2013 ap bio mcq

Figure 1. Melanin synthesis pathway. The peptide hormone α-melanocyte stimulating hormone (α-MSH) activates a signal transduction pathway leading to the activation of MITF. MITF is a transcription factor that increases the expression of the TYR, TRP2, and TRP1 genes (Figure 2). Figure 2.

Replace the dry cotton ball with a water-soaked cotton ball. Constant light or temperature or duration of experiment or time of day, etc. Explanation. (1 point maximum) Ensures that …Kronos Bio News: This is the News-site for the company Kronos Bio on Markets Insider Indices Commodities Currencies Stocks Subscription Needed. Shmoop Practice Tests (free trial available, $24.68 a month for subscription) A subscription to Shmoop will get you access to a diagnostic test plus five full AP Biology practice tests (including both multiple-choice and free-response questions, although these are of course unofficial). Tip 1: Take Detailed Notes. Since you’re taking an advanced biology class, you probably know that taking notes will be important. But in order to get a 5 on the exam, you’ll need to be a detailed note-taker. Detailed note-taking means doing more than just listening and writing down a few key facts that you hear. The AP Biology exam is three hours long, with two sections that take up an hour and a half each. The multiple-choice section has 60 questions, and the free-response section has six questions. The content of the exam spans four major themes, or Big Ideas, that are central to the course. These include the following: When an AP Exam is administered, psychometric analysis determines the score ranges correspondingwith each AP Exam score (5, 4, 3, 2, and 1) based on a composite score scale that combines and weights the different exam parts. Earning 40-50% of the available points can result in a score of 3 or better on many AP Exams. Biology. : Past Exams. Concise resources for the AP College Board Biology course. Practice for your AP Biology test with these past exam papers. Once you've identified any areas where you need more practice, study those topics with …This is the free-response section of the 2012 AP exam. It includes cover material and other administrative instructions to help familiarize students with the mechanics of the exam. (Note that future exams may differ in look from the following content.) AP® Psychology Exam. SECTION II: Free Response.

AP Biology. Multiple Choice Practice Test. Which of the following diseases is caused by the lack of a functional gene responsible for a specific enzyme? Free 2024 AP Biology multiple choice practice tests scored instantly online. Questions, answers and solutions to pass the ap biology test. 22 Nov 2013 ... Ap 2013-biology-scoring-guidelines - Download as a PDF or view online for free. The AP Biology Exam has question types and point values that remain stable and consistent from year to year, so you and your students know what to expect on exam day. Section I: Multiple Choice. 60 Questions | 1 hour 30 Minutes | 50% of Exam Score. Individual questions; Sets of questions with 4–5 questions per set; Section II: Free Response 1. In an investigation of fruit-fly behavior, a covered choice chamber is used to test whether the spatial distribution of flies is affected by the presence of a substance placed at one end of the chamber. To test the flies’ preference for glucose, 60 flies are introduced into the middle of the choice chamber at the insertion point indicated ...Questions 3–8 are short free-response questions that require about 6 minutes each to answer. Questions 3–5 are worth 4 points each and questions 6–8 are worth 3 points each. Read each question carefully and completely. You are advised to spend the 10-minute reading period planning your answers. You may begin writing your responses before ...2.0%. The equation above represents an elementary step in a chemical reaction. Which of the following is the correct expression for the rate law of the elementary step? r = k (NOBr)2. A balloon filled with 0.25 moles He (g) at 273K and 1.0 atm is allowed to rise through the atmosphere. Which of the following explains what happens to the volume ...Starting with the 2024 exam, the layout for the free-response questions (FRQs) will be different from prior exams. For a summary of the changes, and to help you visualize this change to the layout, we’ve applied the 2024 layout to the 2021–2023 AP Biology FRQs. You can find the original scoring guidelines on the past exam questions page.

