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Unformatted text preview: AP® Biology 2009 Scoring Guidelines The College Board
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An experiment on a species of small freshwater fish recorded their behavioral responses to different temperatures. Ten fish were each tested once, one at a time. To begin the experiment, a fish was removed from a stock tank (maintained at 22°C) and placed in the temperature-gradient tank drawn below. After the fish had spent 30 minutes in the temperature-gradient tank, the section where the fish was located was recorded. Additional observations were recorded every 5 minutes, for a total of 7 observations per fish. A summary of the combined data for all 10 fish appears below. Section A B C D E Fish/Section 9 11 34 12 4 (a) On the axes provided, construct the appropriate type of labeled graph showing the relationship between water temperature and fish distribution. Summarize the outcome of the experiment. (4 points maximum) Graph (1 point each; 3 points maximum for graph) • Correctly labeled and scaled axis o Temperature range may be indicated by section with legend • Correct orientation: x-axis = temp; y-axis = # fish observed • Correct bar graph/scatter plot o Discrete data points only if range is indicated o NO point for line graph Summarize (1 point maximum for summary) • Fish were distributed by temperature, e.g., most fish were observed at moderate temperature range, or 12–17°C © 2009 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP® BIOLOGY 2009 SCORING GUIDELINES
Question 1 (continued)
(b) Identify TWO variables that were not specifically controlled in the experimental design, and describe how these variables might have affected the outcome of the experiment. (4 points maximum) Variable* (1 point each; 2 points maximum) Fish characteristics, e.g., age, size, sex, schooling, health Tank characteristics, e.g., depth, shape, size, gravel, plants, sections/ends Water quality, e.g., pH, salt, chemicals, microbes Placement of fish, time in stock tank External stimuli, e.g., light, noise Oxygen concentration Time of day/biological rhythms or when observations recorded Other acceptable variables** Describe (1 point each; 2 points maximum) Age/mating behavior/sex, SA:V ratio, tendency to school may affect activity levels/distribution of fish Depth/shape/size/pressure/ends of tank may affect distribution of fish “control” tank at constant temperature Attraction/avoidance influences fish response to temperature Tendency of fish to remain where placed, effect of shock on fish Attraction/avoidance influences fish response to temperature Attraction/avoidance influences fish response to temperature Temperature preference or activity of fish differs with time of day, e.g., diurnal vs. nocturnal Other acceptable descriptions * 1 point for each variable, may include two from same category ** NOT type of fish, NOT temperature, since these were set by experimenters (c) Discuss TWO ways that water temperature could affect the physiology of the fish in this experiment. (4 points maximum) Effect (directional) (1 point each; 2 points maximum) Metabolic rate/activity increase with temperature increase Heart rate/circulation/blood flow increase with temperature increase Respiration rate, operculum movement, “breathing rate” increase with temperature increase Shock/stress prevent normal activity Gas exchange (O2 or CO2) altered at different temperatures Explanation of effect (1 point each; 2 points maximum) Related to kinetic energy, enzyme activity (NOT denaturation) Related to kinetic energy, blood vessel constriction/dilation, etc. Related to diffusion rates, metabolic rates Nervous system impairment alters fish movements Dissolved oxygen increases at lower temperatures © 2009 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP® BIOLOGY 2009 SCORING GUIDELINES
ATP and GTP are primary sources of energy for biochemical reactions. (a) Describe the structure of the ATP or the GTP molecule. (1 point each; 2 points maximum) • Adenosine + 3 phosphates or guanosine + 3 phosphates. • Elaborating on the phosphate bonds, e.g., unstable, negatively charged. Mentioning without explaining “high-energy bonds” is insufficient. • Adenosine or guanosine described as adenine or guanine bound to ribose. Note: adenine + ribose + 3 phosphates earns 2 points. (b) Explain how chemiosmosis produces ATP. (1 point each; 3 points maximum) • Electron transport, e.g., linked to proton pumps, coenzymes, NADH. • H+ pumped to one side of the membrane, photosynthesis—inside thylakoid, respiration—outside