AP Biology Last-Minute Review (Night Before)

title: "AP Biology Last-Minute Review (Night Before)" description: "The night-before AP Biology checklist: must-know formulas, top traps, graph interpretation, score boundaries, and morning-of advice. Skim in 45 minutes." date: "2026-01-15" examDate: "May AP Exam" topics:

• Formula Sheet
• Common Traps
• Graph Interpretation
• Exam Logistics

The exam is tomorrow. This is not the time to learn new content — it's time to skim, reset, and sleep. Spend 45 minutes on this page, then put your notes away. Get 8 hours of sleep tonight.

AP Biology Formula Sheet (You'll have this on exam day)

| Formula | What It Means | When to Use | |---|---|---| | $p^2 + 2pq + q^2 = 1$ | Hardy-Weinberg equilibrium; $p$ = dominant allele freq, $q$ = recessive | Population genetics, allele frequency, test if population is evolving | | $p + q = 1$ | Sum of allele frequencies | Every Hardy-Weinberg problem | | $\chi^2 = \sum \frac{(O-E)^2}{E}$ | Chi-square test; compare observed to expected | Genetics FRQs, test fit to Mendelian ratios or genetic models | | $\Psi = \Psi_P + \Psi_S$ | Water potential; Ψ_P = pressure, Ψ_S = solute | Osmosis problems, predict cell plasmolysis or lysis | | $Q_{10} = \frac{R_2}{R_1}$ | Temperature coefficient; reaction rate change per 10°C | Enzyme kinetics, compare reaction rates at different temps | | Dilution | $C_1 V_1 = C_2 V_2$ | Prepare solutions, calculate required volumes | | Surface Area / Volume | As size ↑, SA/V ratio ↓ | Why large cells have diffusion problems, prokaryotes vs eukaryotes | | Trophic efficiency | ~10% energy passes to next level | Energy pyramids, calculate biomass at each trophic level |

Top 10 Traps That Cost Real Points

1. Mitosis vs Meiosis Confusion

• Mitosis: produces 2 identical diploid cells. No genetic variation (except somatic mutations). Happens in somatic tissues.
• Meiosis: produces 4 non-identical haploid cells. Crossing over + independent assortment = genetic variation. Happens in gonads.
• Trap: "Meiosis produces four cells" — yes, but they're haploid and unique due to recombination. Don't confuse the number of cells with their uniqueness.

2. Photosynthesis vs Cellular Respiration (Two Opposite, Not Just Opposite)

• Photosynthesis = builds glucose, stores energy. Light reactions (thylakoid): water broken, O₂ released, ATP + NADPH made. Calvin cycle (stroma): CO₂ + ATP + NADPH → glucose.
• Respiration = breaks glucose, releases energy. Glycolysis (cytoplasm): glucose → 2 pyruvate + 2 ATP + 2 NADH. Krebs cycle (matrix): acetyl-CoA oxidized → 3 NADH + FADH₂ + ATP + CO₂. ETC (cristae): NADH/FADH₂ → electrons, H⁺ pumped, chemiosmosis drives ATP.
• Trap: "Photosynthesis makes ATP" — only in light reactions. "Respiration needs oxygen" — only ETC (glycolysis and Krebs don't directly need O₂, though they require NAD⁺ regeneration).

3. Hardy-Weinberg Assumptions Violations

Five assumptions; violate any one → evolution:

1. No mutation (new alleles introduced).
2. No natural selection (differential survival).
3. Large population (no genetic drift / random sampling error).
4. No migration (gene flow in/out).
5. Random mating (inbreeding, sexual selection violate this).

• Trap: Naming only 1–2 assumptions when asked why a population evolves. Name all five, then identify which one(s) are violated.

4. Chi-Square: Observed vs Expected

• Formula: $\chi^2 = \sum \frac{(O-E)^2}{E}$
• O = observed count (your actual data).
• E = expected count (calculated from genetic model, e.g., 3:1 for Aa × Aa).
• Trap: Using expected in the numerator instead of observed. Or plugging in expected in the wrong place. Always: $(O - E)^2 / E$.

5. Signal Transduction Direction: Extracellular → Intracellular

• Signal starts outside the cell (hormone, neurotransmitter).
• Receptor is on cell membrane or inside (depending on hormone type).
• Amplification occurs in cascade (one hormone → many second messengers → many phosphorylated proteins).
• Response happens inside (nucleus activation, metabolic change, etc.).
• Trap: "Signal starts inside the cell" — wrong. "No amplification in signal transduction" — wrong.

6. Active vs Passive Transport

• Passive = no ATP. Simple diffusion (through lipid), osmosis (water), facilitated diffusion (protein channel, down gradient).
• Active = uses ATP. Na⁺/K⁺ pump, endocytosis, exocytosis. Moves against gradient.
• Trap: Calling "facilitated diffusion" active. It's not — the protein channel helps, but the substance still goes down the gradient (no energy needed).

