Unit 8 · Topic 8.7 end-of-topic test
Suggested time: about 48 minutes. Answer everything, then press Submit the test to see the feedback and scoring guides.
Suppose a kind of flowerpecker, a small bird, drinks nectar from deep flowers.
Which of the following is an adaptation?
Suppose a kind of orfe, a river fish, lives in two streams. An allele gives some males bright orange spots. In one stream, large hunting fish eat the orfe; the other stream holds no such hunter. The table below gives the young each kind of male fathers, on average, in each stream.
In which stream are the orange spots an adaptation?
Suppose a kind of medick, a meadow plant, carries an allele K. Plants with two copies of K grow slowly and set few seeds. A stem-boring moth’s caterpillars kill most plants with no copy of K before they flower. Plants with one copy of K set the most seed. The frequency of K has stayed level for forty generations.
Which of the following explains why K stays in the population?
Suppose a kind of water mite, a tiny pond animal, carries an allele V. Mites with one copy of V survive a parasite that kills most mites with no copy; mites with two copies of V grow slowly and leave few young. The graphs below show the frequency of V in four ponds over twelve generations; the x-axis is the generation and the y-axis is the frequency of V. In one pond the parasite died out at generation 4.
In which pond did the parasite die out?
Suppose a juice bottler adds a preservative to its juice to stop yeast spoiling it. After the first batch nearly every yeast cell in the bottling hall is dead, but a few survive, and within a year the hall’s yeast all survive the preservative. A student says: “The preservative made the yeast change so that they could survive it.”
Which of the following observations would show that the student is wrong?
Suppose a council leaves half of a town’s road verges unmown until July and mows the other half every month. Oxlips, spring flowers, are counted on every verge each May for six years, and each verge’s yearly percent change is worked out.
Which of the following is the null hypothesis for the survey?
Suppose four kinds of plant grow on an island.
Which of the following is an invasive species on the island?
Suppose anglers release four kinds of fish from another continent into a large flooded quarry. The table below gives, for each fish, whether its home parasite is present in the quarry lake and whether a native fish there eats the same food.
Which fish is most likely to spread fastest in the quarry lake?
Suppose two similar lakes lie in one valley. A large snail from another continent, which eats water plants, is tipped into the lower lake only. Biologists count four native water plants in both lakes the year the snails arrive and five years later. The table below gives the counts.
Which of the following is the strongest evidence that the snails caused the fall in the lower lake’s native plants?
Suppose a city builds an airport across a stretch of old limestone grassland, and the grassland’s plants and insects lose their habitat. The airport’s aircraft burn fuel and add carbon dioxide to the air.
At which scale does each change act?
Suppose a dye and a solvent wash into a sea inlet from a dye works. Tiny floating animals eat the inlet’s tiny floating plants, small fish eat the tiny animals, and tope, sharks, eat the small fish. The table below gives each chemical’s concentration at each level of the chain.
Which of the following does the table show?
Suppose four chemicals wash into a lake, and a biologist tests each on the lake’s small fish. The table below gives, for each chemical, whether a fish’s cells break it down and whether the fish passes it out in its waste within a few days.
Which chemical’s concentration rises at each trophic level up the lake’s food chain?
Suppose two ponds in one park turn green in the same week. The park’s keepers had measured each pond’s nitrate the week before. In the upper pond the tiny animals that grazed the algae died in a cold snap. A bag of lawn fertilizer split beside the lower pond, and rain washed it in. The table below gives each pond’s nitrate before and during the green week.
In which pond did added nutrients set off the algae’s increase?
Suppose a fishing fleet nets most of the pollack, large hunting fish, from a bank of the sea. Pollack eat the young crabs that shelter among the bank’s rocks.
Predict what happens to the count of young crabs on the bank in the years that follow.
Suppose a new geyser breaks out beside a mountain meadow and floods it with boiling water from deep in the rock, and every plant in the meadow dies. A month later, a week of rain floods the same meadow.
Which kind of event is each flood?
Suppose a landmass splits, and its two halves drift apart for millions of years with a sea between them. Velvet worms, small soil animals, never cross the sea. One group of velvet worm species arose before the split, across the whole landmass. A second group arose on the eastern half long after the split.
Where do the two groups live today?
