B5

1. double helix
   1. pair of bases
2. DNA
   1. controls the production of proteins
      1. gene

         Annotations:

         • is a section of DNA
         1. contains

            Annotations:

            • the code for making one protein it's the order of the bases in a gene that tells the cell how to make protein
      2. proteins are made in the cytoplasm
      3. DNA

         Annotations:

         • a copy of the DNA is made to get the information from the DNA to the cytoplasm

1. cells

   Annotations:

   • new cells are need for grow and repair
2. cells grow in size and copy its content
   1. it has to copy all it contains

      Annotations:

      • this is so that when it splits in half the two new cells will contain the right amount of materials the number of organelles (cell parts) increase during cell growth the chromosomes are copied so that the cell has two copies of its DNA  
      1. mitosis

         Annotations:

         • the chromosomes line up at the centre of the cell there pulled apart to opposite ends of the cell membrane form around each of the sets of chromosomes these become nuclei of the two new cells them the cytoplasm divides you now have two new cells with  exactly the same DNA they're genetically identical to each other and to the parent original cell  
         1. meiosis

            Annotations:

            • gametes are produced by meiosis all the cells in your body divide by mitosis except cells in your reproductive organs they divide by meiosis to form sperm or egg cells gametes
            1. gametes

               Annotations:

               • have half the usual number of chromosomes all human body cells have two copies of each chromosomes but gametes only have one copy of each chromosome so when the sperm and egg combine the zygote will contain two copies of each chromosome - one set from each parent  

1. embryo cells

   Annotations:

   • cells in an early embryo  can turn into any type of cell a zygote divides by mitosis to produce an embryo at the start they are all embryonic stem cells these can divide to produce any other cell all cells in the embryo are unspecialised up to the 8 cell stage after this most the cells start to specialise the embryo then develops tissue and organs tissue are groups of specialised cells organs are groups of specialised tissues adult humans only have stem cells in certain places like the bone marrow adult stem cells only turn into certain types of stem cells.

Annotations:

• meristems is where mitosis happens in plants meristem tissue are found in the roots and the shoots these produced unspecialised cells