2.6

• The role of mitosis and the cell cycle is to produce identical daughter cells for growth and asexual reproduction of cells.
• All the cells produced by mitosis are genetically identical, therefore mitosis does not give rise to genetic variation.
• During the cell cycle, a cell grows and then divides to form daughter cells.
• The cell cycle is controlled by checkpoints.
• Mitosis is a form of cell division that produces identical cells, with four stages: prophase, metaphase, anaphase and telophase.
• Cytokinesis is the process where the parent and replicated organelles move to opposite sides of the cell and the cytoplasm divides, producing two daughter cells.
• Interphase is the stage where the cell grows and prepares to divide, chromosomes and some organelles are replicated, and chromosomes begin to condense.
• During prophase, the nuclear envelope breaks down and subsequently disappears.
• During prophase, the chromosomes condense and the centrioles move to opposite poles of the cell for the purpose of spindle formation.
• During metaphase, the chromosomes move to the equator and attach to the spindle fibres via centromeres.
• In the anaphase stage, the sister chromatids are separated.
• During telophase, the nuclear envelope reforms around haploid nuclei containing half the number of chromosomes.
• Meiosis is a form of cell division that gives rise to genetic variation, with two phases: meiosis I and meiosis II.
• The main role of meiosis is production of haploid gametes, as cells produced by meiosis have half the number of chromosomes.
• Meiosis produces genetically different cells, genetic variation is achieved through crossing over of chromatids and independent assortment of chromosomes.
• Meiosis I consists of prophase I, metaphase I, anaphase I and telophase I, with prophase I closely resembling the prophase stage of mitosis, and metaphase I being when each pair of bivalents align at the equator.
• During anaphase I, the homologous chromosomes separate, and during telophase I the nuclear envelope reforms around haploid nuclei containing half the number of chromosomes.
• Meiosis II consists of prophase II, metaphase II, anaphase II and telophase II, with prophase II being a continuation of prophase I, metaphase II being when each pair of bivalents align at the equator, and anaphase II being when the centromeres split separating chromatids.
• Cells group together to form tissues with the purpose of performing a common function.
• Examples of tissues include xylem and phloem tissues in plants.
• Organs are groups of tissues which work together to perform a wider function, and an organ system is composed of many organs which work together to perform an essential life function.
• Xylem transports water and minerals as well as providing structural support.
• Xylem vessels are long cylinders made of dead tissue with open ends.
• Xylem vessels are thickened with a tough substance called lignin.
• Xylem vessels consist of parenchyma, fibres and vessels and are produced by meristem cells which produce smaller cells that elongate.
• Phloem tubes are made of living cells which are involved in translocation, the movement of food substances and nutrients from leaves to storage organs and growing plants of the plant.
• The meristem tissue produces cells that elongate and line up end-to-end to form a long tube.
• The ends of phloem tubes do not break down completely but produce perforated structures known as sieve plates.
• Metabolically active companion cells are located next to sieve plates and are involved in mediating the movement of photosynthesis products upwards and downwards in the tubes.
• Epithelial tissue is a sheet of cells that serves as a lining/cover a surface.
• There are two types of epithelial tissue, squamous which are smooth, flat and very thin, fitting closely together to create a smooth surface, such as the lining of blood vessels and cheeks, and ciliated epithelium which is composed of column shaped cells containing cilia which form the lining of structures such as trachea and bronchi.
• Ciliated epithelium is also found in the oviducts.
• Connective tissue is involved in providing support and holding various structures together, examples include cartilage and bone.
• Muscle tissue is specialised for movement through contraction.
• Nervous tissue is specialised for impulse conduction.
• Stem cells are undifferentiated cells which are genetically identical and have the ability to develop into any of the various kinds of cells.
• Stem cells have various uses in research and medicine, for instance repair of damaged tissues, treatment of neurological disorders such as Parkinson’s and Alzheimer’s as well as studying development.
• The process by which a cell specialised to carry out a particular function is known as differentiation.
• Stem cells can be found in the bone marrow where they differentiate into erythrocytes (red blood cells) and neutrophils (white blood cells).
• The role of erythrocytes is transporting oxygen in the blood.