AP Biology Sample Student Responses and Scoring Commentary ... · The common bedbug (Cime,,...

2018

AP BiologySample Student Responses and Scoring Commentary

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Free Response Question 4

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Question 4

Figure 1. Percent survival of five strains of bedbugs treated with beta-cyfluthrin. A (+) indicates the gene is present; a (−) indicates the gene is deleted. Error bars represent the 95% confidence interval.

The common bedbug (Cimex lectularius) is a species of insect that is becoming increasingly resistant to

insecticides. Bedbugs possess several genes suspected of contributing to the resistance, including P450, Abc8, and Cps. To investigate the role of these genes in insecticide resistance, researchers deleted one or more of these genes in different strains of bedbugs, as indicated in Figure 1, and treated the strains with the insecticide beta-cyfluthrin. Each strain was genetically identical except for the deleted gene(s) and was equally fit in the absence of beta-cyfluthrin. The percent survival of each strain following beta-cyfluthrin treatment is shown in Figure 1.

(a) Identify the control strain in the experiment. Use the means and confidence intervals in Figure 1 to justify the claim that Abc8 is effective at providing resistance to beta-cyfluthrin.

Identification (1 point)

• Strain I Justification (1 point)

• Error bars/CIs from strain I/control/WT do not overlap with strain III/Abc8 deleted strain. • Mean % survival of strain III/Abc8 deletion falls outside the 95% confidence interval of

strain I/control/WT. • Strain III/Abc8 deletion shows a statistically significant difference from strain I/control.

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Question 4 (continued)

(b) P450 encodes an enzyme that detoxifies insecticides. Abc8 encodes a transporter protein that pumps insecticides out of cells. Cps encodes an external structural protein located in the exoskeleton that greatly reduces the absorption of insecticides. Based on this information and the data in Figure 1, explain how a deletion of both P450 and Abc8 results in lower survival in bedbugs compared with a deletion of Cps only.

Explanation (1 point per row; 2 points maximum)

Strain P450 and Abc8 Cps only Explanation

V Deleted Present Bedbugs can neither detoxify nor pump out insecticide, which results in a lower chance of bedbug survival.

IV Present Deleted Bedbugs can detoxify and pump out insecticide, which results in a higher chance of bedbug survival.

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. Percent survival of fiv�.stralns of bedbugs treated with betacyf,J.ut:hrin: A ( +) imlicates the gene js !'resent; a ( ..:.) ingi�afos the gerieis deleted. Error bars represeiit,the 95% corifideoce .interval.

' I j ' . .•. � \ o�on bedbug· (Ciii1ex lectularius) is a ;pecics of insect that is becom1n'g increasingly resistant to ·

·these insecticides. Bedbugs possess several genes suspected of contributing to the resistance,•including P450, Abc8,and Cps., To investigate the role of these genes in lnsecticide resistance, researchers deleted one or more of

genes in different strains of bedougs; as indicated in Figure 1, and treated the strains with. the insecticidebeta-cyfluthrin�Each strain w�s genetically identkal except for the deleted gene(s) and was equally fit in the. absence of beta-cyflutluin. .The percent survival of each strain followirtg beta-cyfluthrin treatment is shown inFi�e I. · · , , , ,. (a) the c'ontrol\train in the experiment. Use the means and confidence intervals . in Figure l . . to justify

th� Identify

ciaim thatAbc8 is ·effec'tive at pi:oviding-�sist.ance to beta-cyfluthrim /. · · . ... - '

\ . , \ : . .

(b) P450 encodes an enzyme that detoxifies insecticides.

Abc8 encodes a transporter protein that pumps insecticide$ out of cells. Cps encodes an ex.temaI.structural prntein located in the exoskeleton. that greatly reduces the absorption of insecticides. Based on this informatio.n and the data in Figm:e 1, explain how a deletion of both P450 and Abc8 results in lower �urvival_ in be�bugs compared with a deletion of Cps only.

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Figure 1. Percent survival of five strains of bedbugs lreated with betacyfluthrin. A ( +) indicates the gene is present; a (-) indicates thegene is deleted. Error bars represent the 95% confidence interval.

4. The common bedbug (Cimex lectularius) is a species of insect that is becoming increasingly resistant to insecticides. Bedbugs possess several genes suspected of contributing lo the resistance, including P450, AbcB,and Cps. To investigate the role of these genes in insecticide resistance, researchers deleted on'e o�·e of these genes in different strains of bedbugs, as indicated in Figure l, and treated the strains with the insecticidebeta-cyfluthrin. Each strain was genetically identical except for the deleted gene(s) and was equally fit in the absence of beta-cytlulhrin. The percent-survival of each strain following beta-cyfluthrin treatment is shown inFigure l.