Study with Quizlet and memorize flashcards containing terms like Which of the following best describes the processes occurring between the mouse populations and their environments?, Which of the following best explains the relationship between coat color and predation rate in the rock pocket mouse population on the lava flow rocks with respect to the different coat color phenotypes?, Based on ... 1. In an investigation of fruit-fly behavior, a covered choice chamber is used to test whether the spatial distribution of flies is affected by the presence of a substance placed at one …The questions contained in this AP Biology Practice Exam are written to the content specifications of AP Exams for this subject. Taking this practice exam should provide students with an idea of their general areas of strengths and weaknesses in preparing for the actual AP Exam. Because this AP Biology Practice Exam has never been …Biology. : Past Exams. Concise resources for the AP College Board Biology course. Practice for your AP Biology test with these past exam papers. Once you've identified any areas where you need more practice, study those topics with …A structure that is 2 layers in thickness. In biology, most often refers to the phospholipid bilayer of membranes. bile. A mixture of substances that is produced in the liver, stored in the gall bladder, and acts as a detergent to aid in the digestion and absorption of fats. binary fission.The MCQs on the AP Calculus BC exam, collectively called Section I, are split into two parts, A and B. Part A consists of 30 questions on which you are not allowed to use a calculator, and you are given an hour to complete it. Part B consists of 15 questions for which a calculator is allowed, and 45 minutes is allotted for this section.

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1. In an investigation of fruit-fly behavior, a covered choice chamber is used to test whether the spatial distribution of flies is affected by the presence of a substance placed at one …Prepare for the AP World History exam with this practice test from AP Central. The test includes multiple-choice and free-response questions that cover the course content and skills. You can also find sample responses and scoring guidelines for the free-response questions.Advertisement In the previous list, you saw that the BIOS checks the CMOS Setup for custom settings. Here's what you do to change those settings. To enter the CMOS Setup, you must ...AP Microeconomics Practice Exam From the 2 014 Administration This Practic e Exa m is provided by the Colleg e Boar d fo r AP Exam preparation . Teacher s ar e permitted to download the material s an d mak e copies to use wit h thei r student s in a classroo m settin g onl y. T o maintai n th e securit y of this exam , teacher s shoul d collec t al l …Biology Practice Exam. ####### From the 2013 Administration. This is a modified version of the 2013 AP Biology Exam. This practice exam is provided by the College Board for AP Exam preparation. Exams may not be posted on school or personal websites, nor electronically redistributed for any reason.

Figure 1. Melanin synthesis pathway. The peptide hormone α-melanocyte stimulating hormone (α-MSH) activates a signal transduction pathway leading to the activation of MITF. MITF is a transcription factor that increases the expression of the TYR, TRP2, and TRP1 genes (Figure 2). Figure 2.Biology Practice Exam. From the 2013 Administration. This is a modified version of the 2013 AP Biology Exam. This practice exam is provided by the College Board for AP Exam preparation. Exams may not be posted on school or personal websites, nor electronically redistributed for any reason. Figure 1. A model of epinephrine signaling. Two types of cells, alpha and beta cells, produce signaling molecules that affect blood sugar levels in opposite ways (Figure 1). Epinephrine is a chemical, often released during periods of exercise, that ultimately causes an increase in blood sugar levels in the body. The question stem may be as short as a single sentence, but it is not uncommon to see multiple paragraphs for a single question! In addition to words, many question stems will be accompanied by an equation, table, graph or figure. The next question is a typical Stand-Alone. 22. AB+energy→A+B. Which of the following best characterizes the ...gracekang718. AP Biology Unit 5: Heredity Topics - Meiosis, Meiosis and Genetic Diversity, Mendelian Genetics, Non-Mendelian Genetics, Environmental Effects on Phenotype, Chromosomal Inheritance Directions - For each question, choose the best answer (unless otherwise stated) Test Period - You have 22 minutes 30 seconds to answer 30 questions.The AP Biology Exam will test your understanding of the biological concepts covered in the course units, as well as your ability to utilize the scientific method and analyze data. You are allowed to use a four-function calculator (with square root), scientific, or graphing functions throughout exam. Exam Duration. 3hrs.Practice questions, MCQs, Past Year Questions (PYQs), NCERT Questions, Question Bank, Class 11 and Class 12 Questions, NCERT Exemplar Questions and PDF Questions with answers, ... The first word in a biological name represents the genus while the second component denotes the specific epithet. 3. Both the words in a biological name, ...2021 MCQ Practice Exam - AP Biology. The CFTR protein is made up of 1,480 amino acids linked together in a chain. Some humans produce a version of the CFTRprotein in which phenylalanine (an amino acid) has been deleted from position 508 of the amino acid chain. Which of the following best predicts how the amino acid deletion will affect the ... Topics for AP Biology Review. The College Board is very detailed in what they require your AP teacher to cover in his or her AP Biology course. These are the official Big Four Ideas: Big Idea 1: The process of evolution drives the diversity and unity of life. Big Idea 2: Biological systems utilize free energy and molecular building blocks to ... In this video, we’ll unpack sample multiple-choice set-based questions.Download questions here: https://tinyurl.com/2s49nsuyStay motivated and keep preparing...Nucleotide base pairing in DNA is universal across organisms. Each pair (T−A; C−G) consists of a purine and a pyrimidine. Which of the following best explains how the base pairs form? Hydrogen bonds join a double-ringed structure to a single-ringed structure in each pair. AP classroom Learn with flashcards, games, and more — for free.

