AP Exam Prep · AP Biology
AP Biology Unit 4 Practice Test: Cell Communication and Cell Cycle
Unit 4 covers how cells send and respond to signals, how feedback keeps conditions stable, and how the cell cycle is controlled. Questions often ask what happens when one step of a pathway or a checkpoint stops working.
- Exam weighting:
- 10–15%
- Questions:
- 12 multiple choice
- Time:
- about 16 minutes
- Cost:
- Free, no sign-up
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What AP Bio Unit 4 covers
Unit 4, Cell Communication and Cell Cycle, makes up 10–15% of the multiple-choice section and usually takes ~12–14 class periods. These are the topics in the current course framework, and every question in the test above is tagged with one of them.
- 4.1Cell Communication
- 4.2Introduction to Signal Transduction
- 4.3Signal Transduction Pathways
- 4.4Feedback
- 4.5Cell Cycle
- 4.6Regulation of Cell Cycle
Unit 4 key ideas
Signals act at different distances
Cells signal by direct contact, to nearby cells (paracrine) or through the blood to distant cells (endocrine). The response depends on the receptor the target cell has.
Pathways relay and amplify
A signal binds a receptor, then second messengers and phosphorylation cascades relay it. Each step can activate many molecules, so a small signal can cause a large response.
Feedback keeps or pushes change
Negative feedback returns a variable toward a set point. Positive feedback amplifies a change until an endpoint, such as childbirth or blood clotting.
Checkpoints control division
Cyclins and cyclin-dependent kinases move a cell through the cycle. Checkpoints stop division when DNA is damaged; losing them can lead to uncontrolled division.
Common Unit 4 mistakes
- Calling the hormone itself the second messenger.
- Assuming every feedback loop is negative.
- Forgetting that DNA is copied in S phase, so a cell in G2 has twice the DNA of a cell in G1.
How to study this unit
- For any pathway, name the signal, receptor, relay steps and response, then predict what one mutation would do.
- Track chromosome number and DNA amount separately through the cell cycle.
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About these questions
StudyCoach wrote these questions for this test. Each one is mapped to a topic in the College Board's current AP Biology course framework. Every answer key was also checked by a separate AI review, and any disagreement was rechecked by hand. They have not yet been reviewed by an AP Biology teacher. If you think an answer is wrong, email support@studycoach.io.
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