Summary WJEC (England) Eduqas A-Level Biology 2. Continuity of Life - 2. Cell Division
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Course
2. Continuity of life
Institution
WJEC
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Chromosome – 46: DNA + histone protein
- Visible when chromatin condenses – coil & shorten
- Replicated = X: sister chromatids joined at centromere
a. Interphase – cellular activities / ATP production
G1: S: G2:
Protein & RNA synthesis DNA replication Mitochondria / chloroplasts
Cell growth (increase in size) replicate
Mitosis – requires ATP = genetically identical diploid daughter cells
Prophase
Chromosomes condense (coil & thicken) – chromatids visible (to light microscope)
Nuclear membrane & nucleolus disappear
Centrioles separate & move to opposite poles
Spindle fibres begin to form
Metaphase – middle
Spindle fibres extend from centrioles – attach to centromeres
Chromosomes line up at equator
Anaphase – away
Spindle fibres shorten + centromeres split: sister chromatids separated & pulled to opposite poles
Full set of chromosomes at each pole
Telophase – two
Chromosomes decondense – uncoil & lengthen
Nuclear envelope reforms around each group = nuclear division
Spindle fibres break down (animals)
Cytokinesis: cytoplasm division at end of mitosis – produce 2 new daughter cells
Animal: cell membrane folds inwards via cleavage furrow – cytoplasm & organelles divide (2 equal halves)
Plant: cell plates form between dividing cell – vesicles carry cellulose & fuse in centre
b. animal vs plant
Animal Plant
occurs in most tissues only occurs in meristem
centrioles / microfilaments no centrioles / microfilaments involved
spindle fibres break down before cytokinesis spindle fibres remain during cytokinesis
c. significance of mitosis
- growth
- repair damaged/diseased cells
- asexual reproduction
- repeated cell renewal
- maintain chromosome number
- genetically identical
- oncogenes cause unrestricted mitosis = cancerous growth
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