AP Biology FRQs For Unit 2 – Practice Questions, Answers & Full Guide

AP Biology Unit 2 FRQs are common and easy to guess, but a lot of students lose points because they don’t write good answers. This guide talks about important topics, types of FRQs, writing tips, scoring tips, practice questions, and expert advice to help you get all the points.

Where Can You Find AP Biology Unit 2 FRQs and Resources?

What Is AP Biology Unit 2? The Complete Topic Breakdown

AP Biology Unit 2 focuses on Cell Structure and Function and makes up about 10–13% of the exam. Its concepts, especially membrane transport and osmosis, appear across multiple units, making it essential for both MCQs and FRQs.

Full Topic List: AP Biology Unit 2 (Topics 2.1 to 2.11)

FRQ Priority Alert: Topics 2.4, 2.5, 2.6, 2.8, and 2.11 are the most frequently tested in Unit 2 FRQs. If you only have limited study time, master these five topics first.

AP Biology Study Material

What Are AP Biology FRQs? Format, Types, and Scoring

The AP Biology free-response section makes up 60% of your total AP Biology score. This is the highest-weighted section of the exam and the one where most score improvement happens through deliberate practice.

The Three FRQ Types You Will See on Unit 2

AP Biology Unit 2 FRQ Practice Questions (Exam-Level)

FRQ 1 – Membrane Transport (Concept + Explanation)

A cell is placed in a solution containing glucose at a higher concentration outside the cell than inside. Over time, glucose enters the cell, but the rate of entry levels off.

(a) Identify the transport mechanism responsible for glucose movement.
(b) Explain why this mechanism is required for glucose transport.
(c) Explain why the rate of transport levels off over time.

FRQ 2 – Data Analysis (Graph-Based)

A graph shows the rate of solute transport into a cell at increasing external concentrations. The curve increases rapidly at first and then plateaus.

(a) Identify the type of transport shown.
(b) Use the graph trend to justify your answer.
(c) Predict what would happen if ATP production in the cell is inhibited.

FRQ 3 – Osmosis & Water Potential (Calculation + Concept)

A plant cell is placed in a solution with a solute concentration of 0.3 M at 298 K.

(a) Calculate the solute potential using:

Ψs=−iCRT\Psi_s = -iCRTΨs​=−iCRT

(b) Predict the direction of water movement.
(c) Explain the effect on the plant cell.

FRQ 4 – Experimental Design

Design an experiment to determine whether a substance crosses the membrane by passive or active transport.

(a) State a hypothesis.
(b) Identify independent and dependent variables.
(c) Describe a control setup.
(d) Explain how results would indicate active transport.

FRQ 5 – Endosymbiotic Theory

Mitochondria are believed to have evolved from prokaryotic organisms.

(a) State the endosymbiotic theory.
(b) Provide TWO pieces of evidence supporting this theory.
(c) Explain how this theory supports evolutionary relationships.

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AP Biology Unit 2 FRQ Solutions (Full-Credit Answers)

FRQ 1 – Membrane Transport

(a) Answer:
Glucose enters the cell by facilitated diffusion.

(b) Answer:
Glucose is a large, polar molecule and cannot pass through the hydrophobic interior of the phospholipid bilayer. Therefore, it requires carrier proteins to move across the membrane down its concentration gradient.

(c) Answer:
The rate of transport levels off because the carrier proteins become saturated. Once all available transport proteins are occupied, the transport rate cannot increase further even if glucose concentration increases.

FRQ 2 – Data Analysis

(a) Answer:
The transport shown facilitated diffusion.

(b) Answer:
The graph shows an increase in transport rate with increasing concentration, followed by a plateau. This indicates protein saturation, which is characteristic of facilitated diffusion.

(c) Answer:
If ATP production is inhibited, there would be no effect on transport rate because facilitated diffusion does not require energy.

FRQ 3 – Osmosis & Water Potential

(a) Calculation:

Ψs=−iCRT\Psi_s = -iCRTΨs​=−iCRT Ψs=−(1)(0.3)(0.0831)(298)\Psi_s = -(1)(0.3)(0.0831)(298)Ψs​=−(1)(0.3)(0.0831)(298) Ψs=−7.43 bars (approx)\Psi_s = -7.43 \text{ bars (approx)}Ψs​=−7.43 bars (approx)

(b) Answer:
Water will move into the cell because the solution has lower water potential compared to the cell.

(c) Answer:
The plant cell will become turgid due to water entering, increasing turgor pressure.

FRQ 4 – Experimental Design

(a) Hypothesis:
If a substance requires ATP to cross the membrane, then it is transported by active transport.

(b) Variables:

• Independent variable: ATP availability
• Dependent variable: rate of substance transport

(c) Control:
A setup where ATP is available under normal conditions.

(d) Answer:
If transport decreases when ATP is inhibited, it indicates active transport. If transport remains unchanged, it indicates passive transport.

FRQ 5 -Endosymbiotic Theory

(a) Answer:
The endosymbiotic theory states that mitochondria evolved from free-living prokaryotic cells that were engulfed by a host cell.

(b) Evidence:

• Mitochondria contain circular DNA
• Mitochondria have 70S ribosomes

(c) Answer:
This supports evolutionary relationships because it shows that eukaryotic cells share a common ancestry with prokaryotes.

The Most Frequently Tested Unit 2 FRQ Topics

Based on past AP Biology FRQs from 2015 to 2025, these are the Unit 2 topics that appear most often. Every serious AP Biology student should be able to write a complete, rubric-ready FRQ response for each of these.

