Differentiation

Fertilisation is the fusion of a male and female gamete to produce a zygote

In multicellular organisms this cell divides repeatedly to form an embryo with many genetically identical cells

Initially all cells are unspecialised

Cell differentiation: is the process that leads to the formation of specialised cells and tissues

Cells develop to become specialised, each adapted to carry out one role

All cells have the same genetic make up, but when cells become differentiated, certain genes are 'switched on' or expressed, while other are not

When certain genes are expressed, it mean that only specific types of proteins or gene products are produced

Gradients of signalling chemicals indicate a cell's position in the embryo and determine the pathway of differentiation it follows

Once cells have differentiated to become specialised, multi-cellular organisms are made up of many of these cells to form specialised tissues and organs

Each organ and tissue carrying out a specific function

Muscle cell --> muscle tissue --> organ --> organ system

Tissues can be simply made of only one type of cell

Organs are made of several different types of tissues working together

Organ systems are made of several different organs working together

Examples

• Retinal tissue in the retina of the eye

• Striated muscle tissues in skeletal muscles

• Skin tissue

• Transport tissue for water and sugar in plants