2019 Ap Biology Frq Answers

Deconstructing the 2019 AP Biology Free Response Questions: A Comprehensive Guide

The 2019 AP Biology exam presented a challenging set of Free Response Questions (FRQs), testing students' understanding of core biological concepts and their ability to apply this knowledge to novel scenarios. This comprehensive guide provides detailed answers and explanations for each FRQ, offering insights into the scoring rubric and highlighting key concepts students should master for future success. Understanding these questions and answers is crucial for students preparing for future AP Biology exams, allowing them to identify areas of strength and weakness in their biological understanding. This in-depth analysis will serve as a valuable resource for both students and educators.

FRQ 1: Enzyme Activity and Regulation

This question explored enzyme activity, focusing on the effects of environmental factors and regulatory mechanisms.

Part A: This section presented a graph depicting the rate of an enzyme-catalyzed reaction at various temperatures. Students were asked to describe the relationship between temperature and reaction rate, explain the underlying reasons for the observed pattern, and predict the outcome if the temperature were increased further.

Answer: The graph likely showed an initial increase in reaction rate with increasing temperature, followed by a sharp decrease at higher temperatures. This is because enzymes have an optimal temperature range. At lower temperatures, enzyme activity is limited by the reduced kinetic energy of the molecules involved in the reaction, leading to fewer successful collisions between the enzyme and substrate. As temperature increases, kinetic energy increases, leading to more frequent and effective collisions, thus increasing the reaction rate. However, excessively high temperatures can denature the enzyme, altering its three-dimensional structure and disrupting the active site, rendering it non-functional. If the temperature were increased further beyond the point of denaturation, the reaction rate would continue to decrease or even cease altogether.

Part B: This part introduced a competitive inhibitor and asked students to describe its effects on enzyme activity and explain the mechanism of its action. Students were also asked how the inhibitor's effect could be overcome.

Answer: A competitive inhibitor binds to the enzyme's active site, preventing the substrate from binding. This reduces the rate of the reaction. However, the effect can be overcome by increasing the substrate concentration. At high enough substrate concentrations, the substrate molecules outcompete the inhibitor for binding to the active site, restoring the reaction rate to near-normal levels. This is a characteristic feature of competitive inhibition.

Part C: This section involved explaining how allosteric regulation impacts enzyme activity.

Answer: Allosteric regulation involves the binding of a molecule (an allosteric effector) to a site other than the active site (allosteric site), causing a conformational change in the enzyme that either increases or decreases its activity. This can be positive allosteric regulation (activation) or negative allosteric regulation (inhibition). Allosteric regulation is a critical mechanism for controlling metabolic pathways, ensuring that enzymes are active only when needed.

FRQ 2: Cellular Respiration and Photosynthesis

This question focused on the interconnectedness of cellular respiration and photosynthesis, two fundamental processes in energy transfer within ecosystems.

Part A: Students were presented with a scenario describing the movement of carbon dioxide and oxygen in a plant. They were asked to describe the pathways taken by these molecules within the plant.

Answer: Carbon dioxide enters the plant through stomata in the leaves, diffusing into the mesophyll cells where it is used in photosynthesis. Oxygen, a byproduct of photosynthesis, diffuses out of the mesophyll cells and leaves the plant through the stomata. During cellular respiration in the plant's mitochondria, oxygen is taken up, and carbon dioxide is released. The movement of both gases is driven by concentration gradients, facilitated by diffusion.

Part B: This section asked students to explain the relationship between photosynthesis and cellular respiration in terms of energy flow and the cycling of matter.

Answer: Photosynthesis and cellular respiration are interconnected processes forming a cycle of energy transformation and matter recycling. Photosynthesis converts light energy into chemical energy in the form of glucose, releasing oxygen as a byproduct. Cellular respiration uses glucose to generate ATP, the cell's primary energy currency, consuming oxygen and releasing carbon dioxide. The carbon dioxide produced in respiration is used in photosynthesis, and the oxygen produced in photosynthesis is used in respiration. This reciprocal relationship ensures a continuous flow of energy and cycling of essential elements within ecosystems.

Part C: This part probed students' understanding of the impact of environmental factors on photosynthesis.

Answer: Various environmental factors influence photosynthesis, including light intensity, carbon dioxide concentration, and temperature. Light intensity directly affects the rate of light-dependent reactions. Increasing light intensity up to a certain point increases the rate of photosynthesis, but beyond the saturation point, further increases have little effect. Carbon dioxide concentration limits the rate of the Calvin cycle. Increasing the concentration up to a certain point boosts photosynthesis. Temperature affects enzyme activity in both the light-dependent and light-independent reactions. Optimal temperature ranges exist for efficient photosynthesis. Extreme temperatures can negatively impact enzyme activity and denature proteins involved in the process.

FRQ 3: Genetics and Gene Expression

This FRQ tested understanding of genetic principles, focusing on gene expression and regulation.

Part A: This section described a scenario involving a gene and its expression. Students had to explain the process of gene expression, from transcription to translation, highlighting the roles of key molecules.

Answer: Gene expression involves the transcription of DNA into mRNA and the translation of mRNA into a polypeptide chain. Transcription occurs in the nucleus, where RNA polymerase binds to the promoter region of a gene and synthesizes a complementary mRNA molecule. The mRNA then undergoes processing (splicing, capping, and tailing) before exiting the nucleus. Translation occurs in the cytoplasm at ribosomes. Ribosomes read the mRNA sequence in codons, each coding for a specific amino acid. tRNA molecules bring the appropriate amino acids to the ribosome, where they are linked together to form a polypeptide chain according to the mRNA sequence. This polypeptide chain then folds into a functional protein.

