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Biology - Year 9 - Term 1/2 (Cell Division (New cells are needed for the…

- - - - Each cell in your body contains 23 pairs of chromosomes. 46 in total).
      - Chromosomes carry the genes which contain instructions which form the tissues and organs that make you you
      - A gene is a small bit of information that controls a characteristic, or a part of a characteristic. It is a part of DNA that is unique molecule that makes up your chromosome.
      - Most characteristics are made up of lots of different genes rather than a single gene.
      - Chromosomes can carry hundreds and thousands of genes on it grouped together.
      - In every pair of chromosomes half is made up of your father's DNA and the other half is your mother's.
      - In sex cells (gametes) there are only 23 chromosomes because there is only one in a pair of chromosomes.
    - - Body cells divide in a process called the Cell Cycle.
      - Cell division includes a process called Mitosis when identical cells are produced.
      - All normal body cells have the same genetic information.
      - Cell division by mitosis produces additional cells for growth and development in multi-cellular organisms, and for the replacement of worn out or damaged cell.
      - In asexual reproduction, the cells of the offspring are produced by mitosis from the cell of their parents. This is why they contain a few or no different genes.
    - - The length of the cycle varies.
      - This process can take 24 hours or years. It depends on the cells and the stage of life the organism is at.
      - The cell cycle begins short when the baby is being developed. It is fairly rapid during childhood however it slows down after puberty.
      - Even when your an adult there are still regions where there is continued growth and replacement of cells. They include: the skin, the blood and the lining of the digestive.
      - The Cell Cycle Stages
        
        Stage 2: Mitosis
        
        In this process one set of chromosomes is pulled to each end of the dividing cell and the nucleus divides.
        
        Stage 3
        
        During this stage the cytoplasm and cell membrane also divide leaving two identical daughter cells.
        
        Stage 1
        
        The longest stage.
        
        The cells grow bigger, increase their mass and carry out normal activities.
        
        They replicate their DNA to form two copies of each chromosome to prepare for cell division.
        
        Increase the number of sub-cellular structures such as mitochondria, ribosomes and chloroplasts ready for the cell to divide.
      - In some parts of the animal or plant mitotic cell division carries on rapidly all the time. e.g you constantly lose skin cells from your skin's surface and make new cells to replace them.
      - 300 million of your body cells die every minute. Cell division by mitosis is very important.
      - In a child, mitotic cell division happens more quickly than the cells die. As an adult they are roughly balanced. But when you get older they reverse and the cells die more quickly than the new cells are produced. That is when you show typical signs of ageing.