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Cell Division - OCR AS Biology
Transcript of Cell Division - OCR AS Biology
state that mitosis occupies only a small percentage of the cell cycle and that the remaining percentage includes the copying and checking of genetic information.
describe, with the aid of diagrams and photographs, the main stages of mitosis.
explain the meaning of the term homologous pair of chromosomes.
explain the significance of mitosis for growth, repair and asexual reproduction in plants and animals. Why is Mitosis
important? Asexual Reproduction many multicellular organisms rely on mitosis for asexual reproduction and it is the sole form of reproduction for many single-celled organisms. Growth Multicellular organisms grow by producing new extra cells. Each new cell is genetically identical to the parent cells and so can perform the same functions. Repair Damaged cells need to be replaced by new ones that need to be identical so as to perform the same functions Replacement This maintains the organism e.g. red blood cells and skin cells are replaced with new ones Genetic information is checked at numerous stages during interphase to ensure that there are no errors here is an onion root cell during interphase chromatin nucleus The nuclear envelope breaks down and disappears The centriole divides into two, and moves to opposite ends of the cell to form the spindle (protein threads) here is an onion root cell during prophase sister chromatids no nuclear envelope After prophase has occured the cell then moves onto metaphase Anaphase Telophase Cytokinesis The chromosomes move towards the centre of the spindle region and align along the spindle equator. here is an onion root cell during metaphase spindle fibres sister
chromatids after metaphase the cell goes into anaphase Homologous pair of chromosomes Chromosomes which contain the same genes but different alleles
- one from the mother
- one from the father Mother Father e.g.
gene for eye colour brown eyes blue eyes