. A coat that matches the ground makes it easier to sneak up on prey, so the matching color raises the chance of raising pups in each place."
Discussion Questions
Which explanation uses evidence? Which one gives a reason the trait matters?
Explanation B says the foxes change because they need to. Why is that not how inherited variation works?
Rewrite Explanation A so that it names the environment and uses one probability from each place.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Survival of Two Stick Insect Forms on Two Shrubs
Invented counts based on a pattern found in real field studies of Timema stick insects, drawn to scale. The striped form is more likely to survive on chamise and the plain form on ceanothus: the same inherited trait helps in one environment and hurts in the other.
Diagram 2: A Model of Fur Thickness in a Cold Winter
Invented model from the worked examples. Thick fur doubles the probability of surviving a cold winter, so thick-fur mothers raise 2/3 of the young even though they were only 1/2 of the population in autumn.
04
Homework Assignment
~30 min
MS-LS4-4 Homework: Traits, Chances and Explanations
Directions: All data sets are invented for practice. Show each calculation, round probabilities to two decimal places, and write explanations that name the inherited trait, the environment, the evidence and the reason.
Part 1: Probabilities From Data (Problems 1-3)
Eastern gray squirrels inherit either gray or black fur. In a city with very cold winters, researchers followed 40 black and 80 gray squirrels through one winter: 34 black and 56 gray squirrels survived. (a) Find the probability of surviving for each color. (b) By how many percentage points is the black squirrels' probability higher? (c) Black fur may help a squirrel lose body heat more slowly. Use your numbers to explain how the trait affects survival in this city.
Male fireflies flash to attract females, and flash brightness is inherited. In Meadow 1, with no predators that hunt by light, 24 of 60 bright males and 12 of 60 dim males mated. In Meadow 2, a predatory firefly hunts males by their flashes, and 9 of 60 bright males and 12 of 60 dim males mated. (a) Find all four probabilities. (b) Which trait has the advantage in each meadow? (c) Explain why the advantage depends on the meadow.
In a drought year, a young sunflower with long roots has a 0.8 probability of surviving, and one with short roots has a 0.45 probability. A field starts with 200 long-root and 200 short-root seedlings. (a) How many of each are expected to survive? (b) What fraction of the survivors have long roots? (c) Explain why this matters for the seeds the field makes that year.
Part 2: Building and Fixing Explanations (Problems 4-6)
Some seedlings of a roadside grass inherit the ability to grow in salty soil. Near a road salted every winter, 42 of 60 salt-tolerant and 12 of 60 non-tolerant seedlings survived. Far from the road, 48 of 60 salt-tolerant and 51 of 60 non-tolerant seedlings survived. (a) Find the four probabilities. (b) How many times as likely is a salt-tolerant seedling to survive near the road? (c) Write a full claim, evidence and reasoning explanation for both places.
A student wrote: "Cactus plants in the desert grew more spines because they needed protection from animals, and then they passed the new spines to their seeds." Data (invented): where javelinas (wild pig-like animals) feed, 36 of 40 very spiny cacti and 16 of 40 less spiny cacti survived 5 years. (a) Name two problems with the student's explanation. (b) Find both probabilities. (c) Rewrite the explanation using the words inherited, variation and probability.
Some common garter snakes inherit an all-black body and some inherit a striped one. Black skin absorbs more sunlight, so a black snake warms up faster. Plan an investigation to find whether black snakes have a higher probability of surviving and reproducing in a cool, cloudy place than in a warm, sunny place. (a) Describe your groups and the two environments. (b) What will you count, and how will you turn the counts into probabilities? (c) Why should each group contain many snakes, not 4? (d) Describe a result that would support the claim.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Probabilities
Each probability is survivors (or reproducers) ÷ number at the start, correct and rounded, with comparisons stated as times as likely or percentage points
Most probabilities correct, or the comparison is not named
Trait and Environment
Names the inherited trait and the specific environment, and says which form has the advantage there
Names the trait but not the environment, or the reverse
Reasoning
Explains how the trait changes the chance of surviving or reproducing in that place, without saying organisms change because they need to
Reason given but vague, or it treats a probability as a certainty
Investigation Plan (Problem 6)
Two environments, large groups, counts turned into probabilities and a result that would support the claim
Plan missing one of these parts
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data sets are invented. For each question, find what was counted at the start and what was counted at the end, then compare. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which of these is an example of genetic variation in a population?