To retard the breakdown of the catalase. The following questions refer to an experiment that is set up to determine the relative volume of O2 consumed by germinating and nongerminating (dry) pea seeds at two different temperatures. The change in volume is detected by using a respirometer over a given period of time.

When an AP Exam is administered, psychometric analysis determines the score ranges correspondingwith each AP Exam score (5, 4, 3, 2, and 1) based on a composite score scale that combines and weights the different exam parts. Earning 40-50% of the available points can result in a score of 3 or better on many AP Exams. A structure that is 2 layers in thickness. In biology, most often refers to the phospholipid bilayer of membranes. bile. A mixture of substances that is produced in the liver, stored in the gall bladder, and acts as a detergent to aid in the digestion and absorption of fats. binary fission.gracekang718. AP Biology Unit 5: Heredity Topics - Meiosis, Meiosis and Genetic Diversity, Mendelian Genetics, Non-Mendelian Genetics, Environmental Effects on Phenotype, Chromosomal Inheritance Directions - For each question, choose the best answer (unless otherwise stated) Test Period - You have 22 minutes 30 seconds to answer 30 questions.Exam questions assess the course concepts and skills outlined in the course framework. For more information, download the AP Biology Course and Exam Description (CED). … Subscription Needed. Shmoop Practice Tests (free trial available, $24.68 a month for subscription) A subscription to Shmoop will get you access to a diagnostic test plus five full AP Biology practice tests (including both multiple-choice and free-response questions, although these are of course unofficial). Questions 3–8 are short free-response questions that require about 6 minutes each to answer. Questions 3–5 are worth 4 points each and questions 6–8 are worth 3 points each. Read each question carefully and completely. You are advised to spend the 10-minute reading period planning your answers. You may begin writing your responses before ...Figure 1. AIP cascade producing hemolysin toxin. Identify the experimental design that would determine which AIP mimic would most effectively inhibit the production of hemolysin toxin. B. grow s. aureus in ___ culture media containing ___ AIPAIP mimic each and measure the production of hemolysin ___. The most ___ AIPAIP mimic will be in the ...Macroeconomics Practice Exam From the 2013 Administration This Practice Exam is provided by the College Board for AP Exam preparation. Teachers are permitted to download the materials and make copies to use with their students in a classr oom setting only. To maintain the security of this exam, teachers should collect all materials after … Ap Bio Unit 5: MCQ progress check. For sexually reproducing diploid parent cells, which of the following statements best explains the production of haploid cells that occurs in meiosis but not in mitosis? Click the card to flip 👆. Separation of chromatids occurs once, and there are two rounds of cell division in meiosis. Click the card to ... The questions contained in this AP Biology Practice Exam are written to the content specifications of AP Exams for this subject. Taking this practice exam should provide students with an idea of their general areas of strengths and weaknesses in preparing for the actual AP Exam. Because this AP Biology Practice Exam has never been …

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Before 2012, the AP Biology test had 100 multiple-choice questions and four free-response questions rather than the current 63 multiple-choice questions, six grid-in questions, six short free-response questions, and …In the multiple choice section of the AP Biology test, you will have 90 minutes to answer 60 multiple choice questions and 6 grid-in items. The multiple choice questions are composed of two types of questions, stand alone and data questions. Below we provide practice questions for each type and strategies to find the correct answer in …Figure 1. A model of epinephrine signaling. Two types of cells, alpha and beta cells, produce signaling molecules that affect blood sugar levels in opposite ways (Figure 1). Epinephrine is a chemical, often released during periods of exercise, that ultimately causes an increase in blood sugar levels in the body.36 of 36. Quiz yourself with questions and answers for AP Bio Unit 8 Test, so you can be ready for test day. Explore quizzes and practice tests created by teachers and students or create one from your course material.This is a PDF package of the official AP Biology 2019 full Exam, complete with all sections including: 1. SECTION I: Multiple Choice (Part A & B) 2. SECTION