End-of-topic test: Responses to the Environment

Unit 8 · Topic 8.1 end-of-topic test

Suggested time: about 48 minutes. Answer everything, then press Submit the test to see the feedback and scoring guides.

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. Then open the scoring guide and mark your own work against it. Where a question needs a critical value, the chi-square table from the formula sheet is printed beside it.

Question 1

An ecologist records where in a meadow the voles feed and how far each vole keeps from the owls’ perch.

Which feature of the study makes it a study in ecology?

A. It asks how the voles interact with the owls and with the meadow B. It is carried out on wild animals in the open rather than in a laboratory C. It counts whole animals rather than measuring their cells D. It watches the voles without handling them

Question 2

Mean tail movements per minute for 30 tadpoles in plain water and 30 in water from a tank that had held crayfish.

A student puts tadpoles into containers of water they cannot see out of and counts each tadpole’s tail movements. Half the containers hold plain water; half hold water taken from a tank that had held crayfish, which eat tadpoles. No crayfish is present. The table gives the results.

Which of the following is the stimulus the tadpoles detected?

A. The opaque walls of the container B. The crayfish in the neighboring tank C. The chemical in the water that had held crayfish D. The tadpoles’ slower tail movements

Question 3

Snails counted on the open rock and in the shaded cracks of one rock face at four times of day, with the surface temperature at each time.

A student counts the snails on one desert rock face four times in a day, on the open rock and in the shaded cracks, and records the surface temperature each time. The table gives the counts.

Which additional observation would show that a behavioral response by the snails caused the change in the counts?

A. The snails in the cracks have a body temperature below the surface temperature at midday B. Snails the student had marked with a dot of paint crawl into the cracks as the rock warms C. More young snails hatch in the cool months than in the hot months D. Snails on the hot open rock make proteins that protect their cells from heat

Question 4

On one winter morning a hare’s blood glucose falls, and snow covers the grass it feeds on. Both changes send the hare to dig for food.

Which of the following describes the two changes?

A. The fall in blood glucose is internal, the snow is external, and both are stimuli B. Only the snow is a stimulus, because the hare can see it and cannot see its blood glucose C. Only the fall in blood glucose is a stimulus, because it is inside the hare’s body D. Both changes are external, because the snow caused the fall in blood glucose

Question 5

A student puts mites into a dish with a damp half and a dry half and films them for ten minutes.

Which of the following observations would show that the mites’ movement is a kinesis?

A. Most of the mites are in the damp half by the end of the ten minutes B. A mite tipped straight onto the damp half stays there C. Every mite is still moving at ten minutes D. The mites crawl faster in dry air than in damp air, in no fixed direction

Question 6

A grower keeps four potted plants of one kind and watches each for a month.

Which of the following observations is photoperiodism?

A. A plant on a shelf leans toward the nearest window B. A plant grows taller in a warm room than in a cool one C. A plant forms flower buds once the nights pass twelve hours D. A plant flowers earlier in a warm spring than in a cold one

Question 7

One desert lizard through a day: the air temperature in the open, where the lizard was, and its body temperature at five times.

A student follows one desert lizard through a day, recording the air temperature in the open, where the lizard is, and its body temperature. The table gives the record.

Which of the following best describes what the move under the shrub at 13:00 does for the lizard?

A. The move warms the lizard’s body further, so it can keep hunting through midday B. The move stops the lizard’s body warming when the air is hottest, so the lizard survives C. The move changes nothing, because the lizard’s body follows the air temperature wherever it sits D. The move gives the lizard the temperature it decided it wanted

Question 8

The share of unharmed aphids that dropped off the leaf within one minute of three kinds of air blowing over them.

Suppose that when a ladybug attacks a pea aphid, the aphid releases a chemical into the air. Researchers blow air over groups of unharmed aphids feeding on a leaf for one minute and count the aphids that drop off the leaf. The table gives the results.

Which of the following is the signal in this exchange between aphids?

