GCSE · Biology · Edexcel · Spec 1BI0

Mitosis and stages of the cell cycle

How does one cell become two with exactly the same chromosomes? It's all timing: copy first, then share out. Rebuild the cycle below — then try breaking it.

Rebuild it, then break it

The cell cycle

3 stages are missing. Use the rest of the loop to work out which goes where.

Stage 2: Prophase
Get ready: the nuclear membrane breaks down.
Stage 4: Anaphase
Chromatids pulled to either end.
Stage 5: Telophase
A nuclear membrane reforms at each end.

…and stage 6 leads back to stage 1.

Spot the stage

What is happening, and when?

Pick an event, then drop it into the stage where it happens. Each one belongs to exactly one stage.

Still to sort

Interphase (0)

Prophase (0)

Metaphase (0)

Anaphase (0)

Where the line is: Metaphase is only the lining up. The pulling apart comes next, in anaphase.

Telophase (0)

Where the line is: Telophase is prophase in reverse: the nuclear membrane reforms instead of breaking down, and the chromatids decondense instead of condensing.

Cytokinesis (0)

Where the line is: Anaphase pulls the chromatids apart; cytokinesis splits the whole cell.

11 of 11 still to sort.

Follow one chromosome

Reason it through

Why are the two daughter cells genetically identical to the parent cell?

Link 1 of 4

First link · your turn

Before any dividing starts, what has the cell done to its genetic material?

Locked — reveal the link above first

What do you really think?

How many chromosomes does each daughter cell get?

A parent cell divides by mitosis to make two daughter cells.

Compared with the parent cell, how many chromosomes does each daughter cell have? Pick the one closest to what you think right now.

Half as many — the parent's chromosomes get split between two cells.The same full set as the parent.Twice as many — the DNA was copied, so there's double.

How sure are you?

I'm sureI think soI'm guessing

Half as many — the parent's chromosomes get split between two cells.

This is a common misconception

It's a very tempting idea — and it would be true if the cell just shared out its original chromosomes. But it doesn't: it copies them first, in interphase. So mitosis does not produce cells with half the number of chromosomes.

The same full set as the parent.

This matches the evidence

Yes. The chromosomes were copied in interphase, so when they are shared out each daughter cell gets a full set — the same chromosomes as the parent cell.

Twice as many — the DNA was copied, so there's double.

This is a common misconception

The copying is real, but no cell keeps both copies. In anaphase the two identical chromatids from each chromosome are pulled to opposite ends, and cytokinesis puts one set in each daughter cell. There are two copies of each chromosome in the parent just before division — not in each daughter cell.

Copied once, shared once: each daughter cell ends up with the same full set of chromosomes as the parent — never half, never double.

Your turn to write

What is mitosis for?

Describe the uses of cell division by mitosis. For each use, say which kind of organism it applies to, and name one organism that uses mitosis to reproduce. [4 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Growth — in multicellular organisms. (1 mark)
Repair of damaged tissue — in multicellular organisms. (1 mark)
Asexual reproduction — in some unicellular organisms. (1 mark)
Yeast named as an organism that reproduces this way. (1 mark)

Model answer

Multicellular organisms use mitosis for growth and to repair damaged tissue. Some unicellular organisms use mitosis for asexual reproduction — yeast is an example.

Two jobs in multicellular organisms (growth and repair), one in some unicellular organisms (asexual reproduction). Every time, the new cells are genetically identical to the parent.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Interphase copies the chromosomes; mitosis shares the copies out exactly. That is why the two daughter cells are genetically identical to the parent, each with the full set.

What you need to know

The cell cycle has two main phases: interphase and mitosis. Mitosis is a type of cell division that produces genetically identical cells.
In interphase the cell grows, its DNA is replicated (two copies of each chromosome) and its sub-cellular structures, such as ribosomes and mitochondria, are copied. A cell spends most of its life in interphase.
After interphase come prophase, metaphase, anaphase and telophase, followed by cytokinesis.
The chromosomes must be copied in interphase so that each daughter cell gets a full set. Mitosis does not halve the chromosome number.
Mitosis is used for growth and repair of damaged tissue in multicellular organisms, and for asexual reproduction in some unicellular organisms, such as yeast.

