End-of-topic test: Environmental Effects on Phenotype

Unit 5 · Topic 5.5 end-of-topic test

Suggested time: about 46 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. When you have answered every question, press Submit the test; the feedback then gives the reasoning for each. 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 shows means with error bars, read the legend first: every error bar here represents ±2SE.

Question 1

A water buttercup grows with part of its stem under water and part in the air. On the one plant, the leaves under water are cut into fine threads and the leaves in the air are broad and flat.

Which of the following differs between the leaves under water and the leaves in the air?

A. The alleles for leaf shape that each leaf inherited B. The condition each leaf grew in C. Both the alleles each leaf inherited and the condition each leaf grew in D. The DNA in each leaf’s cells, rewritten by the water

Question 2

Two potato plants grown from pieces of one tuber: the plant at 18 °C with large tubers and the plant at 28 °C with small tubers.

Two potato plants grown from pieces of one tuber are drawn below. One grew at 18 °C and formed large tubers; the other grew at 28 °C and formed small tubers. Light, water and soil were the same for both. A student says the plant at 28 °C must carry different alleles from the plant at 18 °C.

Which statement about the student's claim is correct?

A. The student is right: only plants with different alleles can give tubers of different sizes B. The student is right: the warmth changed the alleles of the plant at 28 °C C. The student is wrong: tuber size is set by chance alone, not by alleles or by temperature D. The student is wrong: both plants carry the same alleles, and the temperature set the size

Question 3

A racehorse trained hard for years has much larger leg muscles than its untrained brother. The horse then sires a foal.

Predict the leg muscles of the foal at birth compared with a foal of the untrained brother, and give the reason.

A. Larger, because a parent's acquired change is passed to the foal B. Larger, because the training changed the alleles in his gametes C. Ordinary, because training cannot change which genes a muscle cell uses, so nothing in the horse changed D. Ordinary, because the change in the horse's muscle cells left the DNA in his gametes as it was

Question 4

A gardener grows cuttings of one grass plant in salty soil and in ordinary soil. The plants in salty soil grow short, with thick leaves. A student writes: the salty soil switched the leaf genes off for good, so cuttings taken from the short plants will stay short in ordinary soil.

What is wrong with the student's statement?

A. Nothing; a condition that changes gene use changes it permanently, for the life of the plant B. The salt changed the leaf cells’ gene use only while they grew in salty soil, not for good C. The salt rewrote the leaf alleles, so the change is inherited D. Leaf form is set by alleles alone, so the salt had no effect

Question 5

One clonal line of duckweed grows large fronds in a warm pond and small fronds in a cold pond. Two duckweed strains grown side by side in one warm tank differ in frond size.

Which of the following shows phenotypic plasticity?

A. Neither B. The clonal line in the two ponds only C. The two strains in the tank only D. Both the clonal line and the two strains

Question 6

A pond holds snails of one species with shells of many colors and patterns. A student writes: this variety shows phenotypic plasticity.

What is wrong with the student's statement?

A. Plasticity is the range one genotype can produce; the snails’ variety may be genetic B. Nothing; variety of phenotype across a population is what phenotypic plasticity means C. The variety must be a genetic difference, because shell color in snails is set by alleles alone D. Plasticity needs a change in the snails’ DNA, which the pond water cannot make

Question 7

On one oak tree, the leaves on a shaded branch grow larger and thinner than the leaves on a branch in full sun.

What differs inside the leaf cells of the two branches?

A. The set of genes in use, and how much each one is used B. The sequence of the DNA, and so the set of genes the cells carry C. Which alleles the cells inherited at fertilization D. The number of chromosomes each cell carries

Question 8

Which of the following cases is phenotypic plasticity?

A. A mutation in a pigment gene gives a mouse a white coat B. A red-flowered plant and a white-flowered plant give pink offspring C. Cuttings of one shrub grow tall in a sheltered garden and short in a windy one D. Two breeds of cattle kept on one farm give different amounts of milk

Question 9

A researcher splits alligator eggs from one nest between two incubators, at 30 °C and 34 °C, with the same moisture and light. All the 30 °C hatchlings are female and all the 34 °C hatchlings are male.

What set the sex of the hatchlings, and how do the results show it?

A. The temperature at which each egg developed, the one condition that differed between the two groups B. The alleles each egg received from its father, because sex is set by the sex chromosomes in every animal C. The moisture around each egg, because eggs in a nest of rotting plants develop in damp conditions D. Chance alone, because about half of the eggs in any clutch develop as males whatever the conditions

Question 10

After two weeks of strong sunshine a person's forearms are noticeably darker than they were in winter.

Which condition changed, and which trait responded?

A. The temperature of the air changed, and the skin's thickness responded B. The person's diet changed, and the skin's melanin responded C. UV light from the sun changed, and the skin's melanin responded D. UV light from the sun changed, and the skin's alleles responded

Question 11

Two children of the same parents grow up with very different amounts of food and reach different adult heights.

Which statement about human height fits the case?

