AP Investigation #1 Artificial Selection Teacher s Guide

Transcription

1 AP Investigation #1 Artificial Selection Teacher s Guide Kit # Call Us at for Technical Assistance WILL FIX ALL PAGE # S ONCE EVERYTHING ELSE IS FINALIZED. Table of Contents Abstract. 1 General Overview. 1 Recording Data. 2 Material Requirements/Checklist. 4 National Science Education Content Standards. 5 Correlation to AP Content Standards. 5 Time Requirements. 5 Learning Objectives. 6 Safety Precautions. 7 Pre-Lab Preparations. 8 Background. 11 Part 1: Cell Size & Diffusion. 13 Part 2: Modeling Osmosis in Living Cells. 17 Part 3: Osmosis in Living Plant Cells. 21 Assessment Questions/Additional Questions (Optional). 24 Further Inquiry Investigations. 23 Teacher s Answer Key. 24 LIVE MATERIAL CARE SHEETS. **AP and the Advanced Placement Program are registered trademarks of the College Entrance Examination Board. The activity and materials in this kit were developed and prepared by WARD S Natural Science Establishment, which bears sole responsibility for their contents..

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3 abstract Populations of organisms change their genetic makeup through the process of natural selection/ differential reproduction. Natural selective pressures come from the organisms environment (for example, predators or ambient temperatures). Selection causes an alteration in the prevalence of the genes regulating the expression of phenotypes in a population of organisms (for example, low temperatures might increase the prevalence of a gene that increases the density of hairs in fur). This occurs naturally over many generations and underlies the process of evolution. In this lab, students will artificially select one or more phenotypes in one generation of a population of fast growing plants to determine whether they can change the prevalence of that phenotype in the next generation of plants. The students will learn to apply statistical analyses to evaluate the probability that a conclusion is significant or not. Further, they will consider the interplay between environmental pressures on plant phenotypes and how they may or may not be manifested as phenotypic changes that are passed to the next generation. Page 1

4 general Overview The College Board has revised the AP Biology curriculum to begin implementation in the fall of Advanced Placement (AP) is a registered trademark of the College Entrance Examination Board. The revisions were designed to reduce the range of topics covered, to allow more depth of study and increased conceptual understanding for students. There is a shift in laboratory emphasis from instructor-designed demonstrations to student-designed investigations. While students may be introduced to concepts and methods as before, it is expected that they will develop more independent inquiry skills. Lab investigations now incorporate more student-questioning and experimental design. To accomplish this, the College Board has decreased the minimum number of required labs from 12 to 8 while keeping the same time requirement (25% of instruction time devoted to laboratory study). The College Board has defined seven science practices that students must learn to apply over the course of laboratory study. In brief, students must: 1. Use models 2. Use mathematics (quantitative skills) 3. Formulate questions 4. Plan and execute data collection strategies 5. Analyze and evaluate data 6. Explain results 7. Generalize data across domains The College Board published 13 recommended laboratories in the spring of They can be found at: Many of these laboratories are extensions of those described in the 12 classic labs that the College Board has used in the past. The materials provided in this lab activity have been prepared by Ward s to adapt to the specifications outlined in AP Biology Investigative Labs: An Inquiry-Based Approach (2012, The College Board). Ward s has provided instructions and materials in the AP Biology Investigation series that complement the descriptions in this College Board publication. We recommend that all teachers review the College Board material as well as the instructions here to get the best understanding of what the learning goals are. Ward s has structured each new AP investigation to have at least three parts: Structured, Guided, and Open Inquiry. Depending on a teacher s syllabus, they may choose to do all or only parts of the investigations in scheduled lab periods. The College Board requires that a syllabus describe how students communicate their experimental designs and results. It is up to the teacher to define how this requirement will be met. Having students keep a laboratory notebook is one straightforward way to do this. Page 2

