4.4.3Additional lessons
Mitosis — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 42 of 101
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Phases of Mitosis
The phases run as a continuous sequence, and the names describe what the chromosomes are doing.
1
Prophase: chromosomes condense and become visible, the nucleolus disappears, the spindle starts to form and the nuclear envelope breaks down by the end.
2
Metaphase: spindle microtubules attach to the centromeres and line all the chromosomes up on the equator of the cell.
3
Anaphase: the centromeres divide and the sister chromatids are pulled to opposite poles as spindle microtubules shorten.
4
Telophase: chromosomes reach the poles and uncoil, nuclear envelopes reform around each set and the nucleolus reappears.
5
Cytokinesis usually overlaps telophase, dividing the cytoplasm to give two daughter cells.
Part 2 of 5What Happens to the Chromosomes
Prophase
- Prophase Each chromosome is a pair of sister chromatids, and the centrosomes move to opposite poles to organise the spindle.
Metaphase
- Metaphase Chromosomes sit at the equator, equally distant from both poles, which ensures an even split of the genetic material.
Anaphase
- Anaphase Each chromatid is now a separate chromosome, and the cell has temporarily twice the usual number of chromosomes.
Telophase
- Telophase Two nuclei each hold the same number and type of chromosomes as the parent nucleus.
| Phase | Chromosome position | Nuclear envelope |
|---|---|---|
| Prophase | Condensing, scattered | Breaking down |
| Metaphase | On the equator | Absent |
| Anaphase | Moving to poles | Absent |
| Telophase | At the poles | Reforming |
Part 3 of 5The Result of Mitosis
Genetic identity
- Genetic identity Replication copied the DNA exactly and mitosis shares it equally, so both nuclei are genetically identical to the parent.
Chromosome number
- Chromosome number If the parent is diploid, the daughters are diploid, so the species' chromosome number is maintained from cell to cell.
Uses
- Uses Mitosis drives embryonic growth, tissue repair, replacement of cells and asexual reproduction.
Part 4 of 5Exam Technique
Order
- Order Use the sequence prophase, metaphase, anaphase, telophase, and remember that DNA replication belongs to interphase before it.
Describe, do not list
- Describe, do not list Say what happens to the chromosomes and spindle in each phase, because naming a phase alone earns no marks.
Terminology
- Terminology Use chromatid before the centromere splits and chromosome after separation, as marking schemes require.
Part 5 of 5Exam Checklist & Tips
4.4.3 – Key Points for the Exam
- Prophase The first stage, in which chromosomes condense and the nuclear envelope disappears.
- Metaphase The stage in which chromosomes line up on the cell equator.
- Anaphase The stage in which sister chromatids are pulled to opposite poles.
- Telophase The final stage, in which nuclear envelopes reform around the two chromosome sets.
- Spindle A structure of microtubules that moves chromosomes during division.
Common Mistakes
- Putting DNA replication in prophase when it happens earlier, in interphase.
- Saying chromosomes pair up in mitosis; homologous chromosomes stay separate.
- Writing that the spindle pulls the chromosomes apart by lengthening; the microtubules shorten.
- Confusing metaphase (equator) with anaphase (moving apart).
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