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neurologyYou need to know

• The cell cycle has three main stages: interphase, mitosis and cytokinesis.
• During interphase, the cell grows, increases the number of sub-cellular structures such as mitochondria and ribosomes, and replicates its DNA so there are two copies of each chromosome.
• During most of interphase, the genetic material is spread out as long, thin strands in the nucleus, so individual chromosomes are not clearly visible.
• At the start of mitosis, chromosomes condense and become visible, and each replicated chromosome is made of two identical sister chromatids joined at a centromere.
• During mitosis, chromosomes line up across the middle of the cell and the sister chromatids are pulled to opposite poles, so each new nucleus receives an identical set of chromosomes.
• During cytokinesis, the cytoplasm and cell membrane divide to form two genetically identical daughter cells.
• Mitosis is important in multicellular organisms for growth, repair of damaged tissues and replacement of worn-out cells.
• A chromosome is a long DNA molecule coiled around proteins, and genes are short sections of DNA carried on chromosomes.
• Cell differentiation is the process by which an unspecialised cell becomes specialised for a particular function.
• Most animal cells differentiate early in development and then usually lose the ability to change into other cell types.
• A stem cell is an unspecialised cell that can divide by mitosis and can differentiate into other types of cell.
• Embryonic stem cells can differentiate into almost any type of body cell, but adult animal stem cells can form only a limited range of cell types.
• In adult animals, stem cells in tissues such as bone marrow replace damaged or worn-out cells.
• Plant meristems contain stem cells that can keep dividing and can differentiate into any type of plant cell throughout the plant's life.
• Stem cells can be used in treatment to replace damaged cells, for example in some blood disorders, paralysis and diabetes.
• Risks of stem cell use include the transfer of infection, immune rejection if the cells are not genetically matched, and uncontrolled cell division that may form tumours.
• Therapeutic cloning involves removing the nucleus from an egg cell and replacing it with the nucleus from a patient's body cell to make an embryo that is genetically matched to the patient.
• Stem cells taken from a therapeutically cloned embryo are less likely to be rejected by the patient's immune system because they have the same genetic information.
• The use of embryonic stem cells is ethically controversial because obtaining them destroys embryos, although supporters argue that the potential medical benefits are very large.
• Plant clones can be produced from cuttings or by tissue culture using meristem cells, and this allows rapid production of many genetically identical plants with desirable characteristics.

• Identify the stage of the cell cycle from an image by using chromosome appearance, such as uncondensed DNA in interphase and condensed chromosomes that line up or separate during mitosis.
• Calculate the time spent in each stage of the cell cycle from data using `time in stage = (number of cells in stage / total number of cells counted) \times total cell cycle time`.
• Sequence the three stages of the cell cycle and describe the key events in each stage in the correct order.
• Compare embryonic stem cells, adult animal stem cells and plant meristem cells by stating where they are found and the range of cell types they can produce.
• Explain cell differentiation by linking an unspecialised cell to the specialised cell it becomes and the function it gains.
• Describe the steps of therapeutic cloning clearly, including nucleus removal, nucleus transfer, embryo formation and collection of stem cells.
• Evaluate the use of stem cells by weighing medical benefits against risks and ethical issues, then giving a justified conclusion.
• Describe how plant clones are produced from cuttings or tissue culture, including taking suitable plant tissue, growing it in sterile conditions and producing genetically identical plants.