Ap Biology 2020 Practice Exam 1 Frq

Introduction

The AP Biology 2020 Practice Exam 1 FRQ is a critical resource for students aiming to master the free‑response section of the College Board’s AP Biology exam. By working through the 2020 practice questions, learners can identify common themes, refine their scientific reasoning, and develop the writing skills needed to earn a high score. This article breaks down each FRQ, explains the underlying concepts, offers step‑by‑step strategies for answering, and provides tips for maximizing points on the actual exam.

Why the 2020 Practice Exam Matters

• Authentic format – The 2020 exam was the first to incorporate the new “grid‑in” format for multiple‑choice questions, but the free‑response section remained unchanged, making the FRQs a reliable gauge of current expectations.
• Content alignment – All questions map directly to the six Big Ideas and eight Science Practices outlined in the AP Biology Course Description, ensuring that studying these FRQs covers the breadth of the curriculum.
• Scoring insights – The College Board releases rubrics for each FRQ, allowing students to see precisely how points are awarded for claims, evidence, and reasoning.

Understanding how to approach these questions can boost confidence and improve overall performance on the real exam.

Overview of the 2020 Practice Exam 1 FRQs

The exam contains four free‑response questions (FRQs), each worth 12 points (total 48 points). They can be grouped as follows:

1. Cellular Respiration & Metabolism – A multi‑part question requiring calculations and conceptual explanations.
2. Genetics & Evolution – Focuses on Punnett squares, Hardy‑Weinberg equilibrium, and natural selection.
3. Ecology & Population Dynamics – Asks for interpretation of graphs, energy flow, and trophic interactions.
4. Molecular Biology & Biotechnology – Involves DNA replication, transcription, and experimental design.

Below, each FRQ is dissected with a step‑by‑step guide and the scientific reasoning needed for full credit The details matter here..

FRQ 1 – Cellular Respiration & Metabolism

Prompt Summary

Students are given a diagram of a yeast cell undergoing glycolysis, the citric acid cycle, and oxidative phosphorylation. They must:

1. Calculate the net ATP yield from one glucose molecule.
2. Explain how a mutation that reduces the activity of pyruvate dehydrogenase would affect the ATP yield.
3. Describe how the cell could compensate for the loss of ATP production.

Step‑by‑Step Solution

1. Net ATP Calculation

Note: The College Board uses a P/O ratio of 2.5 for NADH and 1.5 for FADH₂ in the 2020 rubric, yielding a total of 38 ATP per glucose under aerobic conditions.

2. Effect of Pyruvate Dehydrogenase Mutation

• Reduced conversion of pyruvate → acetyl‑CoA means fewer NADH molecules from this step (normally 2 NADH).
• Consequences:
  • Loss of 5 ATP from the missing NADH (2 NADH × 2.5 ATP each).
  • Fewer acetyl‑CoA molecules entering the citric acid cycle, decreasing downstream NADH, FADH₂, and substrate‑level ATP.
  • Overall net ATP could drop to ≈30–32 ATP, depending on the severity of the mutation.

3. Cellular Compensation

• Upregulation of glycolysis (increase glucose uptake, activate hexokinase) to produce ATP via substrate‑level phosphorylation.
• Activation of anaerobic pathways (fermentation to ethanol or lactate) to regenerate NAD⁺, allowing glycolysis to continue despite limited oxidative phosphorylation.
• Mitochondrial biogenesis – the cell may increase the number of mitochondria to maximize the remaining oxidative capacity.

Key Takeaways

• Always convert NADH/FADH₂ to ATP using the 2.5/1.5 P/O ratio (2020 rubric).
• When a mutation affects a single step, trace its downstream impact on all energy‑producing pathways.
• Mention both short‑term (metabolic flux changes) and long‑term (gene expression, organelle number) compensatory mechanisms for full credit.

FRQ 2 – Genetics & Evolution

Prompt Summary

A population of beetles displays two coat‑color alleles: B (black, dominant) and b (brown, recessive). The initial genotype frequencies are:

• BB: 0.36
• Bb: 0.48
• bb: 0.16

Students must:

1. Verify whether the population is in Hardy‑Weinberg equilibrium.
2. Predict genotype frequencies after one generation of random mating.
3. Explain how a selective pressure favoring brown beetles (bb) would shift allele frequencies over several generations.