II: Free Response 3. Answer Key You can obtain full PDF package of the official AP Biology 2019 full exam here. Below is a preview of each sections SECTIO.Study with Quizlet and memorize flashcards containing terms like describe the effect of caffeine on each of the following: short term long term, describe an experiment using artificial flowers and the negative effect of increasing caffeine, identify the null hypothesis, control treatment, and a predicted outcome that rejects the null hypothesis, propose one …Figure 1. AIP cascade producing hemolysin toxin. Identify the experimental design that would determine which AIP mimic would most effectively inhibit the production of hemolysin toxin. B. grow s. aureus in ___ culture media containing ___ AIPAIP mimic each and measure the production of hemolysin ___. The most ___ AIPAIP mimic will be in the ...We can analyze the average AP® Biology score more efficiently by considering a multi-year trend. We can refer to the AP® Student Score Distributions, released by the College Board annually. These reports show us that the mean score in 2014 it was 2.91, 2015 was 2.91, 2016 was 2.85, 2017 was 2.90, 2018 was 2.87, 2019 was …e) Water flows upward from the roots to the leaves in plants. b) A water strider can walk across the surface of a small pond. When two atoms are equally electronegative, they …AP Bio 2013 released test (mackies) Flashcards | Quizlet. 4.1 (7 reviews) 1. A dog is following the scent of a jack rabbit. Which if the following accurately describes how the dog's brain integrates information for smell? (A) Chemoreceptors in the brain send impulses for smell in the nasal cavity.Download free-response questions from past exams along with scoring guidelines, sample responses from exam takers, and scoring distributions. If you are using assistive technology and need help accessing these PDFs in another format, contact Services for Students with Disabilities at 212-713-8333 or by email at [email protected]. The ... There’s three steps to preparing for the AP Exam : study, practice and review. Study : Start by studying the general concepts from every unit of the AP exam. Look over any material and tests from class this year, and go through these AP Biology study guides. AP Practice : Acing the exam is all about being able to recall the information ... ….

Replace the dry cotton ball with a water-soaked cotton ball. Constant light or temperature or duration of experiment or time of day, etc. Explanation. (1 point maximum) Ensures that glucose is the attractant. Other variables must be held constant. Proposed Improvement (includes but not limited to) Directions: Questions 1 and 2 are long free-response questions that require about 25 minutes each to answer. Questions 3 through 6 are short free-response questions that require about 10 minutes each to answer. Read each question carefully and completely. Answers must be written out in paragraph form. AP Biology - Unit 1 Progress Check: MCQ. Figure 1 represents a segment of DNA. Radiation can damage the nucleotides in a DNA molecule. To repair some types of damage, a single nucleotide can be removed from a DNA molecule and replaced with an undamaged nucleotide. Which of the four labeled bonds in Figure 1 could be broken to …www.njctl.org PSI AP Biology Gene Expression Questions #9-10 refer to the following diagram: 5’ 9. The top strand of DNA is able to be replicated in a continuous line while the bottom strand is replicated in small strands that are later connected. The top red strand is referred to as what? a. Template strand b. Leading strand c. Parental ...» Do AP Biology Practice Tests » Download AP Biology Practice Tests » Best AP Biology Books; More AP Tests. AP Biology Test 1; AP Biology Test 2; AP Biology Test 3; AP Biology Test 4; AP Biology Test 5; AP Biology Test 6; AP Biology Test 7; AP Biology Test 8; AP Biology Test 9; AP Biology Test 10; AP Biology Test 11; AP Biology Test 12; AP ...Figure 1. Melanin synthesis pathway. The peptide hormone α-melanocyte stimulating hormone (α-MSH) activates a signal transduction pathway leading to the activation of MITF. MITF is a transcription factor that increases the expression of the TYR, TRP2, and TRP1 genes (Figure 2). Figure 2.Nucleotide base pairing in DNA is universal across organisms. Each pair (T−A; C−G) consists of a purine and a pyrimidine. Which of the following best explains how the base pairs form? Hydrogen bonds join a double-ringed structure to a single-ringed structure in each pair. AP classroom Learn with flashcards, games, and more — for free.AP Psychology Practice Exam From the 2 016 Administration This exam ma y no t be posted on school or persona l websites , no r electronically redistribute d fo r an y