The cell cycle for GCSE Biology: the three stages and why they matter

The cell cycle is the series of stages a cell goes through to divide into two identical cells. For GCSE there are three stages: first the cell enlarges, builds extra ribosomes and mitochondria and replicates its DNA; then, in mitosis, one set of chromosomes is pulled to each end and the nucleus divides; finally the cell splits in two, giving two identical cells.

The three stages of the cell cycle

AQA's GCSE Biology specification (4.1.2.2) says you need to understand these three overall stages, but you don't need to know the different phases of mitosis. During the cycle, the genetic material is doubled and then divided between two identical cells.

Why the cell needs each stage

• Growing and making more organelles means each new cell has enough ribosomes to make proteins and enough mitochondria to release energy.
• Copying the DNA means each new cell gets a full set of chromosomes, so both are genetically identical to the parent.
• Dividing the nucleus before the cell makes sure one complete set of chromosomes ends up in each new cell.

In humans, body cells have 46 chromosomes in 23 pairs, so after the cell cycle each new body cell also has 46.

Why mitosis matters

AQA says cell division by mitosis is important in the growth and development of multicellular organisms, and you should be able to recognise situations where mitosis is happening. Examples include:

• Growth: a seedling growing at its root tip, or a child growing.
• Repair: replacing skin cells after a cut, or healing a broken bone.
• Asexual reproduction: some organisms produce genetically identical offspring by mitosis.

When the cell cycle goes out of control, cells divide again and again, forming a tumour. For the stages of mitosis itself, see our mitosis guide.

Exam questions with answers

Describe what happens during the cell cycle. (4 marks)

The cell grows and makes more sub-cellular structures, such as ribosomes and mitochondria. The DNA replicates, so there are two copies of each chromosome. In mitosis, one set of chromosomes moves to each end of the cell and the nucleus divides. Finally the cell splits, sharing its cytoplasm and membrane between two genetically identical cells.

Why must DNA be copied before a cell divides? (2 marks)

So that each new cell gets a full set of chromosomes, making both new cells genetically identical to the original.

Why are the two cells produced genetically identical? (1 mark)

Because each receives an exact copy of the parent cell's chromosomes, made by DNA replication.

What A-level adds

At A-level, interphase is split into phases (including DNA replication in the S phase), mitosis is divided into prophase, metaphase, anaphase and telophase, and you may calculate a mitotic index from a micrograph. If you're heading that way, try naming the stages of mitosis in our Cell Biology course, then press Mark to check your answer in the course:

Common mistakes

• Saying mitosis is the whole cell cycle. Mitosis is one stage: the division of the nucleus.
• Forgetting that organelles increase too. The cell makes more ribosomes and mitochondria before dividing.
• Saying the chromosomes halve. In mitosis the chromosome number stays the same; halving happens in meiosis.
• Leaving out cytokinesis. The cell isn't two cells until the cytoplasm and membrane divide.

Practise with a short timed paper

The cell cycle is in GCSE Biology and the first year of A-level Biology. The daily GCSE Biology Higher paper, and the The daily A-level Biology: Year 1 paper are short timed papers of 8 questions, with a new one every day.

Read next

Biology · CellsInterphase: G1, S and G2 phases of the cell cycleInterphase is when a cell grows and copies its DNA before dividing. What happens in G1, S and G2, how long it lasts, checkpoints, and worked examples.