The big picture

The cell cycle is the series of phases a cell goes through in order to divide, and it has two main phases: interphase and mitosis. In interphase the cell grows, replicates its DNA so there are two copies of each chromosome, and copies sub-cellular structures such as ribosomes and mitochondria. Mitosis then shares everything out in order — prophase, metaphase, anaphase, telophase — and cytokinesis splits the cell. The result is two daughter cells that are genetically identical to the parent, each with the full set of chromosomes.

Key points

1Interphase: the cell grows, the DNA is replicated and sub-cellular structures are copied.

2Prophase: the nuclear membrane breaks down and the chromosomes condense.

3Metaphase: the chromosomes line up along the equator of the cell.

4Anaphase: each chromosome splits into two identical chromatids, pulled to either end.

5Telophase: a nuclear membrane reforms around the chromatids at each end, and they decondense into strands of DNA.

6Cytokinesis: the cytoplasm and cell membrane divide, giving two genetically identical daughter cells with the same chromosomes as the parent.

.we-_R_18slubsnpfiv5ubrb_ [data-we-step]{display:flex !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-solution]{display:block !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-reveal]{display:none !important}

Worked example

Problem

A student looks at a cell under a light microscope. The chromosomes are clearly visible and lined up along the middle of the cell. Name the stage the cell is in, and describe what happens in the stage that comes next.

⚠ Watch out

Thinking the chromatids are made in anaphase. Anaphase only separates them — the copying already happened back in interphase, when the DNA was replicated.

🧠

Memory hook

Copy, then P-M-A-T, then Cut. Interphase copies. Then Prepare (prophase), Middle (metaphase), Apart (anaphase), Two new membranes (telophase) — and Cytokinesis cuts the cell in two.

✓

Check yourself

Without looking back, say the six stages in order from interphase, with one thing that happens in each. Then explain why each daughter cell gets a full set of chromosomes.

Flashcards

(13)

What is the cell cycle?

The series of phases a cell goes through in order to divide. Its two main phases are interphase and mitosis.

What kind of cells does mitosis produce?

Genetically identical cells. Mitosis is the part of the cell cycle that is a type of cell division.

Three things that happen in interphase

The cell grows; the DNA is replicated (two copies of each chromosome); sub-cellular structures such as ribosomes and mitochondria are copied.

In which phase does a cell spend most of its life?

Interphase.

Why must the chromosomes be copied during interphase?

So that the daughter cells each get a full set of chromosomes. Mitosis does not produce cells with half the number.

The stages of mitosis, in order, after interphase

Prophase, metaphase, anaphase, telophase — then cytokinesis.

Prophase

The nuclear membrane breaks down, and the chromosomes condense, becoming more visible under a light microscope.

Metaphase

The chromosomes line up along the equator (the middle) of the cell.

Anaphase

The chromosomes split into two identical chromatids, which are pulled to either end of the cell.

Telophase

The chromatids decondense to become strands of DNA, and a nuclear membrane reforms around the chromatids at each end of the cell.

Cytokinesis

The cytoplasm and cell membrane divide to form two genetically identical daughter cells, each with the same chromosomes as the parent cell.

Uses of mitosis in multicellular organisms

Growth, and repair of damaged tissue.

Use of mitosis in some unicellular organisms, such as yeast

Asexual reproduction.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

Learning with Lightbulb is opening soon

You can use this lesson now. Join the waitlist and we'll let you know when the full Lightbulb experience is ready.

Keep me posted

The cell cycle

What is happening, and when?

How many chromosomes does each daughter cell get?

What is mitosis for?

More Edexcel GCSE Biology topics