A. The attack by the ladybug B. The leaf the aphids are feeding on C. The unharmed aphids dropping off the leaf D. The chemical the attacked aphid releases

Question 9

Female fiddler crabs that approached, out of 20, under four conditions at a male’s burrow.

Suppose that on a mudflat, a male fiddler crab stands at its burrow and waves its one large claw. Researchers record how many of 20 female crabs approach under four conditions. The table gives the results.

Which conclusion about the male’s signal do the results support?

A. A visual signal: a large claw in motion drew the females B. A chemical signal: a scent from the large claw drew the females C. A tactile signal: the male’s touch drew the females D. An audible signal: the sound of the waving claw drew the females

Question 10

One female deer over two weeks: a reproductive hormone in her blood, the scent marks she left per hour, and the males that approached her.

A researcher follows one female deer for two weeks, recording a reproductive hormone in her blood, the number of scent marks she leaves on plants each hour, and the number of males that approach her. The table gives the record.

Which of the following is most likely the cue for the female’s scent-marking?

A. The scent marks on the plants B. The males approaching her C. The rise in the hormone inside her body D. The length of the days

Question 11

Fifty young woodpeckers raised with experienced adults and fifty raised apart from all adults: the share using the tool at six months, and the share surviving to breeding age among the tool users and among the non-users of each group.

On an island, some woodpeckers of one kind use a twig to pry insects from bark. Researchers raise 50 young birds with experienced adults and 50 apart from all adults, record which young use the tool at six months, and follow every bird to breeding age. The table gives the results.

Which conclusion do the results support?

A. Tool use is innate, because every young bird does it whether or not it saw an adult B. The young raised with adults survived better because the adults cared for them, whatever they learned C. Because tool use is learned, selection cannot make it more common D. Tool use is learned from adults, and the young that use it survive to breed more often

Question 12

The R allele frequency in the eggs laid after one season in three enclosures that each started at 0.50.

Shore crickets carry either an R allele or an r allele. When a hawk’s shadow passes, an R cricket darts into a crevice; an r cricket stays in the open. A researcher stocks three enclosures at an R allele frequency of 0.50: hawks with open crevices, hawks with the crevices filled in, and no hawks with open crevices. After one breeding season she measures the R allele frequency in the eggs laid. The table gives the results.

Which of the following explains why the R allele frequency rose only in the enclosure with hawks and open crevices?

A. The hawk’s shadow made the r crickets develop the R response before they bred B. The crickets that darted into crevices survived to breed more often, so more of the eggs carried R C. Darting into a crevice is good for the crickets as a whole, so every cricket in that enclosure took it up D. The crickets decided to hide from the hawks, so every cricket in that enclosure became an R carrier

Question 13

In a troop of baboons, one baboon spends part of the morning feeding time picking ticks from another baboon’s fur.

Which additional observation would show that the grooming is cooperative behavior: that it costs the groomer now and helps another baboon?

A. The groomer eats less that morning, and the groomed baboon carries fewer ticks afterwards B. The groomer swallows every tick it picks, and the groomed baboon scratches as often afterwards as before C. Several baboons in the troop groom at the same moment D. The groomed baboon sits still and lifts its arm as soon as the grooming starts

Question 14

Twenty vampire bats over one year: how many nights each shared its meal and how often a roost-mate fed it on a night it came back with nothing.

Suppose that in a roost of vampire bats, a bat that has fed well sometimes brings up part of its blood meal for a roost-mate that found nothing to feed on. Over a year, researchers record for each of 20 bats how many nights it shared and how often a roost-mate fed it when it came back with nothing. The table gives the results.

Which conclusion do the results support?

A. Sharing a meal is a one-way gift that the giver never gets back B. A bat is fed on a hungry night by chance, whether or not it has shared C. A bat that shares its meal is fed in turn when it comes back with nothing D. A bat that never shares is fed more often, because it keeps its own meals

Question 15

Birds caught in 30 hawk attacks on a flock of 50 feeding together and in 30 attacks on 50 birds feeding scattered, each alone.

