CELL DIVISION

WHY DO CELLS NEED TO DIVIDE?

The cell membrane is permeable to some substances (semi-permeable) and all nutrients and wastes must pass through it

As cells grow (increased volume), the number of organelles increases – so they require more supplies: nutrients and oxygen

As the cell gets bigger, the volume increases faster than the surface area of the membrane

As cells increase in size, the surface area-to-volume ratio decreases.

This holds true for any cell shape!

At a certain size, there is not enough surface area for nutrients/wastes to cross that is required by the cell

So a cell divides into smaller cells in order to allow enough surface area to suit its needs

FUNCTIONS OF CELL DIVISION Growth – multi-cellular organisms can get

larger Repair – help organisms heal (e.g.cut or

broken bone) Reproduce – so organisms can produce

offspring

A CELL CANNOT JUST BREAK IN TWO!

Why? There is only one nucleus!

Which is not always in the middle of the cellThe contents (chromosomes / DNA) are not organized for easy division

Cell Division includes a multistep process called MITOSIS.

The 1 cell before it divides is called the parent cell.

The 2 new cells are called daughter cells.

THE CELL CYCLE

The cell cycle has 3 parts:Interphase, Mitosis, and Cytokinesis

Mitosis has 4 phases.

THE STEPS

Interphase

Prophase Metaphase Anaphase Telophase

Cytokineseis – division of the cytoplasm

MITOSIS

I – PMAT – C for short

INTERPHASE

Centrioles

Nucleus

Cell Membrane

Duplicated DNA

PROPHASE

Fragments of nuclear membrane

METAPHASE

Mitotic Spindle

ANAPHASE

Daughter chromosomes

TELOPHASE

CYTOKINESIS – ANIMAL CELLS

Cleavage furrow

Cytokinesis in a human kidney cell

CYTOKINESIS – PLANT CELLS Instead of “pinching”, a cell plate

forms which separates the two new nuclei

This cell plate becomes a new cell wall

Cell plate formation

The Cell Cycle

http://www.cellsalive.com/mitosis.htm