Answer: B
Genetic variation means individuals inherit different versions of a trait, and beak length passed from parents fits. Choice A is learned behavior, choice C is a response to the surroundings, and choice D is a repair during the lizard's life; none of them is inherited.
Question 2 of 20 · Multiple Choice
Invented data: of 24 tree seedlings with waxy leaves, 18 survived a dry month. What is the probability that a waxy-leaved seedling survived?
Answer: C
18 ÷ 24 = 0.75. Choice A treats the 18 survivors as if they were out of 100. Choice B is 6 ÷ 24, the probability of dying. Choice D divides the wrong way, 24 ÷ 18 ≈ 1.33, and a probability can never be greater than 1.
Question 3 of 20 · Multiple Choice
On pale sand dunes (invented data), a pale grasshopper has a 0.6 probability of surviving the summer and a dark grasshopper has a 0.2 probability. Which statement is correct?
Answer: B
0.6 ÷ 0.2 = 3, so a pale grasshopper is 3 times as likely to survive. Choice A uses the difference, 0.6 - 0.2 = 0.4, which is 40 percentage points, not a "times as likely" ratio. Choice C swaps the two forms. Choice D repeats the pale grasshopper's own probability instead of comparing the two.
Question 4 of 20 · Multiple Choice
A caterpillar with eyespots (spots that look like large eyes) has a 0.8 probability of surviving a week of bird hunting. What does this mean?
Answer: D
A probability describes what happens on average in a large group: about 8 out of every 10 caterpillars with eyespots are expected to survive, and some still get eaten. Choice B treats a probability as a certainty. Choice C is too exact: in a small group of 10, the count could be 6, 7, 9 or another number. Choice A confuses a probability with a number of days.
Question 5 of 20 · Multiple Choice
Why can the same inherited trait raise the probability of surviving in one environment and lower it in another?
Answer: A
A trait works by interacting with its surroundings: a stripe hides a stick insect among thin leaves but shows up on broad ones. Choice B and choice C both describe organisms changing because of need, which is not how inherited variation works. Choice D is not supported by any of the data.
Question 6 of 20 · Multiple Choice
In a dry year, a desert shrub seedling with a long taproot (a deep main root) has a 0.35 probability of surviving. Out of 400 seedlings with long taproots, about how many are expected to survive?
Answer: D
0.35 × 400 = 140. Choice A reads 0.35 as 35 seedlings. Choice B is the number expected to die, 400 - 140 = 260. Choice C divides instead of multiplying, 400 ÷ 0.35 ≈ 1,143, which is more seedlings than the field had.
Question 7 of 20 · Multiple Choice
A student says: "Polar bears became white because they needed to hide on the snow." Which revision fits the science of this lesson?
Answer: C
The scientific idea is that bears inherited different fur colors, and in a snowy environment the lighter ones had a higher probability of hunting successfully and raising cubs that inherited the color. Choice A gives the bears a choice, choice B describes a change during one bear's life, which is not inherited, and choice D ignores the variation that existed in their ancestors.
Question 8 of 20 · Multiple Choice
Long-tailed widowbirds: females prefer males with longer tails. On a windy island (invented data), a long-tailed male has a 0.5 probability of surviving to the breeding season and then raises about 6 chicks; a short-tailed male has a 0.8 probability and raises about 3 chicks. Which form is expected to leave more chicks per male?
Answer: C
Expected chicks = probability of surviving × chicks raised. Long-tailed: 0.5 × 6 = 3. Short-tailed: 0.8 × 3 = 2.4. The long tail lowers survival but raises reproduction enough to win. Choice B looks only at survival. Choice A swaps the two results. Choice D ignores the short-tailed male's survival probability and counts its 3 chicks as certain.
Question 9 of 20 · Multiple Choice
Two students test whether dark-shelled beach snails survive better than light-shelled ones on dark rocks. Student 1 follows 4 snails of each color. Student 2 follows 100 of each. Why is Student 2's evidence stronger?
Answer: D
In a group of 4, one lucky or unlucky snail moves the probability by 0.25, so the result may come from chance. With 100 snails, chance evens out more. Choice A overstates it: large groups give similar results, not identical ones. Choice B invents a difference that was not described. Choice C is impossible: a probability is never greater than 1.
Question 10 of 20 · Multiple Choice
A gardener feeds some rose bushes extra fertilizer, and they grow more flowers. Why is this NOT an example of the kind of explanation MS-LS4-4 asks for?