Suppose a kind of sea fan, a branching animal fixed to the rock, lives along a coast north of the equator. Its larvae settle within a few hundred meters of their parents, and the adults never move. Over forty years the sea along the coast warms, and the sea fan’s range moves north: its southern edge and its northern edge both move north.
Which of the following explains the move?
Suppose brook lampreys, small eel-shaped fish, are counted each spring on twelve stretches of each of four rivers, and each stretch’s yearly percent change is worked out. The plots below show the four rivers.
On which river does the plot show that 75 % or more of the stretches lost lampreys over the year?
Suppose a river trust builds fish passes, ramps that let fish swim past old barriers, on some stretches of two rivers. Sturgeon, large fish that spawn upriver, are counted on every stretch each spring for eight years, and each stretch’s yearly percent change is worked out. The trust says that its fish passes have stopped the sturgeon’s decline, and counts the decline as stopped if the median change is zero or above. The table below gives the medians.
Which of the following is the verdict on the trust’s claim?
(a) Describe the effect that a larger number of species has on how well the sound’s community recovers from a change. (1 point)
A full-credit answer: A community with more species recovers better, and faster, from a change.
With more species, the sound’s energy has other paths when one species fails, so its animals keep food.
Check the box for each point your answer earns
Common slip: Writing that more species means more animals. The point is the recovery: more species, more paths, a better return after a change.
(b) State a null hypothesis for the experiment. (1 point)
A full-credit answer: The water temperature has no effect on the share of herring embryos that survive to hatch.
Check the box for each point your answer earns
Common slip: Writing ‘warmer water lowers survival’. That claims an effect with a direction: an alternative hypothesis.
(c) Justify the scientists’ choice of 8 °C and today’s carbon dioxide level as the lowest settings in the experiment. (1 point)
A full-credit answer: 8 °C and today’s carbon dioxide level are the sound’s conditions today.
So those tanks show how the embryos do now, and the warmer temperatures and the raised carbon dioxide levels are compared against them.
Check the box for each point your answer earns
Common slip: Writing that the coolest temperature is the easiest for the embryos. The point is the comparison: today’s conditions are the baseline.
(d) The scientists claim that a fall in the number of herring will change the whole community of the sound. Provide reasoning to support the claim. (1 point)
A full-credit answer: Many of the sound’s larger fish and seabirds eat herring.
Fewer herring store less energy, so less energy passes up to every level that eats them.
So those populations shrink, some species are lost, and the community’s diversity and resilience fall.
Check the box for each point your answer earns
Common slip: Writing ‘the herring is a keystone species’ and stopping. The point wants the chain: less food, less energy up the web, the levels above shrink.
(a) Identify the median yearly percent change in the song thrush count on the cleared farms of the Ure valley. (1 point)
A full-credit answer: −7 %: the line across the cleared farms’ box in the Ure valley.
Check the box for each point your answer earns
Common slip: Reading the hedged farms’ box, or the edge of the box. The median is the line across the cleared farms’ box.
(b) Identify the valley and the kind of farm with the largest median yearly decline in the song thrush count. (1 point)
A full-credit answer: The cleared farms of the Wharfe valley, with a median of −9 %.
Check the box for each point your answer earns
Common slip: Picking the highest line on the plot. The largest decline is the median furthest below the zero line, −9 %: the cleared farms of the Wharfe valley.
(c) The trust says that if hedgerows are replanted on the cleared farms of the Ure valley, the song thrushes there will stop declining. Evaluate the trust’s claim, using the plots. (1 point)
A full-credit answer: The claim is not supported.
On the Ure valley’s hedged farms the median is −2 %, below zero, so at least half of those farms still lose song thrushes each year.
Hedgerows slow the decline there, from −7 % on the cleared farms, but do not stop it.
Check the box for each point your answer earns
Common slip: Judging the claim supported because the hedged farms do better than the cleared farms. Better is not stopped: the hedged median is still below zero.
(d) Explain why the resilience of the communities on the cleared farms may fall over time. (1 point)
A full-credit answer: Clearing the hedgerows removes the nesting and feeding places of the song thrushes and of the other species that lived in the hedgerows.
Those species are lost, so the farms’ communities hold fewer species.
With fewer species, the energy has fewer other paths when a species fails, so the communities recover less well from the next change.
Check the box for each point your answer earns
Common slip: Writing that the farms are less resilient because they lost the thrushes. The reasoning names the chain: fewer species, fewer paths, a slower return.