Materials
24 Student Booklets (10 AP® Biology practice free-response questions per booklet, with space for answers)
Teacher Tips
- There are many ways these booklets may be incorporated into an AP® Biology course. Teachers may choose to assign a weekly question as the AP Biology Exam approaches or they may choose to assign the 10 questions as one assignment. The booklet is meant to help teachers prepare students for the AP Biology Exam in a manner befitting teachers’ unique students and classes.
- The booklet includes three 10-point questions and seven 4-point questions. Students should spend approximately 5–10 minutes answering each 4-point question and approximately 20–25 minutes answering each 10-point question. The booklet’s questions cover topics from the four AP Biology big ideas, and individual questions often cover multiple big ideas.
- The AP exam includes two 10-point long answer questions and three 4-point and three 3-point short answer questions. This portion of the exam begins with a 10-minute reading-only period followed by 80 minutes of reading and writing. Students may not take any notes during the reading-only period. For further details, please consult the AP Biology Course and Exam Description published by the College Board.
- Student answers to the questions will vary. The answers provided herein offer guidelines for answers. Student answers should be detailed and answer the question that is being asked. Answers should be in complete sentences.
- Provide a copy of the Equations and Formulas Sheet available from The College Board website for students to use for Questions 7, 8 and 10.
- Reproduction permission for only the student booklet is granted only to the science teacher who purchased FB2091 from Flinn Scientific, Inc. No part of the booklet or the accompanying Teacher’s Notes publication may be included on any website.
Further Extensions
Alignment with the Curriculum Framework for AP® Biology
Question 1
Essential Knowledge
1A1: Natural selection is a major mechanism of evolution.
1A2: Natural selection acts on phenotypic variations in populations. a) Environments change and act as selective mechanisms on populations.
2D1: All biological systems from cells and organisms to populations, communities and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy.
3C1: Changes in genotype can result in changes in phenotype. d) Changes in genotype may affect phenotypes that are subject to natural selection. Genetic changes that enhance survival and reproduction can be selected by environmental conditions.
4C2: Environmental factors influence the expression of the genotype in an organism. a) Environmental factors influence many traits both directly and indirectly. b) An organism’s adaptation to the local environment reflects a flexible response of its genome.
Learning Objectives
1.2: The student is able to evaluate evidence provided by data to qualitatively and quantitatively investigate the role of natural selection in evolution.
1.4: The student is able to evaluate data-based evidence that describes evolutionary changes in the genetic makeup of a population over time.
1.5: The student is able to connect evolutionary changes in population over time to a change in the environment.
2.22: The student is able to refine scientific models and questions about the effect of complex biotic and abiotic interactions on all biological systems, from cells and organisms to populations, communities and ecosystems.
2.23: The student is able to design a plan for collecting data to show that all biological systems (cells, organisms, populations, communities and ecosystems) are affected by complex biotic and abiotic interactions.
3.24: The student is able to predict how a change in genotype, when expressed as a phenotype, provides a variation that can be subject to natural selection.
4.23: The student is able to construct explanations of the influence of environmental factors on the phenotype of an organism.
4.24: The student is able to predict the effects of a change in an environmental factor on the genotypic expression of the phenotype.
Science Practices
1.1: The student can create representations and models of natural or man-made phenomena and systems in the domain.
3.1: The student can pose scientific questions.
3.2: The student can refine scientific questions.
4.2: The student can design a plan for collecting data to answer a particular scientific question.
5.1: The student can analyze data to identify patterns or relationships.
Question 2
Essential Knowledge
1B1: Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today. a) Structural and functional evidence supports the relatedness of all domains. b) Structural evidence supports the relatedness of all eukaryotes.
2B1: Cell membranes are selectively permeable due to their structure. a) Cell membranes separate the internal environment of the cell from the external environment.
2B2: Growth and dynamic homeostasis are maintained by the constant movement of molecules across membranes.
2B3: Eukaryotic cells maintain internal membranes that partition the cell into specialized regions.
2D3:Biological systems are affected by disruptions to their dynamic homeostasis. a) Disruptions at the molecular and cellular levels affect the health of the organism.
Learning Objectives
1.16: The student is able to justify the scientific claim that organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.
2.10: The student is able to use representations and models to pose scientific questions about the properties of cell membranes and selective permeability based on molecular structure.
2.11: The student is able to construct models that connect the movement of molecules across membranes with membrane structure and function.
2.12: The student is able to use representations and models to analyze situations or solve problems qualitatively and quantitatively to investigate whether dynamic homeostasis is maintained by the active movement of molecules across membranes.
2.13: The student is able to explain how internal membranes and organelles contribute to cell functions.
