Edexcel iGCSE Biology-4.28 Mitosis- Study Notes- New Syllabus

Mitosis – Producing Identical Cells

📝 Introduction

• Mitosis is a type of cell division that produces two genetically identical daughter cells.
• It takes place in body (somatic) cells and is essential for growth, repair and replacement of worn-out or damaged cells.
• During mitosis, the number of chromosomes remains the same, so each daughter cell receives a complete set of chromosomes.
• The parent cell is diploid (2n), and the daughter cells formed are also diploid (2n).
• Mitosis ensures that genetic information is passed accurately from one cell to the next.

🧬 What is Mitosis?

• Mitosis is the process in which one diploid parent cell divides once to produce two diploid daughter cells that are genetically identical to each other and to the parent cell.
• Each daughter cell contains the same number and type of chromosomes as the original parent cell.

What Does Diploid Mean?

• A diploid (2n) cell is a cell that contains two complete sets of chromosomes.
• One set of chromosomes is inherited from the mother.
• The other set is inherited from the father.
• In humans:
  • Diploid cells contain 46 chromosomes (23 pairs).
• Most body cells, such as skin cells, muscle cells and liver cells, are diploid.

Why is Mitosis Important?

• Mitosis is necessary because it:
  • Increases the number of cells during growth.
  • Replaces old, worn-out or dead cells.
  • Repairs damaged tissues after injury.
  • Maintains the same chromosome number in body cells.
  • Produces genetically identical cells, ensuring body cells function normally.
  • Allows some organisms, such as certain plants and simple animals, to reproduce asexually.

What Happens Before Mitosis?

• Before the cell divides, it prepares by copying its DNA.

DNA Replication

• Every chromosome makes an exact copy of itself.
• Each copied chromosome now consists of two identical sister chromatids joined together at a centromere.
• This ensures that enough genetic material is available for both daughter cells.

At this stage:

• The chromosome number does not increase.
• Only the amount of DNA has doubled.

⚙️ Stages of Mitosis

1. Chromosomes Become Visible

• The copied chromosomes become shorter and thicker.
• Each chromosome consists of two sister chromatids joined at the centromere.
• The nuclear membrane begins to break down.

2. Chromosomes Line Up

• The chromosomes move to the centre (equator) of the cell.
• Spindle fibres attach to the centromeres of each chromosome.
• This ensures that each chromatid can be pulled to opposite ends of the cell.

3. Sister Chromatids Separate

• The centromeres divide.
• Spindle fibres pull the sister chromatids apart.
• One chromatid moves to each end (pole) of the cell.
• Once separated, each chromatid is called a chromosome.

4. Formation of Two New Cells

• New nuclear membranes form around each set of chromosomes.
• The cytoplasm divides in a process called cytokinesis.
• Two separate daughter cells are produced.

Each daughter cell:

• Has the same chromosome number as the parent cell.
• Contains identical genetic information.

Result of Mitosis

🧬 Why Are Daughter Cells Genetically Identical?

The daughter cells are genetically identical because:

• DNA is copied accurately before cell division.
• Every chromosome is duplicated.
• Sister chromatids are separated equally.
• Each daughter cell receives one copy of every chromosome.
• No genetic information is lost or gained during mitosis.

🌟 Importance of Maintaining the Chromosome Number

If the chromosome number changed every time a body cell divided:

• Cells would not function properly.
• Important genetic information could be lost.
• Growth and repair would be affected.

Mitosis prevents this by ensuring:

• Each daughter cell receives a complete set of chromosomes.
• The chromosome number remains constant.

Functions of Mitosis

Growth

• In multicellular organisms, mitosis increases the number of cells.
• This allows the organism to grow from a single fertilised egg into an adult.

Repair of Damaged Tissues

• Damaged or injured cells are replaced by new cells produced through mitosis.
• This helps wounds heal.

Replacement of Worn-Out Cells

• Cells such as skin and intestinal cells wear out regularly.
• Mitosis replaces these old cells with new ones.

Asexual Reproduction

• Some organisms reproduce without fertilisation.
• Mitosis produces genetically identical offspring.

Examples include:

• Some plants
• Amoeba
• Yeast

🌟 Features of Mitosis

• Occurs in body (somatic) cells.
• Involves one cell division.
• Produces two daughter cells.
• Daughter cells are genetically identical.
• Chromosome number remains diploid (2n).
• Used for growth, repair and cell replacement.

📊 Summary Table

📚 Importance of Mitosis

• Growth → more body cells.
• Repair → replaces damaged cells.
• Asexual reproduction → e.g., in plants (cuttings, runners).
• Genetic stability → no variation introduced.

📌 Quick Recap
Mitosis = 1 division → 2 identical diploid cells.
Maintains chromosome number.
Key uses: growth, repair, asexual reproduction.
Stages in order: IPMATC (Interphase → Prophase → Metaphase → Anaphase → Telophase → Cytokinesis).
💡 Mnemonic for stages: Interesting People Meet At The Café