Mitosis and the cell cycle — AQA GCSE Biology
Test yourself on Mitosis and the cell cycle with AQA GCSE practice questions.
7 days Premium · Then free forever · No card, no charge
Mitosis and the cell cycle explained
The cell cycle is the sequence of events by which a cell grows, copies its genetic material and divides to form two genetically identical cells.
Read the full explanation
It has three main parts: interphase, during which the cell grows, organelles increase and DNA is replicated so each chromosome becomes two identical copies; mitosis, during which the copies are separated and two nuclei form; and cytokinesis, during which the cytoplasm and membranes divide to give two separate cells. Mitosis itself is described as a series of stages in which the chromosomes line up, the copies are pulled apart and new nuclear membranes form. A useful method is to narrate the cycle as grow, copy, separate, split. This process is needed for growth, repair and asexual reproduction, and it keeps the chromosome number constant.
During the cell cycle the genetic material is doubled and then divided into two identical cells.
The cell cycle is the sequence of growth, DNA replication and division that produces two genetically identical cells. It has three main stages: interphase, during which the cell grows and the genetic material is doubled so each chromosome becomes two identical copies; mitosis, when the copies are separated and the nucleus divides; and cytokinesis, when the cytoplasm and cell membrane divide to form two cells. The two daughter cells are identical to each other and to the parent because each receives one complete copy of every chromosome. For example, a human body cell with 46 chromosomes replicates its DNA, then divides so each new cell has 46 chromosomes.
Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria.
Before division, a cell must prepare by growing and making more sub-cellular structures. Interphase is the growth stage of the cell cycle. The cell increases in size, synthesises extra proteins and organelles, and replicates its DNA. Ribosomes are needed because they assemble proteins, and mitochondria are needed because they release energy by respiration for the processes of growth and division. For example, a root tip cell preparing to divide will build up its cytoplasm, ribosome number and mitochondria so that each daughter cell receives enough machinery to function. Without this preparation, division would produce cells that are too small or lack the structures needed for normal metabolism.
The DNA replicates to form two copies of each chromosome.
DNA replication occurs during interphase and produces two identical copies of every chromosome. The DNA double helix unwinds and each strand acts as a template so that new complementary strands are built, giving two identical DNA molecules. Each chromosome therefore consists of two identical copies, often called sister chromatids, held together until mitosis separates them. For example, a human cell with 46 chromosomes replicates its DNA so that there are temporarily 92 chromatids, arranged as two copies of each of the 46 chromosomes. This ensures that when the nucleus divides, each daughter cell receives a complete and identical set of genetic information.
In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides.
Mitosis is the stage of the cell cycle in which the copied chromosomes are separated. The chromosome copies line up at the centre of the cell and are pulled apart by spindle fibres, so that one complete set of chromosomes moves to each end of the cell. The nucleus then divides, forming two nuclei, each with the same chromosome number as the parent cell. For example, in a human body cell the 46 chromosomes are copied, then one set of 46 is pulled to each pole before the nucleus divides. This ensures the two new nuclei contain identical genetic information, ready for cytokinesis to divide the cytoplasm.
Finally the cytoplasm and cell membranes divide to form two identical cells.
This final stage of the cell cycle completes mitosis. After the nucleus has divided, the cytoplasm and cell membranes separate to produce two genetically identical daughter cells. In animal cells, the cell membrane pinches inwards (cleavage furrow) until the cell splits. In plant cells, a cell plate forms across the middle and develops into a new cell wall and membrane. Each daughter cell receives a full set of chromosomes and roughly half the cytoplasm and organelles. The word 'identical' refers to the DNA: both cells have the same chromosome number and the same alleles as the parent cell. This matters for growth, repair and asexual reproduction, where genetic consistency is essential.
Students need to understand the three overall stages of the cell cycle but do not need to know the different phases of the mitosis stage.