Answer: A
MS-LS4-4 is about genetic variation: inherited differences that change the chance of surviving and reproducing. Extra fertilizer is an environmental effect, and the seeds would not inherit it. Choice B is false, since roses make seeds. Choice C is not true, and choice D does not change what kind of cause it is.
Question 11 of 20 · Multiple Choice
Which evidence would best support the claim "a waxy leaf coating increases a plant's probability of surviving a drought"?
Answer: A
To show that a trait changes the probability, you need both forms of one species in the same environment, and the environment must be the one in the claim. Choice B uses the wrong environment and only one form. Choice C has no counts at all. Choice D has no waxy plants to compare with.
Question 12 of 20 · Multiple Choice
Invented data: in a cold spring, 60 of 100 dark crickets and 20 of 100 light crickets survived. What percent of the survivors are dark?
Answer: D
There are 60 + 20 = 80 survivors, and 60 ÷ 80 = 0.75 = 75%. Choice C is the probability that a dark cricket survived, 60 ÷ 100, not the share of the survivors. Choice A divides by all 200 crickets at the start, 60 ÷ 200. Choice B divides 20 by 60, comparing the two survivor counts instead of using the total.
Question 13 of 20 · Multiple Choice
A desert shrub inherits either gray, hairy leaves or green, smooth leaves. Invented data on plants that set seed: open hot desert, gray 30 of 50, green 15 of 50; shaded canyon, gray 20 of 50, green 35 of 50. Which statement is supported?
Answer: B
Open desert: 30 ÷ 50 = 0.6 and 15 ÷ 50 = 0.3, and 0.6 ÷ 0.3 = 2, so gray leaves are twice as likely. Canyon: gray 0.4 and green 0.7, so green wins there; that rules out choice A and choice D. Choice C swaps the two forms.
Question 14 of 20 · Multiple Choice
A student's explanation says: "Claim: thick bark helps oak seedlings survive fires. Evidence: 45 of 50 thick-bark seedlings survived a fire, but only 20 of 50 thin-bark seedlings did." What part is missing?
Answer: A
The student has a claim and evidence (0.9 against 0.4), but no reasoning that links them, such as "thick bark keeps the heat of the fire away from the living layer under it". Choice B and choice C are already present. Choice D is not needed for a complete explanation.
Question 15 of 20 · Short Answer
Invented data: in a meadow grazed by deer, 36 of 60 hooked seeds (seeds with tiny hooks that stick to fur) were carried more than 10 m from their parent plant, and 6 of 60 smooth seeds were. Find both probabilities and explain how the hooks could help the parent plant have more offspring.
Hooked: 36 ÷ 60 = 0.6. Smooth: 6 ÷ 60 = 0.1, so a hooked seed is 6 times as likely to be carried far. Seeds carried away from the parent compete less with it for light and water and can reach open ground, so plants that inherit hooked seeds have a higher probability of having offspring that grow up. The advantage depends on deer being there to carry the seeds.
Question 16 of 20 · Short Answer
Invented model: a population has 40 brown and 40 gray beetles. Brown beetles have a 0.75 probability of surviving to breed and gray beetles 0.25. Each survivor has 10 offspring that share its color. How many offspring of each color are expected, and what fraction are brown?
Brown survivors: 0.75 × 40 = 30, so 30 × 10 = 300 brown offspring. Gray survivors: 0.25 × 40 = 10, so 10 × 10 = 100 gray offspring. Brown offspring are 300 ÷ 400 = 3/4 of the total, even though brown beetles were 1/2 of the parents.
Question 17 of 20 · Short Answer
Invented data on sea grass shrimp, clear or dark-striped bodies. Over clean sand, 70 of 100 clear shrimp and 40 of 100 striped shrimp escaped fish. In a sea grass bed, 45 of 100 clear and 80 of 100 striped shrimp escaped. Write a claim, evidence and reasoning explanation.
Claim: the shrimp form with the higher probability of escaping depends on the environment. Evidence: over sand, clear shrimp 0.70 against striped 0.40; in sea grass, striped 0.80 against clear 0.45. Reasoning: body color is inherited, and a shrimp that matches its background is harder for fish to see, so clear shrimp are more likely to survive over pale sand and striped shrimp among the stripes of the grass blades.
Question 18 of 20 · Short Answer
Rosa says: "Only 2 of 3 spotted frogs survived and 3 of 3 plain frogs survived, so plain skin is better." Give two reasons her conclusion is weak, and say what evidence would be stronger.
