B5- Growth and developement

revision notes on Twenty First Century Science B5, hope they help.

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How does an organism produce new cells?

  • DNA has a double helix structure.
  • Division by mitosis produces two new cells, identical to one another and their parent cell.
  • In cell division (mitosis) the organelles increase, chromosomes then split into two, next protein strands come out from the side of the cell and take half of the chromosomes to each side of the cell to make two nuclei, the cell then finally splits completely in two. 
  •  Meiosis cell division produces gametes.
  • Meiosis only happens in sex cells.
  • In meiosis, the parent cell divides twice, leaving four cells in all at the end. All of these cells have 23 chromosomes in each of them.
  • One gametes has 23 chromosomes, when a sperm gametes fertilizes a egg gametes a zygote is produced, with 46 chromosomes.
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How do genes control growth and developement withi

  • The genitic code for making new proteins (DNA) is found in the nucleus but new proteins are made in the cell cytoplasm.
  • The genes do not actually leave the nucleus but instead a copy is produced to create the protein.
  • Both strands in the DNA helix are made up of the same four bases, in the same pairs. A - T, T - A, G - C, C - G.
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alex colton


nice :)

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