The cell cycle is studied as three broad stages. Stage 1 is growth and DNA replication, where the cell increases in size and copies its chromosomes. Stage 2 is mitosis, where the nucleus divides and one copy of each chromosome moves to each end of the cell. Stage 3 is cytokinesis, where the cytoplasm and cell membranes divide to form two identical cells. You need to know the order and purpose of these three stages, but you do not need to name or describe the individual phases of mitosis such as prophase, metaphase, anaphase and telophase. Focus on what happens overall in each stage and why it matters for growth and repair.
Cell division by mitosis is important in the growth and development of multicellular organisms.
Multicellular organisms grow and develop because cells divide by mitosis to produce more cells. Each division gives two genetically identical daughter cells, so the new cells have the same instructions as the parent. This allows an organism to increase its cell number, build new tissues and replace worn-out or damaged cells. In development, mitosis produces the many cells needed to form specialised tissues and organs, and it also supports repair, for example healing a cut or replacing skin cells. Because the DNA is copied accurately, the organism's cells keep the same chromosome number and the same alleles, which is essential for normal functioning.
Students should be able to recognise and describe situations in given contexts where mitosis is occurring.
You need to apply your knowledge of mitosis to unfamiliar contexts. Look for clues such as growth, repair or asexual reproduction. For example, a gardener taking cuttings produces new plants genetically identical to the parent, so mitosis is occurring. A lizard regrowing its tail, a cut healing, or an embryo developing all involve mitosis. In each case, the key features are: cells are dividing to produce genetically identical copies, the chromosome number stays the same, and the purpose is growth, repair or asexual reproduction. When describing the situation, state what is happening and link it to mitosis, rather than just naming the process.
Your focus
- Describe the stages of the cell cycle, including interphase, mitosis and cytokinesis.
- Explain the importance of DNA replication before mitosis.
- Explain why mitosis produces genetically identical daughter cells.
Show all 27 objectives
- Describe the order of events in the cell cycle, including when the genetic material doubles.
- Explain why the two daughter cells produced are genetically identical.
- Apply the idea of the cell cycle to a named organism or cell type.
- Describe what happens to a cell during interphase before it divides.
- Relate the increase in ribosomes and mitochondria to their roles in the cell.
- Explain why growth and organelle replication are necessary for successful cell division.
- Describe when and how DNA replicates in the cell cycle.
- Explain why replication produces two identical copies of each chromosome.
- Predict the chromosome content of daughter cells after replication and division.
- Describe the movement of chromosomes during mitosis.
- Explain how nuclear division produces two identical nuclei.
- Sequence mitosis correctly within the wider cell cycle.
- Describe the final division of the cytoplasm and cell membranes after nuclear division.
- Explain why the two daughter cells produced are genetically identical.
- Compare how the cytoplasm and membranes divide in animal and plant cells.
- List the three overall stages of the cell cycle in the correct order.
- Describe what happens in each of the three stages.
- Explain why DNA replication must occur before mitosis.
- Explain how mitosis contributes to growth in multicellular organisms.
- Describe how mitosis supports development and repair.
- Relate genetic identity of daughter cells to their role in the organism.
- Identify situations where mitosis is occurring from given contexts.
- Describe the role of mitosis in those situations.
- Explain why the daughter cells are genetically identical in each context.
Mitosis and the cell cycle exam tips
Marking Points
- Names the main stages of the cell cycle: interphase, mitosis and cytokinesis.
- Describes interphase as a period of growth and DNA replication, producing two copies of each chromosome.
- Describes mitosis as the stage in which the copied chromosomes are separated and two genetically identical nuclei form.
- Describes cytokinesis as the division of the cytoplasm to produce two separate cells.
- Explains that the daughter cells are genetically identical and have the same chromosome number as the parent cell.
- Links the cell cycle to growth, repair of tissues and asexual reproduction.
- States that the genetic material is doubled during interphase before division occurs.
- Describes DNA replication as producing two identical copies of each chromosome.
- Explains that mitosis separates the copies so each daughter cell receives one full set of chromosomes.
- Concludes that the two daughter cells are genetically identical to each other and to the parent cell.
- Uses the term cell cycle to link growth, DNA replication, mitosis and cytokinesis in the correct order.