Science Practices
1.4: The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
3.1: The student can pose scientific questions.
6.1: The student can justify claims with evidence.
6.2: The student can construct explanations of phenomena based on evidence produced through scientific practices.
7.2: The student can connect concepts in and across domains to generalize or extrapolate in and/or across enduring understandings and/or big ideas
Question 3
Essential Knowledge
2D3: Biological systems are affected by disruptions to their dynamic homeostasis. a. Disruptions at the molecular and cellular levels affect the health of the organism.
2E1: Timing and coordination of specific events are necessary for the normal development of an organism, and these events are regulated by a variety of mechanisms.
3A3: The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. a. Certain human genetic disorders can be attributed to the inheritance of single gene traits or specific chromosomal changes, such as nondisjunction.
4A1: The subcomponents of biological molecules and their sequence determine the properties of that molecule.
4A2: The structure and function of subcellular components, and their interactions, provide essential cellular processes.
Learning Objectives
2.28: The student is able to use representations or models to analyze quantitatively and qualitatively the effects of disruptions to dynamic homeostasis in biological systems.
2.34: The student is able to describe the role of programmed cell death in development and differentiation, the reuse of molecules, and the maintenance of dynamic homeostasis.
3.12: The student is able to construct a representation that connects the process of meiosis to the passage of traits from parent to offspring.
4.3: The student is able to use models to predict and justify that changes in the subcomponents of a biological polymer affect the functionality of the molecule.
4.5: The student is able to construct explanations based on scientific evidence as to how interactions of subcellular structures provide essential functions.
Science Practices
5.1: The student can analyze data to identify patterns or relationships.
5.3: The student can evaluate the evidence provided by data sets in relation to a particular scientific question.
6.1: The student can justify claims with evidence.
Question 4
Essential Knowledge
1A1: Natural selection is a major mechanism of evolution.
1A2: Natural selection acts on phenotypic variations in populations.
1A3: Evolutionary change is also driven by random processes.
1B1: Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.
4A2: The structure and function of subcellular components, and their interactions, provide essential cellular processes.
Learning Objectives
1.2: The student is able to evaluate evidence provided by data to qualitatively and quantitatively investigate the role of natural selection in evolution.
1.4: The student is able to evaluate data-based evidence that describes evolutionary changes in the genetic makeup of a population over time.
1.16: The student is able to justify the scientific claim that organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.
4.4: The student is able to make a prediction about the interactions of subcellular organelles.
4.5: The student is able to construct explanations based on scientific evidence as to how interactions of subcellular structures provide essential functions.
4.6: The student is able to use representations and models to analyze situations qualitatively to describe how interactions of subcellular structures, which possess specialized functions, provide essential functions.
Science Practices
1.4: The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
1.5: The student can re-express key elements of natural phenomena across multiple representations in the domain.
5.3: The student can evaluate the evidence provided by data sets in relation to a particular scientific question.
6.1: The student can justify claims with evidence.
6.2: The student can construct explanations of phenomena based on evidence produced through scientific practices.
6.4: The student can make claims and predictions about natural phenomena based on scientific theories and models.
7.1: The student can connect phenomena and models across spatial and temporal scales.
Question 5
Essential Knowledge
1A1: Natural selection is a major mechanism of evolution.
1A2: Natural selection acts on phenotypic variations in populations.
3C1: Changes in genotype can result in changes in phenotype.
4A5: Communities are composed of populations of organisms that interact in complex ways.
4B3: Interactions between and within populations influence patterns of species distribution and abundance.
Learning Objectives
1.1: 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.
1.2: The student is able to evaluate evidence provided by data to qualitatively and quantitatively investigate the role of natural selection in evolution.
1.3: 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.
1.4: The student is able to evaluate data-based evidence that describes evolutionary changes in the genetic makeup of a population over time.
1.5: The student is able to connect evolutionary changes in population over time to a change in the environment.
3.24: The student is able to predict how a change in genotype, when expressed as a phenotype, provides a variation that can be subject to natural selection.
3.26: The student is able to explain the connection between genetic variations in organisms and phenotypic variations in populations.
4.11: The student is able to justify the selection of the kind of data needed to answer scientific questions about the interaction of populations within communities.
4.19: The student is able to use data analysis to refine observations and measurements regarding the effect of population interactions on patterns of species distribution and abundance.
4.20: The student is able to explain how the distribution of ecosystems changes over time by identifying large-scale events that have resulted in these changes in the past.
Science Practices
1.3: The student can refine representations and models of natural or man-made phenomena and systems in the domain.
3.1: The student can pose scientific questions.
6.1: The student can justify claims with evidence.
6.4: The student can make claims and predictions about natural phenomena based on scientific theories and models.