reason . Thi s Released Exa m is provided by th e Colleg e Boar d for AP Exam preparation . Teacher s ar e permitted to download th e material s an d mak e copies to use wit h thei … 2013 ap bio mcq, AP Biology Course and Exam Description. This is the core document for this course. It clearly lays out the course content and describes the exam and the AP Program in general. The CED was updated in the summer of 2020 to include scoring guidelines for the example questions. PDF., 8 Questions. Directions: Questions 1 and 2 are long free-response questions that require about 22 minutes each to answer and are worth 10 points each. Questions 3–8 are short free-response questions that require about 6 minutes each to answer. Questions 3–5 are worth 4 points each and questions 6–8 are worth 3 points each., Figure 1. Melanin synthesis pathway. The peptide hormone α-melanocyte stimulating hormone (α-MSH) activates a signal transduction pathway leading to the activation of MITF. MITF is a transcription factor that increases the expression of the TYR, TRP2, and TRP1 genes (Figure 2). Figure 2., Chemicals that are secreted from antigen-presenting cells then activate helper T cells. B. A macrophage cell engulfs a pathogen in the blood. C. Antigens attaching to receptors on memory B cells stimulate the memory B cells to become plasma cells. D. Antigen-presenting cells engulf antigens at the first exposure., To familiarize yourself with the setup of AP® Biology multiple-choice questions and the thought process behind determining the answer, peruse the following …, d. the number of neutrons in the outermost energy level. the pH of water to go down. When HCl is dissolved in water, it makes H+ ions and Cl- ions. This causes _____. a. the pH of the water to go up. b. a pH reading of 15. c. the pH of the water to go down. d. a pH reading of 7. It is a universal solvent., In the multiple choice section of the AP Biology test, you will have 90 minutes to answer 60 multiple choice questions and 6 grid-in items. The multiple choice …, Figure 1. Activity levels of two digestive enzymes over a range of pH. Trypsin and pepsin are enzymes that function in different areas of the digestive tract. One functions in the stomach, where the pH is between 1.5 and 3.5, while the other functions in the small intestines, where the pH is between 6 and 8., All six AP Biology science practices are assessed in the multiple choice section with the following exam weightings This section of the exam will test your ability …, AP Biology - Unit 1 Progress Check: MCQ. Figure 1 represents a segment of DNA. Radiation can damage the nucleotides in a DNA molecule. To repair some types of damage, a single nucleotide can be removed from a DNA molecule and replaced with an undamaged nucleotide. Which of the four labeled bonds in Figure 1 could be broken to remove and replace ..., New sitcoms with lukewarm ratings like "AP Bio" used to be cancelled early on. Now broadcasters are giving freshman shows more chances to find audiences. Not long ago, NBC’s new si..., [PDF] 2013 AP Biology Practice Exam MCQ Multiple Choice Questions with Answers Advanced Placement.pdf | Plain Text Biology Practice Exam From the 2013 …, a. all species were fixed at the time of creation b. acquired physical characteristics can be inherited c. the giraffe's long neck is the result of artificial selection d. the main mechanism of evolution is natural selection e. the interaction of organisms with their environment is important to the evolutionary process., During drought years on ... , e) Water flows upward from the roots to the leaves in plants. b) A water strider can walk across the surface of a small pond. When two atoms are equally electronegative, they …, Jan 23, 2024 · Since 2017, the passing rate for the AP® Biology exam has remained relatively steady. In 2021, the passing rate was 59.2%, and in 2022, it rose slightly to 67.9%. In 2023, the passing rate for the AP® Biology settled back to 64.4%. The AP® Biology exam is generally one of the most popular AP® exams in the Sciences category. , Good morning, Quartz readers! Good morning, Quartz readers! A$AP Rocky awaits his verdict. The American rapper, whose real name is Rakim Meyers, was detained and charged with assau..., AP Psychology Practice Exam F rom the 2 014 Administration This Practic e Exa m is provided by the Colleg e Boar d fo r AP Exam preparation . Teacher s ar e permitted to download the material s an d mak e copies to use wit h thei r student s in a classroo m settin g onl y. T o maintai n th e securit y of this exam , teacher s shoul d collec t al l material s …, Replace the dry cotton ball with a water-soaked cotton ball. Constant light or temperature or duration of experiment or time of