Practice questions · Topic 7.3

Unit 7 · Practice for the Topic 7.3 end-of-topic test

You’ve gone through everything in this topic. The summary video below recaps it all, so you’re ready for the questions.

Watch first: Artificial selection, summed up

Video coming soon

Who chooses the parents; the trait rises and variation falls; a histogram from a list of measurements; a box plot’s box and whiskers; describing data as a point, a trend, a relationship.

These are practice questions in the shape of the topic test. Work through them before you take the test; every question tells you what it wanted.

Answer every question. For each multiple-choice question, pick one option and press Check; the feedback gives the reasoning. For the free-response questions, write one short sentence for each step of your reasoning, each on its own line, and make every link clear (so, because, therefore). That is what the exam’s ‘paragraph form’ means for you: linked sentences, not bullet points. The first free-response question walks you through one investigation one part at a time, and you can open a hint for each part; the second is at the level of the test. When you finish a question, open the scoring guide and mark your own work against it.

Question 1

A coral hatchery’s two groups: how the parent colonies were chosen and the percent of their young surviving a 31 °C trial.

A coral hatchery’s staff choose the 12 adult colonies that came through an earlier 31 °C heat trial in the best condition, and breed from them. For comparison, they also breed from 12 colonies chosen at random from the same reef. They rear all the young at 27 °C for six months and then test the young at 31 °C. The table shows the results.

Which step in the hatchery’s work makes the breeding group a case of artificial selection?

A. Rearing all the young at 27 °C for six months before the trial B. Choosing the comparison group’s parent colonies at random C. Testing all the young at 31 °C after the six months D. Choosing the parent colonies by their condition after the heat trial

Question 2

A salt tide floods a farmer’s rice field and kills the plants that cannot stand salt. The surviving plants set seed, and the farmer sows every survivor’s seed the next spring.

Which kind of selection sorted the rice plants?

A. Artificial selection B. Both kinds of selection C. Natural selection D. Neither kind of selection

Question 3

A duck line bred from high-laying ducks only: the percent of young ducks laying 250 eggs or more a year, in years 0 to 3.

A breeder of ducks breeds, each year, only from the ducks that lay 250 eggs or more in a year. The table shows the percent of young ducks that reach 250 eggs a year. The breeder says: “The share rises about 20 points a year, so every duck will reach 250 eggs in two more years.”

Which of the following is the fault in the breeder’s prediction?

A. The rises shrink each year, so two more years leave the share below 100% B. The rises grow each year, so every duck reaches 250 eggs after one more year C. The share cannot rise past 69% D. The share will fall once most ducks reach 250 eggs

Question 4

A grower keeps seed only from the ten sweetest of thirty melon plants for six generations, pulling up the other twenty before they flower. A student says: “If the grower then keeps seed from all thirty plants for six more generations, the alleles the line lost will come back.”

Is the student correct, and why?

A. Yes: keeping seed from all thirty plants lets every allele pass on again B. Yes: the less sweet plants still carry the lost alleles hidden C. No: the lost alleles return only if the grower keeps the least sweet plants D. No: no plant in the line carries a lost allele, so no plant can pass it on

Question 5

A bean line bred from the longest-podded plants: mean pod length in centimeters against generation.

The graph below shows a bean line’s mean pod length in centimeters against generation, for a line bred from the longest-podded plants. A student describes the graph: “The mean pod length changed over the generations. In generation 5 it was 11.1 cm.”

Which of the following is missing from the student’s description?

A. The direction of the change B. The variable that changed C. The two variables the graph relates D. A value with its unit

Question 6

A student has four sets of measurements.

For which set of measurements would the student make a histogram?

A. The mean height of one tray of plants at each of six generations B. The number of plants of each of four flower colors in a field C. The mean mass of the eggs laid by each of three hen breeds D. The shell lengths of 40 mussels from one rock, each mussel measured once

Question 7

A student’s box plot of eleven seedling heights, drawn below the table of the eleven heights in order.

