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AP Biology Unit 4  ·  Sprint Review  ·  Free

AP Biology Unit 4 — Cell Communication & Cell Cycle

One-page sprint review

Ten pages on cell communication, signal transduction, feedback mechanisms, mitosis, and cancer regulation — the most pathway-tracing unit on the exam.

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Exam Weight
10–15%
MCQs
6–9
FRQ Appearance
Very Frequent
Sprint Time
~2 hours

Quick Glance — all topics in this unit

Priority, exam format, and the trap that most often costs the point. Transcribed from page 1 so this content is searchable.

TopicPriorityFormatKey trap / must-know
4.1 Cell Communication★★★MCQ, FRQProtein hormones NEVER enter the cell; steroid hormones cross freely → intracellular receptor.
4.2 Signal Transduction Intro★★★MCQ, FRQReception → Transduction → Response; amplification via phosphorylation cascade.
4.3 Signal Pathways & cAMP★★★MCQ, FRQcAMP made by adenylyl cyclase (NOT by receptor); GPCR → G-protein → adenylyl cyclase → cAMP.
4.4 Feedback Mechanisms★★★MCQ, FRQPositive feedback does NOT maintain homeostasis — it amplifies toward an endpoint.
4.5 Cell Cycle & Mitosis★★★MCQ, DataDNA replication = S phase, NOT mitosis; sister chromatids separate in anaphase.
4.6 Cycle Regulation & Cancer★★★MCQ, FRQOncogenes = dominant; tumor suppressors = recessive, need both copies lost.

Topic-by-topic visual review

Nine pages, one topic each. Open the PDF for print quality, or scroll to study on screen.

Cover: Unit 4 overview — interlocking systems of communication and cycle control. Mutation-tracing FRQ favorite.
Cover  ·  Unit 4 overview — interlocking systems of communication and cycle control. Mutation-tracing FRQ favorite.
4.1 Cell Communication: Three modes of cell signaling: direct contact, paracrine, endocrine — with hormone-type rules.
4.1 Cell Communication  ·  Three modes of cell signaling: direct contact, paracrine, endocrine — with hormone-type rules.
4.2 Signal Transduction: Reception → transduction → response stages and the phosphorylation cascade for amplification.
4.2 Signal Transduction  ·  Reception → transduction → response stages and the phosphorylation cascade for amplification.
4.3 Signal Pathways & cAMP: GPCR pathway, second messengers, and the canonical adenylyl-cyclase → cAMP → PKA chain.
4.3 Signal Pathways & cAMP  ·  GPCR pathway, second messengers, and the canonical adenylyl-cyclase → cAMP → PKA chain.
4.4 Feedback Mechanisms: Negative feedback for homeostasis (thermoregulation), positive feedback for endpoint amplification (childbirth).
4.4 Feedback Mechanisms  ·  Negative feedback for homeostasis (thermoregulation), positive feedback for endpoint amplification (childbirth).
4.5 Cell Cycle Phases: G1, S, G2, M phase ordering with DNA-replication and chromosome-doubling timing.
4.5 Cell Cycle Phases  ·  G1, S, G2, M phase ordering with DNA-replication and chromosome-doubling timing.
4.5 Mitosis Stages: PMAT — prophase, metaphase, anaphase, telophase — and the sister-chromatid separation rule.
4.5 Mitosis Stages  ·  PMAT — prophase, metaphase, anaphase, telophase — and the sister-chromatid separation rule.
4.6 Cycle Regulation Checkpoints: G1 / G2 / M checkpoints, cyclin-CDK complexes, p53 surveillance.
4.6 Cycle Regulation Checkpoints  ·  G1 / G2 / M checkpoints, cyclin-CDK complexes, p53 surveillance.
4.6 Oncogenes & Tumor Suppressors: Why oncogenes are dominant gain-of-function and tumor suppressors are recessive loss-of-function.
4.6 Oncogenes & Tumor Suppressors  ·  Why oncogenes are dominant gain-of-function and tumor suppressors are recessive loss-of-function.
Final Review — Traps + Checklist: Hormone-receptor mapping, cAMP sequence drill, and the pre-exam checklist for Unit 4.
Final Review — Traps + Checklist  ·  Hormone-receptor mapping, cAMP sequence drill, and the pre-exam checklist for Unit 4.

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