A researcher watches hawks attack small birds of one kind on a plain: 30 attacks on a flock of 50 birds feeding together, and 30 attacks on 50 birds of the same kind feeding scattered, each alone. The table gives the number of birds caught.

Which of the following explains why the hawks caught fewer birds from the flock?

A. The birds in the flock are larger and stronger than the scattered birds B. The hawk cannot see a flock of birds against the ground C. Each bird in the flock decides to protect the others, so it stays to warn them D. More eyes in the flock spot the hawk sooner, so the birds fly up before it strikes

Question 16

Chicks that left the nest from 20 nests with helpers and from 20 nests with the helpers removed.

In a wood, young female birds of one kind spend their first year feeding the chicks at their parents’ nest, their own younger brothers and sisters. Researchers remove the helpers from half the nests. The table gives the chicks that left each set of nests.

Which of the following explains how the helping spreads copies of the helpers’ own alleles?

A. Each chick a helper feeds carries a copy of an allele taken from the helper’s body B. The chicks share many of each helper’s alleles, and more of them survive to breed C. The helper is fed by these chicks in later years, so she leaves more offspring herself D. More chicks in the wood is good for the species, so the species keeps the helping

Question 17

The tray from above: 14 millipedes on the damp half and 8 on the dry half after two minutes.

A student tips 22 millipedes into a tray with a damp cloth on one half and a dry cloth on the other. After two minutes 14 millipedes sit on the damp half and 8 on the dry half, as drawn below. The null hypothesis is that the millipedes have no preference.

Which of the following is chi-square for these counts?

A. 0.55 B. 0.82 C. 1.64 D. 18

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 student tests whether ground beetles of one kind gather under cover. She lays leaf litter on one half of a shallow tray and bare sand on the other half, tips 16 beetles into the middle, and after five minutes counts the beetles on each half. She also sets up a second tray with leaf litter on both halves, 16 beetles, counted the same way. The counts from the first tray are drawn below.

The first tray from above after five minutes: 14 beetles on the leaf-litter half and 2 on the bare-sand half.

(a) Identify the independent variable and the dependent variable in the student’s test. (1 point)

A full-credit answer: The independent variable is the cover on a half of the tray: leaf litter or bare sand, the one condition the student changed.
The dependent variable is the number of beetles counted on each half, the quantity she measured.

Check the box for each point your answer earns

the cover on a half (leaf litter or bare sand) as the independent variable AND the number of beetles on each half as the dependent variable.

Common slip: Naming the number of beetles tipped in as a variable. Sixteen went into every tray; that is a condition kept the same.

(b) State the null hypothesis for the first tray. (1 point)

A full-credit answer: The beetles have no preference between leaf litter and bare sand, so any gap from 8 on each half is due to chance.

Check the box for each point your answer earns

the beetles have no preference (an even split), and any difference from it is due to chance. Accept with or without: 8 and 8.

Common slip: Writing “the beetles prefer leaf litter” as the null hypothesis. The null is no preference; the preference is what the test may reject it in favor of.

(c) Justify the student’s decision to set up the second tray with leaf litter on both halves. (1 point)

A full-credit answer: With leaf litter on both halves the beetles have no difference to choose between.
The second tray shows how 16 beetles spread when nothing is chosen.
So a lopsided count in the first tray can be put down to the cover, and not to the beetles bunching up on their own.

Check the box for each point your answer earns

the second tray has no difference to choose between, so it shows the spread with no preference; a lopsided count in the first tray can then be credited to the cover. Accept: it is the control, with what it shows (the spread with no difference to choose between).

Common slip: Calling the second tray a repeat that makes the result more reliable. It differs from the first tray in one way: it offers no choice.

