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 cell The 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 MITOSIS Interphase Prophase Metaphase Anaphase Telophase Cytokineseis – division of the cytoplasm MITOSIS I – PMAT – C for short

interphase Centrioles Duplicated DNA Cell Membrane Nucleus

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