How do cells divide by mitosis, and why are stem cells so important in growth, repair and medicine?
Chromosomes, the cell cycle and mitosis, the role of mitosis in growth and repair, stem cells in embryos, adult tissue and plant meristems, and the uses and issues of therapeutic cloning and stem cell treatments.
A focused answer to AQA GCSE Biology 4.1.2, covering chromosomes, the cell cycle and mitosis, the role of mitosis in growth and repair, and the sources and uses of stem cells.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
AQA wants you to describe chromosomes, the three stages of the cell cycle including mitosis, why mitosis matters for growth and repair, where stem cells come from, and the benefits and risks of using stem cells in medicine.
Chromosomes and the cell cycle
The cell cycle has three main stages:
- Growth and DNA replication: the cell grows, sub-cellular structures (such as ribosomes and mitochondria) increase in number, and the DNA replicates so each chromosome forms two identical copies joined together.
- Mitosis: the chromosomes line up along the centre of the cell, the cell fibres pull one copy of each chromosome to each end (pole), and the nucleus divides into two.
- Division (cytokinesis): the cytoplasm and cell membrane divide to form two genetically identical daughter cells.
Why mitosis matters
Mitosis produces two cells that are genetically identical to the parent cell and to each other. AQA wants you to link this to three uses:
- Growth of multicellular organisms, increasing the number of cells.
- Repair of damaged tissue and replacement of worn-out cells (for example skin and gut lining cells, which are constantly replaced).
- Asexual reproduction in some organisms (such as bacteria dividing, or a strawberry plant producing runners).
Because mitosis copies the genome exactly, all the cells of an organism normally carry the same genetic information, which is why a skin cell and a liver cell have identical DNA but use different genes.
Stem cells
Stem cells can be used to grow new cells, for example to treat type 1 diabetes (replacing insulin-producing cells in the pancreas) or paralysis (replacing damaged nerve cells). Therapeutic cloning produces an embryo with the same genes as the patient, so the stem cells produced from it are not rejected by the patient's immune system. In plants, meristem stem cells are used to clone whole plants quickly and cheaply, which can preserve rare species or produce disease-resistant crops.
Issues and risks: using embryonic stem cells raises ethical and religious objections because the embryo is destroyed; there is a risk of transferring a viral infection; the cells may be rejected; and there is a small risk of uncontrolled division leading to tumours.
Try this
Q1. Give two uses of mitosis in the body. [2 marks]
- Cue. Growth and repair (replacing damaged or worn-out cells).
Q2. Give one risk of using stem cells to treat patients. [1 mark]
- Cue. Possible transfer of viral infection (or rejection of the cells).
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20194 marksDescribe what happens during the cell cycle, including the role of mitosis, to produce two new cells.Show worked answer →
A 4-mark describe question on Paper 1 rewards the stages in the correct order.
- In the first stage the cell grows, and the number of sub-cellular structures such as ribosomes and mitochondria increases.
- The DNA replicates, so each chromosome forms two identical copies joined together.
- During mitosis the chromosomes line up at the centre of the cell, and one copy of each chromosome is pulled to each end (pole) of the cell as the nucleus divides.
- Finally the cytoplasm and cell membrane divide to form two genetically identical daughter cells.
Markers reward DNA replication before division, the chromosomes separating to opposite ends, and the two cells being genetically identical.
AQA 20214 marksEvaluate the use of stem cells from human embryos to treat medical conditions such as paralysis and diabetes.Show worked answer →
A 4-mark evaluate question wants benefits, drawbacks and a judgement.
Benefits: embryonic stem cells are unspecialised and can differentiate into any cell type, so they could replace damaged cells (for example insulin-producing pancreas cells to treat type 1 diabetes, or nerve cells to treat paralysis), potentially curing rather than just managing the condition.
Drawbacks and issues: some people object on ethical or religious grounds because the embryo is destroyed; there is a risk of transferring a viral infection; and the cells may be rejected unless therapeutic cloning is used. There is also a small risk the cells could cause tumours.
Judgement: the potential to cure currently untreatable conditions is significant, but it must be weighed against the ethical concerns and medical risks. Markers reward at least one benefit, one drawback and a clear conclusion.
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Sources & how we know this
- AQA GCSE Biology (8461) specification — AQA (2016)