QuestionAP® BIOLOGY2014 SCORING GUIDELINESQuestion 1Trichomes are hairlike outgrowths of the epidermis of plants that are thought to provide protection againstbeing eaten by herbivores (herbivory). In a certain plant species, stem trichome density is geneticallydetermined.To investigate variation in stem trichome density within the plant species, a student counted the numberof trichomes on the stems of six plants in each of three different populations. The student used the data tocalculate the mean trichome density (numbers of hairs per square centimeter) for each population. Theresults are provided in the table below.TRICHOME DENSITY IN THREE PLANT POPULATIONS (number of trichomes/cm2)Population Plant 1 Plant 2 Plant 3 Plant 4 Plant 5 Plant 6 SampleMean StandardError of theMean (SEM)1 I 8 11 9 10 8 6 9 II 12 6 15 9 13 8 11 1 III 13 17 9 14 12 16 14 1 (a) On the axes provided, create an appropriately labeled graph to illustrate the sample means of the threepopulations to within 95 percent confidence (i.e., sample mean ± 2 SEM). (3 points maximum; LO 1.1)• Correctly labeled, scaled, with proper units• Bar graph or modified bar graph with appropriately plotted means• 2x standard error (SEM) above and below means(b) Based on the sample means and standard errors of the means, identify the two populations that aremost likely to have statistically significant differences in the mean stem trichome densities. Justifyyour response. (2 points maximum; LO 4.11, 4.19)Identification (1 point)• Populations I and IIIJustification (1 point)• The error bars/95 percent confidence intervals for populations I and III do not overlap• (Sample mean + 2 SEM of population I) < (Sample mean − 2 SEM of population III) © 2014 The College Board.Visit the College Board on the Web: www.collegeboard.org. AP® BIOLOGY2014 SCORING GUIDELINESQuestion 1 (continued)(c) Describe the independent and dependent variables and a control treatment for an experiment to testthe hypothesis that higher trichome density in plants is selected for in the presence of herbivores. Alsoidentify an appropriate duration of the experiment to ensure that natural selection is measured andpredict the experimental results that would support the hypothesis. (5 points maximum; LO 1.5, 1.11)NOTE: Points are earned in a single row only.IndependentDependentControlVariableVariable(1 point)(1 point)(1 point) Duration(1 point) Presence ofherbivores Trichome density Absence ofherbivores More than onegeneration Trichomedensity in thepresence ofherbivores Reproductivesuccess OR# of plants Plants with lowertrichome density More than onegeneration © 2014 The College Board.Visit the College Board on the Web: www.collegeboard.org. Prediction(1 point)Increased trichomedensity relative tocontrolSize of the populationwith higher trichomedensity will be largerthan control population ©2014 The College Board.Visit the College Board on the Web: www.collegeboard.org. ©2014 The College Board.Visit the College Board on the Web: www.collegeboard.org. ©2014 The College Board.Visit the College Board on the Web: www.collegeboard.org. ©2014 The College Board.Visit the College Board on the Web: www.collegeboard.org. ©2014 The College Board.Visit the College Board on the Web: www.collegeboard.org. ©2014 The College Board.Visit the College Board on the Web: www.collegeboard.org.