• Simple Diffusion: Small nonpolar molecules move directly, no protein or energy required
• Facilitated Diffusion: Large or charged particles use proteins, no ATP, move down gradient
• Active Transport: Moves substances against gradient using ATP (e.g., Na⁺/K⁺ pump)
• Key Tip: Movement against concentration gradient = active transport

FRQ Trap

• Don’t just say “passive transport”
• Always name the exact mechanism (simple, facilitated, or active)
• Explain using molecule type and concentration gradient

Plasma Membrane & Selective Permeability

• Phospholipid Bilayer: Hydrophilic heads outward, hydrophobic tails inward → creates selective barrier
• Small Nonpolar Molecules: (O₂, CO₂) diffuse freely
• Water: Moves slowly or via aquaporins
• Large/Charged Molecules: Require transport proteins
• Proteins & Cholesterol: Proteins help transport; cholesterol controls fluidity

Osmosis, Tonicity & Water Potential

• Water Potential: Ψ=Ψs+Ψp\Psi = \Psi_s + \Psi_pΨ=Ψs​+Ψp​, with Ψs=−iCRT\Psi_s = -iCRTΨs​=−iCRT
• Water Movement: High Ψ\PsiΨ → Low Ψ\PsiΨ (low solute → high solute)
• Hypertonic: Water leaves cell → crenation/plasmolysis
• Hypotonic: Water enters cell → lysis/turgid
• Isotonic: No net water movement

Endosymbiotic Theory & Evidence

• Theory: Mitochondria and chloroplasts were once free-living prokaryotes engulfed by a host cell
• Double Membrane: Inner (prokaryote), outer (host cell)
• Own DNA: Circular DNA like prokaryotes
• Own Ribosomes: 70S ribosomes (prokaryotic type)
• Binary Fission: Reproduce independently
• Size: Similar to prokaryotic cells

Complete FRQ Writing Framework for AP Biology Unit 2

Writing strong FRQ answers is not just about knowing biology — it’s about presenting your answer in a way that earns rubric points. AP Biology FRQs are graded based on specific components, not overall writing quality.

The Golden Rule: Every Point Is Independent

Each part of an FRQ is graded separately.
A wrong answer in one part does not affect other parts.

Always attempt every sub-part, even if you are unsure.

5-Step Unit 2 FRQ Framework

• Read First: Identify the task (describe, explain, predict, etc.)
• State Claim: Give a direct, specific answer
• Explain Mechanism: Focus on how and why
• Use Evidence: Refer to data or values if given
• Use Correct Terms: Apply key biology vocabulary

How AP Biology FRQ Scoring Works

Understanding how rubrics work changes how you write. Here is the scoring logic that actual AP Biology exam readers use.

The Point-per-Statement System

AP Biology FRQ rubrics award one point for each specific, correct biological statement. There is no partial credit for a partially correct statement – you either earn the point or you do not. However, there is no penalty for adding extra information (as long as it does not contradict what you already wrote – contradictions cancel points).

How Rubric Points Are Structured for Unit 2 FRQs

• Point for identifying the correct biological concept (example: naming the specific transport mechanism)
• Point for the mechanism or explanation (example: explaining WHY that transport mechanism applies)
• Point for connecting to the data or evidence (example: citing specific concentrations from the graph)
• Point for the consequence or prediction (example: what will happen to the cell as a result)
• Point for using correct vocabulary (example: using the term “water potential” rather than just “osmosis pressure”)

What Happens If You Write Too Much

Giving more correct information won’t lower your score, but changing your own answer can. This is called over-writing. If you know the right answer, write it down clearly and don’t add anything that could make your answer weaker or contradict it.

AP Biology FRQ Score Distribution for Unit 2 Topics (2025)

• Membrane transport identification and mechanism: 2 to 3 rubric points per appearance
• Plasma membrane structure and selective permeability: 2 to 4 rubric points per appearance
• Osmosis and water potential (including calculation): 3 to 5 rubric points per appearance
• Endosymbiotic theory with evidence: 3 to 4 rubric points per appearance
• Experimental design around Unit 2 concepts: 4 to 6 rubric points per appearance

The 3-Week AP Biology Unit 2 FRQ Study Plan

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AP Biology FRQs for Unit 2

What are AP Biology Unit 2 FRQs?

The free-response questions in AP Biology Unit 2 are about cell structure and function, such as how membranes transport substances, how osmosis works, and how organelles work. These questions check your ability to use proper biological reasoning to explain ideas.

How many FRQs appear from Unit 2 in the AP Biology exam?

Unit 2 ideas are usually in at least one part of the FRQ section. Osmosis and membrane transport are two of the most common subjects on AP Biology tests.

What topics are most important for Unit 2 FRQs?

The most important subjects are endosymbiotic theory, tonicity, osmosis and water potential, and the structure of the plasma membrane. They show up a lot in both long and short FRQs.

How do you answer AP Biology Unit 2 FRQs correctly?

To answer correctly, you need to make a clear claim, explain how it works in biology, use the right words, and back up your answer with data if you have it. Be clear and specific in your explanations.

Are AP Biology Unit 2 FRQs difficult?

Unit 2 FRQs are based on concepts, and they can be hard if you don’t practice writing long answers. But if you prepare properly and understand the main ideas, they become predictable and easy to deal with.