5 Recording Data in a Laboratory Notebook All of the Ward s Investigations assume that students will keep a laboratory notebook for studentdirected investigations. A brief outline of recommended practices to set up a notebook, and one possible format, are provided below. 1. A composition book with bound pages is highly recommended. These can be found in most stationary stores. Ward s offers several options with pre-numbered pages (for instance, item numbers and ). This prevents pages from being lost or mixed up over the course of an experiment. 2. The title page should contain, at the minimum, the student s name. Pages should be numbered in succession. 3. After the title page, two to six pages should be reserved for a table of contents to be updated as experiments are done so they are easily found. 4. All entries should be made in permanent ink. Mistakes should be crossed out with a single line and should be initialed and dated. This clearly documents the actual sequence of events and methods of calculation. When in doubt, over-explain. In research labs, clear documentation may be required to audit and repeat results or obtain a patent. 5. It is good practice to permanently adhere a laboratory safety contract to the front cover of the notebook as a constant reminder to be safe. 6. It is professional lab practice to sign and date the bottom of every page. The instructor or lab partner can also sign and date as a witness to the veracity of the recording. 7. Any photos, data print-outs, or other type of documentation should be firmly adhered in the notebook. It is professional practice to draw a line from the notebook page over the inserted material to indicate that there has been no tampering with the records. For student-directed investigations, it is expected that the student will provide an experimental plan for the teacher to approve before beginning any experiment. The general plan format follows that of writing a grant to fund a research project. 1. Define the question or testable hypothesis. 2. Describe the background information. Include previous experiments. 3. Describe the experimental design with controls, variables, and observations. 4. Describe the possible results and how they would be interpreted. 5. List the materials and methods to be used. 6. Note potential safety issues. (continued on next page) Page 3

6 Recording Data in a Laboratory Notebook (continued) After the plan is approved: 7. The step-by-step procedure should be documented in the lab notebook. This includes recording the calculations of concentrations, etc., as well as the weights and volumes used. 8. The results should be recorded (including drawings, photos, data print outs, etc.). 9. The analysis of results should be recorded. 10. Draw conclusions based on how the results compared to the predictions. 11. Limitations of the conclusions should be discussed, including thoughts about improving the experimental design, statistical significance, and uncontrolled variables. 12. Further study direction should be considered. The College Board encourages peer review of student investigations through both formal and informal presentation with feedback and discussion. Assessment questions similar to those on the AP exam might resemble the following questions, which also might arise in peer review: Explain the purpose of a procedural step. Identify the independent variables and the dependent variables in an experiment. What results would you expect to see in the control group? The experimental group? How does XXXX concept account for YYYY findings? Describe a method to determine XXXX. Page 4

7 Materials checklist MATERIALS NEEDED BUT NOT PROVIDED Units per kit Description Plant station with grow light 1 Vermiculite, 1.5 lbs Digital camera 1 Stake & Twist Tie Set/Rapid Magnifiers 2 Professional Jiffy Greenhouse Jug for watering, mixing fertilizer 4 Plant Fertilizer, 2.75 g Graduated cylinders to measure water (1-2 L) 1 Arabidopsis, Wild Type, 300 seeds Water 1 Label, Printed, 8-1/2 x 11 OPTIONAL MATERIALS ( NOT PROVIDED) 1 Label, Plain White, 8/Page Beakers for transporting peat pots to and from growing area 40 Plant Label, 5 inch 3 plastic pots 10 Pipet, 6 graduated Soil 1 Microfuge Tubes, Pkg/30, 1.5 ml 1 Instructions (this booklet) Additional Jiffy pots and Arabidopsis seeds for student directed experiments Other materials as determined by students experimental design Call Us at for Technical Assistance Or Visit Us on-line at for U.S. Customers for Canadian Customers Page 5

