Unit 4: Cell Communication and Cell Cycle bridges how cells send and receive information with how they divide and grow. It makes up about 10–15% of the AP Biology Exam and connects directly to genetics, cancer biology, and homeostasis.
In this RevisionDojo Unit 4 Review, we’ll cover:
- Cell signaling types and pathways
- Signal transduction and cellular responses
- Feedback mechanisms in biology
- Cell cycle stages and regulation
- Common AP exam question formats
- Study strategies for maximum points
Unit 4 Overview
The College Board breaks Unit 4 into two major themes:
- Cell Communication – How cells detect and respond to signals
- Cell Cycle – How cells grow, replicate DNA, and divide
1. Cell Communication
Types of Cell Signaling
- Autocrine: Cell signals itself (e.g., immune cell self-activation)
- Paracrine: Local signaling to nearby cells (e.g., neurotransmitters)
- Endocrine: Long-distance signaling via hormones in bloodstream
- Juxtacrine: Direct contact between cells via membrane-bound molecules
2. Signal Transduction Pathways
Three Stages:
