Cut your knee and within days the skin knits back together; a baby grows from a single fertilised egg into a child made of trillions of cells. Both feats happen because cells can copy themselves. The main way body cells do this is a type of division called mitosis.
Why this matters: mitosis is behind all growth, all healing, and the constant replacement of worn-out cells — you make millions of new ones every second. Understanding it also sets up stem cells, one of the most exciting areas of modern medicine.
Mitosis: one cell → two genetically identical cells
What mitosis does
DNA is copied first, so both daughter cells get a complete matching set.
Before a cell divides, it first copies its chromosomes — the threads of DNA that carry its genetic instructions. This copying step is vital: it means each new cell will receive a full, identical set. The cell then splits into two. Picture photocopying an instruction manual before handing one copy to each of two workers — both end up with the complete, matching booklet.
Mitosis produces two genetically identical daughter cells, each with a full copy of the parent’s DNA. Its jobs are growth, repair and replacing worn-out or damaged cells — for example, repairing a wound.
Stem cells: the undecided cells
An undifferentiated stem cell can become many specialised types.
Most cells in your body are specialised — a nerve cell, a muscle cell, a red blood cell each has a fixed job. But some cells have not committed yet. A stem cell is an undifferentiated cell: it has not specialised, so it can still develop into many different types. Think of a stem cell as a school-leaver who has not chosen a career — still able to become almost anything.
When a cell finally takes on a particular role and becomes specialised, that process is called differentiation.
Feature
Stem cell
Specialised cell
Differentiated?
No (undifferentiated)
Yes
Can become other cell types?
Yes, many
No — job is fixed
Example
Bone marrow stem cell
Muscle cell, nerve cell
Reasoning it out.Both clues — identical cells and growth/repair — point to mitosis.
A question asks: “What type of division produces two identical cells used to repair a wound?” Work through the clues: identical cells rules out anything that makes variety, and repair is a classic growth-and-repair job. Both point to one answer — mitosis. Whenever you see “identical” plus “growth or repair”, reach for mitosis.
Common mix-up: mitosis makes cells that are genetically identical to the parent — not different, and not with half the DNA. (That halving-and-mixing process, which makes sex cells with variation, is a different type of division you meet later.) For mitosis, always answer: two identical cells.
Memory hook: miTOsis makes TWO identical cells. And a STEM cell is one that Still has To decide — undifferentiated until it differentiates.