Question 6
Essential Knowledge
2A2: Organisms capture and store free energy for use in biological processes. a) Autotrophs capture free energy from physical sources in the environment.
2D1: All biological systems from cells and organisms to populations, communities and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy.
4A6: Interactions among living systems and with their environment result in the movement of matter and energy.
Learning Objectives
2.4: The student is able to use representations to pose scientific questions about what mechanisms and structural features allow organisms to capture, store and use free energy.
2.5: The student is able to construct explanations of the mechanisms and structural features of cells that allow organisms to capture, store or use free energy.
2.22: The student is able to refine scientific models and questions about the effect of complex biotic and abiotic interactions on all biological systems, from cells and organisms to populations, communities and ecosystems.
2.23: The student is able to design a plan for collecting data to show that all biological systems (cells, organisms, populations, communities and ecosystems) are affected by complex biotic and abiotic interactions.
Science Practices
1.3: The student can refine representations and models of natural or man-made phenomena and systems in the domain.
1.4: The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
3.2: The student can refine scientific questions.
4.1: The student can justify the selection of the kind of data needed to answer a particular scientific question.
6.2: The student can construct explanations of phenomena based on evidence produced through scientific practices.
7.2: The student can connect concepts in and across domains to generalize or extrapolate in and/or across enduring understandings and/or big ideas.
Question 7
Essential Knowledge
2C2: Organisms respond to changes in their external environments. a) Organisms respond to changes in their environment through behavioral and physiological mechanisms.
2D3: Biological systems are affected by disruptions to their dynamic homeostasis. a) Disruptions at the molecular and cellular levels affect the health of the organism.
Learning Objectives
2.21: The student is able to justify the selection of the kind of data needed to answer scientific questions about the relevant mechanism that organisms use to respond to changes in their external environment.
2.28: The student is able to use representations or models to analyze quantitatively and qualitatively the effects of disruptions to dynamic homeostasis in biological systems.
Science Practices
1.4: The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
4.1: The student can justify the selection of the kind of data needed to answer a particular scientific question.
Question 8
Essential Knowledge
2A3: Organisms must exchange matter with the environment to grow, reproduce, and maintain organization. b) Surface area-to-volume ratios affect a biological system’s ability to obtain necessary resources or eliminate waste products.
2B1: Cell membranes are selectively permeable due to their structure.
2B2: Growth and dynamic homeostasis are maintained by the constant movement of molecules across membranes.
Learning Objectives
2.10: The student is able to use representations and models to pose scientific questions about the properties of cell membranes and selective permeability based on molecular structure.
2.11: The student is able to construct models that connect the movement of molecules across membranes with membrane structure and function.
2.12: The student is able to use representations and models to analyze situations or solve problems qualitatively and quantitatively to investigate whether dynamic homeostasis is maintained by the active movement of molecules across membranes.
Science Practices
1.1: The student can create representations and models of natural or man-made phenomena and systems in the domain.
1.4: The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
2.2: The student can apply mathematical routines to quantities that describe natural phenomena.
3.1: The student can pose scientific questions.
4.1: The student can justify the selection of the kind of data needed to answer a particular scientific question.
6.2: The student can construct explanations of phenomena based on evidence produced through scientific practices.
Question 9
Essential Knowledge
3A1: DNA, and in some cases RNA, is the primary source of heritable information. a) The proof that DNA is the carrier of genetic information involved a number of important historical experiments. These include: Hershey–Chase experiment.
Learning Objectives
3.1: The student is able to construct scientific explanations that use the structures and mechanisms of DNA and RNA to support the claim that DNA and, in some cases, that RNA are the primary sources of heritable information.
3.2: The student is able to justify the selection of data from historical investigations that support the claim that DNA is the source of heritable information.
3.3: The student is able to describe representations and models that illustrate how genetic information is copied for transmission between generations.
Science Practices
1.2: The student can describe representations and models of natural or man-made phenomena and systems in the domain.
4.1: The student can justify the selection of the kind of data needed to answer a particular scientific question.
6.4: The student can make claims and predictions about natural phenomena based on scientific theories and models.
6.5: The student can evaluate alternative scientific explanations.
Question 10
Essential Knowledge
2A3: Organisms must exchange matter with the environment to grow, reproduce, and maintain organization. b) Surface area-to-volume ratios affect a biological system’s ability to obtain necessary resources or eliminate waste products.
2B1: Cell membranes are selectively permeable due to their structure.
2B2: Growth and dynamic homeostasis are maintained by the constant movement of molecules across membranes.
Learning Objectives
2.6: The student is able to use calculated surface area-to-volume ratios to predict which cell(s) might eliminate wastes or procure nutrients faster by diffusion.
