Mitosis (AQA GCSE Biology): Revision Notes
Mitosis
Mitosis is a type of cell division that creates new cells for growth and repair. Understanding this process is essential for your GCSE biology exam.
What are chromosomes?
Inside every cell nucleus, there are structures called chromosomes. These contain DNA molecules that carry thousands of genes - the instructions for making you! In body cells, chromosomes come in pairs, which makes them diploid cells.
Key term: Diploid means having two sets of chromosomes.
The cell cycle
Cells go through a repeating pattern called the cell cycle, which has three main stages:
Stage 1: Interphase
This is the longest stage where the cell:
- Grows bigger and makes more structures like mitochondria
- Copies its DNA so each chromosome becomes two identical copies
- Prepares for division by making everything it needs
Most of a cell's life is spent in interphase - it's like the cell getting ready for the big event!
Stage 2: Mitosis
During this stage:
- The nucleus divides in half
- One complete set of chromosomes moves to each side of the cell
- This ensures each new cell gets exactly the same genetic information
Stage 3: Cell division (cytokinesis)
Right after mitosis:
- The cell membrane pinches in to split the cell
- Two identical daughter cells are formed from one parent cell
How mitosis works
The process starts with one parent cell that contains two sets of chromosomes (diploid). Understanding the step-by-step process is crucial for your exam success.
Worked Example: The Mitosis Process
Step 1: Before division - The parent cell copies each chromosome exactly
Step 2: During mitosis - One copy of each chromosome goes to each side of the cell
Step 3: After division - Two daughter cells are formed
The clever thing about mitosis is that each daughter cell gets exactly the same chromosomes as the parent cell. This means they are genetically identical to the parent and to each other.
The key principle of mitosis: Each daughter cell receives exactly the same genetic material as the parent cell, ensuring genetic consistency across all body cells.
Why is mitosis important?
Mitosis produces new body cells for several essential functions in living organisms:
- Growth - making you bigger as you develop
- Repair - replacing damaged or worn-out cells
- Asexual reproduction - some organisms use mitosis to create offspring
Key facts to remember
Here are three memory tricks to help you remember the key concepts:
Memory Tricks:
- Mi-TO-sis makes TWO cells
- Mi-tosis makes cells that are genetically Identical
- Diploid means Double (two sets of chromosomes)
Remember!
Key Points to Remember:
- Mitosis produces two genetically identical daughter cells from one parent cell
- The cell cycle has three stages: interphase (longest), mitosis, and cell division
- Daughter cells have the same number of chromosomes as the parent cell because DNA is copied exactly
- Mitosis is essential for growth, repair, and asexual reproduction
- Body cells are diploid, meaning they have two sets of chromosomes