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Question 1
Question 2
Question 3
Question 4
For those who did not have the tremendous opportunity to travel to Nebraska and grade AP Exams this year, several veteran readers have offered their evaluations of the essay questions. The grading is an amazing process, and when 357 intimate friends work together, even 101,984 exams can get graded in six days! If you are interested in becoming a part of this process, please click on the Online Reader Application below to submit your name for consideration for next year's exam. Thanks to Leslie Haines, Richard Patterson, Carolyn Schofield, and Bob Seigman for their help on this review!
 Online Reader Application
Question 1
Mean of 2.96
26.8 percent blanks and zeros
(mean of 4.01 without blanks/zeros)
This question had three parts: analysis of three generations of fruit flies to determine original parents and type of genetic transmission, use of a chi-square test to see if observed results were close to expected, and definition/explanation of mutation.
What Students Wrote:
Disappointingly, at least half the students worked this problem as an autosomal cross. Their Punnett squares involved Ee X Ee, or they would use XX and XY but put genes on all the chromosomes! There was every notation known to man for the alleles, and the sex-linkage notations ran from XeY to XeO to eY to e/ -- as long as it was apparent that the student knew the Y carried no gene for this trait, credit was given. Many students said the original cross was Ee X ee because that was the only way to get a 2:2 ratio.... The huge volume of poor answers was most puzzling because this cross is taught not only in AP but also at the first-year biology level and should have been familiar and easy for students.
There were very few students who understood how to do a X2, even when the formula and term explanations were given in the question. This was a surprise because that is one of the stated objectives on Lab 7. Even if the math was done incorrectly (and the math was very simple), points were awarded for correct setup hypothesis of numbers expected and for correct setup of the solution equation. Many, many students would get the correct final answer of 2, but then take the square root of it to get X! Very few could say that the table would be read at 3 degrees of freedom, and almost none explained the significance of the X2 value in this situation.
Mutation was the strongest section on this question: many students answered only this part but earned all 4 points. The simple definition of mutation as "a change in the DNA sequence of an organism" (or change in their genes) was sufficient for a point; many gave good examples of base-substitutions or frame shift mutations and tied that change to possible mild-to-drastic changes in protein structure. A real bright spot.
Common Mistakes/Misconceptions:
- Sex-linked traits have genes on both the X and Y chromosomes.
- Mutations always have phenotypic consequences.
- Mutations only occur at replication.
- Mutations only occur when meiosis is taking place.
- Mutations occur when DNA is misread.
- Mutations occur during transcription or translation.
- Crossing over causes mutations.
- Allele = nucleotide.
- Wild type = dominant (rather like mistakenly assuming having five fingers rather than six must be dominant because it is the most common).M
- If X2 = 2, then the correct answer is X = square root of 2.
- X2 number = the degrees of freedom.
What Teachers Can Do:
Perform Lab 7, if not with Drosophila then with Wisconsin Fast Plants or Nasonia, or do an online simulation or a paper lab with real counts. Be sure students can hypothesize expected outcomes based on Mendelian genetics and run chi-square tests to check their hypothesis.
NEWS FLASH!!! To many of us, the term codon has specifically referred to an mRNA triplet that "coded" for a particular amino acid. Codon is now also used to specify three DNA bases that will ultimately dictate the amino acid to be placed in a protein.
Question 2
Mean of 3.58
16 percent zeros and blanks
This question asked students to pick three out of four situations in which organisms regulated flowering or water loss or body heat and to explain how that was accomplished. "Regulation" was interpreted to be real-time regulation or evolutionary adaptation that allowed regulation, so a wide array of answers received credit.
What Students Wrote:
Regulation of flowering was chosen least often by students, temperature regulation most often.
Far too many students answered the question as a "structure-function" exercise rather than one of "regulation." Many wrote off-task about the structure and function of nephrons, the functions of the various parts of a flower, or the way in which water moves up a plant from root to leaves. Others wrote long essays about why flowering, water regulation, and temperature regulation are important to the survival of organisms, but they received no points for these discussions.
Few students had a solid grasp of the complexities of flowering. Those who did often earned 3-4 points for identifying phytochrome as an important component and explaining critical night length as the important trigger. Water regulation in animals proved very difficult as many students remembered details about kidney structure and nephron function, but too few recognized the pivotal role of the hypothalamus producing ADH, the activation of the RAAS system, and/or the adrenal secretion of aldosterone along with the various effects these hormones have on water regulation.
Students had no difficulty identifying mechanisms for temperature regulation in terrestrial vertebrates such as sweating and shivering, but most failed to get all four of the possible points because they did not explain the mechanism, which the question clearly asked them to do.
Common Mistakes/Misconceptions:
- Sweating is a water-regulation mechanism in animals.
- Stomata close when the guard cells swell up.
- Both CAM and C4 plants close their stomata during the day and open them at night.
- Vasodilatation for heat loss results in blood vessels moving up closer to the skin surface to lose heat and moving back down away from the skin surface to conserve heat.
- Stomata are structures that open when the plant gets too much water (instead of being structures primarily involved in gas exchange).