cristae. • Proton gradient established, has potential energy or capacity to do work. • ATP synthases or channel proteins generate ATP. (c) Describe TWO specific cell processes that require ATP and explain how ATP is used in each process. (4 points maximum) Description of process (1 point per process; 2 points maximum) Muscle, sliding filament; cilia or flagella, propulsion; chromosome movement in mitosis or meiosis Active transport or transport against gradient; sodium-potassium pump; endocytosis or exocytosis Hydrolysis or synthesis; specific chemical reaction, e.g., photosynthesis or glycolysis; kinase activity How ATP is used (1 point per process; 2 points maximum) ATP → ADP + P connected to process or energy coupling, e.g., conformational change in myosin head ATP → ADP + P connected to process, e.g., phosphorylating the transport protein ATP → ADP + P connected to process or energy coupling, e.g., phosphorylating glucose in glycolysis or PGA in Calvin cycle Mechanical Transport Chemical © 2009 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP® BIOLOGY 2009 SCORING GUIDELINES
Question 2 (continued)
(d) An energy pyramid for a marine ecosystem is shown below. Label each trophic level of the pyramid and provide an example of a marine organism found at each level of this pyramid. Explain why the energy available at the top layer of the pyramid is a small percentage of the energy present at the bottom of the pyramid. (3 points maximum) Explanation Label trophic levels Examples of marine organisms Energy transfer (1 point per box; 3 points maximum) Producer or autotroph → 1° consumer or herbivore → 2° consumer or carnivore → 3° consumer; no point for mentioning detritivores or decomposers Algae → zooplankton → small fish → shark Type of plankton must be specified if used above producer level; “fish” can be used once if unspecified; top level may include terrestrial organisms Energy transferred due to metabolic activities, heat, work, entropy Mentioning without explaining 10% energy transfer between trophic levels is insufficient Note: Students must receive points in all four sections to earn a score of 10. © 2009 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP® BIOLOGY 2009 SCORING GUIDELINES
Phylogeny is the evolutionary history of a species. (a) The evolution of a species is dependent on changes in the genome of the species. Identify TWO mechanisms of genetic change, and explain how each affects genetic variation. (4 points maximum) Identification DNA (molecular) (1 point each; 2 points maximum) Mutation, e.g., point, frameshift, insertions, deletions Duplication, e.g., gene, chromosome, genome, sympatric speciation Rearrangement, e.g., gene order, inversions, chromosome fusion, transposons Crossing over, independent assortment, segregation, nondisjunction (meiosis) Random fertilization (sexual reproduction) Genetic drift or bottleneck or founder effects Gene flow (migration) Geographic isolation or allopatric speciation Nonrandom mating (sexual selection) Sympatric speciation Natural selection Explanation (1 point each; 2 points maximum) Change in nucleotide sequence or amino acid sequence or protein structure or gene expression, or change in phenotype Gene “families,” which then diverge by mutation; change in ploidy Chromosome structure altered; change in crossover frequency Increase gamete diversity Many possible gamete combinations Population allelic/gene frequencies altered or gain or loss of alleles/genes Reproductive fitness/differential success Cellular Population © 2009 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP® BIOLOGY 2009 SCORING GUIDELINES
Question 3 (continued)
(b) Based on the data in the table below, draw a phylogenetic tree that reflects the evolutionary relationships of the organisms based on the differences in their cytochrome c amino-acid sequences and explain the relationships of the organisms. Based on the data, identify which organism is most closely related to the chicken and explain your choice. (4 points maximum) THE NUMBER OF AMINO ACID DIFFERENCES IN CYTOCHROME c AMONG VARIOUS ORGANISMS Horse 0 Donkey 1 0 Chicken 11 10 0 Penguin 13 12 3 0 Snake 21 20 18 17 0 Horse Donkey Chicken Penguin Snake Phylogenetic tree: rooted trees with common ancestor, and with snakes, birds, mammals in correct relative order (1 point for tree)
Chicken Penguin Donkey Horse Donkey Chicken Horse Snake Penguin Snake • • • Cytochrome c: the more differences in amino acids of cytochrome c, the less closely related, OR fewer differences, more closely related. (1 point) Penguin is most closely related to chicken. (1 point) Three amino acids differing between penguin and chicken/penguin has fewest differences from chicken. (1 point) © 2009 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP® BIOLOGY 2009 SCORING GUIDELINES
