Biology

• Disappears in metaphase and reforms in telophase.
• Mitosis is the process by which the nucleus divides into two daughter nuclei each with the same number of chromosomes as the parent nucleus, maintaining genetic stability.
• The nuclei formed in mitosis are genetically identical to the parent one, maintaining genetic stability.
• Cells do not divide continuously, but undergo a regular cycle of division separated by periods of cell growth, known as the cell cycle.
• The cell cycle consists of three stages: Interphase, Mitosis, and Cytokinesis.
• Interphase occupies about 95% of the cell cycle and is a period of intense chemical activity divided into three parts: First growth (G1) phase, when the proteins from which cell organelles are synthesised are produced; Synthesis (S) phase, when DNA is replicated; Second growth (G2) phase, when organelles grow and divide and energy stores are increased.
• Mitosis is the stage in the cell cycle when the nucleus divides into two.
• Cytokinesis is the stage in the cell cycle when the cytoplasm of the cell divides into two.
• The rate of cell division is controlled by proto-oncogenes that stimulate cell division and tumour suppressor genes that slow cell division.
• The longest phase in the cell cycle of human liver cells is interphase.
• Mitosis is the basis for the production of new individuals of a species by only one parent.
• During mitosis, a cell divides into two daughter cells, both of which are genetically identical.
• Chromatids break apart at the centromere and are pulled away by microtubules towards the poles during mitosis.
• In animal cells, cytokinesis after mitosis is achieved by the growth of the cell plate at the equator from the centre outwards.
• Animal cells undergoing mitosis have a centriole, but plant cells undergoing mitosis do not.
• In root tip cells, cell plate formation occurs during anaphase.
• The stages of mitosis are: prophase, metaphase, anaphase, telophase, and cytoplasmic cleavage.
• Mitosis does not allow for the growth of multicellular organisms from unicellular zygotes.
• Mitosis is used to replace identical cells and repair tissues in both plants and animals.
• If a proto-oncogene becomes mutated it is called an oncogene and it stimulates cells to divide uncontrollably.
• Mitosis ensures the independent assortment of homologous chromosomes.
• During mitosis, the nucleolus disappears in prophase and reforms in anaphase.
• If a tumour suppressor gene mutates it becomes inactive, allowing the rate of cell division to increase.
• Cells that start to divide uncontrollably are often removed by the immune system; if not they may grow into tumours such as benign and malignant cancers.
• The genetic information (DNA) of cells is packaged into chromosomes.
• When chromosomes are visible, they appear as long, thin threads around 50μm long, made up of two strands called chromatids, joined at a point called the centromere.
• The centromere is a constricted region of the chromosome containing a specific DNA sequence, to which is bound two discs of protein called kinetochores.
• Centrioles organise the formation of the spindle in animal cells.
• Centrioles are found only in animal cells and a pair of centrioles are found within a centrosome.
• Chromosome numbers vary across species, with some protozoa having 300 chromosomes.
• In animal cells, cytokinesis involves the formation of a
• In animal cells, centrioles organise the formation of the spindle.
• In plant cells, there is no cleavage furrow, instead vesicles derived from the Golgi apparatus move to the middle of the cell where they join together to form a cell plate.
• Metaphase chromosome, Kinetochore, microtubules, Centromere, region of chromosome, Sister Chromatids, pronunciation, Kinetochore (Key - neto - chore)
• In plant cells, there are no centrioles, hence no centrioles organise the formation of the spindle.
• Kinetochores serve as points of attachment for microtubules that move the chromosomes during cell division.
• In animal cells, cytokinesis involves the formation of a cleavage furrow which pinches the cell in two.
• The cell plate enlarges until its surrounding membrane fuses with the plasma membrane along the perimeter of the cell thus forming two daughter cells.