Identify
Name the process, structure, or molecule.
Where Unit 4 FRQ Practice Fits in the Journey
The previous page, Unit 4 Practice Questions, mixed MCQs and short checks across the full unit. This page focuses on longer free response practice, where students must explain mechanisms in complete biological reasoning. Use it after reviewing signaling, feedback, cell cycle checkpoints, cancer, and apoptosis.
- 1 Unit 4 Hub
- 2 Cell Communication
- 3 Ligands and Receptors
- 4 Reception, Transduction, Response
- 5 Cell Signaling Pathways
- 6 Feedback Mechanisms
- 7 Negative Feedback
- 8 Positive Feedback
- 9 Cell Cycle
- 10 Cell Cycle Checkpoints
- 11 Cyclins and CDKs
- 12 Signal Amplification
- 13 Second Messengers
- 14 Phosphorylation Cascade
- 15 Cancer and Cell Cycle Regulation
- 16 Apoptosis
- 17 Unit 4 Practice Questions
- 18 Unit 4 FRQ You are here
How do you answer AP Biology Unit 4 FRQs?
To answer AP Biology Unit 4 FRQs, identify the biological process, explain the mechanism, use evidence from the prompt, and predict the result of a change. For cell communication, trace reception, transduction, and response. For cell cycle questions, explain how checkpoints, cyclins, CDKs, apoptosis, or cancer regulation affect cell behavior.
Say it fast
Name the process, explain the mechanism, and predict the outcome.
Unit 4 FRQ Writing Coach
Build a strong FRQ sentence by choosing a topic, task verb, and evidence type. Use the frame as a starting point, then add prompt-specific details.
Generated sentence frame
Select options above, then generate a sentence frame.
The Unit 4 FRQ Method
Strong Unit 4 FRQs identify, explain, use evidence, and predict.
Most Unit 4 FRQs reward mechanism-based reasoning. Naming a term is only the first step. To earn explanation points, connect the term to what changes in the cell and why that change affects the response.
Describe
State what it does.
Explain
Connect the cause to the effect.
Predict
Say what changes if the pathway is blocked or overactive.
Justify
Use evidence from the prompt.
Know the AP Biology FRQ Verbs
| Verb | What it asks | Strong Unit 4 example |
|---|---|---|
| Identify | Name the answer | The receptor is involved in reception. |
| Describe | State features or role | The receptor binds a specific ligand. |
| Explain | Give cause-and-effect | If the receptor changes shape, the ligand may not bind and the pathway may not activate. |
| Predict | State likely result | The cellular response will decrease. |
| Justify | Support with evidence | Because cAMP activates downstream kinases, lower cAMP reduces target protein activation. |
| Compare | Show similarity/difference | Negative feedback reduces change, while positive feedback amplifies change. |
AP Biology Unit 4 FRQ Practice Set
Answer each prompt in your own words before opening the rubric or sample. Use the review links to revisit weak topics.
Prompt
A hormone binds to a receptor on the surface of a target cell. Binding activates a G protein pathway that increases cAMP levels. cAMP activates protein kinases that phosphorylate target proteins, producing a cellular response.
- A. Identify the step of cell communication in which the hormone binds the receptor.
- B. Explain how cAMP functions in the pathway.
- C. Explain how phosphorylation can change target protein activity.
- D. Predict the effect of a mutation that prevents the receptor from changing shape after hormone binding.
Scoring rubric
- Reception is named for hormone binding to the receptor.
- cAMP is described as a second messenger that relays the signal inside the cell.
- Phosphorylation changes protein shape or activity, altering the cellular response.
- If the receptor cannot change shape, ligand binding or pathway activation may fail and the response decreases.
Sample answer
A. Reception. B. cAMP acts as a second messenger that activates protein kinases inside the cell, allowing the signal to be relayed and amplified. C. Phosphorylation adds a phosphate group that can change target protein shape or activity, turning the response on or off. D. If the receptor cannot change shape after binding, the G protein pathway may not activate, cAMP may not increase, and the final cellular response will decrease.