2.7: Students will be able to explain how cell size and shape affect the overall rate of nutrient intake and the rate of waste elimination.
2.10: The student is able to use representations and models to pose scientific questions about the properties of cell membranes and selective permeability based on molecular structure.
2.11: The student is able to construct models that connect the movement of molecules across membranes with membrane structure and function.
2.12: The student is able to use representations and models to analyze situations or solve problems qualitatively and quantitatively to investigate whether dynamic homeostasis is maintained by the active movement of molecules across membranes.
Science Practices
1.1: The student can create representations and models of natural or man-made phenomena and systems in the domain.
1.4: The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
2.2: The student can apply mathematical routines to quantities that describe natural phenomena.
3.1: The student can pose scientific questions.
4.1: The student can justify the selection of the kind of data needed to answer a particular scientific question.
6.2: The student can construct explanations of phenomena based on evidence produced through scientific practices.
Answers to Questions
Question 1
You have been asked to design a procedure to create a strain of Escherichia coli that will survive in a nutrient broth that contains 11% sodium chloride. In order to focus on the procedure itself, the use of aseptic technique will be assumed.
- Design the procedure. The procedure must include reference to the following: (4 points maximum) (1 point maximum for controls, 1 point maximum for defining the starting culture, 1 point maximum for the procedure, 1 point maximum for a method to ensure the end bacteria is the same strain as the starting bacteria.)
Appropriate responses include but are not limited to the following:
- Controls: A single strain of E. coli, temperature, humidity control, incubation time, nutrients provided.
- Description of starting point: Nutrient broth with no salt added.
- Procedure: Incremental addition of sodium chloride to successive cultures.
- Method to ensure starting and ending bacteria are the same: PCR and electrophoresis or Gram stain.
- Based upon your procedure, list three of the materials needed to conduct the procedure you developed above. Equipment for aseptic technique is assumed and should not be listed. For each item, explain its purpose in the experiment. (6 points maximum)
Appropriate materials and their purpose include but are not limited to the following: (2 points each correct pair; 6 points maximum).
{11238_Answers_Table_1}
Question 2
Yeast cells are hardy, unicellular, eukaryotic organisms that divide quickly. Consequently yeast cells are used as a model organism to study eukaryotic organelles, nuclear components, cytoplasm and the cell membrane. In order to study the transportation of molecules across the cell membrane, the study must take into account the features of the cytoplasm and the cell’s external environment. The study must also include a way to record a change in the cytoplasm due to the molecule of interest. This experiment will test the transportation of alkaline molecules across the yeast cell membrane. Two considerations when working with living cells are to pick a stain that does not immediately kill the cell and to pick a stain that will change color to show the item being studied. Many stains used in biology change color based upon the pH of the system. These are called acid–base indicators. Untreated yeast cytoplasm has a pH of about 5.3. The experiment will test three different alkaline solutions. All are 0.01 M with a pH of 8.5. Data Table 1. Possible Acid–Base Indicators
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Data Table 2. Yeast–Indicator Results
{11238_Answers_Table_3}
- From the list in Data Table 1, identify the best indicator to use. Explain what makes that indicator the best choice.(2 points maximum)
Identification: Neutral red (1 point maximum)
Explanation: Neutral red appears red in solutions with a pH less than 6.8. However, neutral red appears yellow in solutions with a pH greater than 8.0. The pH of the three solutions is 8.5, so if the alkaline solution crossed into the cytoplasm, the neutral red will change from red to yellow. None of the other indicators have a color change between 5.3 and 8.5 so the indicator will not change color as needed for this experiment. (1 point maximum)
- Identify the best indicator for the same experiment replicated using three different dilute acid solutions all with a pH of 2.5. Explain what makes that indicator the best choice. (2 points maximum)
Identification: Congo red (1 point maximum)
Explanation: Congo red appears red in solutions with a pH greater than than 5.0. However, congo red appears blue in solutions with a pH less than 3.0. The pH of the three solutions is 2.5, so if the acid solution crossed into the cytoplasm, the congo red will change from red to blue. None of the other indicators have a color change between 5.3 and 2.5, so the indicator will not change color as needed for this experiment. (1 point maximum)
- In the initial experiment, identical amounts of the yeast suspension and alkaline solutions were mixed. Small samples of the resulting mixture were viewed using a light microscope. Data Table 2 contains the results of the experiment. Evaluate the observations in Data Table 2. Is there any evidence for transport of the alkaline solution into the yeast cell? Identify which, if any, alkaline solution(s) show transport across the yeast cell membrane. Justify your answer. (2 points maximum)
Identification: Sodium hydroxide solution (1 point maximum)
Justification: Only the sodium hydroxide solution crossed the yeast cell membrane. All three alkaline solutions had a pH of 8.5. When neutral red is within a solution with a pH more alkaline than 8.0, it will appear yellow instead of the red shown in the untreated cytoplasm. Consequently the color change noted in Data Table 2 for sodium hydroxide indicates that the neutral red is now in an alkaline solution that was created when the sodium hydroxide moved into the cytoplasm from the solution outside of the cell. (1 point maximum)
- Explain why is it important to view the yeast cells using a light microscope? (1 point maximum)
Explanation: As part of the experiment, it is important to ensure the cells did not rupture because of the experiment. The cells are easily visible using a light microscope to make sure they still have the same shape as the cells in the control sample.