Step‑by‑Step Solution

1. Hardy‑Weinberg Test

• Calculate allele frequencies:

  • p (frequency of B) = f(BB) + ½f(Bb) = 0.36 + 0.24 = 0.60
  • q (frequency of b) = 1 – p = 0.40

• Expected genotype frequencies:

  • BB = p² = 0.36
  • Bb = 2pq = 0.48
  • bb = q² = 0.16

Since observed = expected, the population is in Hardy‑Weinberg equilibrium (no evolutionary forces acting, assuming large population, random mating, no migration, mutation, or selection).

2. Frequencies After One Generation

Because the population already meets HW expectations, the genotype frequencies remain BB = 0.Practically speaking, 48, bb = 0. 36, Bb = 0.16 after random mating Easy to understand, harder to ignore. Surprisingly effective..

3. Effect of Positive Selection for bb

• Selection coefficient (s) for bb > 0 (e.g., s = 0.1 means bb individuals have 10 % higher fitness).

• Change in allele frequency:

  Δq ≈ (spq) / (1 – sq²)

  Plugging p = 0.Practically speaking, 60, q = 0. 40, s = 0.1 → Δq ≈ 0.In real terms, 1 × 0. Consider this: 60 × 0. 40 / (1 – 0.That's why 1 × 0. 16) ≈ 0.Because of that, 024 / 0. 984 ≈ **0 Easy to understand, harder to ignore. Practical, not theoretical..

  New q ≈ 0.40 + 0.024 = 0.424; new p ≈ 0.576 Not complicated — just consistent..

• Iterating this calculation over multiple generations shows a gradual increase in the b allele, eventually driving the population toward a higher proportion of brown beetles Which is the point..

• Graphical expectation: A classic selective sweep curve where the frequency of the favored recessive allele accelerates once its homozygotes become common enough for selection to act efficiently.

Key Takeaways

• Hardy‑Weinberg equilibrium is a baseline; any deviation signals an evolutionary force.
• Use the selection coefficient formula to quantify allele‑frequency change.
• point out both the short‑term (heterozygote advantage/disadvantage) and long‑term (fixation) consequences of selection.

FRQ 3 – Ecology & Population Dynamics

Prompt Summary

A graph depicts the population size of a predator (lynx) and its primary prey (snowshoe hare) over 10 years. Students must:

1. Identify the type of interaction displayed.
2. Explain the lag between prey peak and predator peak.
3. Discuss how a severe winter could alter the cycles.

Step‑by‑Step Solution

1. Interaction Type

• The classic predator‑prey (consumer‑resource) cycle is evident: hare numbers rise, followed by a rise in lynx, then both decline.

2. Reason for the Lag

• Numerical response: Lynx reproduction depends on hare abundance; it takes time for increased food to translate into higher lynx birth rates.
• Functional response: As hare density increases, lynx consumption per individual rises until it saturates (Type II functional response).
• Time delay (often 1–2 years) creates the observed phase shift, a hallmark of the Lotka‑Volterra model.

3. Impact of a Harsh Winter

• Direct mortality: Snow depth and low temperatures increase hare mortality, reducing the prey base.
• Bottom‑up effect: Fewer hares mean fewer lynx births; lynx may experience starvation, leading to a sharper decline.
• Potential for a phase shift: The cycle could be dampened or even collapse, resulting in a longer period of low predator numbers until hare populations recover.

Key Takeaways

• Relate the graph to mathematical models (Lotka‑Volterra, logistic growth).
• Discuss both top‑down (predation) and bottom‑up (resource limitation) forces.
• Highlight environmental stochasticity (e.g., severe winter) as a factor that can disrupt regular cycles.

FRQ 4 – Molecular Biology & Biotechnology

Prompt Summary

A researcher uses CRISPR‑Cas9 to knock out a gene encoding an enzyme in the glycolytic pathway of E. coli. The question asks:

1. Outline the steps required to design the guide RNA (gRNA).
2. Predict the metabolic consequence of the knockout.
3. Propose an experiment to verify that the targeted gene was successfully disrupted.

