Curriculum Portal

neurologyYou need to know

• Mitosis is important in multicellular organisms because it produces genetically identical cells for growth, repair of damaged tissues and replacement of worn-out cells.
• A chromosome is a long molecule of DNA coiled around proteins, and before mitosis each chromosome is copied so it consists of two identical chromatids joined at a centromere.
• Genes are short sections of DNA on chromosomes that carry the instructions for making proteins and so influence inherited characteristics.
• In the first stage of the cell cycle, a cell grows, increases the number of sub-cellular structures such as ribosomes and mitochondria, and replicates its DNA.
• In mitosis, one set of chromosomes is pulled to each end of the cell nucleus so that the nucleus divides and both new nuclei contain identical genetic information.
• In the final stage of the cell cycle, the cytoplasm and cell membrane divide to form two genetically identical daughter cells.
• A stem cell is an undifferentiated cell that can divide by mitosis and can differentiate into specialised cell types.
• Embryonic stem cells in animals can differentiate into most types of body cell, whereas most adult body cells are already specialised and cannot change into other cell types.
• Adult animal stem cells are found in some tissues such as bone marrow and can differentiate into a limited range of specialised cells.
• Plant stem cells are found in meristems and can differentiate into any type of plant cell throughout the life of the plant.
• In embryos, stem cells enable rapid growth and development because they produce many different specialised cells.
• In adult animals, stem cells replace damaged or worn-out cells, for example by making new blood cells in the bone marrow.
• In plants, meristem cells allow growth at the roots and shoots and can be used to produce clones of a plant.
• Stem cells can be used in treatment to replace damaged cells or tissues, for example in bone marrow transplants, and they may help treat conditions such as paralysis or type 1 diabetes.
• Risks of using stem cells include the transfer of infection, possible immune rejection if the cells are not genetically matched, and uncontrolled cell division that could form tumours.
• Therapeutic cloning involves placing the nucleus from a patient's body cell into an egg cell whose nucleus has been removed, then stimulating the egg cell to divide so that embryonic stem cells genetically matched to the patient can be collected.
• A major advantage of therapeutic cloning is that the stem cells are genetically identical to the patient, so the risk of immune rejection is low.
• Some people object to the use of embryonic stem cells because embryos are destroyed, so the use of stem cells involves ethical as well as medical issues.
• Plant clones can be produced from cuttings or by tissue culture, where small groups of cells from meristems are grown on sterile nutrient media with plant hormones.
• Cloning plants can rapidly produce large numbers of genetically identical plants with desired characteristics and can help conserve rare species.

• Explain the importance of mitosis by linking it clearly to growth, tissue repair and cell replacement in multicellular organisms.
• Label or describe a chromosome diagram, including DNA, two identical chromatids and the centromere when the chromosome has been copied.
• Sequence the stages of the cell cycle from a diagram or description, stating what happens to cell growth, DNA and cell division at each stage.
• Compare embryonic, adult animal and plant stem cells by stating where they are found and the range of cell types they can form.
• Describe the role of stem cells in embryos, adult animals and plant meristems using specific examples such as bone marrow and root or shoot tips.
• Explain therapeutic cloning in the correct order, including removal of the egg nucleus, insertion of a patient nucleus, cell division and collection of matching stem cells.
• Evaluate the use of stem cells by weighing medical benefits against risks and ethical concerns, then giving a justified conclusion.
• Describe how plant clones are produced from cuttings or tissue culture, including the use of meristem cells and sterile nutrient conditions.
• Justify advantages of plant cloning with relevant examples, such as rapid mass production of crops or conservation of rare plants.