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Mitosis is the cell division process that creates two cells genetically identical to the parent cell. Free notes with key terms and 14 questions answered.
Mitosis and Cell Division Process is part of Cell division in GCSE AQA Higher Biology.
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Mitosis is the cell division process that creates two cells genetically identical to the parent cell. Free notes with key terms and 14 questions answered.
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Use this lesson to stay inside Cell division while connecting the detail back to the wider Cell biology topic.
Read the core explanations from Mitosis and Cell Division Process before testing yourself from memory.
Right now, millions of your cells are dividing. Every second, your body creates around 25 million new cells to replace worn-out ones, heal cuts, and help you grow. But here's the crucial bit - each new cell must be an exact copy of the original, carrying identical genetic instructions.
If cell division went wrong and created different cells, chaos would follow. Imagine if a skin cell suddenly tried to behave like a brain cell, or if a muscle cell lost the instructions for making muscle proteins. This is why mitosis exists - it's your body's photocopying system, ensuring every new cell gets exactly the same genetic blueprint.
Trap: Many students confuse mitosis with meiosis. Mitosis creates identical cells for growth and repair. Meiosis creates genetically different gametes (sex cells) for reproduction.
Picture a cell getting ready to divide. Inside its nucleus are chromosomes - long strands of DNA containing all the genetic instructions. Before division begins, each chromosome copies itself, creating two identical copies joined at the centre.
Now comes the critical moment. The nucleus breaks down and protein fibres called spindle fibres attach to each chromosome. These fibres act like molecular ropes, pulling one copy of each chromosome to opposite ends of the cell. This ensures each end gets exactly the same genetic information.
Think of it like sorting a deck of cards. You have two identical sets of cards (the copied chromosomes). The spindle fibres ensure one complete set goes to each side of the cell, so both new cells end up with the full deck of genetic instructions.
Once the chromosomes reach opposite ends, new nuclei form around each set. But the cell isn't finished dividing yet. The cytoplasm - all the cell contents outside the nucleus - must also split equally between the two new cells.
The cell membrane pinches inward from all sides, like tightening a belt around the cell's middle. This creates a groove that gets deeper and deeper until the cell completely separates into two independent cells. Each new cell has its own nucleus, its own set of chromosomes, and its own share of cytoplasm.
Worked example: The Complete Mitosis Process
Describe what happens when a human skin cell divides by mitosis
Answer: Two identical skin cells, each with 46 chromosomes and the same genetic information as the original cell
Key Point: The result is always two cells that are genetically identical to each other and to the original parent cell. This is essential for maintaining the organism's characteristics as it grows.
Mitosis is the engine of growth in multicellular organisms. When you were born, you had about 2 trillion cells. Now you have roughly 37 trillion cells - all those extra cells came from mitosis. Every time a cell divides, one becomes two, two become four, four become eight, and so on.
But mitosis isn't just about getting bigger. It's also your body's repair system. When you cut your finger, skin cells around the wound start dividing rapidly to close the gap. When you break a bone, bone cells use mitosis to rebuild the damaged area. Without mitosis, you couldn't heal from injuries.
Different parts of your body use mitosis at different rates. Your skin cells divide every 2-3 weeks, replacing the outer layer that gets worn away. Your intestinal lining replaces itself every 3-5 days because it faces harsh digestive chemicals. Meanwhile, your brain cells rarely divide after childhood - which is why brain injuries are so serious.
You need to recognise when mitosis is happening in different situations. Look for these key clues: rapid cell production, growth, healing, or replacement of worn-out cells.
Growth situations: A teenager's height increase, a plant's stem getting longer, a tadpole developing into a frog. In all these cases, mitosis creates the extra cells needed for the organism to get bigger.
Repair situations: A cut healing, a broken bone mending, a plant regrowing after being pruned. Here, mitosis replaces damaged or lost cells with identical new ones.
Replacement situations: Skin cells being shed and replaced, red blood cells being renewed, the lining of your stomach being refreshed. These are maintenance jobs where old cells are constantly replaced by new identical ones.
Examiners test mitosis in predictable ways. Master these key points and you'll handle any question they throw at you.
Command word focus: 'Describe' questions want you to state what happens in sequence. 'Explain' questions want you to say why mitosis is important - focus on the need for identical cells in growth and repair.
Common exam mistake: Students often forget to mention that the cytoplasm divides as well as the nucleus. The question might ask about 'cell division' - make sure you cover the complete process ending with two separate cells.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Mitosis is the cell division process that creates two cells genetically identical to each other and to the original parent cell. It is the body's photocopying system for growth and repair, ensuring every new cell gets exactly the same genetic instructions.
Mitosis creates identical cells for growth and repair, while meiosis creates genetically different gametes, or sex cells, for reproduction. Because mitosis gives every new cell identical genetic instructions, it maintains the organism's characteristics as it grows.
Mitosis is important for growth, repair and replacement in multicellular organisms. It takes the body from about 2 trillion cells when born to roughly 37 trillion, heals cuts, mends broken bones, and replaces worn-out cells such as skin cells and red blood cells.
Before mitosis, each chromosome copies itself; then the nucleus breaks down and spindle fibres pull one copy of each chromosome to opposite ends of the cell. New nuclei form around each set, then the cytoplasm divides and the cell membrane pinches inward until two separate cells form.
Examples of mitosis include growth, such as a teenager's height increase or a tadpole developing into a frog; repair, such as a cut healing or a broken bone mending; and replacement, such as skin cells being replaced or red blood cells being renewed.
Spindle fibres are protein fibres that attach to each chromosome during cell division once the nucleus breaks down. They act like molecular ropes, pulling one copy of each chromosome to opposite ends of the cell so each end gets exactly the same genetic information.
In cell division by mitosis, each chromosome first copies itself, then the nucleus breaks down and spindle fibres pull one copy of each chromosome to opposite ends of the cell. New nuclei form around each set, and the cell membrane pinches inward until the cytoplasm divides and two identical cells form.
At the end of mitosis, the cytoplasm splits equally between the two new cells. The cell membrane pinches inward from all sides, creating a groove that gets deeper until the cell completely separates into two cells, each with its own nucleus and share of cytoplasm.
After mitosis, each new human cell has 46 chromosomes, the same as the original parent cell. Spindle fibres pull one copy of each chromosome to opposite ends, so each end gets a complete set and the two cells are genetically identical.
Mitosis repairs the body by replacing damaged or lost cells with identical new ones. When a finger is cut, skin cells around the wound divide rapidly to close the gap, and when a bone breaks, bone cells use mitosis to rebuild the damaged area.
The intestinal lining replaces itself every 3-5 days by mitosis because it faces harsh digestive chemicals. Skin cells divide every 2-3 weeks, while brain cells rarely divide after childhood.
Brain injuries are so serious because brain cells rarely divide after childhood, so mitosis cannot easily replace damaged ones. Other parts of the body, such as the intestinal lining and skin, use mitosis to replace cells all the time.
The body creates around 25 million new cells every second by mitosis, to replace worn-out cells, heal cuts and allow growth. Each new cell must be an exact copy of the original, carrying identical genetic instructions.
A common mistake when describing cell division is not mentioning that the cytoplasm divides as well as the nucleus. A complete answer covers the whole process, ending with two separate, genetically identical cells.