Self-check
Review: Ligands and Receptors · Reception, Transduction, Response · Second Messengers · Phosphorylation Cascade
Prompt
A biological system detects that blood glucose has increased after a meal. A hormone is released, causing body cells to take up more glucose and blood glucose returns toward its set point.
- A. Identify the type of feedback described.
- B. Explain how the response affects the original stimulus.
- C. Predict what would happen if target cells could not respond to the hormone.
- D. Explain why this feedback mechanism helps maintain homeostasis.
Scoring rubric
- Negative feedback is identified.
- The response reduces the original increase in blood glucose.
- If cells cannot respond, blood glucose stays elevated.
- Homeostasis is maintained because the change is reversed toward the set point.
Sample answer
A. Negative feedback. B. The hormone response causes cells to take up glucose, which reduces the original increase in blood glucose. C. If target cells cannot respond, glucose uptake does not increase and blood glucose remains high. D. This helps maintain homeostasis because the response opposes the initial change and returns blood glucose toward its set point.
Self-check
Review: Feedback Mechanisms · Negative Feedback · Cell Communication
Prompt
A cell has DNA damage before entering S phase. A checkpoint protein normally stops the cell cycle to allow repair. A mutation prevents this checkpoint protein from functioning.
- A. Identify the checkpoint most likely involved.
- B. Explain why entering S phase with damaged DNA is risky.
- C. Predict how daughter cells may be affected if the damaged cell divides.
- D. Explain how this mutation could increase cancer risk.
Scoring rubric
- G1 checkpoint (or DNA damage checkpoint before S phase) is named.
- Damaged DNA may be replicated and passed to daughter cells.
- Daughter cells may inherit mutations.
- Checkpoint failure allows uncontrolled division and increases cancer risk.
Sample answer
A. The G1 checkpoint (or DNA damage checkpoint before S phase). B. Entering S phase with damaged DNA allows the damage to be replicated, so mutations may be copied into new DNA strands. C. Daughter cells may inherit the same DNA damage or mutations. D. If the checkpoint fails, damaged cells can continue dividing, increasing the chance of uncontrolled growth and cancer.
Self-check
Review: Cell Cycle · Cell Cycle Checkpoints · Cancer and Cell Cycle Regulation
Prompt
Cyclin levels rise before a cell-cycle transition. Cyclin binds to a CDK, forming an active complex that phosphorylates target proteins. A mutation causes the cyclin level to remain high.
- A. Describe the role of cyclins.
- B. Explain why CDKs are called cyclin-dependent kinases.
- C. Predict how constantly high cyclin levels could affect cell-cycle progression.
- D. Explain how checkpoints may reduce the risk of unsafe progression.
Scoring rubric
- Cyclins rise and fall to regulate cell-cycle timing.
- CDKs require cyclin binding to become active kinases.
- Constantly high cyclin may keep CDKs active and push unsafe progression.
- Checkpoints pause the cycle until conditions are safe.
Sample answer
A. Cyclins are proteins whose levels rise and fall during the cell cycle to control when transitions occur. B. CDKs are inactive until cyclin binds; only then can they phosphorylate target proteins, so their activity depends on cyclin. C. Constantly high cyclin may keep CDK active too long, causing the cell to progress even when conditions are unsafe. D. Checkpoints detect problems such as DNA damage and pause the cycle until repair occurs or apoptosis is triggered.
Self-check
Review: Cyclins and CDKs · Cell Cycle Checkpoints · Cancer and Cell Cycle Regulation
Prompt
A cell has severe DNA damage that cannot be repaired. A signaling pathway activates programmed cell death, but a mutation blocks the final death response.
- A. Identify the programmed cell death process.
- B. Explain how this process normally protects the organism.
- C. Predict what could happen if damaged cells avoid this process.
- D. Compare this process with necrosis.
Scoring rubric
- Apoptosis is named.
- Apoptosis removes damaged cells in a controlled way.
- Damaged cells may survive and divide, increasing mutation transfer or cancer risk.
- Apoptosis is controlled and orderly; necrosis is uncontrolled cell death with inflammation.
