Ap Biology Frq 2017 Answers

AP Biology FRQ 2017: A Comprehensive Guide with Answers and Explanations

The AP Biology exam is notoriously challenging, and the free-response questions (FRQs) often determine whether a student achieves a high score. This comprehensive guide delves into the 2017 AP Biology FRQs, providing detailed answers and explanations to help you understand the concepts tested and improve your exam preparation. Understanding these questions and their answers is crucial for success on future AP Biology exams. This guide covers each question in detail, emphasizing the key biological principles and providing examples of how to approach such questions effectively.

Question 1: Cellular Respiration and Energy Production

Question: This question focused on cellular respiration, specifically the processes of glycolysis, Krebs cycle (citric acid cycle), and oxidative phosphorylation (electron transport chain and chemiosmosis). Students were asked to analyze data, explain the processes, and apply their knowledge to predict the effects of various experimental conditions.

(a) Describe the role of oxygen in cellular respiration.

Answer: Oxygen is the final electron acceptor in the electron transport chain (ETC) of cellular respiration. Without oxygen, the ETC would halt, preventing the pumping of protons across the inner mitochondrial membrane. This disruption leads to a significant decrease in ATP production because chemiosmosis, the process that utilizes the proton gradient to synthesize ATP, would be impaired. In the absence of oxygen, cells resort to anaerobic respiration (fermentation), producing far less ATP.

(b) Explain how the processes of glycolysis, the Krebs cycle, and oxidative phosphorylation contribute to ATP synthesis.

Answer:

• Glycolysis: This process, occurring in the cytoplasm, breaks down glucose into two pyruvate molecules, producing a net gain of 2 ATP molecules through substrate-level phosphorylation and 2 NADH molecules. The NADH carries high-energy electrons to the ETC.

• Krebs Cycle (Citric Acid Cycle): In the mitochondrial matrix, pyruvate is converted into acetyl-CoA, which enters the Krebs cycle. This cycle produces 2 ATP molecules via substrate-level phosphorylation, 6 NADH molecules, and 2 FADH2 molecules. Both NADH and FADH2 carry high-energy electrons to the ETC.

• Oxidative Phosphorylation: This process takes place in the inner mitochondrial membrane. Electrons from NADH and FADH2 are passed down the ETC, releasing energy used to pump protons (H+) across the membrane, establishing a proton gradient. This gradient drives ATP synthesis through chemiosmosis as protons flow back across the membrane through ATP synthase. The majority of ATP produced during cellular respiration (~34 ATP) is generated through oxidative phosphorylation.

(c) Predict the effect on ATP production if the inner mitochondrial membrane becomes permeable to protons.

Answer: If the inner mitochondrial membrane becomes permeable to protons, the proton gradient established during electron transport would dissipate. This would prevent the efficient flow of protons through ATP synthase, significantly reducing or eliminating ATP production through chemiosmosis. Therefore, the overall ATP yield of cellular respiration would drastically decrease.

Question 2: Plant Biology and Environmental Adaptations

Question: This question explored concepts related to plant biology, focusing on adaptations to environmental conditions such as light intensity and water availability. Students were asked to interpret graphs, explain physiological processes, and apply their knowledge to real-world scenarios.

(a) Describe how the structure of a plant leaf is adapted to maximize photosynthesis.

Answer: Plant leaves possess several adaptations to maximize photosynthesis:

• Large Surface Area: A broad, flat leaf surface increases the area exposed to sunlight, capturing more photons for light-dependent reactions.

• Thinness: A thin leaf ensures that sunlight can penetrate to reach chloroplasts located throughout the leaf tissue.

• Chloroplast Distribution: Chloroplasts are densely packed within mesophyll cells, particularly in the palisade mesophyll layer, maximizing light absorption.

• Stomata: Stomata regulate gas exchange, allowing CO2 uptake for the Calvin cycle and O2 release. Their location and density are adapted to the plant's environment.

• Veins: Extensive vein networks efficiently deliver water and nutrients to photosynthetic cells and transport sugars produced during photosynthesis.

(b) Explain how environmental factors such as light intensity and water availability affect the rate of photosynthesis.

Answer:

• Light Intensity: Photosynthesis rate increases with light intensity up to a saturation point. Beyond this point, increasing light intensity has no further effect because other factors (e.g., enzyme availability) become limiting. At very high light intensities, photoinhibition can occur, damaging photosynthetic machinery.

• Water Availability: Water is a reactant in photosynthesis, and its availability directly influences the rate. Water stress (drought) causes stomata to close to reduce water loss, but this also limits CO2 uptake, thus reducing the rate of photosynthesis.

(c) Describe adaptations found in plants that are adapted to arid environments (deserts).

Answer: Plants in arid environments exhibit numerous adaptations to conserve water:

• Reduced Leaf Surface Area: Smaller leaves or spines reduce water loss through transpiration.

• Thick Cuticle: A thick waxy cuticle on the leaf surface minimizes water evaporation.

• Deep Roots: Extensive root systems access deeper water sources.

• CAM Photosynthesis: Certain desert plants utilize CAM photosynthesis, opening stomata at night to minimize water loss during the day's high temperatures.

• Succulence: Some plants store water in their stems or leaves.

Question 3: Genetics and Gene Expression

Question: This question focused on genetics, specifically gene expression, mutations, and their effects on phenotype. Students were asked to analyze data, explain genetic concepts, and apply their knowledge to predict outcomes.