- Identifies interphase as the growth stage before mitosis.
- States that the cell increases in size and mass before dividing.
- Names ribosomes and mitochondria as examples of sub-cellular structures that increase in number.
- Links ribosomes to protein synthesis and mitochondria to energy release by respiration.
- Explains that the extra structures are shared between the two daughter cells so each can function.
- States that DNA replication happens during interphase before mitosis.
- Describes the formation of two identical copies of each chromosome.
- Explains that the copies are identical because each is made from the original DNA template.
- Links DNA replication to the production of genetically identical daughter cells.
- Uses the idea that each daughter cell receives one copy of every chromosome.
- States that chromosome copies are separated during mitosis.
- Describes one set of chromosomes being pulled to each end of the cell.
- Explains that the nucleus divides to form two nuclei.
- Links the separation of chromosomes to the production of genetically identical nuclei.
- Places mitosis correctly between DNA replication and cytokinesis in the cell cycle.
- State that the cytoplasm divides after the nucleus has divided, producing two separate cells.
- Describe membrane division in animal cells as the cell membrane pinching inwards until the cell splits.
- Describe plant cell division as a cell plate forming across the cell, becoming new cell wall and membrane.
- Explain that the two daughter cells are genetically identical because each receives an identical set of chromosomes.
- Link this final stage to the earlier stages: DNA replication, then nuclear division, then cytoplasmic division.
- Recognise that 'identical' refers to genetic material, not necessarily to size or cytoplasmic contents.
- Name the three overall stages: growth and DNA replication, mitosis, and cytokinesis.
- State that DNA replication occurs before mitosis so each daughter cell receives a full set of chromosomes.
- Describe mitosis as the stage where the nucleus divides and chromosomes separate.
- Describe cytokinesis as the stage where the cytoplasm and cell membranes divide.
- Explain that the cycle produces genetically identical cells for growth and repair.
- Recognise that naming individual mitosis phases is not required at this level.
- State that mitosis produces genetically identical daughter cells.
- Explain that increasing cell number allows growth of multicellular organisms.
- Describe how mitosis provides new cells for development of tissues and organs.
- Give an example of repair, such as replacing skin cells or healing a wound.
- Link genetic identity to the correct functioning of new cells.
- Recognise that mitosis maintains the chromosome number in body cells.
- Identify a context involving growth, repair or asexual reproduction as a site of mitosis.
- State that the new cells produced are genetically identical to the parent cell.
- Describe the purpose of the division in that context, such as healing a wound or growing a new plant from a cutting.
- Recognise that the chromosome number remains constant in the daughter cells.
- Use correct terminology such as 'daughter cells' and 'genetically identical'.
- Explain why mitosis, rather than meiosis, is the relevant process in the given context.
Examiner Tips
- 💡Structure longer answers using the three headings interphase, mitosis and cytokinesis so every stage is covered.
- 💡Include what happens to the DNA in each stage, because replication and separation are the key events examiners look for.
- 💡If asked why mitosis is important, give at least two contexts such as growth and repair rather than a single example.
- 💡Sequence your answer as interphase, mitosis, cytokinesis so the doubling and dividing are clearly linked.
- 💡Use the phrase genetically identical and refer to chromosome number to show precise understanding.
- 💡If asked to compare, mention that meiosis halves the chromosome number while this division keeps it the same.
- 💡Name specific sub-cellular structures rather than saying organelles in general.
- 💡Link each named structure to its function to gain explanation credit.
- 💡Use the term interphase to show you know where growth fits in the cell cycle.
- 💡State clearly that replication happens in interphase, before mitosis.
- 💡Use the phrase two identical copies of each chromosome to match the specification wording.
- 💡Explain the consequence: identical copies allow identical daughter cells to form.
- 💡Use the phrase one set of chromosomes to each end to match the specification.
- 💡Distinguish clearly between mitosis and cytokinesis in your answer.
- 💡Mention that the two nuclei formed are genetically identical to support your explanation.