day, etc. Explanation. (1 point maximum) Ensures that glucose is the attractant. Other variables must be held constant. Proposed Improvement (includes but not limited to) , 60 of 60. Quiz yourself with questions and answers for AP Bio | 2020 Practice Exam 2 MCQ, so you can be ready for test day. Explore quizzes and practice tests created by teachers and students or create one from your course material., Visit the College Board on the Web: www.collegeboard.org. AP® Statistics Exam. Regularly Scheduled Exam Date: Wednesday afternoon, May 16, 2012 Late-Testing Exam Date: Wednesday morning, May 23, 2012. Section I: At a Glance Section II: At a Glance Part A: Number of Questions:, The AP Biology Exam is three hours in length and consists of a multiple-choice section and a free-response section. • The 80-minute multiple-choice section contains 100 questions and accounts for 60 percent of the final grade. • The 100-minute free-response section consists of a 10-minute reading period and a 90-minute writing period., When HCl is dissolved in water, it makes H+ ions and Cl- ions. This causes _____. a. the pH of the water to go up. b. a pH reading of 15. c. the pH of the water to go down. d. a pH reading of 7. the pH goes above 7. speed up chemical reactions. the pH of water to go down., gracekang718. AP Biology Unit 5: Heredity Topics - Meiosis, Meiosis and Genetic Diversity, Mendelian Genetics, Non-Mendelian Genetics, Environmental Effects on Phenotype, Chromosomal Inheritance Directions - For each question, choose the best answer (unless otherwise stated) Test Period - You have 22 minutes 30 seconds to answer 30 questions., Don't know? 35 of 35. Quiz yourself with questions and answers for AP Bio Midterm Review Multiple Choice Questions, so you can be ready for test day. Explore quizzes and …, The one area that can’t be perfectly accurate is how we determined the final predicted scores (College Board doesn’t publish the “cut points” for each scores.) We used old released exams and other calculators to estimate “if you earned this % of points, you would earn this score”: 0-29% = 1. 30-44% = 2. 45-59% = 3. , 10 | 550 AP Biology Practice Questions BIOLOGY SECTION I Time—1 hour and 30 minutes Part A: Multiple-choice Questions (63 Questions) Directions: Each of the questions or incomplete statements below is followed by four suggested answers or completions. Select the one that is best in each case and then fill in the corresponding oval on the ..., AP Bio Released 2014 MCQ. Term. 1 / 59. (A) With no natural predators, the lionfish population will become very large and outcompete native species. Click the card to flip 👆. Definition. 1 / 59. The lionfish is a venomous fish found primarily in the Red Sea and the Indian Ocean. In the 1990s, the lionfish were accidentally released into the ..., 60 of 60. Quiz yourself with questions and answers for AP Bio | 2020 Practice Exam 2 MCQ, so you can be ready for test day. Explore quizzes and practice tests created by teachers and students or create one from your course material., Hereditary spherocytosis (HS) is a disorder of red blood cells that causes the cells to be smaller and spherical instead of having the usual flattened, biconcave shape. The average diameter of normal red blood cells is 7.2μm, and the average diameter of red blood cells in a person with HS was found to be 6.7μm., Study with Quizlet and memorize flashcards containing terms like 1. Which of the following is NOT true regarding factors that affect the dispersion of organisms in nature? A. Most environmental resources are randomly distributed. B. Biological conditions tend to be non-uniform. C. Dispersal of offspring is often limited or controlled by environmental factors. D. The development of societies in ..., 1. In an investigation of fruit-fly behavior, a covered choice chamber is used to test whether the spatial distribution of flies is affected by the presence of a substance placed at one end of the chamber. To test the flies’ preference for glucose, 60 flies are introduced into the middle of the choice chamber at the insertion point indicated ... , AP Biology. Multiple Choice Practice Test. Which of the following diseases is caused by the lack of a functional gene responsible for a specific enzyme? Free 2024 AP Biology multiple choice practice tests scored instantly online. Questions, answers and solutions to pass the ap biology test. , Nucleotide base pairing in DNA is universal across organisms. Each pair (T−A; C−G) consists of a purine and a pyrimidine. Which of the following best explains how the base pairs form? Hydrogen bonds join a double-ringed structure to a single-ringed structure in each pair. AP classroom Learn with flashcards, games, and more — for free.