- The experiment described was designed to determine if one or more alkaline solutions cross the yeast cell membrane. Assuming that an indicating stain exists, a new experiment is being designed to test if the three cations listed in the experiment above are transported if they are combined with chlorine anions instead of hydroxide anions. Name the three chemicals to be tested.(3 points maximum, one point for each chemical)
The three new chemicals to be tested are ammonium chloride, potassium chloride, and sodium chloride.
Question 3 Tay-Sachs is a disease that occurs following an autosomal recessive pattern. The disease is caused by one or more changes in the hexosaminidase-A (HEXA) gene on the long arm of chromosome 15. The HEXA gene and a separate gene called the HEXB gene are responsible for making the two parts of an enzyme that breaks down a fatty substance called GM2-ganglioside within nerve cell lysosomes. It is the build-up of GM2-ganglioside that causes damage to nerves and ultimately death.
- If the father is a known carrier, but the mother is not, what are the chances of their children exhibiting the symptoms of Tay-Sachs disease? Explain. (1 point maximum)
Explanation: Since only the father is a carrier, none of the children will show symptoms of Tay-Sachs disease.
- If the mother and father both have abnormal HEXA genes, what are the chances of their children having Tay-Sachs? Explain. (1 point maximum)
Explanation: Since Tay-Sachs is an autosomal recessive disease, each child would have a 25% chance of acquiring a mutated gene from both parents. The child must have two copies of the faulty gene in order to show Tay-Sachs disease.
- Which areas of the body show the most GM2-ganglioside buildup? Justify your answer. (1 point maximum)
Justification: Since the GM2-ganglioside buildup is within nerve cell lysosomes, the damage would be seen within areas with numerous nerve cells such as the brain and spinal cord.
- Since the symptoms of the disease occur due to damage caused by a buildup of the toxic GM2-ganglioside, would you expect this disease to cause death immediately or would a slow decline occur? Justify your answer. (1 point maximum)
Justification: For death to occur, numerous nerve cells would have to be damaged by the buildup of GM2-ganglioside. Therefore a slow decline in nerve processes would occur.
- Detailed DNA sequencing of both carriers and affected individuals has revealed several types of mutations. The most common mutation is a four base pair insertion in the gene. A new termination codon results from this insertion. Explain how insertion leads to a defective protein. (1 point maximum)
Explanation: Transcription of the gene would cease at the termination codon. The mRNA would be translated, but it would be a truncated and mutated protein that is formed. This part of the protein would be nonfunctional and even if paired with the HEXB gene, the entire unit is not able to rid the cell of GM2-ganglioside.
- The second most common mutation is a single nucleotide change from guanine to cytosine. Explain how a single point mutation leads to a defective protein. (1 point maximum)
Explanation: If the single mutation occurs in the first or second position of a codon, then the codon may code for a different amino acid. Since the amino acid sequence determines the primary and often secondary and tertiary structure, the mutation could lead to an altered, nonfunctional protein.
- The third most common mutation is a 7.6 kb deletion. Explain how a deletion leads to a defective protein. (1 point maximum)
Explanation: This mutation would remove over 2500 amino acids from the finished protein. The primary, secondary and tertiary levels of protein structure would all be affected, and the protein would be compromised.
- Predict the consequences of a normal HEXA gene but a mutated HEXB gene. (1 point maximum)
Prediction: Mutations in the HEXB gene would also lead to enzyme problems that could cause Tay-Sachs or another, closely related disease.
- Pose two treatments for Tay-Sachs patients. (2 point maximum)
Possible treatments include but are not limited to the following: Gene therapy, STEM cell therapy, and enzyme replacement therapies.
Question 4Wild-type Drosophila melanogaster have brick-red eyes. The brick-red eye color is actually the product of two biochemical pathways—the ommochrome pathway leading to the synthesis of brown pigments and the pteridine pathway that contributes to the red, yellow and blue pigments. Each pathway consists of several steps, shown below. Genetic mutations that affect any of the proteins involved in either pathway give rise to the variety of eye colors seen in D. melanogaster. The following diagrams are simplified versions of the two pigment pathways. Note the intermediary proteins, the enzymes (represented by arrows) and the resulting pigments.
