Ap Bio 2017 Frq Answers

AP Bio 2017 FRQ Answers: A Comprehensive Guide and Analysis

The 2017 AP Biology exam presented students with challenging Free Response Questions (FRQs) that tested their understanding of core biological concepts and their ability to apply that knowledge to novel scenarios. This comprehensive guide delves into each FRQ from the 2017 exam, providing detailed answers, explanations, and strategies for maximizing your score on future AP Biology exams. Understanding these questions and their answers is crucial for mastering fundamental biological principles and preparing for success on the AP Biology exam.

FRQ 1: Enzyme Activity and Regulation

This question focused on enzyme activity, specifically the effects of temperature and pH on enzyme function and the mechanisms of enzyme regulation.

(a) Describe the effect of temperature on enzyme activity.

Answer: Enzyme activity generally increases with temperature up to a certain point, the optimal temperature. Beyond this optimal temperature, enzyme activity decreases rapidly due to denaturation. Heat causes the enzyme's three-dimensional structure, crucial for its function, to unravel, disrupting the active site and preventing substrate binding. At very low temperatures, enzyme activity is slowed due to reduced kinetic energy of the molecules, resulting in fewer successful collisions between enzyme and substrate.

(b) Explain how the structure of an enzyme determines its function.

Answer: The three-dimensional structure of an enzyme, including its specific amino acid sequence and folding pattern, directly determines its function. The enzyme's active site, a specific region with a unique shape and charge distribution, is responsible for binding the substrate. The precise fit between the active site and the substrate (lock and key model, or induced fit model) is critical for the catalytic activity of the enzyme. Any alteration in the enzyme's structure, such as through mutations or environmental changes (temperature, pH), can affect the active site's shape and consequently its ability to bind and process the substrate.

(c) Describe TWO different mechanisms of enzyme regulation.

Answer:

• Competitive Inhibition: A competitive inhibitor molecule resembles the substrate and competes for binding to the active site. This reduces the enzyme's efficiency by decreasing the rate of substrate binding.
• Allosteric Regulation: Allosteric regulators bind to a site on the enzyme other than the active site (allosteric site), causing a conformational change that either enhances or inhibits enzyme activity. This is a non-competitive form of regulation.

(d) Explain how a mutation in the gene encoding an enzyme could result in a change in the enzyme’s activity.

Answer: A mutation in the gene encoding an enzyme can alter the enzyme's amino acid sequence. This change in sequence can lead to a change in the enzyme's three-dimensional structure, affecting the shape and function of the active site. If the mutation alters the active site, it could result in a decrease or complete loss of enzyme activity, an increase in enzyme activity, or a change in the enzyme's substrate specificity. Some mutations might also affect the enzyme’s stability or its interaction with regulatory molecules.

FRQ 2: Cellular Respiration and Photosynthesis

This question examined cellular respiration and photosynthesis, emphasizing the interconnectedness of these processes and the flow of energy within and between them.

(a) Describe the role of ATP in cellular processes.

Answer: ATP (adenosine triphosphate) is the primary energy currency of the cell. It stores energy in its high-energy phosphate bonds. When these bonds are broken through hydrolysis, energy is released, powering various cellular processes, including active transport, muscle contraction, protein synthesis, and signal transduction. ATP is constantly being regenerated through cellular respiration and other energy-producing pathways.

(b) Explain how the structure of the chloroplast facilitates the process of photosynthesis.

Answer: The chloroplast's structure is optimized for photosynthesis. The thylakoid membranes house the chlorophyll and other pigment molecules that absorb light energy. The arrangement of these pigments into photosystems allows for efficient energy capture. The thylakoid lumen is essential for the chemiosmotic gradient generation required for ATP synthesis. The stroma, the fluid-filled space surrounding the thylakoids, contains the enzymes necessary for the Calvin cycle, where carbon dioxide is converted into sugars. The double membrane of the chloroplast also provides compartmentalization, ensuring the proper functioning of each stage of photosynthesis.

