What is the difference between mitosis and meiosis, and how are stem cells useful?
Mitosis and meiosis and their purposes, the difference between haploid and diploid cells, the nature and uses of stem cells, and uncontrolled cell division leading to cancer.
A focused answer to the WJEC GCSE Biology section 2.2 topic on cell division and stem cells, covering mitosis and meiosis and their purposes, haploid and diploid cells, the nature and uses of embryonic and adult stem cells, and uncontrolled cell division leading to cancer.
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What this dot point is asking
WJEC wants you to describe mitosis and meiosis and their purposes, explain the difference between haploid and diploid cells, describe what stem cells are and their uses and issues, and explain how cancer results from uncontrolled cell division.
Mitosis
Mitosis is used for:
- growth (making more cells as an organism develops),
- repair (replacing damaged or worn-out cells),
- asexual reproduction (producing genetically identical offspring in some organisms).
Before mitosis, the chromosomes are copied, so each daughter cell receives a complete, identical set.
Meiosis
Meiosis is important for sexual reproduction because it halves the chromosome number, so that when a sperm and egg join at fertilisation the full number is restored. It also creates genetic variation, because the four cells it makes are all genetically different.
Haploid and diploid
- A diploid cell has the full set of chromosomes, in pairs. Human body cells are diploid, with 46 chromosomes (23 pairs).
- A haploid cell has half the number, with one of each pair. Human gametes are haploid, with 23 chromosomes.
At fertilisation, a haploid sperm (23) joins a haploid egg (23) to make a diploid cell (46), which then divides by mitosis to form the new organism.
Stem cells
There are two main sources:
- Embryonic stem cells come from early embryos and can become almost any type of cell.
- Adult stem cells are found in some tissues (such as bone marrow) and can become a more limited range of cell types.
Stem cells can be used in medicine, for example to replace damaged cells (treating conditions such as leukaemia, and potentially repairing damaged tissues). However, using embryonic stem cells raises ethical issues, because the embryo is destroyed, and there can be risks such as rejection or uncontrolled growth.
Cancer
Normally, cell division by mitosis is carefully controlled. If this control fails, cells divide uncontrollably and form a lump of cells called a tumour. This is cancer. Factors that increase the risk include certain chemicals (carcinogens), ionising radiation and some lifestyle factors.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksCompare mitosis and meiosis, including the number and type of cells each produces.Show worked answer →
A 4-mark compare question.
Mitosis produces two daughter cells that are genetically identical to the parent cell and to each other; it is used for growth, repair and asexual reproduction, and the daughter cells are diploid. Meiosis produces four cells that are genetically different from each other; it makes gametes (sex cells), which are haploid (half the number of chromosomes).
Markers reward: mitosis gives two identical diploid cells; meiosis gives four genetically different haploid gametes; their purposes (growth/repair versus making gametes). Saying both produce identical cells, or muddling the cell numbers, are common errors.
WJEC style4 marksExplain what stem cells are and describe one medical use, including one issue with using them.Show worked answer →
A 4-mark question.
Stem cells are undifferentiated cells that can keep dividing and can become (differentiate into) different types of specialised cell. A medical use is treating disease, for example using stem cells to replace damaged cells, such as in treating some blood disorders (like leukaemia) or potentially repairing damaged tissue.
An issue is that embryonic stem cells are taken from embryos, which some people object to on ethical grounds, or that there is a risk the cells could grow uncontrollably or be rejected.
Markers reward: undifferentiated cells that can divide and differentiate; one medical use; one valid ethical or safety issue. Just saying "they cure diseases" without explaining what they are misses marks.
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Sources & how we know this
- WJEC GCSE Biology specification (from 2016) — WJEC (2016)