4.4.3Additional lessons
Mitosis — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 110 of 142
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 4Preparation for Mitosis
Before a nucleus can divide, the DNA must be copied and packaged so it can be moved accurately.
DNA replication
- DNA replication During the S phase of interphase each chromosome is copied, giving two identical sister chromatids joined at a centromere.
Condensation
- Condensation DNA wraps around histone proteins and is supercoiled, so chromosomes become short and thick and can be moved without tangling.
Spindle
- Spindle Microtubules, assembled from tubulin dimers, form a spindle that attaches to the centromere of each chromosome.
Centrosomes
- Centrosomes Centrosomes organise the microtubules and move to opposite poles of the cell as the spindle forms.
Packaging benefit
- Packaging benefit Tightly coiled chromosomes are less likely to tangle or break as they are pulled across the cell.
Part 2 of 4Phases of Mitosis
Mitosis is a continuous process that is divided into four phases for study: prophase, metaphase, anaphase and telophase.
1
Prophase: chromosomes condense and become visible, the nucleolus disappears and the nuclear envelope breaks down as spindle microtubules grow.
2
Metaphase: spindle fibres attach to centromeres and line up the chromosomes along the equator of the cell.
3
Anaphase: the centromeres split and the sister chromatids are pulled apart towards opposite poles, each now a chromosome.
4
Telophase: chromosomes reach the poles and begin to decondense, the spindle breaks down and nuclear envelopes and nucleoli re-form.
5
Cytokinesis then divides the cytoplasm, giving two genetically identical daughter cells.
Part 3 of 4Outcome and Significance
Mitosis conserves the chromosome number and genetic information from one cell generation to the next.
Outcome and Significance
Genetic identity
- Genetic identity Each daughter nucleus receives one copy of every chromosome, so both are genetically identical to the parent nucleus.
Growth
- Growth Repeated mitosis increases the number of cells in a growing organism.
Repair
- Repair Damaged or worn-out tissues are replaced by new cells formed by mitosis.
Asexual reproduction
- Asexual reproduction Some organisms form offspring by mitosis, which produces clones of the parent.
Clones
- Clones Because there is no mixing of alleles, mitosis does not increase genetic variation, except through rare mutations.
| Phase | Key event |
|---|---|
| Prophase | Condensation, envelope breakdown |
| Metaphase | Alignment at equator |
| Anaphase | Chromatids separate |
| Telophase | Nuclei re-form |
Part 4 of 4Exam Checklist & Tips
4.4.3 – Key Points for the Exam
- Sister chromatids Two identical copies of a chromosome joined at the centromere.
- Centromere The region of a chromosome where spindle fibres attach.
- Spindle A structure of microtubules that moves chromosomes during nuclear division.
- Mitosis Nuclear division that gives two genetically identical nuclei.
- Histone A protein around which DNA is wrapped.
- Chromatid One of the two identical halves of a replicated chromosome.
Common Mistakes
- Saying DNA replicates in prophase; it replicates during S phase before mitosis begins.
- Mixing the sequence of phases or confusing metaphase with anaphase.
- Calling the separated chromatids chromatids after anaphase; they are now chromosomes.
- Claiming the number of chromosomes halves in mitosis.
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