Unit 7 · Topic 7.8 end-of-topic test
Suggested time: about 44 minutes. Answer everything, then press Submit the test to see the feedback and scoring guides.
Biologists compare 100 adult songbirds collected in one valley in 1932 with 100 collected there in 2024. The table gives the mean bill depth and the frequency of one allele at each of two genes in each sample.
Which conclusion do the data support?
A wildlife park breeds pelicans and keeps almost every chick alive to adulthood. A keeper says: “These pelicans have stopped evolving, because almost every chick survives.”
Is the keeper correct?
Biologists group the evidence that evolution continues today into four kinds. Researchers read one stretch of DNA from 20 preserved beetles of one island population in each of three years, as the table shows.
Which kind of evidence is this case?
Which of the following observations is the evolution of resistance?
Researchers grow a bacterium in a flask and give it two courses of one antibiotic. After each course they move the survivors to fresh broth and let them regrow. The table gives the counts of all cells and of resistant cells.
Which statement explains the change in the counts?
The graph shows the share of resistant cells in one flask of bacteria over ten generations with a low dose of an antibiotic.
Between which two generations did the share rise the most?
The table compares four pathogens: how many are in one infected person, how long one generation takes, and how many copying errors each copy of its genes carries.
Which pathogen would most quickly produce a variant that escapes a drug?
Health officers list four diseases of people in one country, as the table shows.
Which disease is an emergent disease?
A stomach virus spreads through two towns in one winter. In the first town most people had the same virus the winter before, so their blood carries antibodies that bind that virus’s surface protein. In the second town few people had it. In both towns a variant with a changed surface protein appears.
In which town does the variant become the common form sooner, and why?
The greenkeepers of a golf course want resistance to a new fungicide to rise as slowly as possible in the fungus that attacks their turf.
Which policy would do that?
Two cotton farms spray the same insecticide against a caterpillar that eats cotton bolls. One farm sprays every week; the other sprays every fourth week. The graph shows the share of each farm’s caterpillars that survive the insecticide, year by year.
Which farm sprays every week, and what in the graph shows it?
A student wants to know what share of the leafhoppers on a rice farm carry an allele for surviving a pesticide. The day after the farm sprays, she collects 50 leafhoppers from the sprayed field and finds that 47 carry the allele. She reports that 94% of the farm’s leafhoppers carry the allele.
What is the flaw in her study?
A student estimated the share of a valley’s leafhoppers that carry an allele for surviving a pesticide. She read the allele in 40 leafhoppers that had hatched from the eggs laid on one rice plant: 30 carried it.
Which study would give a better estimate of the share in the valley’s leafhopper population?
A biologist counts the cells of a bacterium in a jar of rainwater each day for four days. Each day’s count is ten times the day before’s, from 300 cells per mL on day 0 to 3,000,000 cells per mL on day 4. She plots the counts on a log scale.
What does her graph look like?
A technician counts the cells of a bacterium in a vat of fermenting cabbage each day. The graph plots the counts on a log scale; its minor gridlines sit at 2, 3 and 5 times each mark.
What is the count on day 3?
A student counts the cells of a bacterium in a bowl of soup left out at room temperature, once a day: 70, 500, 4,000 and 25,000 cells per mL on days 0 to 3. She plots the four counts on a log scale, as the graph shows.
Which day’s point has the student placed at the wrong height?
(a) Identify the count of all cells at 12 hours, and state the mark or gridline at which you read it. (1 point)
A full-credit answer: All cells at 12 hours: 3,000,000 cells per mL.
The point sits on the second minor gridline above the 1,000,000 mark, which is 3 times that mark: the 3,000,000 gridline.
Check the box for each point your answer earns
(b) At 16 hours the flask held 10,000,000 cells per mL, of which 8,000,000 were resistant. Calculate the percentage of the cells that were resistant at 16 hours. (1 point)
Write down the values in the question:
resistant cells at 16 hours = 8,000,000 per mL
all cells at 16 hours = 10,000,000 per mL
Write down the equation:
Substitute the values into the equation:
A full-credit answer: 8,000,000 of the 10,000,000 cells per mL were resistant.
8,000,000 ÷ 10,000,000 = 0.80, which is 80%.
(c) Describe how the share of the cells that were resistant changed between 8 and 12 hours. Use the graph. (1 point)
A full-credit answer: At 8 hours about 150,000 of the 1,000,000 cells per mL were resistant: about 15%.
At 12 hours about 2,000,000 of the 3,000,000 cells per mL were resistant: about 67%.
So the resistant share rose from about 15% to about 67%.
Check the box for each point your answer earns
Common slip: Giving the two resistant counts alone, without turning each into a share of all the cells.
(d) Determine whether the antibiotic created the allele for resistance or selected an allele already present. Support your answer with evidence from the graph. (1 point)
A full-credit answer: The antibiotic selected an allele already present.
At 0 hours, before the antibiotic was added, about 400 cells per mL already survived a full dose: the point sits between the 300 and 500 gridlines.
So the allele was in the flask before the drug.
The drug then killed cells without the allele, and the cells with it divided, so their share rose.
Check the box for each point your answer earns
(a) Describe two features of the virus population that let it produce variants quickly. (1 point)
A full-credit answer: The virus population is huge: an infected person carries millions of copies.
Its generations are short: a copy is made within hours.
It mutates often: each copying of its genes brings copying errors.
Any two of these.
Check the box for each point your answer earns
(b) Explain how the antibodies of the people who recovered act as a selective pressure on the virus population, and why a variant with a changed surface protein spreads among them. (1 point)
A full-credit answer: Their antibodies bind the first year’s surface protein, and the body destroys the viruses they bind.
The antibodies fail to bind a variant whose surface protein has a changed shape, so that variant survives in them.
The variant copies itself and spreads; the first year’s form is destroyed.
So the antibodies sorted the variants: natural selection with immunity as the selective pressure.
Check the box for each point your answer earns
(c) Predict whether a variant with a changed surface protein has an advantage over the first year’s form among people who stayed healthy through the first year, and give the reason. (1 point)
A full-credit answer: No advantage.
Those people have no antibodies against either form.
So the first year’s form and the variant infect them alike, and neither is favored.
Check the box for each point your answer earns
(d) Evaluate whether the evidence supports classifying this disease as an emergent disease, and identify one further piece of evidence a health officer would need. (1 point)
A full-credit answer: The evidence supports it.
No one around the lake had had the disease before, so it appeared in a population for the first time.
Its cases rose from 12 to 900 in a year, and it was reported around two other lakes: rising fast and spreading into new places.
A health officer would still need the virus’s gene sequence from patients at the other lakes, to show that the same changed virus causes the cases there.
Check the box for each point your answer earns