8 This lab activity is aligned with the 2012 AP Biology Curriculum (registered trademark of the College Board). Listed below are the aligned Content Areas (Big Ideas and Enduring Understandings), the Science Practices, and the Learning Objectives of the lab as described in AP Biology Investigative Labs: An Inquiry Approach (2012). This is a publication of the College Board that can be found at Curriculum alignment Big Ideas Big Idea 1: The process of evolution drives the diversity and unity of life. Big Idea 3: Living systems store, retrieve, transmit, and respond to information essential to life processes. Enduring Understandings 1A1: Natural selection is a major mechanism of evolution. 1A2: Natural selection acts on phenotypic variations in populations. 3.C.1: Changes in genotype can result in changes in phenotype. 3.A.4: The inheritance pattern of many traits cannot be explained by simple Mendelian genetics. Science Practices 1.5 The student can re-express key elements of natural phenomena across multiple representations in the domain. 2.2 The student can apply mathematical routines to quantities that describe natural phenomena. 5.3 The student can evaluate the evidence provided by data sets in relation to a particular scientific question. 7.1 The student can connect phenomena and models across spatial and temporal scales. Learning objectives The student is able to convert a data set from a table of numbers that reflect a change in the genetic makeup of a population over time and to apply mathematical methods and conceptual understandings to investigate the cause(s) and effect(s) of this change (1A1 & SP 1.5, SP 2.2). The student is able to evaluate evidence provided by data to qualitatively and quantitatively investigate the role of natural selection in evolution (1A1 & SP 2.2, SP 5.3). The student is able to apply mathematical methods to data from a real or simulated population to predict what will happen to the population in the future (1A1 & SP 2.2). The student is able to evaluate data-based evidence that describes evolutionary changes in the genetic makeup of a population over time (1A2 & SP 5.3). The student is able to connect evolutionary changes in a population over time to a change in the environment (1A1 & SP 7.1). Page 6

9 Time Requirements TIME FRAME TEACHER TASK(S) STUDENT TASK(S) 2 days prior to starting lab 1 day prior to starting lab START LAB WEEKS 1-3 Days 1-2 Days 1-21 Day 21 Cold snap. (See page ) Expand peat pots. (See page ) Plant seeds before class, unless you decide to have students do this step (See page ) _ Go over background material; Start Lab Part 1: Plant seeds (*); set up notebook, * - Teacher may do this before class to save time) Observe plants; record data; Maintain plants (approx. 10 minutes/day) Analyze data and choose traits during one 45-min lab period. WEEKS 4-6 Days _ 10 minutes a day observation and care including collecting seed pods Days Drying time can be extended, to accommodate scheduling Dry seeds WEEKS 7-8 Day 54 Day 55 Cold snap seeds (students or teacher) 15 min Expand peat pots (students or teacher) 15 min Cold snap seeds (students or teacher) 15 min Expand peat pots (students or teacher) 15 min Day 56 (F1 Day 0) Plant F1 generation 30 min (optional lab period) WEEKS 8-11 Days (F1 Weeks 1-3) Observe plants; record data; Maintain plants (approx. 10 minutes/day) Day 77 _ Analyze data Page 7

10 Notes General Safety Precautions If you are setting up a light system for your plants, make sure that water does not get on electrical connectors. The teacher should be familiar with safety practices and regulations in their school (district and state). Know what needs to be treated as hazardous waste and how to properly dispose of nonhazardous chemicals or biological material. Consider establishing a safety contract that students and their parents must read and sign off on. This is a good way to identify students with allergies to things like latex so that you (and they) will be reminded of what particular things may be risks to individuals. A good practice is to include a copy of this contract in the student lab book (glued to the inside cover). Students should know where all emergency equipment (safety shower, eyewash station, fire extinguisher, fire blanket, first aid kit etc.) is located. Make sure students remove all dangling jewelry and tie back long hair before they begin. Remind students to read all instructions, MSDSs and live care sheets before starting the lab activities and to ask questions about safety and safe laboratory procedures. Appropriate MSDSs and live care sheets can be found on the last pages of this booklet. Additionally, the most updated versions of these resources can be found at under Living Materials (Note that in this particular lab, there are no chemicals which require a MSDS.) In student directed investigations, make sure that collecting safety information (like MSDSs) is part of the experimental proposal. As general laboratory practice, it is recommended that students wear proper protective equipment, such as gloves, safety goggles, and a lab apron. At end of lab: All laboratory bench tops should be wiped down with a 20% bleach solution or disinfectant to ensure cleanliness. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Page 8

