5 · The Mitotic Cell Cycle
Cambridge A Level Biology — Full F-drive source: 5 · The Mitotic Cell Cycle — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
5 min read 8 parts Lesson 12 of 12 Unit quiz
Lesson summary
5.2 The Stages of Mitosis and Cytokinesis — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Identify and describe prophase, metaphase, anaphase, telophase and cytokinesis, and calculate a mitotic index.
- Animal cells
- Plant cells
- Features to check
- Genetic stability
- Meaning — cytokinesis divides the cytoplasm, while mitosis divides the nucleus
- Cut the apical meristem of a root tip
Part 1 of 6Overview of mitosis
1Mitosis
- Mitosis nuclear division that produces two genetically identical nuclei with the same number of chromosomes as the parent nucleus.
2Stages
- Stages it is one continuous process divided into four stages for description: prophase, metaphase, anaphase and telophase (PMAT).
Part 2 of 6Stage by stage
| Stage | What happens |
|---|---|
| Prophase | Chromatin condenses so chromosomes are visible as two chromatids; centrioles move to opposite poles and spindle fibres form (animal cells); the nucleolus disappears and the nuclear envelope breaks down |
| Metaphase | Chromosomes line up at the equator; each centromere attaches to a spindle fibre |
| Anaphase | Centromeres divide; spindle fibres shorten and pull sister chromatids (now chromosomes) to opposite poles, centromere first, using ATP |
| Telophase | Chromosomes reach the poles and decondense; nuclear envelopes and nucleoli reform; the spindle breaks down |
Part 3 of 6Cytokinesis
Animal cells
- Animal cells the cell surface membrane pinches inward at the equator, forming a cleavage furrow, through a contractile ring of protein.
Plant cells
- Golgi vesicles line up at the equator and fuse to form a cell plate, which develops into a new cell wall and membrane.
Meaning
- Meaning cytokinesis divides the cytoplasm, while mitosis divides the nucleus.
Part 4 of 6Mitotic index and slide preparation
- Mitotic index = number of cells in mitosis ÷ total number of cells counted.
- It shows how actively tissue is dividing and is high in root tips and many tumours.
1
Cut the apical meristem of a root tip.
2
Hydrolyse it in warm hydrochloric acid to separate the cells.
3
Stain with acetic orcein or toluidine blue.
4
Squash under a coverslip.
5
Observe with an optical microscope and count the cells at each stage.
Part 5 of 6Recognising the stages
| Stage | Appearance under the microscope |
|---|---|
| Prophase | Chromosomes as tangled threads in a defined nucleus |
| Metaphase | Chromosomes in a line across the middle |
| Anaphase | V-shaped chromatids with centromeres leading |
| Telophase | Two clusters at opposite ends with a furrow or plate forming between them |
1Features to check
- Features to check whether the nuclear envelope is visible, where the chromosomes are and what shape they are.
2Drawing
- Drawing use sharp pencil lines with no shading, and label the chromosome, spindle and cell membrane.
3Genetic stability
- Genetic stability daughter cells are clones, so organisms grow from a single zygote and repair tissue without introducing variation.
Part 6 of 6More from the specification
More from the specification
Spindle Apparatus and Centrosomes
- During prophase, centrosomes begin moving toward opposite cellular poles to organize microtubules into the mitotic spindle apparatus.
Replicated Chromosomes in Diploid Cells
- A diploid parent cell undergoing division contains duplicated DNA molecules paired as sister chromatids held together at the centromere.
Micrograph Identification of Mitosis
- In a light micrograph showing dividing root tip cells, stages of mitosis are distinguished by condensed chromosome alignment and separation.
Mitosis Function
- The nuclear division called mitosis produces two genetically identical daughter nuclei, maintaining the diploid chromosome number of the parent cell.
Spindle Apparatus and Centrosomes
- During prophase, centrosomes begin moving toward opposite cellular poles to organize microtubules into the mitotic spindle apparatus.
Replicated Chromosomes in Diploid Cells
- A diploid parent cell undergoing division contains duplicated DNA molecules paired as sister chromatids held together at the centromere.
Micrograph Identification of Mitosis
- In a light micrograph showing dividing root tip cells, stages of mitosis are distinguished by condensed chromosome alignment and separation.
Mitosis Function
- The nuclear division called mitosis produces two genetically identical daughter nuclei, maintaining the diploid chromosome number of the parent cell.
Microtubule
- Hollow protein filament used for support and transport.
Micrograph
- A photograph taken through a microscope.
Centrosome
- A pair of centrioles at right angles that organises the spindle.
Diploid
- Having two sets of chromosomes.
Key terms
| Term | Meaning |
|---|---|
| Prophase | First stage of mitosis; chromosomes condense and become visible. |
| Metaphase | Chromosomes line up at the equator. |
| Anaphase | Chromatids separate and move to the poles. |
| Telophase | Nuclei reform at each pole. |
| Cytokinesis | Division of the cytoplasm. |
| Mitotic index | Fraction of cells undergoing mitosis. |
Avoid these mistakes
1
Saying chromosomes line up at the poles in metaphase — they line up at the equator.
2
Forgetting the stage names are in the order PMAT.
3
Saying the nuclear envelope reforms in anaphase — it reforms in telophase.
4
Describing cell plate formation in animal cells — it occurs in plant cells.
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