(d) Calculate chi-square for the counts in the first tray against the null hypothesis. (1 point)

Write down the values in the question:

o = 14 (leaf litter), 2 (bare sand)

e = \frac{16}{2} = 8 on each half

Write down the equation:

χ^{2} = \sum \frac{{(o - e)}^{2}}{e}

Substitute the values into the equation, one half per line:

leaf litter: \frac{{(14 - 8)}^{2}}{8} = \frac{36}{8} = 4.5

bare sand: \frac{{(2 - 8)}^{2}}{8} = \frac{36}{8} = 4.5

Add the halves:

χ^{2} = 4.5 + 4.5 = 9.0

A full-credit answer: Under no preference e = 16 ÷ 2 = 8 on each half.
Leaf litter: $\frac{{(14 - 8)}^{2}}{8} = 4.5$ .
Bare sand: $\frac{{(2 - 8)}^{2}}{8} = 4.5$ .
So $χ^{2} = 4.5 + 4.5 = 9.0$ .

(e) Determine whether the null hypothesis is rejected at p = 0.05, and justify the verdict with the two numbers it rests on. (1 point)

The chi-square table from the formula sheet.

A full-credit answer: Two halves give one degree of freedom.
The p = 0.05 row reads 3.84 at one degree of freedom.
9.0 is larger than 3.84.
So the null hypothesis is rejected: a gap this large is too large to be chance, and the counts support a preference for the leaf litter.

Check the box for each point your answer earns

reject the null hypothesis, because chi-square (9.0) is larger than the critical value (3.84) at one degree of freedom. Accept: reject, so the data support a preference.

Common slip: Writing “accept the preference” as the verdict. The verdict is about the null hypothesis: reject it, or fail to reject it.

Free-response score: 0 of 5

Free response 2 · Conceptual Analysis · 4 points

In a clear stream, the males of one kind of small fish turn bright red on the belly each spring and swim in short darts in front of the females. A female swims toward the male with the reddest belly and lays her eggs in his nest, where he fertilizes them. Fish of this kind mate only at a nest, and the males’ nests lie several meters apart along the stream bed. In the clear water a female can see a red belly from ten meters away. A quarry then opens upstream, and from that spring on the stream is cloudy with fine clay through the whole breeding season; a female can now see a male’s belly only from within half a meter.

(a) Describe the job the red belly does for the male that shows it. (1 point)

A full-credit answer: The red belly wins the male a mate: a female sees it, swims toward the reddest male and lays her eggs in his nest.

Check the box for each point your answer earns

the red belly wins a mate (draws a female to the male’s nest).

Common slip: Saying the red belly marks the male’s territory. A territory mark keeps rivals out; this display draws females in.

(b) Explain how the red belly gives some males more offspring than others. (1 point)

A full-credit answer: A female detects the red belly and swims toward the reddest male.
So the reddest males are reached by more females.
More females lay eggs in those males’ nests, and those males fertilize them.
So the reddest males leave more offspring than the duller males.

Check the box for each point your answer earns

females move toward the reddest males, so those males mate with more females and leave more offspring.

Common slip: Stopping at “the red belly attracts females”. The point needs the step from attracting females to more eggs fertilized, and so more offspring.

(c) Predict how the number of young fish in the stream changes in the springs after the quarry opens. (1 point)

A full-credit answer: The number of young fish falls.

Check the box for each point your answer earns

the number of young fish falls (is smaller than before the quarry).

Common slip: Predicting no change because the males still turn red. The signal is sent as before, but it no longer reaches the receivers.

(d) Justify your prediction. (1 point)

A full-credit answer: The clay clouds the water, so a female can see a red belly only from close by.
So the red belly reaches fewer females.
Fewer females swim to a male’s nest, so fewer pairs mate.
Fewer eggs are laid and fertilized, so fewer young fish hatch.
So the number of young fish in the stream falls.

Check the box for each point your answer earns

the chain in order — the cloudy water stops the signal reaching the females → fewer females reach a nest and mate → fewer eggs fertilized → fewer young fish. Accept the chain with the mating step and the egg step written as one link.

Common slip: Jumping from “cloudy water” to “fewer fish”. Each link has to be stated: the signal fails to reach the receiver, so the receiver’s behavior changes, so the matings fall, so the young fall.

Free-response score: 0 of 4

Feedback and scoring guides appear after you submit.

Multiple choice checked: 0 of 17 correct.

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