-./{a) Identify the conlrol strain in the experiment. Use· the means and confidence intervals in Figure l to justifythe claim that Abc8 is effective at providing resistance to bcta-cyfluthrin.

v'lb) P450 encodes an enzyme that detoxifies inseclicides. Abc8 encodes a transporter protein that pumps insecticides out of cells. Cps encodes an external structural protein located in the exoskeleton that greatlyreduces the absorption of insecticides. Based on this infonnation and the data in Figure 1, explain how a deletion of both P450 and Abc8 results in lower survival in bedbugs compared with a deletion of Cps only.

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Figure 1. Percent survival of five strains of bedbugs treated with betacyfluthrin. A ( +) indicates the gene is present; a (-) indicates the

· gene is deleted. Error bars represent the_ 95% confidence interval.

4.

(a)

(b)

The common bedbug (Cime,, /ectularius) is a species of insect that is becoming increasingly resistant toinsecticides. Bedbugs possess several genes -suspected of cont:tibuting to the resistance, including P450, Abc8,and Cps. To investigate the role of these genes in insecticide resistance, researchers deleted one or more ofthese genes in different strains of bedbugs, as indicated in Figure 1, and treated the strains with the insecticidebeta-cyfluthrin. Each strain was genetically identical except for the deleted gene(s) and was equally fit-in theabsence of beta-cyfluthrin. The percent survival of each strain foJlowing beta-cyfluthrin treatment is shown inFigure 1.

Identify the control strain in the experiment. Use the means and confidence intervals in Figure 1 to justifythe claim that Abc8 is effective at providing resistance to beta-cyfluthrin.P450 encodes an enzyme that detoxifies insecticides. Abc8 encodes a transporter protein that pumpsinsecticides out of cells. Cps encodes an external structural p_rotein ·located in the exoskeleton_ that greatlyreduces the absorption of insecticides. Based on this infonnation and the data in Figure 1, explain how adeletion of both P450 and Abc8 results in lower survival in bedbugs compared with a deletion of Cps only.

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AP® BIOLOGY 2018 SCORING COMMENTARY


Question 4

Overview

The first part of the question focused on the interpretation of data presented both in graphic and tabular form. Students were provided with the results of an experiment involving five different strains of genetically altered bedbugs. The presence or absence of three different genes, P450, Abc8, and Cps, was given for each strain. The corresponding graph showed the average percent survival, with corresponding 95 percent confidence intervals, when each of the strains was exposed to the insecticide beta-cyfluthrin. Students were asked to identify the control strain and to justify the claim that Abc8 is effective at providing resistance to the insecticide. Next, the students were provided with information on how each gene product functions in contributing to insecticide resistance. The students were then asked to explain the relationships among the functions of the gene products in providing resistance when either: 1) P450 and Abc8 are both deleted, or 2) when only Cps is deleted. The key understandings and skills students were expected to demonstrate included the following:

• Knowledge of how organisms are affected by abiotic factors was used to investigate insecticide resistance.

• The understanding that expression, or lack thereof, of genes can alter phenotypes was used in an experimental investigation to help determine the function of the gene products in a biological process (insecticide resistance).

• Knowledge of experimental design and statistics was used to interpret the results of an experiment.

Sample: 4A Score: 4 The response earned 1 point in part (a) for correctly identifying the control strain in the experiment as Strain I. The response earned 1 point in part (a) for correctly justifying the claim by stating that “the confidence intervals between the strain without Abc8 (III) and the control (I) did not overlap.” The response earned 1 point in part (b) for correctly explaining that when both P450 and Abc8 are deleted the insecticide “remains toxic and has no way of leaving.” Lower survival is implied because the response specifies a higher survival rate when just Cps is deleted. The response earned 1 point in part (b) for correctly explaining that “when just Cps is deleted the survival rate is much higher” because insecticide “is getting detoxified and being removed through the transporter pumps.”

Sample: 4B Score: 3 The response earned 1 point in part (a) for correctly identifying the control strain in the experiment as Strain I. The response earned 1 point in part (b) for correctly explaining that “with the deletion of P450 the insecticides would be toxic and with the deletion of Abc8, the transporter protein would not be able to pump the insecticides out … which leads to a lower survival rate.” The response earned 1 point in part (b) for correctly explaining “when only Cps is deleted … P450 and Abc8 ... fight off the insecticide ... by pumping it out of the cell and detoxifying it,” resulting in a higher survival rate.

AP® BIOLOGY 2018 SCORING COMMENTARY


Question 4 (continued)

Sample: 4C Score: 2 The response earned 1 point in part (a) for correctly identifying the control strain in the experiment as Strain I. The response earned 1 point in part (b) for correctly explaining that the “deletion of both P450 and Abc8 results in lower survival … because … there is no mechanism … that detoxifies or pumps out the insecticides.”

AP Biology Sample Student Responses and Scoring Commentary ... · The common bedbug (Cime,,...

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