First, the groups are tiny: one frog more or less changes a probability by about 0.33, so the difference may be chance. Second, she does not say which environment the frogs lived in, and an advantage can depend on the place. Stronger evidence: many frogs of each form (for example 100), followed in the same environment, with the probabilities compared.
Question 19 of 20 · Short Answer
Invented data: in a dry season, a seed-eating bird with a thick bill has a 0.65 probability of surviving. Explain what this probability statement does and does not tell you about one thick-billed bird.
It tells you that out of many thick-billed birds in a dry season, about 65 in 100 (roughly 2 in 3) are expected to survive, so a thick-billed bird has a better than even chance. It does not tell you what will happen to any single bird: that one could still starve or be caught by a hawk. Probability describes a large group, not a promise to one individual.
Question 20 of 20 · Short Answer
Use the invented vole model (Diagram 2), but with a less severe winter: 45 of 50 thick-fur and 25 of 50 thin-fur females survive, and each survivor again raises 4 young. What fraction of the young have thick-fur mothers? Compare it with the cold-winter result and explain the difference.
Young: 45 × 4 = 180 and 25 × 4 = 100, so 180 ÷ 280 = 9/14, about 64%. That is a little less than the 2/3 (about 67%) after the cold winter. Here thick fur raises the chance of surviving 0.9 ÷ 0.5 = 1.8 times, not 2 times, so the advantage, and the shift toward thick-fur young, is smaller. How much a trait matters depends on how harsh the environment is.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-LS4-4 mean?
MS-LS4-4 asks students to explain, using evidence, how inherited differences in a trait give some individuals in a population a better chance of surviving and reproducing in a particular environment. The code means Middle School, Life Science, core idea 4 (Biological Evolution: Unity and Diversity), performance expectation 4.
What grade level is MS-LS4-4?
It is a middle school standard for grades 6-8, usually taught in grade 7 or 8 life science. It often comes in a unit on evolution, after heredity and before the standards on how populations change over time.
What math do students need for MS-LS4-4?
Students need simple probabilities and ratios. The Clarification Statement puts the emphasis on "simple probability statements and proportional reasoning". In practice, that means dividing survivors by the starting number, comparing two probabilities ("twice as likely") and multiplying a probability by a group size to find an expected count.
What is the difference between genetic variation and other differences?
Genetic variation is passed from parents to offspring; other differences come from an individual's life. A stick insect's stripe is inherited, but a bird's broken feather or a well-fed plant's extra leaves are not. Only inherited differences can be passed on to the next generation, which is why the standard focuses on them.
Does a trait that helps survival always help?
No: an advantage depends on the environment. A stripe hides a stick insect on needle-like leaves but makes it easier to spot on broad leaves. Tall flower stalks attract more bees but snap on a windy hill. Students should always name the environment when they say a trait is an advantage.
Why does the standard mention reproducing and not only surviving?
Because a trait matters for the next generation only if its owner leaves offspring. Some traits help mainly with reproducing, such as flashes or long tails that attract mates, and they can even lower survival. The useful measure combines both: the probability of surviving times the number of offspring.
What are common mistakes students make on MS-LS4-4?
A frequent mistake is saying an organism changed a trait because it needed to. Others are dividing by the wrong number, treating a probability as a guarantee, forgetting to name the environment, and drawing a conclusion from a group of 3 or 4 individuals.
How is MS-LS4-4 different from MS-LS4-6?
MS-LS4-4 looks at one generation: how a trait changes an individual's chance of surviving and reproducing. MS-LS4-6 follows a population over many generations and uses math to show traits becoming more or less common. Natural selection, the process in which inherited traits that help survival and reproduction become more common over generations, connects the two.
Is it OK to teach evolution in this lesson?
Yes: MS-LS4-4 is part of the NGSS core idea on biological evolution, which is established science supported by many lines of evidence. This standard gives students the first step of the explanation, using data from real kinds of organisms, and the later standards build on it.
How can parents help with MS-LS4-4 at home?
Parents can ask "how likely?" questions about nature. For example, in a park, ask which color of insect or seed would be easiest for a bird to find, and why it might be different on another kind of ground. Asking a child to say "about 3 out of 4" instead of "always" builds the probability habit.
07
Related Standards
5 standards
These standards connect to MS-LS4-4: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
3-LS4-2Prerequisite
Explain how variations among individuals can help in surviving, finding mates and reproducing
Lesson coming soon
7.SP.C.5Prerequisite
Understand probability as a number from 0 to 1 that shows how likely an event is
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