11 Notes Pre-Laboratory Preparation PLANTING OF PARENT GENERATION 1. Place arabidopsis seeds in about 1 ml of fresh water in a microfuge tube, and place in a refrigerator for 2-4 days (but not longer than a week). This cold snap will improve germination. 2. Expand Jiffy peat pellets. Add 1 envelope of fertilizer to 2.5 L of water and soak the peat pellets in their tray for about 2 hours or until peat pellets are more than 2.5 cm tall. Pour off excess water if necessary. Additional watering does not require additional fertilizer. Set up only 1 Jiffy tray/greenhouse for first generation. 3. Set up growing area as close to optimal as possible. Optimal temperature is degrees C. Grow lights on a timer to deliver 16 hours of light/8 hours of dark at an intensity of µmol/m 2 /s. One generation should take 5-7 weeks from germination to seed pod. Arabidopsis self-fertilizes, so it does not need to be manually fertilized. An additional 2 weeks of seed dry time is recommended followed by the cold snap process (see in Step 1 on the previous page) will improve germination rates. 4. Seventy-two (72) peat pots should provide 9 plants for each of 8 groups to examine and measure. (Some pots may have more than one plant, others may not have any.) The trays for the peat pots may be separated for observation and returned to the reservoir for further growth in 3 x 3 blocks of 9 pots. 5. If you would like to reduce the time devoted to growing and handling the first generation of plants, the instructor may choose to tend a flat of plants for the first 7-10 days (Steps 1-3, in the Student Instructions, Part 1), then distribute peat pots amongst student groups for observations starting as Step 4 in Student Instructions. (continued on next page) Page 9

12 Pre-Laboratory Preparation (CONtinued) Notes PLANTING OF PARENT GENERATION (CONtinued) 6. Arabidopsis is a model organism with characterized mutations available. See: or These sites with offer more information on arabidopsis care, mutations that result in phenotypes, genetic sequencing, and mapping. Students may be interested in extending their studies into more sophisticated genetics. PLANTING OF SECOND GENERATION 1. Optional: Repeat Steps 1-2 from the previous page (parent generation) before the lab period for second generation. (If you prefer, you can have students do this as part of the lab.) Page 10

13 OBJEcTIVES Convert a data set from a table of numbers that reflect a change in the genetic makeup of a population over time and to apply mathematical methods and conceptual understandings to investigate the cause(s) and effect(s) of this change. Evaluate evidence provided by data to qualitatively and quantitatively investigate the role of natural selection in evolution. Apply mathematical methods to data from a real or simulated population to predict what will happen to the population in the future. Evaluate data-based evidence that describes evolutionary changes in the genetic makeup of a population over time. Connect evolutionary changes in a population over time to a change in the environment. Introduction In this experiment, you will artificially select one or more phenotypes in one generation of a population of Arabidopsis thaliana to determine whether they can change the prevalence of that phenotype in the next generation of plants. You will be required to use statistical methods to measure and express differences (or lack thereof) in populations. Background Arabidopsis thaliana is a plant from the mustard family (Brassicaceae) which includes many human food species. Arabidopsis itself is a weed that originated in Europe and Asia, but is now distributed worldwide, from tropical to sub-arctic environments, with the ability to grow in many soil types. It is a food source for a variety of insects and their larvae as well as a source of nectar for insects. Due to the ease of culture and short life cycle, Arabidopsis thaliana has been studied as a model organism for plant genetics (see as a resource website). The entire genome has been sequenced and many mutants are available from research labs and stock collections. Normally, it is a self - pollinating species with a low frequency of out-crossing. It is easy to experimentally control pollination and create crosses by manually pollinating separate plants with a paintbrush to transfer pollen. The life cycle of arabidopsis is illustrated in Figure 1, below. Figure 1 Page 11