Step‑by‑Step Solution

1. Designing the gRNA

1. Identify target sequence – locate a 20‑nt region in the coding strand adjacent to a PAM (NGG) motif.
2. Check off‑target potential – use BLAST or a genome‑wide alignment to ensure minimal similarity elsewhere.
3. Add overhangs – incorporate restriction‑site overhangs for cloning into the CRISPR plasmid (e.g., BbsI sites).
4. Synthesize oligonucleotides – order the forward and reverse oligos, anneal, and ligate into the Cas9 expression vector.

2. Metabolic Consequence

• Loss of the enzyme halts the specific step of glycolysis, causing accumulation of the substrate upstream and depletion of downstream metabolites (e.g., ATP, NADH).
• Phenotypic effect: Reduced growth rate on glucose as the bacterium cannot efficiently extract energy; the strain may shift to alternative carbon sources (e.g., acetate) or rely on fermentation pathways.

3. Verification Experiment

• PCR screening: Design primers flanking the target site. Amplify genomic DNA from transformed colonies; a successful edit will show a size shift if a repair template introduced an insertion/deletion.
• Sequencing: Sanger sequence the PCR product to confirm the presence of indels at the cleavage site.
• Enzyme assay: Measure activity of the targeted enzyme in cell lysates; a dramatic reduction (≈0 % of wild‑type) confirms functional knockout.

Key Takeaways

• stress specificity (PAM requirement) and off‑target analysis when designing gRNAs.
• Connect the molecular disruption to physiological outcomes (growth, metabolite flux).
• Use multiple lines of evidence (genotypic and phenotypic) for solid verification.

General Strategies for Scoring High on AP Biology FRQs

1. Read the prompt twice. Identify the claim, evidence, and reasoning components the rubric expects.
2. Outline before writing. A brief bullet plan ensures you address every sub‑part and stay within the word limit.
3. Use scientific terminology accurately. Terms like allosteric regulation, gene flow, or photosynthetic electron transport earn points when used correctly.
4. Show calculations clearly. Write each step, label units, and round only at the final answer to avoid rounding errors.
5. Link back to the Big Ideas. To give you an idea, when discussing a mutation, reference Big Idea 1 – Evolution and Science Practice 2 – Developing and Using Models.
6. Time management. Allocate ~12–15 minutes per FRQ; if stuck, move on and return with fresh eyes.

Frequently Asked Questions

Q1: How many points are typically lost for missing reasoning?
A: The rubric awards 0–4 points for reasoning in each sub‑question. Missing or vague reasoning can cost up to half the points for that part Not complicated — just consistent..

Q2: Can I use the 3‑ATP per NADH rule instead of 2.5?
A: For the 2020 exam, the College Board explicitly states the 2.5 ATP per NADH and 1.5 ATP per FADH₂ conversion. Using the older 3/2 ratio may lead to a lower score Easy to understand, harder to ignore..

Q3: Are diagrams required?
A: Diagrams are optional but highly encouraged when they clarify a process (e.g., a simplified glycolysis pathway). Label clearly; unlabeled sketches may not receive full credit.

Q4: How many words should each response contain?
A: There is no strict word count, but aim for 150–250 words per sub‑question to provide enough detail without being overly verbose.

Conclusion

Mastering the AP Biology 2020 Practice Exam 1 FRQ involves more than memorizing facts; it requires a systematic approach to interpreting prompts, applying core biological concepts, and communicating reasoning with precision. By dissecting each question, practicing the outlined strategies, and reviewing the scoring rubrics, students can transform practice into performance. Remember to:

• Calculate accurately (use the correct P/O ratios).
• Trace causal chains (mutations → pathway effects → cellular compensation).
• Integrate evolutionary and ecological context (Hardy‑Weinberg, selection, predator‑prey dynamics).
• Validate molecular techniques with both genetic and functional evidence.

With diligent practice and a clear understanding of how the College Board evaluates responses, you’ll be well‑equipped to earn a top score on the free‑response section and demonstrate the depth of knowledge expected of an AP Biology scholar Less friction, more output..