Cell division is when your cells divide. The original cell ( parent cell ) divides into two daughter cells .
Needed for growth, repair and reproduction.
When you grow, you need more cells so your existing cells divide to make more cells.
New cells need to be made to replace dead or injured cells.
Cell division is also needed to make babies. Cells need to divide to make egg cells (ova) and sperm cells.
Remember: All cells have a nucleus and each nucleus have DNA. DNA controls everything.
This means that if one cell is to divide into two cells, DNA needs to be copied.
One DNA can be copied to make two DNA in DNA replication .
The DNA unzips. Each DNA strand copies itself to become two DNA.
DNA needs to copy exactly
DNA needs to copy themselves exactly so everything looks the same and works the same. Eg. Skin cells dividing into skin cells.
Sometimes when DNA are copying themselves, they will make mistakes. These mistakes are called mutations .
Most of the time, the body will fix the mutations.
When mutations aren’t fixed, diseases such as cancer can occur.
But sometimes mutations can be good for the organism.
What happens next?
So far only DNA has copied.
Remember: DNA are located on chromosomes.
After DNA has copied itself, chromosomes become double stranded.
Now the cell can start dividing.
Mitosis : when cells divide
Mitosis – when body cells divide
Meiosis – when sex cells divide
Differences between mitosis and meiosis Mitosis Meiosis Number of parent cells 1 1 Number of daughter cells 2 4 DNA and genes in daughter cells Exactly the same as parent cells Different from parent cells Number of chromosomes in daughter cells 2n = 46 n = 23 Purpose Growth and repair Reproduction
Why 23 chromosomes?
Fertilisation – 23 chromosomes from sperm + 23 chromosomes from egg = 46 chromosomes
Cell Division – mitosis and meiosis
Cell division is when one parent cell divides into two daughter cells
Needed for growth, repair and reproduction
Before a cell can divide, DNA needs to replicate
DNA needs to copy itself exactly to make sure all cells look and function the same way as the parent cell
A mutation is when DNA doesn’t copy itself exactly. This can lead to diseases such as cancer.
However, sometimes a mutation can give an organism an advantage.
After DNA has replicated, the cell will have double-stranded chromosomes
Then the cell can undergo mitosis to divide into two cells – daughter cells are genetically identical and have 46 chromosomes
Meiosis is the division of sex cells – daughter cells genetically different and have 23 chromosomes