14 Figure 2 Background (COntinued) The speed of cycling is dependent upon many factors including water availability, nutrition and light cycle. This cycle is very typical of most dicot plants. While self-fertilizing more than 90% of the time in the wild, the flower has evolved to attract insects that would drive cross fertilization by making nectar (see Figure 2). CAN WE ASK JANA S DAUGHTER TO DRAW THIS? The world-wide distribution of this plant is stimulating comparisons of genomes from plants grown in different environments for many generations. Populations of organisms change their genetic makeup through the process of natural selection/differential reproduction. Natural selective pressures come from the organisms environment (for example, predators or ambient temperatures). Selection causes an alteration in the prevalence of the genes regulating the expression of phenotypes (visible characteristics) in a population of organisms. This occurs naturally over many generations and underlies the process of evolution. Speciation occurs when the differences between two populations becomes so great that they can no longer interbreed to produce fertile offspring. Artificial selection can speed this process and the end result can be seen in many domesticated species. All of the living species from the mustard plant family share a common ancestor from the evolutionary past. This means that arabidopsis, commonly known as thale cress, shared an ancestor with cabbage, broccoli, cauliflower, kale and radish. Many of the differences in these cultivated vegetables came about or became exaggerated through artificial selection by human farmers. For example, broccoli displays exaggerated flower structures, while kale displays more prominent leaf structures. Page 12

15 Materials List Notes MATERIALS NEEDED Description Vermiculite Plant station with grow light Digital camera Stake & Twist Tie Set/Rapid Magnifiers Professional Jiffy Greenhouse Jug for watering, mixing fertilizer Plant Fertilizer Graduated cylinders to measure water (1-2 L) Arabidopsis seeds, Wild Type Water Labels, Printed, Labels, Plain White Plant Label Pipet, 6 graduated Microfuge Tubes Instructions (this booklet) OPTIONAL MATERIALS ( NOT PROVIDED) Beakers for transporting peat pots to and from growing area 3 plastic pots Soil Additional Jiffy pots and arabidopsis seeds for student directed experiments Other materials as determined by your experimental design Page 13

16 Notes Safety Precautions If you are setting up a light system for your plants, make sure that water does not get on electrical connectors. As general safe laboratory practice, it is recommended that you wear proper protective equipment, such as gloves, safety goggles, and a lab apron. As general lab practice, read the lab through completely before starting, including any MSDSs and live materials care sheets at the end of this booklet as well as any appropriate MSDSs for any additional substances you would like to test. One of the best sources is the vendor for the material. For example, when purchased at Wards, searching for the chemical on the Ward s website will direct you to a link for the MSDS. (Note: There are no MSDSs included in this particular lab.) At the end of the lab: All laboratory bench tops should be wiped down with a 20% bleach solution or disinfectant to ensure cleanliness. Wash your hands thoroughly with soap and water before leaving the laboratory. Page 14

17 Procedure TipS Part 1 Structured INQUIRY: Observations of arabidopsis phenotypes/traits When performing this lab activity, all data should be recorded in a lab notebook. You will need to construct your own data tables, where appropriate, in order to accurately capture the data from the investigation. PROCEDURE Structured Inquiry 1. Add about 5 ml (small scoop) of vermiculite to the top of the peat pellet and mix into the top half of the peat pot to fluff peat and increase drainage. 2. Label pots for your lab group then sow 1-2 seeds on top of each peat pellet and make sure soil stays moist. The seed should NOT be buried since it requires light to germinate. It is easiest to see and to transfer 1-2 of the tiny seeds by using a disposable pipet to transfer seeds suspended in water into the peat pot. 3. Cover the Jiffy tray to reduce evaporation and keep soil constantly moist (maintain about 1 cm water in channels of Jiffy pot reservoir tray). 4. Germination should occur in 1-5 days. Carefully monitor moisture until plants get to 4-5 leaf stage (7-10 days after planting). At this point, the top of the Jiffy tray can be removed. 5. After about a week and a half after planting, the pots can and should be allowed to dry for brief periods of time (a day or so). As the plants grow, they can be staked with the supplied plant stakes and ties to keep them upright and from becoming tangled. If you would like to transfer your peat pots to a larger pot for further growth, the entire peat pot can be planted in a larger pot with fresh soil to continue growth (materials not supplied). 6. Set up your laboratory notebook as directed by your teacher. For Part 1 of this laboratory, include a written record of your observations with drawings or photos when necessary as well as the day/time observations were made. Save about five pages for qualitative observations. Set up tables for each trait (for example, a trait like plant height; see sample table on the following page) to fill in measurements over the duration of the experiment. (continued on next page) Page 15