Sample answer
A. Apoptosis. B. Apoptosis removes damaged or unnecessary cells in a controlled way, preventing harmful mutations from being passed to daughter cells. C. If apoptosis is blocked, damaged cells may survive and continue dividing, increasing cancer risk. D. Apoptosis is programmed and orderly with little inflammation, while necrosis is uncontrolled cell death that can damage surrounding tissue.
Self-check
Review: Apoptosis · Cancer and Cell Cycle Regulation · Cell Signaling Pathways
Unit 4 FRQ Scoring Guide
Score points by connecting vocabulary to mechanism.
- Uses correct Unit 4 vocabulary
- Explains cause-and-effect
- Traces signal pathway order correctly
- Identifies feedback direction correctly
- Connects checkpoints to DNA damage or chromosome control
- Explains cyclin-CDK phosphorylation
- Connects failed regulation to cancer risk
- Explains apoptosis as programmed cell death
- Uses evidence from the prompt
- Avoids overclaiming or vague phrases
Sample Unit 4 FRQ Answer Phrases
Use these phrases as models for mechanism-based sentences—not scripts to memorize.
Signal transduction
- The ligand binds a specific receptor during reception.
- Transduction passes the signal through intracellular relay molecules.
- Ca2+ concentration increases when calcium enters through channels or is released from internal stores, allowing Ca2+ to bind target proteins and change the response.
- The response changes enzyme activity, gene expression, or cell behavior.
- Ligand binding causes RTK dimerization, allowing tyrosine phosphorylation and relay protein docking.
- Ligand binding opens the ion channel receptor, allowing ions to move down their electrochemical gradient and change the cellular response.
- Because the ligand is lipid-soluble, it can cross the membrane and bind an intracellular receptor that changes gene expression.
Amplification
- One activated molecule can activate many downstream molecules.
- This increases the size of the cellular response.
- Adenylyl cyclase converts ATP to cAMP, and cAMP activates PKA to phosphorylate target proteins.
- A kinase adds a phosphate group to a target protein, while a phosphatase removes a phosphate group to change or reset protein activity.
Feedback
- Negative feedback reduces the original change and helps restore the set point.
- Positive feedback amplifies the original change until an endpoint occurs.
Cell cycle
- The checkpoint prevents the cell from continuing until the problem is repaired.
- If the checkpoint fails, damaged DNA may be passed to daughter cells.
- DNA replication occurs during S phase before M phase separates duplicated chromosomes.
- Mitosis separates duplicated chromosomes during M phase, while cytokinesis divides the cytoplasm.
Cancer/apoptosis
- Cancer risk increases when damaged cells continue dividing.
- Apoptosis removes damaged cells in a controlled way.
Fix Vague Unit 4 FRQ Answers
Vague answers become stronger when they explain the mechanism.
Before: “The signal does not work.”
After: If the receptor changes shape, the ligand may not bind, so the signal transduction pathway will not activate and the cellular response will decrease.
Before: “The checkpoint stops cancer.”
After: The checkpoint pauses the cell cycle when DNA damage is detected, giving the cell time to repair damage or trigger apoptosis before division.
Before: “cAMP makes the response happen.”
After: cAMP acts as a second messenger that activates downstream proteins, allowing the signal to be relayed and amplified inside the cell.
Before: “Apoptosis kills bad cells.”
After: Apoptosis removes damaged or unsafe cells in a controlled way, reducing the chance that mutations are passed to daughter cells.
