GCSE · Biology · Edexcel · Spec 1BI0

Importance of mitosis in growth, repair and asexual reproduction

A seedling sprouting leaves, a cut closing over, a yeast cell becoming two: three different events, one trick — a cell dividing into two genetically identical cells.

Biology · Cell division

What is the division doing?

Pick a situation, then pick the job you think cell division is doing there.

What is cell division doing here: growth, repair or asexual reproduction?

Still to sort

Growth (0)

The organism is getting bigger.

Where the line is: Growth makes the organism bigger. Repair makes new cells to mend tissue that has been damaged — nothing is getting bigger.

Repair (0)

Damaged tissue is being mended.

Where the line is: Repair starts with damage. If nothing was broken and the organism is simply getting bigger, it's growth.

Asexual reproduction (0)

New organisms are being made.

Where the line is: Here the division isn't adding to one organism — it is making new ones.

5 of 5 still to sort.

Every situation below depends on cells dividing. Sort them by the job the division is doing — then flip to the second rule and sort the same five again.

Watch out: Don't file yeast under growth. When a yeast cell divides, one yeast doesn't get bigger — you end up with more yeast.

Growth

So how does a seedling actually get bigger?

A seedling pushes out roots, a stem and leaves and ends up far bigger than it started. A baby does the same thing over years, growing into an adult.

Be honest — which of these is closest to what you'd have said before today?

Its cells swell up. Each cell gets bigger, so the whole organism gets bigger.It makes more cells. Its cells divide, so it ends up with more of them.It takes in food and adds it onto its body, a bit like adding bricks.

How sure are you?

I'm sureI think soI'm guessing

Its cells swell up. Each cell gets bigger, so the whole organism gets bigger.

This is a common misconception

It's a really natural picture — but it misses where growth actually comes from. A multicellular organism grows by increasing the NUMBER of cells it has. The grown plant and the adult are bigger mainly because they are made of far more cells than they started with, and every one of those extra cells came from cell division.

It makes more cells. Its cells divide, so it ends up with more of them.

This matches the evidence

That's it. Multicellular organisms grow by increasing the number of cells they have, and the number goes up because cells divide: one cell becomes two, and each of those can divide again. So growth is really a story about counting cells, not just measuring them.

It takes in food and adds it onto its body, a bit like adding bricks.

This is a common misconception

Growing isn't material being stuck onto the outside. The organism gets bigger because it has more cells — and each extra cell was made by an existing cell dividing into two. If you picture bricks at all, picture the bricks making more bricks.

Growth = more cells. Multicellular organisms grow by increasing the number of their cells, and cell division is what makes the new ones.

Why the copies match

Reason it through

When one cell divides into two, why are the two new cells genetically identical?

Link 1 of 3

First link · your turn

The cell is about to split into two. What has to happen to its DNA first?

Locked — reveal the link above first

Predict, then check

Use what you've just worked out about copying the DNA.

A parent yeast cell divides to give two daughter yeast cells. Compared with the parent, what chromosomes will each daughter cell have?

What about when you've stopped growing?

Growth and repair aren't quite the whole story in a multicellular organism.

An adult stopped growing years ago and has no injuries at all. Is cell division still going on in their body?

Your turn to write it

Explain it like an exam answer

Priya is 35 and stopped growing years ago. Last week she grazed her knee. Explain why cells are still dividing in Priya's body — both at the graze and in parts of her body that are not damaged. [3 marks]

Your answer

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

The mark scheme

At the graze: damaged tissue (skin) must be repaired, and the new cells needed for this are made by cell division. (1 mark)
Elsewhere: many types of cell are renewed (almost) continuously by cell division. (1 mark)
This renewal keeps her tissues / organs / organ systems working correctly. (1 mark)

Model answer

The graze is damaged skin tissue. Repairing it needs new cells, and these are made by cell division. In the parts of her body that aren't damaged, many types of cell are being renewed almost continuously by cell division, which keeps her tissues, organs and organ systems working correctly.

Growing stops; cell division doesn't. In a grown body it repairs damage where there is some, and keeps renewing cells everywhere else.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

The same division grows an organism, mends it, and makes new yeast.

What you need to know

Mitosis is a type of cell division that produces genetically identical cells. It is part of the cell cycle.
One cell divides to produce two cells. The DNA is copied before the cell divides, so both new cells contain the same DNA as the original cell.
Multicellular organisms grow by increasing the number of cells they have, and the extra cells come from cell division — for example a seedling growing roots, stem and leaves, or a baby growing into an adult.
Repairing damaged tissue needs new cells, made by cell division — for example healing a broken bone or broken skin.
Many types of cell undergo almost continuous renewal by cell division. This highly regulated process keeps tissues, organs and organ systems working correctly.
Unicellular organisms such as yeast typically reproduce asexually by cell division: a parent yeast cell divides to give daughter cells that are genetically identical, with the same chromosomes as the parent.

The big picture

Mitosis is a type of cell division that turns one cell into two genetically identical cells, because the DNA is copied before the cell divides. Multicellular organisms use it to grow (by increasing their number of cells), to repair damaged tissue, and to renew many types of cell almost continuously. Unicellular organisms such as yeast use it to reproduce asexually, so the daughter cells are identical to the parent.

Key points

1One cell in, two genetically identical cells out — that's mitosis.

2Copy first, then divide: that's why the new cells match the original.

3Multicellular organisms: cell division is usually for growth and repair, plus the constant renewal of many cell types.

4Unicellular organisms such as yeast: cell division is asexual reproduction.

5Growth means more cells, made by cell division.

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Worked example

Problem

A student's broken arm bone heals. Explain the part that cell division plays in this. (2 marks)

⚠ Watch out

Writing that when a cell divides it shares its DNA out, so each new cell gets half. The DNA is copied before the cell divides, so each new cell gets the same DNA as the original.

🧠

Memory hook

Grow it, mend it, make more of it — one cell in, two identical copies out.

✓

Check yourself

Cover the page. Name the three jobs cell division does, say which kind of organism uses each, and explain in one sentence why the new cells are genetically identical.

Flashcards

(13)

What is mitosis?

A type of cell division that produces genetically identical cells. It is one part of the cell cycle.

What must happen to a cell's DNA before the cell divides?

It must be copied.

When one cell divides by mitosis, how many new cells does it produce?

Two.

What does it mean to say the two new cells are 'genetically identical'?

They contain the same DNA as the original cell.

How do multicellular organisms grow?

By increasing the number of cells they have — the extra cells come from cell division.

Give two examples of growth that depend on cell division.

A seedling growing roots, a stem and leaves; a baby growing into an adult.

Why does repairing damaged tissue need cell division?

Repair needs new cells, and new cells are made by cell division.

Give two examples of repair by cell division.

A broken bone healing; broken skin healing.

What happens to many types of cell in a multicellular organism, even when it isn't growing or injured?

They undergo almost continuous renewal by cell division.

Why does the almost continuous renewal of cells matter?

It is highly regulated and keeps tissues, organs and organ systems working correctly.

How do unicellular organisms such as yeast typically reproduce?

Asexually, using cell division.

How do the chromosomes in daughter yeast cells compare with the parent cell's?

They are the same — the daughter cells are identical to the parent.

Multicellular vs unicellular: what is cell division usually used for in each?

Multicellular: growth and repair. Unicellular (e.g. 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.

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What is the division doing?

So how does a seedling actually get bigger?

Explain it like an exam answer

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