18 Part 1 Structured Inquiry PROCEDURE (Continued) 7. Record observations of growth daily in your laboratory notebook look for traits that you can observe easily and measure. Make sure to define and document how you are making your measurements so that they will be repeatable. Sample Data Table Ht. in cm Plant # #1 #2 #3 #4 #5 #6 #7 #8 #9 Total Avg. Std. Deviation Monday Week 2 Wednesday Friday Monday Week 3 Wednesday Friday Page 16

19 Procedure TipS Part 2 GUIDED INQUIRY: VARIABLE SELECTION, ANALYSIS, REFLECTIONS, AND ASSESSMENT When performing this lab activity, all data should be recorded in a lab notebook. You will need to construct your own data tables, where appropriate, in order to accurately capture the data from the investigation. Record all data immediately in your laboratory notebook. Introduction You (along with your class) will need to select a target trait for the artificial selection part of this experiment. An ideal trait would be something that varies widely from plant to plant; for example, height, number of leaves, numbers of hairs on leaves. Procedure 1. Decide on which trait or traits that the entire class would like to select or target, and assess all of your plants for that trait at a given developmental time, then pool the entire class data for about 72 individual data points per trait. You may want to pool data on a number of traits and choose one or two traits with high variability for class selection. 2. Describe the pooled data by calculating average score, range of scores, standard deviation of score etc. Display the data for the class population graphically for each measured trait. 3. Before flowers appear (about 3 weeks after planting) the class should have chosen the traits you would like to select or target in the next generation. Isolate about 10 plants that display the most extreme selected phenotype (for example, choose the 10 tallest or shortest plants from the entire class) from the other plants, either by moving them or placing clear plastic bags loosely over the tops of the isolated plants. (This ensures that no cross-fertilization will occur for these plants.) Document the measurements on this sub-population and calculate and graphically display descriptive statistics as in Step I above. 4. Allow both the selected and non-selected plants to flower. Arabidopsis plants are self-fertilizing when left alone. (continued on next page) Page 17

20 Part 2 GUIDED INQUIRY Procedure (CONTINUED) Notes 5. Continue to maintain the selected and non-selected plants through the formation of seed pods in about 6 weeks from initial planting. Watering can be decreased; however, if watering is stopped altogether, you risk impairing seed health. The development of more than 10 seed pods per plant risks impairing seed health, so pods that form in excess of 10 should be removed from the plant before maturation. Seed pods (seliques) are mature when they start to turn yellow/brown. The mature pods can be cut from the plant with scissors and seeds harvested by applying gentle pressure to the pod to release seeds on to a collecting piece of paper below. A convenient way to save the seeds is to transfer them to a microcentrifuge tube labeled as either Selected or Nonselected. If seeds are allowed to dry for 2 weeks, the germination rate will be better than if the seeds are planted immediately. 6. Place the arabidopsis seeds in about 1 ml of fresh water in a microfuge tube and place them in a refrigerator for 2-4 days (but not longer than a week). This cold snap will improve germination. 7. Plant the seeds in pre-wetted Jiffy peat pots/greenhouse (half selected and half not selected) and care for them as described in Part 1. Collect the pre-determined trait data at a pre-determined time as decided by the class in Step 1 of this section (Part 2). Collect data sets for both the selected and non-selected progeny. 8. Analyze data sets and compare the two second generation populations both to each other and to the parental population. Provide detailed documentation in your lab notebook. Page 18