(c) Describe the role of electron transport chains in both photosynthesis and cellular respiration.

Answer: In both photosynthesis and cellular respiration, electron transport chains are used to generate a proton gradient across a membrane. This gradient drives the synthesis of ATP through chemiosmosis. In photosynthesis, the electrons originate from water molecules, and the electron transport chain leads to the reduction of NADP+ to NADPH. In cellular respiration, electrons originate from NADH and FADH2, and the electron transport chain results in the reduction of oxygen to water. The energy released during electron transport is used to pump protons across the membrane, creating the proton gradient essential for ATP synthesis by ATP synthase.

(d) Explain the relationship between photosynthesis and cellular respiration in terms of energy flow and matter cycling.

Answer: Photosynthesis and cellular respiration are interconnected processes that represent a cycle of energy flow and matter cycling. Photosynthesis captures light energy and converts it into chemical energy in the form of glucose, releasing oxygen as a byproduct. Cellular respiration then utilizes this glucose, breaking down its chemical bonds to release energy in the form of ATP. Carbon dioxide, a byproduct of cellular respiration, is then used by plants in photosynthesis, and water, a byproduct of cellular respiration, is used in photosynthesis. This cycle ensures a constant flow of energy through the ecosystem and the recycling of essential elements like carbon and oxygen.

FRQ 3: Population Genetics and Evolution

This question explored concepts in population genetics, including Hardy-Weinberg equilibrium and the factors that can disrupt it.

(a) Explain the conditions required for a population to be in Hardy-Weinberg equilibrium.

Answer: A population in Hardy-Weinberg equilibrium remains genetically stable across generations. This requires five conditions:

1. No mutations: No new alleles should be introduced into the population.
2. Random mating: Individuals must mate randomly, without any preference for certain genotypes.
3. No gene flow: No migration of individuals into or out of the population.
4. No genetic drift: The population must be large enough that allele frequencies are not significantly altered by random chance.
5. No natural selection: All genotypes must have equal survival and reproductive rates.

(b) Describe how the process of natural selection can alter allele frequencies in a population.

Answer: Natural selection favors individuals with certain heritable traits that enhance their survival and reproduction in a particular environment. Individuals with advantageous alleles are more likely to survive and pass on those alleles to their offspring, increasing the frequency of those alleles in the population. Conversely, alleles that decrease survival or reproductive success will decrease in frequency. This differential survival and reproduction based on genotype leads to changes in allele frequencies over time, driving evolution.

(c) Explain how genetic drift can alter allele frequencies in a population.

Answer: Genetic drift is the random fluctuation of allele frequencies in a population, particularly pronounced in small populations. Chance events, such as natural disasters or random sampling of gametes during reproduction, can disproportionately affect the frequency of certain alleles. This random change in allele frequency can lead to the loss of alleles or the fixation of alleles (reaching 100% frequency) over time, even if those alleles are not advantageous. The bottleneck effect and founder effect are prominent examples of genetic drift.

(d) Explain ONE mechanism, other than natural selection, that could lead to changes in allele frequencies in a population.

Answer: Gene flow: The movement of alleles between populations (migration) can significantly alter allele frequencies. If individuals carrying different allele frequencies migrate into or out of a population, the recipient population's allele frequencies will change, potentially leading to increased genetic diversity or a homogenization of allele frequencies between populations.

FRQ 4: Plant Responses to Environmental Stimuli

This FRQ tested understanding of plant responses to environmental stimuli, focusing on tropisms and hormone signaling.

(a) Explain how phototropism and gravitropism are involved in the growth and development of a plant.

Answer: Phototropism is the directional growth response of a plant towards or away from a light source. Plants exhibit positive phototropism, growing towards light, which optimizes their ability to capture light for photosynthesis. Gravitropism is the directional growth response of a plant in response to gravity. Shoots exhibit negative gravitropism (growing upwards against gravity) while roots exhibit positive gravitropism (growing downwards towards gravity). These tropisms ensure that the plant's shoots are exposed to sunlight for photosynthesis while roots are anchored in the soil for water and nutrient uptake.

