How do cells divide by mitosis and meiosis, and what are stem cells used for?
Cell division by mitosis and meiosis, the differences between them, and stem cells and their uses.
A focused answer to the WJEC GCSE Science Double Award Unit 4 topic on cell division, covering mitosis and meiosis and the differences between them, and stem cells and their uses in growth, repair and medicine.
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What this dot point is asking
WJEC Double Award Unit 4 wants you to describe cell division by mitosis and meiosis, give the differences between them, and describe stem cells and their uses.
Mitosis
Mitosis is used for growth (making more cells), repair (replacing damaged cells) and asexual reproduction. Before a cell divides, it copies its DNA so each new cell gets a complete, identical set of chromosomes.
Meiosis
Meiosis happens in the reproductive organs to make gametes (sperm and egg, or pollen and ovule). Having half the chromosomes means that when two gametes join at fertilisation, the full number is restored. The variety produced is one source of variation.
Comparing mitosis and meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Number of cells made | 2 | 4 |
| Chromosomes in each | Full number | Half the number |
| Genetically | Identical | Different |
| Used for | Growth, repair | Making gametes (reproduction) |
Stem cells
In the body, stem cells allow growth and the replacement of cells such as blood cells. In plants, stem cells in the meristems let plants grow throughout life.
How a fertilised egg builds a body
A new organism starts as a single fertilised egg (zygote), which divides by mitosis to make many identical cells. At first these are stem cells that can become any type. As the embryo grows, the cells differentiate (specialise) into the many cell types of the body - nerve, muscle, blood and so on - by switching on different genes. This is why mitosis (for identical copies) and stem cells (for specialising) work together to build a whole organism from one cell, which is a common link tested in exams.
Plant cloning from stem cells
Because plant stem cells in the meristems can keep dividing and specialising, plants can be cloned easily. A small piece of a plant can grow a whole new identical plant, which is the basis of taking cuttings and of tissue culture in the lab. This lets growers make many identical copies of a useful plant quickly. Animals cannot be cloned this easily from ordinary body cells because their cells lose this ability once specialised, which is a useful contrast to remember.
Uses and issues of stem cells
Stem cells could be used in medicine to replace damaged or diseased cells, for example to treat diabetes (replacing insulin-making cells), paralysis (replacing nerve cells) or to grow new tissue. However, using embryonic stem cells raises ethical concerns because it involves embryos, and there are risks such as rejection or infection. These benefits and concerns are often weighed up in exam questions.
Try this
Q1. How many cells does meiosis produce? [1 mark]
- Cue. Four.
Q2. State one use of mitosis in the body. [1 mark]
- Cue. Growth or repair (or asexual reproduction).
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. Refer to the number of cells produced and whether the cells are identical.Show worked answer →
A Unit 4 compare question worth 4 marks. Reward: mitosis produces two cells (1) that are genetically identical to the parent cell, used for growth and repair (1); meiosis produces four cells (1) that are genetically different and have half the number of chromosomes (gametes for reproduction) (1). Markers credit the number of cells and whether they are identical for each. A common error is to say both produce identical cells.
WJEC style3 marksWhat is a stem cell, and give one medical use of stem cells.Show worked answer →
A Unit 4 recall question. A stem cell is an undifferentiated cell that can divide to produce more cells and can differentiate into different specialised cell types (1). A medical use is to replace damaged or diseased cells, for example to treat conditions such as diabetes or paralysis, or to grow new tissue (1); a second valid use or example (1). Markers credit the definition (undifferentiated, can specialise) and a valid use. A common error is to describe a stem cell as already specialised.
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