G1
Cell grows and carries out normal functions
Where Cell Cycle Phases Fit in Unit 4
The core Cell Cycle page explains the broad idea of cell growth, DNA replication, division, and regulation. This Phase 2 page zooms in on the order and role of each phase. Use it when a prompt asks what happens in G1, S, G2, M phase, or cytokinesis.
Current
Cell Cycle Phases
Phase-by-phase sequence.
Regulation links: Cyclins and CDKs push phase transitions, and cancer and cell cycle regulation shows what happens when control fails.
When to Use This Page vs the Cell Cycle Page
Use the Cell Cycle guide to learn the broad AP Biology overview of cell growth, DNA replication, division, and regulation. Use this Cell Cycle Phases guide when you need to distinguish G1, S, G2, M phase, and cytokinesis in order and predict what happens when a phase is blocked or skipped.
| Page | Best for | Link |
|---|---|---|
| Cell Cycle | Broad overview: cell cycle purpose, regulation, and checkpoints | Open guide |
| Cell Cycle Phases | Phase details: G1, S, G2, M, and cytokinesis sequence | You are here |
| Cell Cycle Checkpoints | Regulation points that stop unsafe progression | Open guide |
| Cyclins and CDKs | Protein regulators that push phase transitions | Open guide |
What are the phases of the cell cycle in AP Biology?
The cell cycle phases are G1, S, G2, M phase, and cytokinesis. G1 is cell growth, S phase is DNA replication, G2 is preparation for division, M phase separates chromosomes, and cytokinesis divides the cytoplasm. AP Biology often tests phase order and asks students to predict what happens if DNA replication, chromosome separation, or cytokinesis fails.
Say it fast
G1 grows, S copies DNA, G2 prepares, M separates, cytokinesis splits.
Cell Cycle Phase Sequence Simulator
Click phases in order: G1 → S → G2 → M → Cytokinesis. Then choose a blocked phase to predict consequences.
DNA replication must happen before chromosome separation.
Click the first phase: G1.
Progress: Growth
The Full Cell Cycle Phase Sequence
The cell cycle moves through a sequence of events. Interphase includes G1, S, and G2. M phase and cytokinesis then complete cell division.
S
DNA is replicated
G2
Cell prepares for division
M phase
Chromosomes are separated
Cytokinesis
Cytoplasm divides into daughter cells
Interphase: G1, S, and G2
Interphase is not a resting stage. During interphase, the cell grows, copies DNA, and prepares for division. G1, S, and G2 together make up interphase.
G1 Phase: Growth and Normal Function
In G1, the cell grows and performs normal cellular activities. The cell may also receive signals that influence whether it should continue toward DNA replication. If conditions are not favorable, the cell may pause before entering S phase.
The G1 checkpoint helps control entry into S phase when damage or poor conditions are detected.
S Phase: DNA Replication
S phase is when DNA is copied. This produces duplicated chromosomes that can later be separated during M phase. A common AP Biology mistake is saying DNA replication happens during mitosis; it happens before mitosis, during S phase.
G2 Phase: Preparation for Division
In G2, the cell prepares for chromosome separation and division. The cell checks whether DNA replication was completed correctly and whether the cell is ready for mitosis. If DNA is damaged or replication is incomplete, progression should pause.
M Phase: Chromosome Separation
M phase includes mitosis, when duplicated chromosomes are separated into two nuclei. M phase is about nuclear and chromosome division, not DNA replication. AP Biology questions often ask students to connect M phase to chromosome movement and spindle attachment.
Mitosis is the chromosome-separation part of M phase, and the Mitosis in the Cell Cycle guide explains how spindle attachment and checkpoint control affect daughter cells.
Cytokinesis: Cytoplasm Division
Cytokinesis divides the cytoplasm and physically separates the cell into two daughter cells. It usually follows mitosis. If cytokinesis fails, a cell may have divided nuclei but not complete separation into two cells.
How Checkpoints Regulate Cell Cycle Phases
Checkpoints help ensure that cells do not move into the next phase when conditions are unsafe. The G1 checkpoint helps control entry into S phase, the G2 checkpoint checks DNA replication and damage before mitosis, and the M checkpoint checks chromosome attachment. These checkpoints connect phase order to cancer prevention.
Study cell cycle checkpoints for stop/go logic and cyclins and CDKs for the proteins that drive phase transitions.
How AP Biology Tests Cell Cycle Phases
“DNA is copied”
S phase.
“Cell grows before DNA replication”
G1 phase.
“Cell prepares for mitosis”
G2 phase.
“Chromosomes separate”
M phase.
“Cytoplasm divides”
Cytokinesis.
“DNA replication incomplete”
G2 checkpoint may stop progression.
How to Answer Cell Cycle Phase FRQs
Identify the phase named or described
Name G1, S, G2, M phase, or cytokinesis.
State what normally happens in that phase
Connect growth, DNA copying, preparation, or division.
Explain how the phase supports later events
Show why order matters before mitosis or cytokinesis.
Predict what happens if that phase is blocked or fails
Link to checkpoints or daughter-cell outcomes.
AP FRQ writing frame
The cell is in ___ phase because ___. Normally, this phase ___. If this step fails, the cell may ___ because ___.