21 Part 2 assessment questions 1. Is the selected population significantly different from the non-selected population? How would you determine this statistically? Descriptive means may differ, but overlapping standard errors would indicate that those differences were not significant. Depending on the statistical background of students, choosing an appropriate T test would be another way to make that decision. 2. How do the two second generation populations compare to the parental population? Ideally, a parental histogram would be a standard distribution while the two second generation populations would have standard distributions with the means shifted to the left and right of the parental mean. This would indicate that the phenotype chosen is likely to be heritable. If not, the phenotype chosen is likely to be more dependent upon environmental variation. Have students consider whether all selected plants came from one side of the tray (spatial bias likely associated with nutrition or light) and that the second generation does not display a similar spatial bias. 3. In your lab notebook, graphically display the comparisons. Students may choose various ways to display this information, such as bar graph with error bars, histograms, etc. 4. Explain reasons why you might not observe differences between the two plant generations or between the two selected populations. Answers will vary. See the answer to question #2, above. 5. If you did observe differences between the two plant generations,, how could you tell whether an observed difference resulted from changes at the genetic level or was due to changing, uncontrolled environmental factors? Answers will vary. See the answer to question #2, above. Ways to determine this might include pattern analysis, will the traits carry through more generations, etc. 6. Describe the similarities and differences between artificial selection and natural selection. Answers will vary. Some information can be found in the Background section of this booklet. Students may be required to do some additional research on this topic; for example, researching subspecies vs speciation. 7. What role does arabidopsis play within its natural ecosystems? What organisms eat arabidopsis? What are the environmental challenges to which it has adapted? Answers will vary. Some information can be found in the Background section of this booklet. Students may be required to do some additional research. Temperature is the easiest environmental challenge to discuss. (continued on next page) Page 19

22 assessment questions (continued) 8 What types of traits might be important for this plant s survival and successful reproduction? Answers will vary. Students may be required to do some additional research. Using the trait of temperature, sample answers might include: Short generation time for multiple generations in a summer; ability to overwinter in a mature seedling state, ability for seeds to stay fertile through winter to sprout in spring, self pollination is associated with harsher or less predictable climates to ensure viable progeny if insects not available during fertile period, etc. 9. Arabidopsis is a model organism with characterized mutations available. (See or ) Choose a mutation that produces a phenotype and describe how you think selective pressures would or would not act on such a mutation. Most obvious is albino. Low chlorophyll would make nutrition inefficient and, thus, the plant is not likely to thrive unless a lot of light available. There are many flower and life cycle mutants which would also have obvious effects. Page 20

23 EXPERIMENT DESIGN Tips The College Board encourages peer review of student investigations through both formal and informal presentation with feedback and discussion. Assessment questions similar to those on the AP exam might resemble the following questions, which also might arise in peer review: Part 3: artificial selection open inquiry: design an experiment What kinds of questions occurred to you as you completed the artificial selection activity with arabidopsis? Now that you are familiar with artificial selection for phenotypes, design an experiment to investigate one of your questions. Questions may involve artificial selection in other types of organisms, the interplay between genes and environment under different selective pressures, or the generation of genetic variability in a population. Explain the purpose of a procedural step. Identify the independent variables and the dependent variables in an experiment. What results would you expect to see in the control group? The experimental group? How does XXXX concept account for YYYY findings? Describe a method to determine XXXX. NOTE Drosophila or C.elegans offers behavioral selection and short generation time. Environmental pressure like water deprivation automatically eliminates the non-selected plants by killing them. Environmental toxins is a more topical pressure. Genetic variability provided by mutagens-most pretty dangerous. UV exposure is one of safest/easiest to control. Before starting your experiment, have your teacher check over your experiment design and initial your design for approval. Once your design is approved, investigate your hypothesis. Be sure to record all observations and data in your laboratory sheet or notebook. Use the following steps when designing your experiment. 1. Define the question or testable hypothesis. 2. Describe the background information. Include previous experiments. 3. Describe the experimental design with controls, variables, and observations. 4. Describe the possible results and how they would be interpreted. 5. List the materials and methods to be used. 6. Note potential safety issues. After the plan is approved by your teacher: 7. The step by step procedure should be documented in the lab notebook. This includes recording the calculations of concentrations, etc. as well as the actual weights and volumes used. Page 21