Review Before Writing Unit 4 FRQs
| FRQ clue | Topic to review |
|---|---|
| ligand, receptor, target cell | Ligands and Receptors |
| reception, transduction, response | Reception, Transduction, Response |
| second messenger, cAMP, Ca2+ | Second Messengers |
| GPCR, adenylyl cyclase, cAMP, PKA, ATP to cAMP | cAMP Signaling Pathway |
| Ca2+, calcium channels, internal stores, cytosolic calcium, calcium target proteins | Calcium Signaling Pathway |
| kinase, phosphate, phosphatase | Phosphorylation Cascade |
| kinase, phosphatase, ATP, phosphorylation, dephosphorylation, pathway reset | Kinases and Phosphatases |
| dimerization, tyrosine, phosphorylation, docking proteins | Tyrosine Kinase Receptors |
| ligand-gated channel, ion movement, membrane potential, channel blocker | Ion Channel Receptors |
| steroid hormone, lipid-soluble, nonpolar ligand, nuclear receptor, gene expression | Intracellular Receptors |
| set point, homeostasis | Feedback Mechanisms |
| reduces change | Negative Feedback |
| amplifies change | Positive Feedback |
| G1, S, G2, M | Cell Cycle |
| G1, S, G2, M phase, cytokinesis, DNA replication, chromosome separation | Cell Cycle Phases |
| M phase, mitosis, spindle fibers, chromosome separation, cytokinesis | Mitosis in the Cell Cycle |
| DNA damage, spindle | Cell Cycle Checkpoints |
| cyclin, CDK | Cyclins and CDKs |
| oncogene, tumor suppressor | Cancer and Cell Cycle Regulation |
| programmed cell death | Apoptosis |
AP Biology Unit 4 FRQ Clues
“Specific receptor”
Meaning: Explain target cell specificity.
“Pathway blocked”
Meaning: Predict downstream response decreases or changes.
“Second messenger increases”
Meaning: Explain intracellular relay and amplification.
“Kinase inactive”
Meaning: Downstream proteins may not be phosphorylated.
“Set point restored”
Meaning: Negative feedback.
“Response amplifies stimulus”
Meaning: Positive feedback.
“DNA damage detected”
Meaning: Checkpoint, repair, or apoptosis.
“Damaged cell keeps dividing”
Meaning: Cancer regulation failure.
How to Use This FRQ Page
1
Choose one FRQ and answer without notes.
2
Compare your answer to the rubric.
3
Rewrite one weak sentence using the mistake fixer.
4
Review the linked topic page and try another FRQ.
Do not memorize full sample answers. Learn the sentence logic.
AP Biology Unit 4 FRQ FAQs
What topics appear on AP Biology Unit 4 FRQs?
AP Biology Unit 4 FRQs can include cell communication, signal transduction, feedback mechanisms, cell cycle regulation, checkpoints, cancer, and apoptosis. Many prompts ask students to predict what happens when a pathway is blocked or overactive. Strong answers explain mechanisms, not just vocabulary.
How do I answer a cell communication FRQ?
Start by identifying reception, transduction, or response. Then explain how the signal moves from receptor activation to an intracellular change. If the prompt changes a receptor or pathway protein, predict how the final response changes.
How do I answer a signal transduction FRQ?
Trace the pathway in order from receptor to relay molecule to response. Include second messengers, phosphorylation, or amplification if the prompt mentions them. Avoid jumping directly from ligand binding to response without explaining the pathway.
How do I answer a feedback mechanism FRQ?
Identify whether the loop is negative or positive feedback. Explain whether the response reduces the original change or amplifies it. Then connect the feedback loop to homeostasis or a specific endpoint.
How do I answer a cell cycle checkpoint FRQ?
Name the checkpoint involved and state what it checks. Then explain what happens if the checkpoint works or fails. For DNA damage questions, connect checkpoint failure to mutation transfer or cancer risk.
How do I answer a cyclins and CDKs FRQ?
Explain that cyclins activate CDKs and that active CDKs phosphorylate target proteins. Then connect phosphorylation to cell-cycle progression. If cyclin or CDK regulation fails, predict unsafe progression or reduced progression.
How do I answer a cancer regulation FRQ?
Identify the failed control, such as an oncogene, tumor suppressor, checkpoint, or apoptosis pathway. Explain the normal role of that control. Then predict how failure changes cell division or cancer risk.
How do I answer an apoptosis FRQ?
Define apoptosis as programmed cell death. Explain why removing damaged or unnecessary cells protects the organism. If apoptosis is blocked, predict that damaged cells may survive and continue dividing.
What is the biggest mistake on Unit 4 FRQs?
The biggest mistake is using vocabulary without explaining the mechanism. Saying “transduction happens” or “the checkpoint fails” is usually not enough. You need to explain how that change affects the cell response.
How can I improve my Unit 4 FRQ score?
Practice writing one clear cause-and-effect sentence for every answer part. Use the prompt evidence and connect it to a biological mechanism. Then compare your response to a rubric and rewrite weak sentences.