2019 ap biology frq answers

Charlotte

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01-03-2025

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The 2019 AP Biology exam presented students with challenging free-response questions (FRQs) that tested their understanding of core biological concepts. This article provides answers and detailed explanations for each FRQ, helping students understand the reasoning behind the correct responses and improve their exam preparation. Remember, these are sample answers, and slight variations in wording can still receive full credit. Always consult the official AP Biology scoring guidelines for the most accurate assessment.

Question 1: Photosynthesis and Cellular Respiration

This question explored the interconnectedness of photosynthesis and cellular respiration, focusing on energy transfer and the role of various organelles.

(a) Describe the role of chloroplasts in photosynthesis.

Chloroplasts are the sites of photosynthesis in plant cells. Within the chloroplast, light-dependent reactions occur in the thylakoid membranes, converting light energy into chemical energy in the form of ATP and NADPH. The Calvin cycle, which takes place in the stroma, uses this energy to fix carbon dioxide into glucose.

(b) Explain how the products of photosynthesis are used in cellular respiration.

The glucose produced during photosynthesis serves as the primary fuel for cellular respiration. Cellular respiration breaks down glucose, releasing the stored energy to produce ATP, the cell's primary energy currency. Oxygen, a byproduct of photosynthesis, is also essential for cellular respiration as the final electron acceptor in the electron transport chain.

(c) Describe the role of mitochondria in cellular respiration.

Mitochondria are the powerhouses of the cell. The processes of glycolysis (in the cytoplasm), the Krebs cycle (in the mitochondrial matrix), and oxidative phosphorylation (in the inner mitochondrial membrane) all contribute to ATP production within the mitochondria.

(d) Explain how the products of cellular respiration are used in photosynthesis.

The carbon dioxide (CO2) produced during cellular respiration is used as a reactant in photosynthesis. Water (H2O), also a product of cellular respiration, is used in the light-dependent reactions of photosynthesis.

Question 2: Population Ecology

This question focused on population dynamics and factors affecting population growth.

(a) Describe two different density-dependent factors that can limit population growth.

• Competition: As population density increases, competition for resources like food, water, and mates intensifies, limiting growth.
• Disease: Higher population densities facilitate the spread of diseases, leading to increased mortality and decreased population growth.

(b) Describe two different density-independent factors that can limit population growth.

• Natural disasters: Events like floods, fires, and earthquakes can significantly impact populations regardless of density.
• Climate change: Changes in temperature or precipitation patterns can affect resource availability and survival, regardless of population size.

(c) Explain how the carrying capacity of an environment might affect the growth of a population.

Carrying capacity is the maximum population size an environment can sustainably support. As a population approaches its carrying capacity, resources become limiting, leading to decreased birth rates, increased death rates, or both. This results in a leveling off of population growth, causing the population to stabilize around the carrying capacity.

Question 3: Evolution and Natural Selection

This FRQ delved into the mechanisms of evolution, specifically natural selection.

(a) Explain how natural selection can lead to the evolution of a new species.

Natural selection favors individuals with traits better suited to their environment. Over time, these advantageous traits become more common within a population. If populations become reproductively isolated (e.g., through geographic separation or behavioral changes), genetic divergence occurs. Eventually, this divergence can result in the formation of new species that are unable to interbreed.

(b) Describe two different mechanisms of reproductive isolation that can lead to speciation.

• Geographic isolation: Physical barriers (mountains, rivers, etc.) separate populations, preventing gene flow.
• Behavioral isolation: Differences in mating rituals or courtship displays prevent interbreeding between populations.

(c) Explain how genetic drift can affect the evolution of a population.

Genetic drift is the random change in allele frequencies within a population. It's particularly impactful in small populations, where random events can have a disproportionate effect. Genetic drift can lead to the loss of genetic variation and the fixation of certain alleles, potentially influencing the direction of evolution regardless of selective pressures.

(d) Explain how gene flow can affect the evolution of a population.

Gene flow is the movement of genes between populations through migration and interbreeding. It introduces new alleles into a population, increasing genetic diversity and potentially preventing genetic divergence between populations. If gene flow is extensive, it can counteract the effects of natural selection and genetic drift.

Preparing for the AP Biology Exam

These explanations are designed to help you understand the concepts behind the 2019 FRQs. To truly master the material, review your textbook, class notes, and practice additional FRQs from past exams. Remember to focus on understanding the underlying biological principles and practicing clear and concise communication of your knowledge. Good luck!