A student measures the heights of eleven seedlings, puts them in order in the table, and draws the box plot below from them.

Which of the following is the fault in the drawing?

A. The median line is in the wrong place B. The box reaches the smallest and the largest height instead of the quartiles C. The axis carries no unit D. The line inside the box should be at the mean height, 10.7 cm

Question 8

A grower saves seed only from marigolds with flowers of middle width each generation: the five widest-flowered and the five narrowest-flowered of thirty plants are pulled up before they set seed.

After six generations, which change would box plots of generation 0 and generation 6 most likely show?

A. The center moved up and the box narrowed B. The center stayed the same and the box narrowed C. The center stayed the same and the box widened D. The center moved down and the box widened

Question 9

Heights of the 40 plants of generation 4, to the nearest centimeter, in five 4 cm bins.

A class breeds a line from its tallest plants. In generation 0, 6 of the 40 plants were 30 cm or taller. The histogram shows the heights of the 40 plants of generation 4.

How many more plants are 30 cm or taller in generation 4 than in generation 0?

A. 6 B. 14 C. 16 D. 22

Question 10

A fish farm’s two ponds: the feed each group received and the mean length of the parents and of their offspring.

A fish farmer wants longer fish. Pond A’s fish get high-nutrient feed and Pond B’s get standard feed. The farmer breeds from the longest fish in Pond A and rears their offspring, and offspring of Pond B fish, on standard feed. The table shows the results.

Which of the following explains why the offspring of the chosen Pond A fish grew to about the same length as the offspring of the Pond B fish?

A. Artificial selection needs at least five generations before any change shows B. The standard feed caused mutations that made the offspring small C. The Pond A fish were long because of their feed, not their alleles D. The offspring inherited a recessive allele for small size that the parents hid

How to tackle the free-response questions. Read the verb first: describe asks what you see or know; explain asks why or how, so name the mechanism; predict asks what will happen and why; justify asks for the evidence that supports a claim. Each point is earned by one idea, stated in a sentence that names the thing and the mechanism. Extra words earn nothing; a wrong extra can lose the point. If there is a figure or table, use what it shows. When you finish, check the box for each point your answer earns and compare your sentences with the full-credit answer.

Free response 1 · Scientific Investigation · 5 points

A company that supplies moths as pollinators for cool greenhouses keeps two lines of one moth from the same starting stock. Every generation, technicians chill each adult at 8 °C for one hour and score it active or inactive ten minutes after warming. In line C they breed only from the moths scored active. In line R they breed from moths picked at random, whatever their score. Both lines get the same food, light and temperature. The table shows the percent of adults scored active in each generation.

Two moth lines from one stock: the percent of adults scored active after chilling, in generations 0 to 4.

(a) Identify who chooses which moths breed in line C. (1 point)

Hint: Who decides which moths go into the breeding cages?

A full-credit answer: In line C, the technicians choose the breeders.

Check the box for each point your answer earns

the technicians (the company’s people) choose the breeders. Accept with or without the trait they choose for, staying active after chilling.

Common slip: Naming the cold as the chooser. The cold gives each moth a score; the technicians decide which moths breed.

(b) Identify line C’s percent of active adults in generation 4. (1 point)

Hint: Find the generation-4 row and read line C’s column.

A full-credit answer: In generation 4, 77% of line C’s adults were scored active.

Check the box for each point your answer earns

77%.

Common slip: Reading line R’s column, 45%. Line C is the first column of results.

(c) Describe how the percent of active adults changed across the generations in line C, and how line R’s compares. (1 point)

Hint: Name the direction for line C, compare each rise with the one before it, and say what line R did.

A full-credit answer: In line C the percent rose from 45% to 77%, by less each generation: 13, 9, 6, then 4 points.
In line R the percent stayed near 45%.

Check the box for each point your answer earns

line C’s percent rose (from 45% to 77%) and line R’s stayed near 45%. Accept with or without: the rises shrank each generation.

Common slip: Writing that line C ‘changed’. Name the direction: it rose.

