Cells and organisation · GCSE Biology
Mitosis
Describe mitosis for GCSE Biology: DNA replication, two genetically identical diploid body cells, and why growth, repair and asexual reproduction use mitosis — not meiosis.
Mitosis: copy the DNA, then split into two identical diploid cells. Use it for growth, repair and asexual reproduction. Meiosis is the other process — four different haploid gametes.
The important bits
What you need to know
- 1
The cell cycle has a growth stage (cell grows, organelles increase, DNA replicates so each chromosome is two chromatids) then mitosis (chromosomes are separated) then the cytoplasm divides.
- 2
Mitosis produces two daughter cells, each with the same number of chromosomes as the parent and genetically identical to it (clones). Human body cells are diploid (46 chromosomes, 23 pairs).
- 3
Functions of mitosis: growth of multicellular organisms, repair of damaged tissues (for example skin), replacement of worn-out cells (blood, gut lining), and asexual reproduction in plants and some animals.
- 4
Before mitosis, DNA replication is essential. Without it each daughter would get half the genome. After replication, copies are pulled apart so each new nucleus receives a full identical set.
- 5
In diagrams, chromosomes become visible, line up at the equator, sister chromatids separate to opposite poles, and two nuclei form. Combined papers need the outcomes more than every stage name; Triple may expect prophase, metaphase, anaphase, telophase.
- 6
Asexual reproduction (runners, tubers, binary fission in eukaryotes such as yeast budding) uses mitosis, so offspring are genetically identical unless mutation occurs.
- 7
Mitosis is not meiosis. Meiosis makes gametes with 23 chromosomes (haploid) that are genetically different. If the question says healing a cut, a growing shoot, or replacing blood cells, the answer is mitosis.
- 8
Cancer is mitosis that has escaped control: the cell cycle runs too often. That link belongs with tumours, but the mechanism is still mitosis.
Quotations worth analysing
Short evidence. Real method.
“Mitosis produces two genetically identical diploid cells for growth and repair.”
Pack identical, diploid (or same chromosome number), two cells, and a function into one sentence. That is the core mark cluster.
“DNA is replicated before mitosis so each daughter cell receives a full set of chromosomes.”
The copying step is not optional. “The cell just splits” loses the replication mark.
“Mitosis is used for growth, repair and asexual reproduction; meiosis is used to make gametes.”
If sperm, egg or variation appear in the stem, you have left mitosis. Stay on this page only for body cells and clones.
Go deeper
What actually happens in the cell cycle before the split?
In the growth phase the cell makes more cytoplasm, more mitochondria and ribosomes, and it replicates DNA. Each chromosome becomes two identical chromatids joined at a centromere. Mitosis then lines those chromosomes up and pulls the chromatids apart so each pole gets one copy of every chromosome. Two nuclei form, then the cytoplasm divides (cytokinesis) into two cells. Skin cells, bone-marrow cells and meristem cells do this repeatedly. Nerve cells in adults rarely divide, which is why spinal injuries are hard to repair. In the exam, write replicate DNA then two identical cells. Stage names help Triple answers but will not rescue a candidate who says mitosis halves the chromosome number — that error describes meiosis.
Go deeper
How do I keep mitosis and meiosis from collapsing into each other?
Build a four-row comparison and stick to it. Number of divisions: mitosis one, meiosis two. Number of cells: two versus four. Chromosome number: stays diploid (46 → 46) versus halves to haploid (46 → 23). Genetics: identical versus different (crossing over and independent assortment in meiosis). Purpose: growth, repair, asexual versus gametes for sexual reproduction. A growing root tip is mitosis in meristems; formation of pollen or sperm is meiosis. Fertilisation then restores 46, and the zygote grows by mitosis. If you write “mitosis makes four sperm”, you have mixed the processes and will lose a cluster of marks on both papers.
Go deeper
Where do I see mitosis in plants as well as animals?
Plant meristems in shoot tips, root tips and the cambium are mitosis factories. That is why a stained onion root-tip squash shows chromosomes: those cells are dividing. Cuttings work because meristem cells can keep dividing and then differentiate into xylem, phloem, roots and leaves. Animals cannot generally grow a whole new body from a skin cell, because most animal cells have already specialised. The identical-clone idea also explains why strawberry runners produce plants that look like the parent, while strawberry seeds (sexual, meiosis plus fertilisation) vary. When a six-mark asks you to compare sexual and asexual reproduction, mitosis is the asexual mechanism and meiosis is the sexual one.
See the idea in action
A cut on the skin heals. Cells at the edge of the wound go through the cell cycle: they grow, replicate DNA, then divide by mitosis to produce two genetically identical diploid cells. Repeated mitosis replaces the damaged tissue. This is not meiosis: no gametes are made, the chromosome number stays 46, and the new cells match the surrounding skin genetically. If mitosis here were uncontrolled, a tumour could form.
Exam technique
Turn knowledge into marks
Lead with two identical cells, same chromosome number, DNA copied first, used for growth and repair. Mention meiosis only to say it is different. Do not claim mitosis produces variation or gametes.
Common mistakes
Do not give these marks away
- 01
Saying mitosis produces gametes, four cells, or genetically different daughters.
- 02
Forgetting that DNA is replicated before the nucleus divides.
- 03
Writing that body cells are haploid, or that mitosis halves the chromosome number.
What is the purpose of mitosis in human body cells?
ATo make gametes with half the chromosomes
BTo produce two genetically identical cells for growth and repair
CTo create variation in offspring
DTo swap genes between chromosomes
Show the answer
To produce two genetically identical cells for growth and repair. Mitosis copies the chromosomes and splits them evenly so each daughter cell matches the parent. Gametes and variation come from meiosis.
Quick questions
If this is the bit you searched
What is mitosis in GCSE Biology?
A type of cell division that produces two genetically identical diploid cells. It is used for growth, repair and asexual reproduction.
Does mitosis make sperm and egg cells?
No. Gametes are made by meiosis. Mitosis makes body cells that are genetically identical to the parent cell.
Why is DNA replicated before mitosis?
So each daughter cell can receive a full set of chromosomes. Without replication, each cell would get only half the DNA.
How many chromosomes are in human cells after mitosis?
46, the same as the parent body cell. Mitosis does not halve the chromosome number.