Question 3 (continued)
(c) Describe TWO types of evidence—other than the comparison of proteins—that can be used to determine the phylogeny of organisms. Discuss one strength of each type of evidence you described. (4 points maximum) Description (1 point per box; 2 points maximum) Fossil Observe past organisms Homology: morphology Organismal structure/form Vestigial structures Homology: embryology/development Morphology of embryos; changes in gene expression during development Homology: reproduction Comparison of reproductive strategies or life cycles: cell division, gamete production, gamete type, etc. DNA sequence Comparison of DNA sequences in specific genes; molecular homologies Biogeography Analysis of organism distribution(s) Direct observation/behavior Watch organism in natural setting Strength (1 point each; 2 points maximum) Shows direct evidence of common ancestor, follow evolution (changes over time) from common ancestor Similarities in form(s) show common ancestry/DNA Similarities in development show common ancestry/DNA Similarities in reproduction strategies show common ancestry/DNA Similarities in sequences show common ancestry Uses both past and present information to show common ancestry/DNA Similarities in behaviors indicate common ancestry/DNA © 2009 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP® BIOLOGY 2009 SCORING GUIDELINES
The flow of genetic information from DNA to protein in eukaryotic cells is called the central dogma of biology. (a) Explain the role of each of the following in protein synthesis in eukaryotic cells. (5 points maximum) Description (1 point each) RNA polymerase Spliceosomes (snRNPs) Codons Ribosomes tRNA DNA → RNA Removes the introns and connects (splices) the exons in RNA Codes for amino acids/signals RNA → protein or site of protein synthesis Transports amino acids (b) Cells regulate both protein synthesis and protein activity. Discuss TWO specific mechanisms of protein regulation in eukaryotic cells. (4 points maximum) Idea of the mechanism (1 point) Discussion (1 point) Protein Synthesis Promotor ................................. increases RNA polymerase binding Enhancer................................. increases transcription Methylation ............................ adding methyl group inhibits transcription Acetylation ............................. adding acetyl group promotes transcription DNA packaging...................... loosening/tightening chromatin promotes/inhibits transcription RNA processing ..................... GTP cap or Poly-A tail RNA editing............................ removing of introns Alternative splicing ............... editing in different ways to get new/different RNA/polypeptides mRNA degradation ................ targets RNA for destruction (miRNA or siRNA) Protein processing ................. polypeptide → protein modifications (folding, chaperonins, cleavage, etc.) Protein degradation ............... proteases break down proteins Feedback: negative/positive..correct explanation of the identified feedback loop Allosteric/noncompetitive ... conformational change/binding to alternative site Competitive ............................ binding to (or blocking) active site Intracellular Protein Activity Environmental conditions…..intracellular control by pH/temperature/substrate/enzyme concentration Phosphorylation ..................... protein kinase/phosphorylase activating enzyme/altering 3-D shape Hormones ............................... correct action for steroid or protein hormone Coenzymes/Cofactors............ presence/absence controls reactions
© 2009 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP® BIOLOGY 2009 SCORING GUIDELINES
Question 4 (continued)
(c) The central dogma does not apply to some viruses. Select a specific virus or type and explain how it deviates from the central dogma. (3 points maximum) Names a specific RNA virus or type of RNA virus (HIV, flu virus, etc.) Deviation from the central dogma (RNA → DNA or RNA → protein or RNA → RNA) More detailed explanation of the deviation from the central dogma (1 point) (1 point) (1 point) © 2009 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. ...
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This note was uploaded on 08/19/2010 for the course BIOLOGY 101 taught by Professor Mancino during the Spring '10 term at Abant İzzet Baysal University.
- Spring '10