Single cell --> cell division --> multi-cells --> organisms

Cell division: Single-cell (e.g. diatoms) forms new cells --> in multi-cellular organisms, form new cells & replace old cells

Types: prokaryotic (no nucleus, DNA together other protein mechanisms); eukaryotic cell (nucleolus inside nucleus with double membrance nuclear envelope, outside is cytoplasm with membrane-bound organelles)

Chromosomes: proteins + DNA inside cell

1 DNA = many genes carrying genetic information for everything the cell is & will be

Prokaryotic DNA: no nucleus --> with circular chromosomes

Prokaryotic cell division: binary fission --> DNA replicates --> cytoplasms splits --> into 2 ~identical cells

Eukaryotic cell division: by mitosis --> division of the nucleus --> cytokinesis --> division of the cytoplasm into two equal portions --> into two ~identical cells

Cell cycle: M phase: Mitosis + Cytokinesis --> cytokinesis --> G1 phase: cell grows more proteins & cellular organelles --> S phase: each chromosome duplicates to form double stranded DNA chromosome pairs of chromatids, connected by centromeres --> G2 phase: cell continues to grow & metabolise

Mitosis stages: prophase --> metaphase --> anaphase --> telophase

Interphase: chromosome set doubles

Prophase: longest --> chromosomes doubled, elongated & indistinguishable --> condensed chromosomes --> centriole pair outside cell nucleus move towards opposite poles of nucleus --> Late prophase --> nucleolus & nuclear membrane disappear --> microtubules connect to the centriole pair forming spindles --> some microtubules connect to the chromatids of the chromosome pairs --> chromosomes move towards the "equator" of the cells: metaphase plate --> microscope: no distinct nucleus & nucleolus with very condensed chromosomes

Metaphase: all chromosomes align along the metaphase plate

Anaphase: sister chromatids of all choromosome pairs separate --> attracted towards opposite poles of the cells --> creating a complete set of chromosomes at each side of the cell

Telophase: chromosomes continue to move towards poles of cells --> spindles disappear --> cell membranes form around each poles --> 2 nuclei --> with 2 nucleoi inside them --> mitosis complete --> followed by cytokinesis

Cytokinesis: animal cells --> divided by original cell membrane --> plant cells --> divided by cell plates

Mystery: what actually triggers cell division? --> cells of the body divide at different rates