B2 Cell Division

• You have 46 chromosomes in the nucleus of your body cells. This is 23 pairs. In each pair of chromosomes, one is inherited from your mother and one from your father. As such, sex cells (gametes) only have one chromosome from each pair so only have 23 chromosomes in total. 
• Cells divide when an organism grows and/ or an organism becomes damaged and needs to produce new cells. 
• Stage 1: the longest stage in the cell cycle. The cells grow bigger and increase their mass. The DNA then replicates to form 2 copies of each chromosome. (prophase)  the amount of sub cellular structures is also increased.
• Stage 2: one set of chromosomes is pulled to each end of the cell and the nucleus then divides. 
• Stage 3: the cytoplasm also divides to form 2 new daughter cells 
• cell growth > DNA replication > chromosomes line up in the centre > one set of chromosomes pulled to each end the the cell > nucleus divides > cytoplasm also divides
• the cell cycle is relatively short for a baby, because you are undeveloped. as you become an adult, after puberty, the cell cycle slows down
• every cell has a nucleus, every nucleus contains chromosomes. chromosomes carry genes. genes are packets of information that control a characteristic. a chromosome can carry several hundred genes.
• the cell cycle is a series of stages where cells grow and divide to form new cells, this process involves mitosis.
• as cells divide, grow and develop, they also begin to differentiate. differentiation is the process when a stem cell becomes specialised. a stem cell is an undifferentiated cell.
• in early development of plant and animal cells, they are unspecialised. these are stem cells that can become any type of cell.
• most specialised cells can divide by mitosis. muscle cells divide to produce more muscle cells, red blood cells and skin cells cannot divide so adult stem cells must replace them.
• unlike animal cells, plant cells can differentiate al throughout their life. plants can differentiate into one cell then re-differentiate into another kind. undifferentiated cells are found at the meristems of the plant.
• cloning is the process of producing identical offspring
• egg and sperm cells fuse to form a zygote. zygotes will then divide and become a hollow ball of cells, this is the embryo. the inner cells of this ball are called embryonic stem cells. these can differentiate into any different cells of the body
• even when you are an adult, some of your stem cells still remain. these are called adult stem cells.
• the stem cells from plant meristems can be used to make clones of the mature parent plant, this can be used in research to make a large amount of identical plants. as well as for general use to make large amounts of rare plants reliably.
• embryonic stem cells can be used for research and medicinal uses. these cells come from aborted embryos. some people view this as a violation of human rights as well as running the risk that the adult stem cells may be infected with a virus.
• stem cell research is being used to treat spinal cord injuries, blind people (eyesight), diabetes, heart issues and damaged bone and cartilidge.