{11238_Answers_Figure_1}
- Evaluate the data presented. If a scientist wanted to conduct a study using just brown-eyed D. melanogaster, identify which pigment(s) would need to be mutated? Justify your choice. (2 points maximum)
Identification: 2-Amino-4-hydroxypteridine (1 point maximum)
Justification: Mutating the precursor 2-amino-4-hydroxypteridine would keep all of the pigments in the pteridine pathway from contributing to the final eye color leaving only the ommochrome pathway and therefore brown-eyed flies. (1 point maximum)
- Pose one possible explanation which would result in a no eye pigment phenotype. (1 point maximum)
Appropriate explanations include but are not limited to the following:
- No eye pigments would result in a white-eyed D. melanogaster. In order to not have any eye pigments present, their must be mutations early in both the pteridine and ommochrome pathways.
- White-eyed D. melanogaster may be the result of a mutation in the gene that codes for the proteins responsible for transporting the pigments to the eye.
- Pigments are often evolutionarily conserved. The pigments in the pteridine pathway are among those highly conserved in Animalia. A recent study conducted by a UCLA scientist found that female guppies preferred a particular shade of orange when choosing a mate. Assuming the pigments and pathways were conserved, identify which pigment(s) are likely present in the preferred male guppies? (1 point maximum)
Identification: Both drosopterin and isosepiapterin must be present in the proper ratio to create the preferred orange coloration in the male guppy.
Question 5 The Sonoran Desert biome is filled with tan rocks and sand interspersed with sturdy, drought-tolerant plants such as cacti. Ancient volcanoes and cinder cone “islands” are also located throughout the Sonoran Desert area. In these areas, the ground is a darker brown-black color. Beginning in the 1930s, researchers began studying coat color in populations of the rock pocket mouse on the islands of dark lava and cinders versus the predominant light-colored desert areas. Decades of data point to a natural selection due to predation pressure. In the last decade, researchers have begun to study the molecular basis of the variations seen in the rock pocket mouse. In one study, DNA was collected and sequenced from two adjacent light and dark area populations. DNA sequencing of two specific genome areas determined that differences in coat color for the populations was a result of a mutation in the Mc1r gene. This mutation follows a dominant inheritance pattern.
- Predict the predominant coat color of a population of rock pocket mice living on a volcanic cinder cone. Explain your reasoning. (2 points maximum)
Prediction: Darker coat (1 point maximum)
Explanation: Appropriate explanations include but are not limited to the following (1 point maximum):
- The lighter-colored rock pocket mouse would be more easily seen by predators on the dark-colored ground leading to a greater predation rate.
- The rock pocket mice born with the Mc1r mutation would be camouflaged on the dark-colored ground thus evading predators.
- A genetic mutation can be random but natural selection is not. State a hypothesis that could be tested. (1 point maximum)
Appropriate hypotheses include but are not limited to the following:
- The color coat found on mice in the darker-colored region will not differ from that in an adjacent light region.
- Design an experiment to confirm this occurrence is a result of natural selection. (1 point maximum)
Appropriate experiments include but are not limited to the following:
- In order to determine that this natural selection is not random, mice should be examined in a different geographical region under similar conditions. For example, find another location that has been subjected to a volcanic eruption for a similar amount of time. Capture the mice and study which gene was mutated to result in the color change. If it is a different gene that resulted in the color change then it is not random. Natural selection is occurring if that phenotype takes over a greater percentage of the population.
Question 6 A group of students decided to study the transfer of energy from wheat to mealworms. The data from the first part of their lab follows.
{11238_Answers_Table_4}
- Explain why it is best to dry the plants when determining the amount the plant has grown. (1 point maximum)
Appropriate explanations include but are not limited to the following:
- The mass of the water within a plant varies because the availability of water changes as the time since watering changes. By removing the mass of water from the equation, only the plant solids are considered.
- Justify the need to mass more than one plant at each step of the procedure. (1 point maximum)
Appropriate justifications include but are not limited to the following:
- Like all living things, plants vary in size. Using 100 plants allows the scientist to calculate the average plant mass for a large population of plants, thus reducing the influence of a single plant in the experiment.
Mealworms are the larval form of the Tenebrio beetle. Tenebrio undergo complete metamorphosis. The larval and adult forms eat wheat bran, which is part of the wheat seed. One of the metabolic pathways used by the Tenebrio is able to convert carbohydrates in the wheat bran into metabolic water, and therefore they do not need to consume water. A literature search revealed that dehydrated Tenebrio weigh about 65% less than living Tenebrio and that Tenebrio larva has an overall energy value of 6.5 kcal/gram. Assume the same experimental design used in Part A was used to determine the net productivity of the Tenebrio.
