Mitosis (Cambridge (CIE) IGCSE Biology): Revision Note

New cells are made by mitosis: Extended

Extended Tier Only

Mitosis - basics

• Most body cells have two copies of each chromosome

• We describe these cells as diploid

• When cells divide their chromosomes double beforehand

• This ensures that when the cell splits in two, each new cell still has two copies of each chromosome (is still diploid)

• This type of cell division is used for growth, repair of damaged tissues, replacement of cells and asexual reproduction and is known as mitosis

• Mitosis is defined as nuclear division giving rise to genetically identical cells

What is the process of mitosis?

• Just before mitosis, each chromosome in the nucleus copies itself exactly (forming X-shaped chromosomes)

• Chromosomes line up along the centre of the cell where cell fibres pull them apart

• The cell divides into two; each new cell has a copy of each of the chromosomes

Why is mitosis important?

• All cells in the body (excluding gametes) are produced by mitosis of the zygote (opens in a new tab)

• Mitosis is important for replacing cells e.g. skin cells, red blood cells and for allowing growth (production of new cells e.g. when a zygote divides to form an embryo)

When does mitosis occur?

• Growth: mitosis produces new cells

• Repair: to replace damaged or dead cells

• Asexual reproduction: mitosis produces offspring that are genetically identical to the parent

Mitosis & stem cells: Extended

Extended Tier Only

• Many tissues in the human body contain a small number of unspecialised cells called stem cells

• Stem cells divide by mitosis to produce new daughter cells that can become specialised for specific functions

• All stem cells originate from the zygote, which divides several times by mitosis to form a ball of unspecialised cells (roughly 150-200, depending on the exact stage), all of which are embryonic stem cells

• These cells are initially identical, but begin to differentiate as the foetus develops, gradually forming the recognisable specialised tissues and features of the body