Key Learning Objectives
- Explain the purpose of mitosis (growth, repair of damaged tissues, and asexual reproduction).
- Describe the stages of the cell cycle: DNA replication, nuclear division, and cell splitting.
- Understand that mitosis produces two genetically identical diploid daughter cells.
Topic Summary & Core Notes
Understand how body cells divide for growth, tissue repair, and asexual reproduction. Step through DNA replication, chromosome alignment, spindle separation, and cytokinesis.
Key Rules, Formulas & Definitions
Daughter Cells Rule
1 Parent Diploid Cell (46 chromosomes) → 2 Identical Diploid Daughter Cells (46 chromosomes each)
Chromosome Duplication
Before division, every single DNA strand replicates to form X-shaped sister chromatids
2 Step-by-Step Worked Examples
Worked Example 1
Worked Example 1: Chromosome Number Conservation
Question: A human skin cell has 46 chromosomes. How many chromosomes will be in each daughter cell following mitosis?
Step-by-Step Solution:
- Step 1: Identify division type: Skin growth occurs via mitosis.
- Step 2: Recall mitosis rule: Mitosis produces genetically identical daughter cells with the exact same chromosome number.
- Step 3: State value: 46 chromosomes (23 pairs).
Final Answer: 46 chromosomes
Senior Examiner Insight: Mitosis conserves the diploid chromosome number (46 in humans). Do not halve to 23 (that is meiosis).
Worked Example 2
Worked Example 2: Biological Significance of Mitosis
Question: State two reasons why an injured athlete requires rapid mitotic cell division.
Step-by-Step Solution:
- Step 1: Tissue repair: Mitosis generates replacement cells to heal torn muscle fibres and ligaments.
- Step 2: Genetic fidelity: The new cells must be genetically identical to perform the exact same physiological function.
Final Answer: 1. Repairing damaged tissues/muscles. 2. Producing genetically identical replacement cells.
Senior Examiner Insight: Examiners reward 'repair of damaged tissue', but reject 'repairs damaged cells' (cells are replaced, not repaired).
Common Pitfalls & Examiner Warnings
Common Mistake: Saying mitosis 'repairs damaged cells'
Damaged cells die and are REPLACED by new cells produced via mitosis.
Common Mistake: Confusing Mitosis with Meiosis
Mitosis makes 2 identical body cells (diploid); Meiosis makes 4 genetically different sex cells/gametes (haploid).
Common Mistake: Forgetting that DNA doubles BEFORE division
DNA must replicate during Interphase so each daughter cell receives a full set.
Interactive Self-Check Quiz (3 Questions)
Question 1 of 3
How many daughter cells are produced from one parent cell during mitosis?
Click to Reveal Answer & Mark Scheme
Correct Answer: B) 2
Detailed Explanation: Mitosis involves one division cycle producing exactly 2 genetically identical daughter cells.
Mark Scheme & Scoring Points: 1 mark for 2 daughter cells.
Question 2 of 3
Why is it essential that daughter cells produced by mitosis are genetically identical?
Click to Reveal Answer & Mark Scheme
Correct Answer: A) To ensure they can carry out the same function as the parent tissue without rejection or mutation.
Detailed Explanation: Identical genetic copies ensure consistent tissue structure and function in multicellular organisms.
Mark Scheme & Scoring Points: 1 mark for maintaining identical function and tissue structure.
Question 3 of 3
During which phase of the cell cycle does DNA replicate?
Click to Reveal Answer & Mark Scheme
Correct Answer: B) Interphase
Detailed Explanation: During interphase, the cell grows, replicates its DNA, and synthesises proteins before dividing.
Mark Scheme & Scoring Points: 1 mark for Interphase.
Created by Fiaraz Iqbal
Former Headteacher & Senior Science / Maths Examiner
Fiaraz produces structured video walkthroughs, Tier 3 literacy packs, and exam mark scheme breakdowns to help secondary students achieve top grades.
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