(d) Predict line C’s percent of active adults in generation 5, to the nearest 1%. (1 point)

Hint: How big was the last rise, and is the next one bigger or smaller?

Read the last two rows:

generation 3: 73%

generation 4: 77%

Find the rises so far:

13, 9, 6, 4 points

each rise smaller than the last

Predict the next rise and add it:

next rise = about 3 points

prediction for generation 5 = about 80%

A full-credit answer: About 80% of line C’s adults will be scored active in generation 5.

(e) Explain, in terms of alleles, why the size of each generation’s rise in line C’s percent of active adults differed from the one before. (1 point)

Hint: Think about how many moths still carry alleles for staying inactive by generation 4.

A full-credit answer: Each generation, more of line C’s moths already carry alleles for staying active after chilling, so fewer moths carry alleles for staying inactive.
Choosing only active moths removes alleles for staying inactive, and each generation there are fewer of them left to remove.
So each generation’s choosing adds fewer percentage points.

Check the box for each point your answer earns

fewer alleles for staying inactive remain each generation, so choosing removes fewer of them and the percent changes by less.

Common slip: Writing that the moths ‘got used to the cold’. No moth changes its own alleles; the share of moths carrying alleles for staying active is what changes.

Free-response score: 0 of 5

Free response 2 · Analyze Data · 4 points

A grower breeds a carrot line, saving seed each generation only from the plants with the longest roots. The box plots show the root lengths, in millimeters, of 40 plants in generation 0 and of 40 plants in generation 4, on an axis with a gridline every 5 mm.

Root length of 40 carrot plants in generation 0 (upper plot) and of 40 plants in generation 4 (lower plot).

(a) Identify the median root length in generation 4. (1 point)

A full-credit answer: The median root length in generation 4 is 85 mm.

Check the box for each point your answer earns

85 mm.

Common slip: Reading the upper quartile, 90 mm, or generation 0’s median, 65 mm. The median is the line inside the lower box.

(b) Identify the generation with the wider spread of root length, and support your answer with data from the box plots. (1 point)

A full-credit answer: Generation 0 has the wider spread.
Its roots range from 40 mm to 95 mm; generation 4’s range from 60 mm to 100 mm.

Check the box for each point your answer earns

generation 0 AND evidence from the plots (the ranges 40–95 mm against 60–100 mm, or the box widths 55–75 mm against 80–90 mm).

Common slip: Giving the box ends as the range. The range runs from whisker end to whisker end.

(c) A student claims: “The grower’s selection made the roots longer and left the plants as varied as before.” Evaluate the student’s claim, using the box plots. (1 point)

A full-credit answer: The first part of the claim is supported: the median moved from 65 mm to 85 mm, so the roots did get longer.
The second part is not supported: the box narrowed from 20 mm wide, 55 to 75 mm, to 10 mm wide, 80 to 90 mm, and the whisker span fell from 55 mm to 40 mm.
So the plants did become less varied.

Check the box for each point your answer earns

the judgement (the second part of the claim is not supported) AND its ground (the box narrowed from 20 mm to 10 mm wide, or the whisker span fell from 55 mm to 40 mm, so variation fell).

Common slip: Judging the claim by the median alone. The claim also says the plants are no less varied; the box width tests that part.

(d) Explain how saving seed only from the longest-rooted plants changed the position of the box between generation 0 and generation 4. (1 point)

A full-credit answer: The plants varied in root length, and root length is heritable.
Each generation, only the longest-rooted plants set the seed, so only their alleles passed to the next generation.
Alleles for long roots made up a larger share each generation.
So more plants grew long roots, and the median and the box moved to longer root lengths.

Check the box for each point your answer earns

only the longest-rooted plants bred, so their alleles for long roots passed on and made up a larger share each generation, so more plants had long roots.

Common slip: Writing that the plants ‘grew longer roots to please the grower’. No plant changes its alleles; the share of plants carrying alleles for long roots is what rose.

Free-response score: 0 of 4

Multiple choice checked: 0 of 10 correct.

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