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neurologyYou need to know

• A chromosome is a long molecule of DNA wound around proteins and it carries many genes.
• Body cells usually contain chromosomes in pairs, with one chromosome in each pair inherited from each parent.
• Before a cell divides, each chromosome is copied to form two identical sister chromatids joined at a centromere.
• During interphase, chromosomes are not usually visible as separate structures because the DNA is long, thin and spread out in the nucleus.
• During mitosis, chromosomes become shorter and thicker, line up in the middle of the cell, and the sister chromatids are pulled to opposite ends of the cell.
• The cell cycle has three main stages: cell growth and DNA replication, mitosis, and division of the cytoplasm to form two cells.
• Mitosis produces two genetically identical daughter cells with the same number of chromosomes as the parent cell.
• Mitosis is important in multicellular organisms for growth, repair of damaged tissues, replacement of worn-out cells and asexual reproduction.
• Cell differentiation is the process by which a cell becomes specialised by developing structures needed for a particular function.
• Most animal cells differentiate at an early stage of development, but many plant cells can differentiate throughout the life of the plant.
• A stem cell is an undifferentiated cell that can divide to produce more cells and can differentiate into specialised cells.
• Embryonic stem cells can differentiate into almost any type of body cell, whereas adult stem cells can usually differentiate into only a limited range of related cell types.
• Adult stem cells help to repair and replace damaged cells in some tissues, such as stem cells in bone marrow producing different types of blood cell.
• Plant stem cells are found in meristems, where they divide and can differentiate into many different types of plant cell throughout the plant’s life.
• Stem cells may be used in medicine to replace damaged cells and treat conditions such as blood disorders, diabetes or spinal cord injuries.
• Risks of stem cell treatments include tumour formation, transmission of infections and rejection of transplanted cells by the immune system.
• Therapeutic cloning produces an embryo with the same genes as the patient, so stem cells from it are less likely to be rejected after transplantation.
• The use of embryonic stem cells is controversial because it involves creating and destroying embryos, while supporters argue it could reduce suffering by treating serious diseases.
• Plant clones can be produced from cuttings or by tissue culture using small groups of cells from a parent plant.
• Cloning plants can produce large numbers of genetically identical plants quickly, preserve desirable characteristics and help protect rare plant species.

• Describe the stages of the cell cycle in order, including cell growth, DNA replication, mitosis and division of the cytoplasm.
• Explain chromosome behaviour during mitosis by linking copying, lining up, separation of sister chromatids and formation of two identical nuclei.
• Calculate the time spent in a stage of the cell cycle using the proportion of cells in that stage, for example `time in stage = (number of cells in stage ÷ total cells counted) × total cell cycle time`.
• Compare embryonic, adult and plant meristem stem cells by stating how widely each type can differentiate and where each is found.
• Evaluate stem cell treatments by balancing potential medical benefits against risks such as tumours, infection, immune rejection and ethical concerns.
• Describe therapeutic cloning as a sequence of steps involving a patient’s genetic material, embryo formation and harvesting compatible stem cells.
• Describe how to produce plant clones by taking cuttings or using tissue culture, including that the new plants are genetically identical to the parent plant.