Common AP Bio Cell Cycle Phase Mistakes
Saying DNA replication happens during mitosis
Fix: DNA replication happens in S phase before mitosis.
Confusing M phase and cytokinesis
Fix: M phase separates chromosomes; cytokinesis divides cytoplasm.
Saying interphase is inactive
Fix: Interphase includes growth, DNA replication, and preparation.
Forgetting G2 preparation
Fix: G2 helps prepare the cell for mitosis and checks replication problems.
Ignoring checkpoints
Fix: Checkpoints regulate whether the cell can move to the next phase.
Duplicating the broad Cell Cycle page
Fix: The Cell Cycle page is the broad guide; this page focuses on phase sequence and phase-specific predictions.
Cell Cycle Phases MCQ Practice
Answer all eight questions. Choices shuffle on reload—focus on phase order, not letter memorization.
Question 1 of 8
Start
Correct: 0
Answered: 0
Accuracy: 0%
More drills: Unit 4 practice questions or the Unit 4 FRQ guide.
Cell Cycle Phases FRQ Practice
Open each card, draft your response, then reveal the rubric and sample.
0 of 2 FRQs opened
Prompt
A cell completes G1 and enters S phase. A mutation prevents DNA replication from being completed.
- A. Identify the phase in which DNA replication normally occurs.
- B. Explain why incomplete DNA replication is a problem before M phase.
- C. Predict how a functioning checkpoint should respond.
Scoring rubric
- 1 pt — Identifies S phase as DNA replication phase.
- 1 pt — Explains duplicated chromosomes are needed before separation.
- 1 pt — Connects incomplete replication to unsafe mitosis.
- 1 pt — Predicts G2 checkpoint pause or block before M phase.
- 1 pt — Uses accurate phase order (G1, S, G2, M).
- 1 pt — Clear cause-effect reasoning.
Sample response
DNA replication normally occurs during S phase. If replication is incomplete, the cell may lack fully duplicated chromosomes needed for mitosis, so separating chromosomes in M phase could produce daughter cells with incorrect DNA content. A functioning G2 checkpoint should detect incomplete or damaged DNA and pause the cycle before the cell enters M phase.
Self-check
Status: Draft your answer first—then open the rubric or sample.
Prompt
A cell separates duplicated chromosomes but fails to complete cytokinesis.
- A. Identify the phase in which chromosomes are separated.
- B. Describe the role of cytokinesis.
- C. Predict the consequence of failed cytokinesis.
Scoring rubric
- 1 pt — Identifies M phase (mitosis) for chromosome separation.
- 1 pt — Describes cytokinesis as cytoplasm division.
- 1 pt — Distinguishes nuclear/chromosome division from cytoplasm division.
- 1 pt — Predicts one cell with two nuclei or incomplete separation.
- 1 pt — Uses accurate phase vocabulary.
- 1 pt — Clear prediction linked to mechanism.
Sample response
Chromosomes are separated during M phase, which includes mitosis. Cytokinesis divides the cytoplasm and separates the cell into two daughter cells after nuclear division. If cytokinesis fails, the cell may contain two nuclei in one cytoplasm, so the organism does not get two fully separate daughter cells.
Self-check
Status: Draft your answer first—then open the rubric or sample.
Cell Cycle Phases FAQs
What are the phases of the cell cycle in AP Biology?
The main phases are G1, S, G2, M phase, and cytokinesis. G1, S, and G2 together make up interphase. M phase and cytokinesis complete cell division.
What happens during G1 phase?
During G1, the cell grows and carries out normal functions. The cell may also receive signals that affect whether it continues toward DNA replication. If conditions are not right, the cell can pause before S phase.
What happens during S phase?
S phase is when DNA replication occurs. The cell copies its DNA so duplicated chromosomes can later be separated. This happens before mitosis, not during mitosis.
What happens during G2 phase?
During G2, the cell prepares for mitosis. It checks that DNA replication is complete and that the cell is ready for chromosome separation. Problems in G2 can stop progression into M phase.
What happens during M phase?
M phase includes mitosis, when duplicated chromosomes are separated into two nuclei. It is not the phase where DNA is copied. M phase prepares the genetic material for two daughter cells.
What is cytokinesis?
Cytokinesis is the division of the cytoplasm. It usually follows mitosis and separates one cell into two daughter cells. If cytokinesis fails, the cell may not fully split.
Is interphase a resting phase?
No. Interphase includes G1, S, and G2, which are active stages of growth, DNA replication, and preparation. Calling interphase inactive is a common AP Biology mistake.
When does DNA replication happen in the cell cycle?
DNA replication happens during S phase. This must happen before chromosomes can be separated during M phase. If replication is incomplete, checkpoints should stop the cell from continuing.
How are checkpoints related to cell cycle phases?
Checkpoints monitor whether the cell is ready to move to the next phase. They can stop progression if DNA is damaged, replication is incomplete, or chromosomes are not attached correctly. This helps prevent unsafe division.
How should I answer cell cycle phase FRQs?
Identify the phase first, then state what normally happens during that phase. Next, explain why that phase matters for later cell-cycle events. Finish by predicting what changes if the phase is blocked or fails.