Cell Division and Growth Learning Objectives understand that

Cell Division and Growth Learning Objectives: understand that mitosis results in production of new cells for growth, repair and replacement and describe the process recall that before each division genetic information must be copied so that all new cells have the same genes explain differentiation of cells and describe how the cells produced by mitosis differentiate into a variety of specialised cells

Cell Division and Growth Mitosis is a type of cell division to produce new cells. Before dividing, each cell copies all of the DNA in its nucleus. This ensures that the genetic material is identical to the original cell that gave rise to them; genetically identical cells are the result of mitosis The fertilised egg… …divides repeatedly by mitosis… …to produce a ball of genetically identical cells - the early embryo.

Cell Division and Growth Watch the video showing cells dividing under a microscope (timelapsed):

Cell Division and Growth Watch the video showing a 3 D animation of cell division:

The epithelial cells lining the intestine are continually being replaced by mitosis such that the entire lining is replaced every five days Epithelial cells

The dead layers of cells at the surface of the skin are constantly being lost and are replaced by the mitotic divisions of the cells in the layer beneath them Dead cells Constantly dividing cells replacing those lost at the surface

These nerve cells have lost the ability to undergo mitosis – once grown they do not divide

NB na ! Y m ou es w of ill ea no ch t b st e e ag xp e, e on cte ly d t th o e re m m aj em or b ev er e n th ts e ! Prophase The chromosomes have condensed and each chromosome can be seen to consist of two strands of DNA Chromosomes – made of 2 DNA strands

Metaphase Chromosomes line up at the “equator” of the cell and each attaches to a spindle fibre Spindle fibres Pole Equator

This electron micrograph shows a metaphase chromosome Two strands of DNA

Spindle fibres pull the 2 DNA strands apart and the separated daughter chromosomes move to opposite poles of the cell Anaphase

Anaphase (cont. . )

The chromosomes begin to uncoil and a nuclear membrane begins to form around new each set of chromosomes Telophase Division of the cytoplasm

Summary of Mitosis Metaphase – chromosomes line up along the equator and spindle attaches Prophase – chromosomes condense and are visible as two strands of DNA Anaphase – spindle pulls the DNA strands apart Telophase – the chromosomes uncoil. A nuclear membrane begins to form around each set of chromosomes

Photomicrograph showing cells from an onion root tip Note that many of the cells are not dividing

A D Normal cell before division These photographs are taken from prepared slides of onion root tip cells that were undergoing mitosis: Identify the photographs showing the four stages of mitosis – Prophase, Metaphase, Anaphase and Telophase Correct order: B – A – D – C C B

Cell differentiation embryo development

Cell differentiation Cellular differentiation: The process by which a unspecialised cell becomes a more specialised cell type. Differentiation occurs numerous times in the womb, as an animal changes from a single fertilised egg (stem cell) to a complex system of tissues and cell types. Cell differentiation produces dramatic changes to a cell’s size, shape and activity.

Cell Division and Growth Learning Objectives - review: understand that mitosis results in production of new cells for growth, repair and replacement and describe the process recall that before each division genetic information must be copied so that all new cells have the same genes explain differentiation of cells and describe how the cells produced by mitosis differentiate into a variety of specialised cells