Biology • Year 12 • Module 5 • Lesson 7
Mitosis — Maintaining Genetic Stability in Somatic Cells
Lock in the vocabulary, the stage order, and the central idea that mitosis keeps daughter cells genetically identical to the parent body cell.
1. Label the stages of mitosis
The diagram below shows a somatic cell moving through DNA replication and the stages of mitosis to produce two daughter cells. Write the missing labels into boxes A–H. Labels are drawn from the lesson's Key Terms and Cards 1–3. 8 marks
- A — process that occurs before mitosis to copy the DNA _______________________
- B — two identical copies of a replicated chromosome joined at the centromere _______________________
- C — stage where chromosomes condense and the nuclear envelope breaks down _______________________
- D — stage where chromosomes line up at the cell equator _______________________
- E — stage where sister chromatids separate and move to opposite poles _______________________
- F — stage where two new nuclei form around each chromosome set _______________________
- G — division of the cytoplasm to form two separate daughter cells _______________________
- H — chromosome number of each daughter cell, compared with the parent (same / halved / doubled?) _______________________
| Box | Your label |
|---|---|
| A | |
| B | |
| C | |
| D | |
| E | |
| F | |
| G | |
| H |
2. Term–definition match
The ten definitions below are shuffled. In the right-hand column, write the matching term chosen from: mitosis, somatic cell, chromosome, chromatid, centromere, cytokinesis, genetic stability, prophase, metaphase, anaphase. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 2.1 | Cell division that produces two daughter cells with the same chromosome number as the parent body cell. | |
| 2.2 | A body cell that is not a gamete (e.g. skin cell, gut-lining cell). | |
| 2.3 | A condensed DNA–protein structure carrying hereditary information. | |
| 2.4 | One of two identical copies of a replicated chromosome joined to its partner before separation. | |
| 2.5 | The region joining two sister chromatids together. | |
| 2.6 | Division of the cytoplasm to form two separate daughter cells, completing cell division. | |
| 2.7 | Maintenance of the correct chromosome number and hereditary information in daughter cells. | |
| 2.8 | The stage of mitosis where chromosomes condense and the nuclear envelope begins to break down. | |
| 2.9 | The stage where replicated chromosomes line up at the equator of the cell. | |
| 2.10 | The stage where sister chromatids separate and migrate to opposite poles. |
3. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version on the line. 8 marks (1 for T/F, 1 for the correction where needed)
3.1 DNA is replicated during anaphase so that each daughter cell can receive a full set of chromosomes. T / F
3.2 The two daughter cells produced by mitosis are genetically identical to each other and to the parent somatic cell (apart from any replication errors). T / F
3.3 Mitosis halves the chromosome number, which is why it is used for gamete production. T / F
3.4 Mitosis only occurs during childhood growth; once an adult stops growing, mitosis no longer happens. T / F
4. Function recall
Answer each in 1–2 sentences using precise terms from the lesson. 10 marks (2 each)
4.1 What is the function of DNA replication in the lead-up to mitosis?
4.2 What is the function of metaphase in mitosis?
4.3 What is the function of anaphase (separating sister chromatids) in maintaining chromosome number?
4.4 What is the function of cytokinesis at the end of mitosis?
4.5 What is the function of mitosis at the level of a tissue (e.g. epidermis or gut lining)?
5. Cloze — the mitosis paragraph
Fill each blank with the correct term. Word bank (each word used once): replication · prophase · metaphase · anaphase · telophase · cytokinesis · chromatids · same · somatic · growth. 10 marks
Before mitosis begins, the cell carries out DNA __________ (a) so each chromosome becomes two identical sister __________ (b) joined at a centromere. In __________ (c), the chromosomes condense and the nuclear envelope breaks down. The replicated chromosomes then line up at the cell equator in __________ (d). In __________ (e), the sister chromatids are pulled to opposite poles of the cell. New nuclei form around each chromosome set during __________ (f), and __________ (g) then divides the cytoplasm to produce two separate daughter cells. Because each daughter cell receives one complete set of chromosomes, the chromosome number is the __________ (h) as in the parent cell. Mitosis is used by __________ (i) cells to support __________ (j), repair and some asexual reproduction — never to produce gametes.
| Blank | Your word |
|---|---|
| (a) | |
| (b) | |
| (c) | |
| (d) | |
| (e) | |
| (f) | |
| (g) | |
| (h) | |
| (i) | |
| (j) |
Q1 — Labelled stage strip
A: DNA replication. B: sister chromatids. C: prophase. D: metaphase. E: anaphase. F: telophase. G: cytokinesis. H: the same chromosome number as the parent cell.
Q2 — Term–definition matches
2.1 mitosis • 2.2 somatic cell • 2.3 chromosome • 2.4 chromatid • 2.5 centromere • 2.6 cytokinesis • 2.7 genetic stability • 2.8 prophase • 2.9 metaphase • 2.10 anaphase.
Q3 — True / false with correction
3.1 False. Correction: DNA is replicated before mitosis begins (during interphase / S phase), not during anaphase. Anaphase is where the already-replicated sister chromatids are separated.
3.2 True.
3.3 False. Correction: mitosis maintains chromosome number — daughter cells have the same chromosome number as the parent cell. Halving chromosome number for gamete production is the role of meiosis, not mitosis.
3.4 False. Correction: mitosis continues throughout life in tissues that need ongoing renewal (e.g. skin, gut lining, blood cells, wound repair). Some cells such as neurons and cardiac muscle have very limited mitotic capacity.
Q4.1 — Function of DNA replication
DNA replication copies each chromosome before mitosis so that the cell has two identical sister chromatids ready to be separated. Without this, daughter cells would not inherit a full set of hereditary information.
Q4.2 — Function of metaphase
Metaphase aligns the replicated chromosomes along the cell equator. This alignment is what makes the next step — even separation of sister chromatids — possible.
Q4.3 — Function of anaphase
Anaphase separates the sister chromatids and pulls them to opposite poles of the cell. This means each future daughter nucleus receives exactly one copy of each chromosome, preserving chromosome number.
Q4.4 — Function of cytokinesis
Cytokinesis divides the cytoplasm into two, producing two separate daughter cells. Each cell ends up with one nucleus and the same chromosome number as the original somatic cell.
Q4.5 — Function of mitosis at the tissue level
At the tissue level, mitosis replaces lost or damaged cells with genetically identical new cells of the same type, so the tissue keeps functioning normally (e.g. epidermis regenerating after a cut; gut lining renewing daily).
Q5 — Cloze answers
(a) replication · (b) chromatids · (c) prophase · (d) metaphase · (e) anaphase · (f) telophase · (g) cytokinesis · (h) same · (i) somatic · (j) growth.