7. Osmosis is Movement of Water, Not Solute

• Osmosis = water diffuses across semipermeable membrane toward higher solute concentration (lower water concentration).
• Hypotonic = cell gains water (cell swells or cell membrane ruptures in animal cells). Hypertonic = cell loses water (plasmolysis in plant cells).
• Trap: "Salt moves into the cell by osmosis" — no, salt moves by active transport or diffusion. Water moves by osmosis toward the salt.

8. Enzyme Inhibition: Competitive vs Non-Competitive

• Competitive: inhibitor looks like substrate, competes for active site. $K_m$ increases (need more substrate to saturate). $V_{max}$ unchanged (if you add enough substrate, inhibitor loses).
• Non-competitive: inhibitor binds elsewhere (allosteric site), prevents enzyme from working. $V_{max}$ decreases (even with excess substrate, some enzyme is blocked). $K_m$ unchanged.
• Trap: Mixing up which parameter changes. Remember: competitive = $K_m$ changes (harder to saturate); non-competitive = $V_{max}$ changes (maximum speed reduced).

9. Evolution by Natural Selection: Variation → Selection → Inheritance

• Variation (genetic diversity in population) + differential survival (some phenotypes survive/reproduce better) + inheritance (trait passes to offspring) = allele frequency change.
• Evidence for evolution: fossil record (transitional forms), biogeography (distribution), comparative anatomy (homologous structures), molecular (DNA/protein similarity).
• Trap: "Evolution = change within an organism's lifetime." No — evolution is population-level change over generations. Also: "Natural selection directs evolution" — selection acts on variation; it doesn't create variation (mutations do).

10. Energy Pyramids: ~10% Energy Transfer Between Levels

• Primary productivity (plants) = 100% of energy captured.
• Primary consumers (herbivores) ≈ 10% of primary productivity (rest lost as heat, used in respiration, etc.).
• Secondary consumers ≈ 10% of primary consumers.
• Trap: "100% of energy moves up the food chain" — no, ~90% is lost to metabolism and heat. Also: "More biomass at top levels" — wrong, biomass decreases moving up (energy limits).

The AP Biology Formula: Claim-Evidence-Reasoning (CER)

Every FRQ must follow this structure:

1. Claim: State your answer clearly.
2. Evidence: Provide data, examples, or observations.
3. Reasoning: Explain the biological principle.

Example: "Why does increasing temperature speed up enzyme reactions?"

Claim: Higher temperature increases enzyme-catalyzed reaction rates by increasing molecular motion.

Evidence: In a typical enzyme kinetics experiment, reaction rate doubles or triples for every 10°C increase in temperature (up to the enzyme's optimum, ~37°C for most human enzymes).

Reasoning: At higher temperature, substrate and enzyme molecules move faster, increasing collision frequency. More collisions between substrate and active site mean more successful enzyme-substrate complexes form and more product is made per unit time. However, at very high temperatures, the enzyme's hydrogen bonds break, causing denaturation and loss of activity.

Graph Interpretation Quick Tips

1. Read the axes carefully.

• What is the x-axis? (Time, temperature, substrate concentration, light intensity?)
• What is the y-axis? (Rate, count, frequency, percentage?)
• Are there units? (mL/min, cells, %, bp?)

2. Identify the trend.

• Positive correlation (both increase together): "As X increases, Y increases."
• Negative correlation (inverse): "As X increases, Y decreases."
• Plateau/saturation: "As X increases, Y increases until [threshold], then plateaus."
• Parabola (inverted U): "Y increases with X initially, reaches a maximum at [value], then decreases."

3. Propose a biological explanation.

• Use enzyme kinetics: limiting factors, saturation, substrate availability.
• Use population dynamics: carrying capacity, exponential vs logistic growth.
• Use thermodynamics: temperature effects, energy availability.

Example scenario: Graph shows population size (y-axis) vs time (x-axis). Curve is S-shaped (logistic).

• Trend: Population grows slowly at first, then rapidly, then plateaus.
• Explanation: At small population sizes, few individuals reproduce, so growth is slow. As population grows, more individuals breed, so growth accelerates. Eventually, the population hits carrying capacity (K) — resources limit further growth, and population stabilizes.

Water Potential ($\Psi$) Quick Reference

$\Psi = \Psi_P + \Psi_S$

Where:

• $\Psi$ (psi) = total water potential (kPa or bars).
• $\Psi_P$ = pressure potential (turgor pressure in plant cells; 0 in animal cells).
• $\Psi_S$ = solute potential (always ≤ 0; more solute = more negative).