(a) Describe the process of transcription and translation in eukaryotes.

Answer:

• Transcription: This process occurs in the nucleus. RNA polymerase binds to the promoter region of a gene, unwinding the DNA double helix. It then synthesizes a complementary mRNA molecule using the DNA template strand. The mRNA undergoes processing (e.g., splicing, capping, polyadenylation) before exiting the nucleus.

• Translation: This process occurs in the cytoplasm at ribosomes. The mRNA molecule binds to a ribosome, and tRNA molecules, carrying specific amino acids, recognize codons (three-nucleotide sequences) on the mRNA. The ribosome facilitates the formation of peptide bonds between amino acids, forming a polypeptide chain. The polypeptide chain folds into a functional protein.

(b) Explain how a mutation in the promoter region of a gene can affect gene expression.

Answer: The promoter region is a crucial DNA sequence that regulates gene transcription. Mutations in this region can alter the binding affinity of RNA polymerase, affecting the rate of transcription. A mutation that strengthens the promoter could increase transcription, leading to increased protein production. Conversely, a mutation that weakens the promoter could decrease or completely abolish transcription, resulting in reduced or absent protein production.

(c) Describe the different types of mutations that can occur in DNA and explain how they might affect the resulting protein.

Answer:

• Point Mutations: These involve changes in a single nucleotide. Substitutions replace one nucleotide with another, potentially resulting in a silent mutation (no change in amino acid sequence), a missense mutation (change in one amino acid), or a nonsense mutation (premature stop codon). Insertions or deletions add or remove nucleotides, potentially causing a frameshift mutation that alters the reading frame and dramatically changes the amino acid sequence downstream.

• Chromosomal Mutations: These involve larger-scale changes in chromosome structure, such as deletions, duplications, inversions, or translocations. These mutations can have significant effects on gene expression and protein function, often leading to severe consequences.

Question 4: Ecology and Population Dynamics

Question: This question investigated ecological principles, focusing on population dynamics, carrying capacity, and limiting factors. Students had to analyze data and explain concepts related to population growth and regulation.

(a) Describe the factors that influence the carrying capacity of a population.

Answer: Carrying capacity (K) represents the maximum population size that an environment can sustainably support. Factors influencing K include:

• Resource Availability: The abundance of food, water, shelter, and other essential resources directly limits population growth.

• Competition: Intraspecific (within a species) and interspecific (between species) competition for resources can reduce population size.

• Predation: Predators can significantly reduce prey populations, limiting their carrying capacity.

• Disease: Disease outbreaks can dramatically decrease population size.

• Environmental Factors: Abiotic factors like temperature, rainfall, and space also limit carrying capacity.

(b) Explain the concept of exponential growth and logistic growth, and describe the conditions under which each type of growth is likely to occur.

Answer:

• Exponential Growth: This occurs when a population grows at a constant rate, without limitations. It is characterized by a J-shaped curve. Exponential growth is likely to occur in environments with abundant resources and low competition, typically during the initial stages of colonization or when a population experiences a sudden increase in resources.

• Logistic Growth: This takes into account environmental limitations. The population initially grows exponentially, but as it approaches carrying capacity, the growth rate slows, eventually stabilizing around K. This is represented by an S-shaped curve. Logistic growth is more realistic for most natural populations.

(c) Explain how limiting factors can regulate population size.

Answer: Limiting factors prevent a population from exceeding its carrying capacity. These factors can be density-dependent (e.g., competition, disease, predation), increasing in intensity as population density increases, or density-independent (e.g., natural disasters, climate change), affecting the population regardless of its density. Limiting factors can reduce birth rates, increase death rates, or cause emigration, ultimately maintaining population size within the carrying capacity of the environment.

Question 5: Evolution and Natural Selection

Question: This FRQ focused on evolution, emphasizing natural selection, adaptations, and the evidence supporting evolutionary theory.

(a) Describe the process of natural selection.

Answer: Natural selection is a mechanism of evolution driven by differential reproductive success. It involves four main components:

1. Variation: Individuals within a population exhibit variations in their traits.

2. Inheritance: These traits are heritable, passed from parents to offspring.

3. Differential Survival and Reproduction: Individuals with certain traits are better adapted to their environment and have a higher chance of surviving and reproducing.

4. Adaptation: Over time, the frequency of advantageous traits increases in the population, leading to adaptation to the environment.

(b) Explain how natural selection can lead to the evolution of antibiotic resistance in bacteria.

Answer: Antibiotic resistance evolves through natural selection. Within a bacterial population, some bacteria may possess genes that confer resistance to a particular antibiotic. When exposed to the antibiotic, susceptible bacteria are killed, while resistant bacteria survive and reproduce. This leads to an increased frequency of resistance genes in the population over time, resulting in antibiotic resistance.

(c) Describe two different types of evidence that support the theory of evolution.

Answer:

• Fossil Evidence: The fossil record shows a progression of life forms over time, documenting the appearance and extinction of species and providing evidence of transitional forms between different groups of organisms.

• Molecular Evidence: Similarities in DNA and protein sequences among different species provide strong evidence of common ancestry. Closely related species share more similarities in their genetic makeup than distantly related species.

This comprehensive guide provides detailed answers and explanations for the 2017 AP Biology FRQs. Remember to practice answering FRQs regularly using past exams and sample questions. Understanding the underlying biological principles and developing a structured approach to answering these questions are key to success on the AP Biology exam. Good luck!