What Teachers Can Do:
At the end of each unit, discuss with your students the ways in which each of the AP Biology themes has been addressed in the unit. Perhaps this will help them appreciate the subtle differences between the themes of "structure/function" and "regulation," which are certainly interrelated but can and should be understood independently of one another.
Test for student understanding of the major objectives in each of the labs (transpiration, for example). The lab questions tend to come directly from these published objectives.
Question 3
Mean of 3.17
7 percent zeros and blanks
40 percent grades were 0, 1, or 2
Understanding the elements of and the factors affecting a simple population growth curve that stabilizes at carrying capacity was the focus of this question. Students were also asked to distinguish between "r" and "K" life strategies and how that would affect population growth.
What Students Wrote:
The students seemed to ignore the fact that they were asked in part A to describe what was happening to the population in the curve and focused too completely on the why response. They recognized that the midsection was an exponential growth curve but missed the first section of the curve where growth was "flat." More students recognized there was a slowing of the growth rate to get to the carrying capacity. Often, only one point was awarded in this section and that was always for exponential growth.
In part B, the most common correct answer dealt with predator-prey interactions; use of the availability of natural resources was also well done. The stronger answers also recognized that any factor that worked would have to be explained through density-dependent factors.
The difference between "r" and "K" strategies and their effects gave the students the most trouble. Knowledgeable students often correctly said that "r" strategists had many offspring with little parental investment, while "K" strategists had few offspring with much parental care. Very frequently they only had one part of this description correct, such as many offspring, but did not complete the description. And very frequently they reversed the definitions. It was the rare student who correctly linked the "r" strategy with the classic "boom-bust" cycle and "K" strategy with the logistic pattern.
Common Mistakes/Misconceptions:
- Part A curve in its entirety was exponential growth.
- Part A curve approached or arrived at the carrying capacity without a change in growth rate.
- Density independent factors such as volcanoes could explain fluctuations in part B.
- Disease or parasites were named as causing the periodic fluctuations in the graph but not explained in a way that would make that reasonable.
What Teachers Can Do:
This is a question in population growth; while it does fit into ecology, it also plays an evolutionary role, so be sure to include this additional context. Ecology is not just an "Environmental Science" topic and should be covered as diligently as the rest of the AP Biology syllabus.
Remind students not to prepare endless lists when responding to a question. The readers can only accept the first three the students cover. Even though this question was fairly direct, too many students rambled on and on. Students gave a great deal of good biology, but much of it did not really apply to this question; teach them to be more efficient in essay responses.
Question 4
Mean of 1.73
30 percent zeros or blanks
(Mean of 2.46 without zeros and blanks)
"The Death Question" was at three levels: cellular, recycling within organisms, and evolutionary. While some felt this question was very challenging for students, others felt it was the best question on the test because it asked students to take what they knew and apply it. Some thought kids "panicked" when they saw an unfamiliar way of asking a question about concepts that they were familiar with.
What Students Wrote:
In general, the writing was too vague, written at a too-basic level and demonstrating little understanding about cells, body systems, etc. Many students had a good understanding of the value of programmed cell death; even more could relate natural selection to the selective death of organisms.
Common Mistakes/Misconceptions:
- Organisms evolve (instead of populations).
- Populations evolve because "they need to," "they want to."
- CO2 is "turned into" O2 during photosynthesis (and vice versa during respiration).
What Teachers Can Do:
Encourage students, when faced with an unfamiliar question, to calmly begin to mentally run through major topics they have covered in AP and try to make connections. "What have we covered in this class that might relate to the question?" Too many seem to be randomly pulling ideas out of the air: "Let me see, I guess if my brain cells died, then my nerves wouldn't work."
Be careful not to "bleed" from one question to the next: many threw in food chains and trophic pyramids in for the last section, apparently because they still had Question 3 on their minds.
General Reader Comments:
Stress to kids that answers on AP Exams must include specific information that is at an AP level, not simple common knowledge or nebulous ramblings about a topic. "Fluff" does not earn points! Be concise and precise! Explain! Describe! Give concrete and explicit examples!
Leslie Haines has been teaching for a total of 24 years, 16 of which have included AP Biology. She currently teaches AP Biology, honors biology, and oceanography at Walter Williams High School in Burlington, North Carolina.
Richard Patterson is the head of the science department at Athens Academy in Athens, Georgia, and has been teaching Honors Biology and AP Biology there for the past 26 years. He has had the honor of being part of the AP Reading 15 times since 1986 as a Reader, Table Leader, and Question Leader.
Carolyn Schofield is the AP Central Content Advisor for Biology. Carolyn has taught at Spring Branch's Memorial High School and Tyler's Robert E. Lee High School in Texas. Traveling as a consultant for the College Board since 1979, she also reads the AP Exam each June, authored the new Teacher's Guide -- AP Biology, created the AP Teacher's Corner, and is a member of the Biology Development Committee. She is a winner of the Presidential Award for Excellence, the OBTA for Texas, the Tandy Award, and the Texas Excellence Award.
Bob Seigman has taught at McDonogh School, outside of Baltimore, since 1969, and has taught AP Biology for more than 25 years. He became an Exam Reader in 1987, and has since served as a Table Leader and a Question Leader. Bob is both a past president and president-elect of the Maryland Association of Biology Teachers.
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