A. Height is set by one gene alone, whatever a child eats B. Nutrition sets height entirely, whatever alleles a child carries C. Food changes the height alleles a child carries, so the taller child’s alleles changed D. Many genes set the range, and nutrition moves the person within it

Question 12

A cutting of one plant grown in shade has large, thin leaves. The cutting is moved into full sun and grows new leaves.

Predict the new leaves, and give the reason.

A. Large and thin, because the fixed genotype makes the cells use the same genes in any light B. Smaller and thicker, because in sun the leaf cells use some genes more and others less C. Smaller and thicker, because the sun changed the cutting's leaf alleles D. Large and thin, because the leaf form set in shade is kept by every leaf grown afterward

Question 13

The grower's design: two groups of sunflower plantlets from one clonal line, with the temperature and the watering of each group.

A grower wants to know whether temperature changes the height of sunflowers. The design is in the table below. After four weeks the plants in group A are taller.

What is wrong with the design?

A. The two groups came from different plants, so their genes may differ B. Two conditions differ between the groups, so neither can be credited with the difference C. There is no control, because neither group was left completely unwatered D. Nothing; the taller plants in group A show that 20 °C makes sunflowers taller

Question 14

A grower gives 12 cuttings of one grapevine the vineyard's usual watering and 12 twice as much, with soil, light and temperature the same. She measures the sugar in each plant's grapes.

Which group is the control, and what does it show?

A. The usual-watering group; it shows the sugar reached under the condition already in use B. The double-watering group; it shows the sugar reached under the changed condition, which is the result under test C. Both groups; each shows what one vine's genes can do, because every cutting came from the same plant D. Neither group; a control must receive none of the condition, and both groups were given water

Question 15

Mean leaf length in millimeters of rosemary cuttings from one plant grown at 60 % and at 90 % humidity, 15 cuttings per group; error bars represent ±2SE.

A student grew cuttings of one rosemary plant at two humidities, 15 in each, and recorded the mean leaf length of each group. The bars below carry ±2SE error bars.

What do the bars show about the two humidities?

A. The two humidities give leaves of exactly the same length B. The higher humidity makes leaves longer C. The data do not show a difference between the two humidities D. The cuttings must have carried different alleles

Question 16

A gardener roots 20 cuttings from a rose bush of one variety and 20 cuttings from a bush of a different variety. She grows the first 20 in a cold frame and the second 20 in a warm greenhouse, with the same soil, water and light for every plant. The greenhouse roses grow taller.

What can the gardener conclude about the cause of the height difference?

A. The warmth caused it, because the soil, water and light were the same for both groups of cuttings B. The genes caused it, because the two groups came from bushes of different varieties C. Neither the warmth nor the genes can be credited, because both differed between the groups D. Both the warmth and the genes caused it, each adding some of the extra height

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 grower has 40 strawberry plants grown from runners of one plant. She wants to know whether the temperature the plants grow at changes the mass of fruit they produce. She grows 20 plants at 18 °C and 20 at 26 °C in one glasshouse divided by a partition, with the same light, water and soil for every plant. At the end of the season she weighs the fruit of each plant and finds the mean fruit mass per plant for each group. The means are drawn below; each error bar represents ±2SE.

Mean fruit mass per plant in grams for strawberry plants of one clonal line grown at 18 °C and at 26 °C, 20 plants per group; error bars represent ±2SE.

(a) Identify the independent variable and the dependent variable in the grower's test. (1 point)

A full-credit answer: The independent variable is the temperature the plants grow at, 18 °C or 26 °C, the one condition the grower changed.
The dependent variable is the mass of fruit per plant, the quantity she measured to see the effect.

Check the box for each point your answer earns

temperature as the independent variable and fruit mass per plant as the dependent variable.

Common slip: Naming the light, water or soil as the independent variable. Those were held the same; the one condition changed was the temperature.

(b) Predict what the two means and their ±2SE error bars would look like if temperature had no effect on fruit mass. (1 point)

A full-credit answer: The two mean values would be about the same.
The ±2SE error bars of the 18 °C group and the 26 °C group would overlap.
So the data would show no difference between the two temperatures.

Check the box for each point your answer earns

means about the same with overlapping ±2SE error bars (the data show no difference).

Common slip: Predicting that the two means would be exactly equal. Two sample means almost always differ a little by chance; the prediction is that the bars overlap.

(c) Evaluate the claim that the temperature changed the fruit mass, using the error bars drawn above. (1 point)

A full-credit answer: The mean fruit mass was 240 g per plant at 18 °C and 175 g at 26 °C.
The error bars represent ±2SE: 222 to 258 g at 18 °C and 160 to 190 g at 26 °C.
The two bars do not overlap, so the difference between the mean values is unlikely to be chance.
The plants share one genotype and only the temperature differed between the groups.
So the claim is supported: the temperature changed the fruit mass.

Check the box for each point your answer earns

the judgement (the claim is supported) AND the ground (the ±2SE bars do not overlap, so the difference is unlikely to be chance; with the same genes and one condition changed, the temperature is credited).