Pure water: $\Psi = 0$. Cell in hypertonic solution: $\Psi$ is negative (cell loses water). Cell in hypotonic solution: $\Psi$ is positive/less negative (cell gains water).

Example: Plant cell has $\Psi_P = 0.5$ MPa and $\Psi_S = -0.8$ MPa. Then $\Psi = 0.5 + (-0.8) = -0.3$ MPa. Water will move into the cell from pure water (which has $\Psi = 0$).

Chi-Square Critical Values (df = degrees of freedom; α = 0.05 significance level)

| df | $\chi^2_{\text{crit}}$ | |---|---| | 1 | 3.84 | | 2 | 5.99 | | 3 | 7.81 | | 4 | 9.49 |

If your calculated $\chi^2$ > critical value, reject the hypothesis (data deviate significantly from expected).

Score Boundaries (Approximate, Out of 108 Total)

| Score | Range | |---|---| | 5 | ~70–108 | | 4 | ~58–69 | | 3 | ~42–57 | | 2 | ~30–41 | | 1 | < ~30 |

You do not need to answer every question perfectly to earn a 5. ~65% correct earns a 5. Missing 3–4 MC questions and getting 1 FRQ mostly right can still yield a 5.

Highest-Yield Topics to Skim Tonight

1. Hardy-Weinberg: know $p^2 + 2pq + q^2 = 1$, calculate allele/genotype frequencies, identify violations.
2. Photosynthesis vs respiration: light reactions make ATP/NADPH; Calvin cycle uses them to make glucose. Respiration releases energy from glucose.
3. Mitosis vs meiosis: mitosis = 2 identical diploid; meiosis = 4 unique haploid. Meiosis I separates homologs (reductional); meiosis II separates sister chromatids (like mitosis).
4. Signal transduction: signal enters → receptor → cascade → amplification → response in nucleus or cytoplasm.
5. Natural selection: variation + differential survival + inheritance = evolution. Evidence: fossils, geography, anatomy, DNA.
6. Energy pyramids: ~10% energy per level. Why? Metabolic heat loss and cellular respiration.
7. Chi-square: $(O-E)^2/E$, compare to critical value, draw conclusion about fit.

Morning-of Checklist

• ☐ 8 hours of sleep last night.
• ☐ Real breakfast: protein (eggs, yogurt) + slow carbs (oatmeal, toast), not just sugar. Brain needs fuel.
• ☐ 2–3 sharpened #2 pencils, blue or black pen (for FRQs).
• ☐ Calculator (if allowed) + fresh batteries + test it works.
• ☐ Photo ID + AP Student ID label sheet.
• ☐ Water bottle (sip between sections).
• ☐ Snack for the break (granola bar, fruit).
• ☐ Arrive 30 minutes early.

During the Exam: Time Management

Multiple Choice (~80 min for 60 questions):

• Spend ~1.5 min per MC question (80 min ÷ 60 = ~1.3 min average).
• Mark and skip anything that takes >90 seconds. Circle the question number, come back.
• Use process of elimination aggressively. Wrong answers are often tempting distractors.
• No-calc section (30 min): Focus on conceptual reasoning, not computation.
• Calculator section (50 min): Use it for Hardy-Weinberg, chi-square, stoichiometry. Don't rely on it for simple logic.

Free Response (~90 min for 6 questions, points vary):

• Read all 6 FRQs first (2 min). Identify which type each is (data interpretation, experimental design, short answer, etc.).
• Start with your strongest FRQ to build confidence and lock in easy points.
• Long FRQs (1–2): 20–25 min each. Claim-evidence-reasoning structure.
• Short FRQs (3–6): 8–12 min each. Still needs CER, just more concise.
• Don't leave blanks. Partial credit exists. If stuck, write a claim, even if you're unsure of evidence/reasoning.

During the Exam: Common Mistakes to Avoid

1. ✋ Misreading axis labels. Read every word on a graph's axis.
2. ✋ Forgetting to show work on calculations (chi-square, Hardy-Weinberg, water potential). Show your setup, not just the answer.
3. ✋ Writing a list instead of a paragraph. FRQs want reasoning; bullet points are fast but often lose nuance. Write 2–3 sentences per part.
4. ✋ Using informal language. "The enzyme gets broken" vs "the enzyme denatures." Use precise terminology.
5. ✋ Assuming the grader knows what you mean. Be explicit: name the structures, cite the process, identify the principle.

One Last Thing

You have prepared. You know this material. The work is done. Trust your preparation. Show up rested, breathe between sections, and remember:

• The rubric wants to give you points. Write clearly so it can.
• You don't need perfection to earn a 5. ~65% correct is the target.
• If a question stumps you, skip it, answer the others, and come back if time allows.

You've got this. 🎯

Need more focused review before bed? Browse the AP Biology topic library → or the FRQ practice guide →.