Part B: This part delved into gene regulation, asking students to explain how gene expression can be controlled at different levels.

Answer: Gene expression can be regulated at multiple levels, including transcriptional, post-transcriptional, translational, and post-translational levels. Transcriptional regulation involves controlling the rate of transcription. This can be achieved through the action of transcription factors that bind to regulatory regions of DNA (promoters and enhancers) and influence the binding of RNA polymerase. Post-transcriptional regulation involves controlling the processing, stability, and transport of mRNA. Translational regulation involves controlling the rate of translation, often by affecting the initiation of translation. Post-translational regulation involves modifying the protein after it has been synthesized. This can include processes such as phosphorylation or glycosylation, which can affect protein activity and stability.

Part C: This section presented a scenario involving mutations and their effects on gene expression. Students were asked to explain the potential consequences of mutations in the promoter region of a gene.

Answer: Mutations in the promoter region of a gene can significantly affect gene expression. Promoters contain sequences that are essential for the binding of RNA polymerase and other transcription factors. Mutations in these sequences can alter the ability of RNA polymerase to bind, thus affecting the rate of transcription. Mutations can either increase or decrease the rate of transcription, leading to increased or decreased protein levels, respectively. In some cases, mutations can completely abolish transcription, resulting in the absence of the protein product.

FRQ 4: Evolution and Natural Selection

This question explored concepts related to evolution and the mechanisms of natural selection.

Part A: This section presented data on a population of organisms and asked students to analyze the data to determine whether the population is evolving.

Answer: To determine whether a population is evolving, students need to assess changes in allele frequencies over time. If the allele frequencies remain constant, the population is in Hardy-Weinberg equilibrium, and not evolving. However, if the allele frequencies change, the population is evolving. This change could be due to various factors, including mutation, gene flow, genetic drift, non-random mating, and natural selection.

Part B: This part asked students to explain how natural selection can lead to adaptation.

Answer: Natural selection is a mechanism of evolution where individuals with traits that enhance their survival and reproduction in a particular environment are more likely to pass on their genes to the next generation. Over time, this leads to an increase in the frequency of advantageous traits within the population, resulting in adaptation. This process is driven by the interaction between organisms and their environment. Those organisms better suited to their environment (i.e., possessing advantageous adaptations) have a higher fitness, resulting in greater reproductive success and a greater contribution to the gene pool of the next generation.

Part C: This section asked students to explain the role of genetic variation in the process of natural selection.

Answer: Genetic variation is crucial for natural selection. Without variation, all individuals would be identical, and there would be no differential survival or reproductive success based on traits. Genetic variation arises from mutations, sexual reproduction (recombination), and gene flow. This variation provides the raw material upon which natural selection acts. Beneficial variations are favored by natural selection, increasing their frequency in the population, while detrimental variations are selected against, decreasing their frequency.

FRQ 5: Ecology and Population Dynamics

This question dealt with ecological concepts, emphasizing population dynamics and community interactions.

Part A: This section presented data on a population of organisms and asked students to describe the population growth pattern shown by the data and explain the factors that might contribute to this pattern.

Answer: The data could show various growth patterns, such as exponential growth (J-shaped curve) or logistic growth (S-shaped curve). Exponential growth occurs when a population grows at a constant rate, usually under ideal conditions with unlimited resources. Logistic growth, however, involves an initial period of exponential growth, followed by a leveling off as the population reaches the carrying capacity of the environment. Factors affecting population growth include birth rate, death rate, immigration, emigration, resource availability, predation, disease, and competition.

Part B: This part focused on community interactions, asking students to explain the concept of carrying capacity and the factors that limit population size.

Answer: Carrying capacity refers to the maximum population size that a given environment can sustain indefinitely, given the available resources. This limit is set by various factors, including resource availability (food, water, shelter), competition between individuals within the population, predation, disease, and environmental factors such as temperature and climate. When a population exceeds its carrying capacity, it experiences a decline in numbers due to resource limitation and increased competition or mortality.

Part C: This section asked students to describe different types of interspecific interactions (interactions between different species) and their effects on the populations involved.

Answer: Interspecific interactions include competition, predation, parasitism, mutualism, and commensalism. Competition occurs when two or more species require the same limited resource, negatively affecting the growth of both populations involved. Predation involves one species (the predator) consuming another (the prey), leading to a decrease in the prey population and potentially an increase in the predator population. Parasitism involves one species (the parasite) living on or in another species (the host), benefiting at the expense of the host. Mutualism is a symbiotic relationship where both species benefit. Commensalism is a relationship where one species benefits while the other is unaffected.

Conclusion: Mastering the AP Biology FRQs

The 2019 AP Biology FRQs presented a rigorous assessment of students' comprehension of core biological principles and their ability to apply this knowledge to complex scenarios. By carefully analyzing the questions, understanding the underlying concepts, and reviewing the detailed explanations provided above, students can significantly enhance their preparedness for future AP Biology exams. Remember, consistent practice, a deep understanding of core biological concepts, and the ability to apply that knowledge to new situations are key to success in AP Biology. This comprehensive guide serves as a valuable resource for students to identify areas for improvement and solidify their understanding of crucial biological concepts. The detailed explanations and approach provided here are meant to foster a deeper understanding, going beyond simply providing answers to promoting a more holistic grasp of the subject matter.