(b) Describe the role of auxin in the phototropic response of plants.

Answer: Auxin is a plant hormone that plays a crucial role in phototropism. When light shines on one side of a plant stem, auxin accumulates on the shaded side. This uneven distribution of auxin stimulates cell elongation on the shaded side, causing the stem to bend towards the light. The exact mechanism involves auxin’s effect on cell wall extensibility, influencing the uptake of water and cell expansion.

(c) Describe the role of one other plant hormone in plant growth or development.

Answer: Gibberellins: Gibberellins stimulate stem elongation, seed germination, and fruit development. They are important for overall plant growth and contribute to the overall size and architecture of the plant. They work synergistically with other hormones to regulate growth and development.

(d) Explain how the responses of plants to environmental stimuli enhance their survival and reproduction.

Answer: Plant responses to environmental stimuli enhance survival and reproduction in several ways. Phototropism ensures efficient light capture for photosynthesis, maximizing energy production. Gravitropism ensures proper orientation of roots and shoots, improving nutrient and water uptake, and optimal light exposure. Responses to other stimuli such as drought or herbivory trigger adaptive mechanisms such as water conservation or defense responses, increasing survival chances. The successful adaptation to the environment enhances reproductive success by ensuring sufficient resources for growth, development, and the production of seeds or fruits.

FRQ 5: Animal Behavior

This question examined animal behavior, focusing on proximate and ultimate causes.

(a) Explain the difference between proximate and ultimate causes of behavior.

Answer: Proximate causes of behavior address the how of a behavior – the immediate mechanisms and physiological processes involved. This includes the underlying sensory systems, neural pathways, and hormonal responses that trigger and control the behavior. Ultimate causes of behavior address the why of a behavior – the evolutionary reasons behind the behavior. This considers how the behavior affects an animal’s survival and reproduction, and how the behavior has evolved through natural selection.

(b) Describe ONE example of a proximate cause and ONE example of an ultimate cause for a specific animal behavior.

Answer:

• Proximate Cause: The proximate cause of a bird singing is the activation of specific brain regions and vocal muscles by hormones, in response to environmental cues like daylight changes.
• Ultimate Cause: The ultimate cause of a bird singing is that the song attracts mates and defends territory, increasing its reproductive success and survival.

(c) Explain how the concept of inclusive fitness can account for altruistic behavior in animals.

Answer: Inclusive fitness combines an individual’s own reproductive success (direct fitness) with the reproductive success of its relatives (indirect fitness). Altruistic behavior, where an individual sacrifices its own fitness to benefit others, can be explained by inclusive fitness if the altruistic act increases the survival and reproduction of close relatives who share similar genes. The benefit to the relatives’ fitness, weighted by their relatedness to the altruistic individual, can outweigh the cost to the altruistic individual’s own fitness. Kin selection, a form of natural selection favoring altruistic behavior toward relatives, is based on inclusive fitness.

(d) Explain how environmental factors can influence the expression of a behavior in an animal.

Answer: Environmental factors significantly influence the expression of animal behavior. These factors can act as stimuli that trigger a behavior, affect the development of behavioral traits, or alter the cost-benefit ratio of expressing a behavior. For example, food availability can influence foraging behavior, the presence of predators can influence defensive behaviors, and social interactions can influence mating behaviors and social hierarchies. The same genotype can lead to different phenotypes depending on environmental conditions, showcasing the importance of gene-environment interactions in shaping behavior.

This comprehensive guide provides a thorough analysis of the 2017 AP Biology FRQs. By understanding the reasoning behind the answers and the underlying biological principles, you can significantly improve your preparation for future AP Biology exams. Remember to practice writing your own FRQ responses and seek feedback to further enhance your understanding and scoring ability. Good luck!