Outline the mitotic cell cycle
Interphase includes growth in G1 and G2 and DNA replication in S phase; mitosis divides the nucleus before cytokinesis divides the cytoplasm.
Section 5.1 · Replication and division of nuclei and cells
AS Level · Cambridge International Biology 9700, 2028–2030. These lessons explain cell-cycle concepts and image interpretation. Written practice is self-checked; it does not demonstrate practical microscopy competence or replace teacher-reviewed assessment.
Before you begin
- Recognise DNA as genetic material and use the terms cell, nucleus and chromosome accurately.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
During which phase is DNA replicated?
What you will learn
- Put G1, S, G2, mitosis and cytokinesis in the correct sequence
- Describe growth and DNA replication during interphase
- Distinguish nuclear division from cytoplasmic division
Interphase prepares the cell for division
During G1 the cell grows and carries out its functions. During S phase DNA is replicated. During G2 the cell continues growing and prepares for nuclear division. Interphase is an active part of the cell cycle, not a resting stage.
DNA replication occurs before mitosis. It produces a copy of each chromosome so that the two daughter nuclei can receive equivalent genetic information. The cell also needs enough cytoplasm and cellular components to support two daughter cells.
Nuclear division comes before cytokinesis
Mitosis is nuclear division. Its stages organise and separate the replicated chromosomes into two nuclei. Cytokinesis is division of the cytoplasm and cell surface membrane to form separate daughter cells.
The order is G1, S, G2, mitosis, then cytokinesis. Some diagrams call G1, S and G2 interphase. The stages differ in length; a circular diagram does not imply that each takes equal time.
Pause and explain
What does cytokinesis divide?
Worked example
A student writes G1 → S → mitosis → G2 → cytokinesis. Correct the sequence and state what happens in S.
Show the worked solution
- Place G2 between S and mitosis.
- S is when DNA is replicated.
Answer The correct order is G1 → S → G2 → mitosis → cytokinesis. During S phase, DNA is replicated before the nucleus divides.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Put these events in order: cytokinesis, S phase, G2, mitosis, G1.
Give me a hint
Start with the first growth phase and end with cell division.
Compare my reasoning
- G1 is followed by DNA replication in S.
- G2 follows S; mitosis precedes cytokinesis.
G1 → S phase → G2 → mitosis → cytokinesis.
Look for these in your work
- All five events ordered
- Mitosis before cytokinesis
Distinguish interphase, mitosis and cytokinesis.
Give me a hint
State what the cell does and what is divided.
Compare my reasoning
- Interphase includes G1 growth, S-phase DNA replication and G2 growth/preparation.
- Mitosis divides the nucleus; cytokinesis divides the cytoplasm.
Interphase includes growth in G1 and G2 and DNA replication in S. Mitosis divides the nucleus, and cytokinesis divides the cytoplasm and cell surface membrane to form daughter cells.
Look for these in your work
- Interphase phases described
- Nuclear and cytoplasmic division distinguished
A cell has completed S phase but has not yet begun mitosis. What must happen next, and why is the cell not “resting” during interphase?
Give me a hint
Name the remaining interphase phase and its role.
Compare my reasoning
- The cell enters G2 and continues growing and preparing for division.
- Interphase includes active growth and DNA replication.
The cell enters G2, where it continues growing and prepares for mitosis. Interphase is active: it includes growth in G1 and G2 and DNA replication in S phase.
Look for these in your work
- G2 identified
- Interphase activity explained
Common mistakes
- Describing interphase as inactivity
- Placing DNA replication after mitosis
- Using mitosis and cytokinesis as synonyms
What can you explain now?
During which phase is DNA replicated?
Compare with the explanation
S phase
S is the synthesis phase of interphase.
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Make it stick
What is the order of G1, S, G2, mitosis and cytokinesis, and what is divided at each stage?
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