Common slip: Arguing only that 240 is larger than 175. Two means can differ by chance; the non-overlapping error bars are what make chance unlikely.

(d) Explain why any difference in fruit mass between the two groups can be credited to the temperature rather than to a genetic difference between the groups. (1 point)

A full-credit answer: Every plant grew from runners of one plant, so all 40 plants carry the same DNA.
So the two groups cannot differ in their genes, and a difference in fruit mass cannot be genetic.
Light, water and soil were the same for every plant, so the temperature is the only condition that differed.
So any difference in fruit mass between the groups can be credited to the temperature.

Check the box for each point your answer earns

the plants grew from runners of one plant, so both groups share one genotype and a difference cannot be genetic; with everything else the same, the temperature is the only condition that differed.

Common slip: Pointing to the equal group sizes. Twenty in each group helps the comparison; it is the shared genotype that rules the genes out.

(e) Describe what the result shows about how the plants' genes and the temperature together set the mass of fruit. (1 point)

A full-credit answer: The same genotype gave heavier fruit at 18 °C and lighter fruit at 26 °C.
The DNA is the same in both groups.
So the temperature changed which genes the plants' cells used and how much.
The genes set the range of fruit mass the plants can reach, and the temperature decided where in that range each group fell.

Check the box for each point your answer earns

EITHER: the same genes gave two phenotypes because the condition changed which genes the cells used and how much, with the DNA unchanged; OR: the genes set the range of fruit mass and the temperature decided where in that range each group fell.

Common slip: Saying the warmth changed the plants' genes. The DNA is the same in both groups; the temperature changed which genes the cells used, not the genes themselves.

Free-response score: 0 of 5

Free response 2 · Conceptual Analysis · 4 points

Aphids on a bean plant reproduce without mating, so all the aphids on one plant are a clonal line with the same DNA. A researcher keeps 10 bean plants crowded with aphids of one line and 10 bean plants carrying only a few aphids of the same line, all in one greenhouse with the same light and temperature. On the crowded plants, 84 % of the newborn aphids develop wings; on the uncrowded plants, 2 % do. A winged aphid that flies to an empty bean plant produces wingless offspring there.

(a) Identify the condition that changed and the trait that responded to it in the aphids. (1 point)

A full-credit answer: The condition is how crowded the plant is with aphids; the trait that responded is whether a newborn aphid develops wings.

Check the box for each point your answer earns

crowding as the condition and wing development as the trait.

Common slip: Naming the bean plant or the food as the condition. The aphids on the crowded and the uncrowded plants eat the same kind of plant; what differs is how many aphids share it.

(b) Explain how crowding can change whether an aphid develops wings while its DNA stays the same. (1 point)

A full-credit answer: Crowding is a condition outside the aphid that acts as a signal to its cells.
A condition outside the organism changes which genes its cells use and how much, so in a crowded plant the developing aphid's cells use the genes that build wings, and in an uncrowded plant they do not; the DNA is the same in both.

Check the box for each point your answer earns

the condition changes which genes the cells use and how much (gene expression), so the phenotype changes while the DNA does not.

Common slip: Saying crowding causes a mutation that gives wings. The wingless offspring of a winged aphid show that its DNA still carries the same genes.

(c) Justify the claim that the winged aphid's wings were a response to conditions rather than a change in its genes, using the winged aphid that flew to the empty plant. (1 point)

A full-credit answer: The winged aphid's offspring on the empty plant have no wings, although they are copies of her DNA.
If the wings had come from a change in her genes, her offspring would carry that change and be winged too.
They are wingless because the condition, crowding, is gone, so the wings were the same genes used differently under crowding.

Check the box for each point your answer earns

the offspring share the winged aphid's DNA yet are wingless, so the wings were not written in the genes but produced by the condition.

Accept also: aphids of one line carry the same DNA, yet 84 % of newborns grew wings on the crowded plants and 2 % on the uncrowded plants, so the condition and not the genes set the wings.

Common slip: Saying the offspring lost the wing allele. Offspring of a clonal line carry the same DNA as their mother; nothing was lost.

(d) Two different clonal lines of aphids feed on identical, uncrowded bean plants in one greenhouse, and the aphids of one line are green while those of the other are red. Make a claim about whether this color difference is phenotypic plasticity or a genetic difference, and support your claim with evidence from the greenhouse. (1 point)

A full-credit answer: Claim: the color difference is a genetic difference.
Evidence: the two lines feed on identical, uncrowded plants in one greenhouse, so the conditions are the same for both.
Phenotypic plasticity is one genotype producing different phenotypes under different conditions.
Here the conditions do not differ, and the two lines are two genotypes.
So the difference in color must come from their genes.

Check the box for each point your answer earns

the claim (a genetic difference) AND the support (the conditions are the same for both lines, so the difference cannot be plasticity; the two lines are two genotypes).

Common slip: Calling any difference in phenotype plasticity. Plasticity is a property of one genotype; two lines that differ under the same conditions differ in their genes.

Free-response score: 0 of 4

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Multiple choice checked: 0 of 16 correct.

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