- Identify one other factor that should be measured in addition to the amount of food consumed and the mass of the Tenebrio larva? Justify your answer. (2 points maximum)
Identification: Waste (frass) (1 point maximum)
Justification: In order to determine the total energy used by the Tenebrio, the frass (waste) must be massed as well. The Tenebrio use their food for growth and homeostasis. The energy used for growth is converted into new animal mass, but wastes produced during homeostasis are eliminated from the Tenebrio. The mass of the waste is not part of the food but must be calculated as part of the Tenebrio energy use. (1 point maximum)
Question 7 A study was conducted to determine if wild-type Drosophila melanogaster become sedated when exposed to high concentrations of ethyl alcohol. In the initial study, 150 adult wild-type Drosophila were exposed to 100 ppm ethyl alcohol in a specially designed one-liter chamber called an inebriometer. The 150 flies were released in the top of the chamber and allowed to become acclimated to the gentle flow of humidified air for 20 minutes before the experiment began. After 20 minutes most of the flies were still near the top of the chamber and none were sedated. The humidity remained constant, but a stream of ethyl alcohol was fed into the air stream. After 20 minutes the number of sedated flies was counted and the stream of ethyl alcohol was stopped. In 20 minutes, 29 adult flies had become sedated in the test chamber while no flies were sedated in an identical control chamber into which no ethyl alcohol was streamed. A second study was conducted using the same experimental parameters except the adult flies were separated into two groups. Neither group had been previously exposed to ethyl alcohol. The data are in the following table. Data Table 1
{11238_Answers_Table_5}
- Pose one scientific question that the researchers were most likely investigating in the second study? (1 point maximum)
Students should be specific and state the study animal, the tested outcome and any relevant study parameters.
Appropriate scientific questions include but are not limited to the following:
- Does gender affect the number of Drosophila sedated by ethyl alcohol?
- Specify the null hypothesis that could be tested to address the question you posed in part a. Perform a chi-square test on the data for the second study. (2 points maximum)
The equation for chi-square and the chi-square table both appear on the AP Biology Equations and Formulas Sheet given to students during the exam.
Null Hypothesis: (1 point)
Gender is not a factor in the sedation of adult wild-type Drosophila by 100 ppm ethyl alcohol over a 20-minute period in a 1-L inebriometer.
{11238_Answers_Table_6}
- Explain whether the null hypothesis is supported by the chi-square test and justify your explanation. (1 point maximum)
Using one degree of freedom and a p value of 0.05, the maximum value to fail to reject the null hypothesis is 3.84. The calculated chi-square value for the adult male Drosophila is 1.24, which is less than 3.84, so the null hypothesis fails to reject. The calculated chi-square value for the adult female Drosophila is 52.4, which is greater than 3.84, so the null hypothesis is rejected.
Question 8 In a water potential investigation, cylinders of crosne (a type of tuber plant) are placed in sucrose solutions of various concentrations in order to determine the water potential of the crosne. Each cylinder of crosne has a 0.3-cm radius and a 2-cm height. The lab was conducted at a constant temperature of 20 ºC in an open beaker.
{11238_Answers_Table_7}
- When a crosne cylinder is placed in a 2 M sucrose solution, will water flow into or out of the tuber? Explain your reasoning. (1 point maximum)
Explanation: Must include information about how water will move from the area with a higher solute potential to the area with a lower solute potential. At sucrose concentrations ≥ 0.4 M, the crosne loses mass as it loses water to the surrounding solution indicating the potential of the surrounding solution is lower than that of the tuber.
- Based on the data above, calculate the water potential of the crosne. (1 point maximum)
This equation is on the AP Biology Equations and Formulas Sheet that will be available on the exam day.
Ψs = –iCRT
“i” is the ionization constant (for sucrose this is 1.0 because it does not ionize in water).
C is the molar concentration.
R is the pressure constant (R = 0.0831 liters • bar/mole • K).
T is the absolute temperature of solution in Kelvin (K = 273 + °C).
