MITOSIS

Primary purpose is to increase the number of cells Daughter cells are genetically identical to the parents Occurs during growth and asexual reproduction. Mitosis is a continuous process which is divided for convenience into a number of stages.

MITOSIS Interphase Sometimes called the “resting stage” between divisions BUT cells are metabolically very active The amount of DNA in the nucleus doubles New organelles such as mitochondria are made.

MITOSIS Interphase No chromosomes are visible The chromosome material, chromatin, is spread through the nucleus in a diffuse form.

MITOSIS Prophase The longest stage Chromosomes become visible In animal cells, the centrioles divide and move to opposite ends of the nucleus

MITOSIS Prophase Protein microtubules develop from each centriole forming spindle fibres. (In plant cells there are no centrioles and the spindle forms independently)

MITOSIS Prophase Towards the end of prophase each chromosome can be seen to consist of two chromatids held together by a centromere.

MITOSIS Prophase At the end of prophase the nucleolus disappears and the nuclear envelope breaks down.

MITOSIS Metaphase Chromosomes line up on the equator of the spindle. They attach themselves to the spindle by their centromere

MITOSIS Anaphase The centromeres divide The free chromatids move to the poles

MITOSIS Anaphase This movement results from the contraction of the spindle fibres. As they shorten they pull the chromatids apart.

MITOSIS Telophase The chromatids have reached the poles and are now regarded as distinct chromosomes again. A nuclear envelope forms around each group of chromosomes

MITOSIS Telophase The chromosomes uncoil returning to chromatin The cytoplasm divides by cytokinesis.

CYTOKINESIS Animal cells The centre of the cell ‘pinches in’ to form a division furrow. As the division deepens, the cell surface membrane on each side joins up. Two separate cells result.

CYTOKINESIS Plant cells Vesicles produced by the Golgi body collect on equator of cell These vesicles fuse to form a cell plate. The cell plate eventually stretches right across the cell forming the middle lamella. Cellulose builds up on lamella to form cell walls.

CYTOKINESIS