Cell Division

• The nucleus of a cell contains chromosomes. Each chromosome carries a large number of genes made of DNA molecules. In normal body cells, chromosomes are usually found in pairs. Humans have 23 pairs of chromosomes (23 from mum and 23 from dad).
• DNA is the name for the entire double helix structure that makes up the chromosomes. Genes are small sections of DNA which hold instructions for making proteins.
• DNA is what makes the characteristics of organisms and helps to control both the cell and mitosis.
• During stage 1 of the cell cycle, the cell grows bigger, DNA replicates (chromosomes duplicate) and there is an increase in the number of sub-cellular structures.
• During stage 2 of the cell cycle, mitosis occurs. A complete set of chromosomes are pulled to each end of the cell and the nucleus divides to form two nuclei.
• During stage 3 of the cell cycle, the cytoplasm and cell membrane divide to form two genetically identical daughter cells.
• Cell division occurs by mitosis and is important for the growth and repair of cells. An example of when it is used is for the replacement of skin cells.
• Stem cells are unspecialised cells which have not been differentiated.
• Adult stem cells are found in specific parts of the body in adults and children. An example of where they are found is in bone marrow.
• Embryonic stem cells are found in early human embryos and are often taken from spare embryos in fertility clinics.
• Plant stem cells are found in meristem regions in roots and shoots of the plants.
• Adult stem cells can only differentiate into certain types of cells.
• Embryonic stem cells can differentiate into any type of cell in the body.
• Plant stem cells can differentiate into any cell type and can be used to create clones of whole plants.
• Adult stem cells don't carry ethical issues as adults are able to consent. They can treat diseases such as leukaemia and are relatively safe with quick donor recovery time.
• Embryonic stem cells can treat a wide range of diseases and it may be possible to grow whole replacement organs. There is usually no donor required.
• Plant stem cells allow rare species to be cloned to prevent extinction as well as plants with desirable characteristics. They also allow fast and low cost production of a large number of plants.
• Adult stem cells require a donor leading to potentially long waiting times and can only differentiate into certain types of cells.
• Embryonic stem cells hold ethical issues as they are a potential human life. There is also a risk of transferring viral infections and it is under-researched.
• Plant stem cell clones are genetically identical meaning a whole crop could be at risk of being destroyed by a single disease or genetic defect (it reduces the gene pool).
• In therapeutic cloning, cells from a patient's own body are used to create a cloned early embryo. Stem cells can then be used for medical treatments and growing new organs. This decreases the chances of rejection as they have the same genes as the patient.