= –1(0.4 mole/liter)(0.0831 liter • bar/mole • K)(293 K)
= –9.739 bars
- Assume the same sucrose solutions were used and a sweet potato trial was conducted simultaneously with the crosne experiment above. A literature search determined that a sweet potato has a water potential of –19.5 bars. At what sucrose concentration would you expect to find minimal mass loss or gain in the cylinders of sweet potato? (1 point maximum)
–19.5 bars = –1(X mole/liter)(0.0831 liter • bar/mole • K)(293 K)
–19.5 bars = –24.35X
X = 0.8 M
- Apply the concept of water potential to the following question. Explain why most experiments that involve cells or living organisms use buffer solutions instead of deionized water as the matrix in which the experiment is conducted. (1 point maximum)
Explanation: Must include information about how deionized water has a water potential of zero and the cells or living organisms have negative water potential so water would move into the cells, potentially damaging the cells or organism.
Question 9In 1952, Alfred Hershey and Martha Chase conducted a series of experiments using a T2 bacteriophage. At that time it was generally thought that proteins were the molecules responsible for genetic instructions, but others felt that DNA was responsible. Hershey and Chase conducted a set of experiments to determine which molecule was responsible. The structure of the T2 bacteriophage was already known, its host was easy to culture, and the method of infection had been visualized using transmission electron microscopy. The T2 bacteriophage infects Escherichia coli. This simple phage consists of a protein outer coat and a double strand of DNA. The experimental procedure used radioisotopes of phosphorus and sulfur. Two cultures were set up. In one, the phage and initial host E. coli were cultured with radioactive sulfur. In the other, the phage and initial host E. coli were cultured with radioactive phosphorus.
- Explain, in detail, why radioisotopes of carbon or nitrogen would not have provided the same conclusion and justify your explanation. (1 point maximum)
Explanation with justification: Response must clarify the following:
Both carbon and nitrogen are found in many cellular components.
The source of the radioactivity would have been inconclusive since they would have been found everywhere in the culture.
Sulfur is not found in DNA but is found in proteins.
Phosphorous is found in proteins but is very prevalent in DNA.
In the 1952 experiment, the phage was allowed to infect, replicate, and lyse the initial host E. coli within a culture media that contained radioactive sulfur. Then the culture was separated to harvest the radioactive phage from the remnants of the host cells. Next, the radioactive phages were introduced into a new E. coli culture that did not contain radioactive isotopes. The phages were allowed to infect, but not rupture, the host cells. The culture was agitated to dislodge the now empty protein outer coat from the infected bacteria. Then the sample was centrifuged and separated into supernatant and cells. The supernatant contained the less dense material including the culture media and empty viral coat.
- Explain, in detail, why the culture wasn’t allowed to progress beyond infection? Justify your explanation. (1 point maximum)
Explanation with justification: Response must clarify the following:
The components must be separated before the infected cells rupture.
Rupture would release newly formed phages into the supernatant and away from the enclosure that the infected cell provides so radioactivity would be found in both the supernatant and the cell debris. No conclusion could be drawn.
- In the second half of the experiment, the same growth protocol was followed, but instead of radioactive sulfur, the culture media contained radioactive phosphorus. Instead of simply separating the sample into supernatant and cells, the cells were ruptured and further separated into organelles, proteins and nucleic acids. Predict the location of the largest amount of the radioactive phosphorus at the end of the experiment. Justify your answer. (2 points maximum)
Prediction: 1 point maxiumum
Within the DNA portion.
Justification: 1 point maximum
Response must include reference to: DNA contains a far greater quantity of phosphorus than proteins.
Question 10 When agar is prepared using phenolphthalein and sodium hydroxide, the solidified agar has a pink color. Phenolphthalein is an indicator that is colorless below pH 10 but pink at any pH greater than 10. In a diffusion experiment, a phenolphthalein agar sphere (2 cm diameter) and phenolphthalein agar cube (each side 2 cm long) were placed in a dilute 0.1 M hydrochloric acid solution for 10 minutes. Both shapes were gently agitated every minute to ensure the areas adjacent to each shape did not reach equilibrium. After 10 minutes both the sphere and the cube were cut in half and the colorless agar depth was measured using a standard ruler.
{11238_Answers_Figure_2}
- Calculate the diffusion rate of the hydrochloric acid for each shape. (2 points maximum)
Sphere: 1 point maximum
5mm/10 minutes = 0.5 mm/min
Cube: 1 point maximum
5mm/10 minutes = 0.5 mm/min
- If the two shapes were actual living cells, does one shape offer an advantage for the diffusion of nutrients into and wastes out of the cell? Explain and justify your answer mathematically. (2 points maximum)
The following equations are on the AP Biology Equations and Formulas that will be available on the exam day.
In order to answer this question, one must determine the surface area-to-volume ratio of each shape.
{11238_Answers_Equation_1}
Explanation: 1 point maximum
According to the data presented in this experiment they would be equally efficient because they have the same diffusion rate and surface area-to-volume ratio.
Mathematical justification: 1 point maximum
{11238_Answers_Table_9}
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