- 💡Use the phrase 'genetically identical' rather than just 'identical' to show precision.
- 💡If asked to sequence the cell cycle, place cytoplasmic division last, after nuclear division.
- 💡When comparing plant and animal cells, mention the cell plate for plants and membrane pinching for animals.
- 💡Use a simple three-step flow diagram to remember the order of the stages.
- 💡If a question asks for the stages of the cell cycle, give the three overall stages, not the phases of mitosis.
- 💡Link each stage to its purpose: growth, nuclear division, then cell separation.
- 💡Use the phrase 'genetically identical' when explaining the importance of mitosis.
- 💡Give a named example of repair, such as skin healing, to support your answer.
- 💡Distinguish clearly between growth (more cells) and development (specialised tissues and organs).
- 💡Underline the key clue in the question, such as 'healing' or 'cutting', before answering.
- 💡Always link your description back to mitosis and genetic identity.
- 💡If asked to explain, state the purpose of the division in that context.
Common Mistakes
- Treating mitosis as the whole cell cycle; the correction is that mitosis is one stage within the cycle, alongside interphase and cytokinesis.
- Saying DNA replication happens during mitosis; the correction is that DNA is replicated during interphase, before mitosis begins.
- Describing the daughter cells as genetically different; the correction is that mitosis produces genetically identical diploid cells.
- Thinking the cell divides first and then doubles its DNA; correct this by placing DNA replication in interphase before mitosis.
- Saying the daughter cells are similar rather than genetically identical; correct this by stating they have the same chromosome number and identical DNA.
- Confusing the cell cycle with meiosis; correct this by noting that meiosis produces gametes with half the chromosome number, whereas the cell cycle described here produces identical body cells.
- Believing the cell divides immediately without a growth phase; correct this by stating that interphase must occur first.
- Thinking mitochondria make energy rather than release it by respiration; correct this by saying respiration releases energy that the cell uses.
- Assuming only the nucleus prepares for division; correct this by including growth of the cytoplasm and an increase in organelles such as ribosomes and mitochondria.
- Saying the chromosome number doubles permanently; correct this by explaining that the copies are separated during mitosis so each daughter cell has the original number.
- Confusing replication with transcription; correct this by stating that replication copies the whole DNA molecule, whereas transcription makes RNA from a gene.
- Thinking new chromosomes are made from scratch; correct this by describing copies made from the original DNA strands.
- Saying the whole cell divides during mitosis; correct this by stating that mitosis is nuclear division and cytokinesis divides the cytoplasm.
- Thinking the chromosome number is halved; correct this by explaining that each end receives a full set, so the number stays the same.
- Describing chromosomes being pulled together rather than apart; correct this by saying one set moves to each end of the cell.
- Thinking the cell membrane divides before the nucleus; correction: nuclear division occurs first, then cytoplasm and membranes divide.
- Believing the two daughter cells are identical in every way including cytoplasm; correction: they are genetically identical but cytoplasmic contents may differ slightly.
- Describing plant cell division as the membrane pinching inwards; correction: plant cells form a cell plate that becomes a new cell wall and membrane.
- Listing prophase, metaphase, anaphase and telophase as required knowledge; correction: only the three overall stages are needed.
- Placing DNA replication after mitosis; correction: replication occurs in the first stage, before nuclear division.
- Confusing mitosis with the whole cell cycle; correction: mitosis is just the nuclear division stage within the cycle.
- Saying mitosis produces gametes; correction: mitosis produces body cells, while meiosis produces gametes.
- Thinking growth is only about cell enlargement; correction: growth also involves an increase in cell number by mitosis.
- Believing daughter cells are genetically different; correction: mitosis produces genetically identical cells.
- Confusing mitosis with meiosis in contexts such as gamete production; correction: mitosis occurs in growth and repair, meiosis in gamete formation.
- Assuming any cell division is mitosis; correction: check whether the daughter cells are genetically identical and whether the purpose is growth, repair or asexual reproduction.
- Describing the context without linking it to mitosis; correction: explicitly state that mitosis is occurring and why.