24 Part 3: open inquiry (continued) Notes 8. The results should be recorded (including drawings, photos, data print outs). 9. The analysis of results should be recorded. 10. Draw conclusions based on how the results compared to the predictions. 11. Limitations of the conclusions should be discussed, including thoughts about improving the experimental design, statistical significance and uncontrolled variables. 12. Further study direction should be considered. Page 22

25 Live material care guide Arabidopsis thaliana (Thale Cress or Mouse-Ear Cress) Species: : thaliana Genus: Arabidopsis Family: Brassicaceae Order: Brassicales Class: : Rosid Phylum: Angiosperm Kingdom: Plantae Conditions for Customer Ownership We hold permits allowing us to transport these organisms. To access permit conditions, click here. Never purchase living specimens without having a disposition strategy in place. There are currently no USDA requirements for this organism. In order to protect our environment, never release a live laboratory organism into the wild. Limited numbers of these seeds or plants may be shipped to Canada. Primary Hazard Considerations None Availability Arabidopsis seeds are generally available year-round. These are supplied in seed packages of 150 or 300 wild type seeds ( ). Mutant seeds are available. Seeds that are kept dry and in the refrigerator will continue to germinate past the expiration date, but at a lower rate. Individual plants are supplied are supplied by special order and are in the vegetative growth phase. These plants are shipped in pots with soil, wrapped in a plastic bag, then wrapped in corrugated cardboard Captive Care Upon receipt remove the potted plant from the bag and water immediately. is a website devoted to arabidopsis that also contains teaching resources. Set up for growth: Optimal growth temperature is C. Grow lights on a timer to deliver 16 hrs of light: 8 hrs of dark at an intensity of µmol/m 2 /s is optimal. Media: A mixture of equal parts potting soil, perlite and vermiculite is optimal, although arabdopsis is very tolerant of many types of welldrained soil. Alternatively: agar medium in a Petri dish is often used for germination studies for better visibility. The agar is generally 0.1% in water. A weak standard fertilizer, like Miracle Grow, can be added to the water, but be careful not to over-fertilize or leaves will yellow and the plant will fall over. Full grown plants are cm tall. Page 23

26 Live material care guide (continued) Captive Care (continued) Planting: Place arabidopsis seeds in about 1 ml of fresh water in microfuge tube and place in a refrigerator for 2-4 days (but not longer than a week). This cold snap will improve germination. Seeds should be sown on top of fluffy soil since they need light to germinate efficiently. Germination should occur in 1-5 days. Carefully monitor moisture until plants get to 4-5 leaf stage (7-10 days after planting). After this time, the tray can dry out periodically. Fungus gnats and aphids are the most common pests affecting lab-grown arabidopsis. Orthene, at a 1:50 dilution misted onto the plants can control aphids; gnats are harder to eliminate. Information Lfie Cycle/Span: Typical dicot, 1-5 days for germination. Flowers appear about 3 weeks from planting. Seeds mature about 6 weeks from initial planting. These plants are generally self fertilizing, with a low rate of cross-fertilization. Cross-fertilization can be accomplished in a laboratory, using a paintbrush to transfer pollen from the flower of one plant to the pistil of the plant to be fertilized. Arabidopsis is a member of the mustard family (Brassacacaea or Crusiferea) which includes many human food species including radishes, cress, cabbage, broccoli, cauliflower, kale and Brussels sprouts. Arabidopsis is a weed with a small genome of about 125 Mb that has been fully sequenced since Agrobacterium tumefaciens can be used for molecular transformation. Many mutants and their sequences have been characterized. Wild Habitat Arabidopsis originated in Europe, Asia and Africa but it is now found world-wide as you might expect for a successful weed. It is consumed by herbivores like rabbits, flea beetles and butterfly or gnat larvae. It is usually an annual plant that can overwinter in the early part of its vegetative life cycle followed by flowering in the spring. Disposition We do not recommend releasing any laboratory specimen into the wild, and especially not specimens that are not native to the environment. When finished with your plant please dispose of it by incineration in a well-ventilated area. US: P.O. Box Rochester, NY A Fiero Lane San Luis Obispo, CA Canada: 399 Vansickle Road St. Catharines, ON L2S 3T Page 24