Growth and Development - B5 21st Science OCR


  • Plant Development
  • Animal Development
  • DNA
  • Mitosis and Meiosis
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  • Created by: Tulsi P
  • Created on: 17-02-14 18:07
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Science Notes
Biology B5
DNA ­ Making proteins
A DNA molecule has two strands spiralled together(double helix)
Each strand of DNA is made up of small units of Nucleotides
Nucleotides are made up of small molecules which are called a base.
It has four different bases A T G C
The two strands are held together by the pair of bases they line up in A-T , C-G this is called
base pairing
Production of Protein
The instructions for a protein can be found in the gene , which is part of the DNA
Proteins are made by the joining of amino acids , which are kept in a particular order
The bases in the gene , gives instructions to the cell , in which order they should be kept in
There are 3 bases(triplet) codes for one amino acid
Proteins are made in the cytoplasm by Ribosomes (organelles) and the DNA is found in the
To get a copy to the Ribosomes , a copy must be made of the DNA , using Messenger RNA (A
Messenger RNA
The DNA strands untangle as a template
The Messenger RNA leaves the nucleus , as the DNA cannot leave because it is too
big and it goes into the cytoplasm to join the ribosome
The ribosome has to work to stick the amino acids together in a chain in order to
make a protein , which include bases and the order of which the amino acids should
be put it through Messenger RNA
Mitosis is used for the type of cell division that makes animals and plants grow
It is the way cells that are damaged or old get replaced
First Stage
The cell has to grow and duplicate the content
It splits everything in half , so the new two cells will contain the same information and
The number of organelles increases when the cell is growing
The chromosomes are copied so that the cell has two copies of the DNA
Second Stage
The two copies of its DNA are spread out in long strings

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The DNA forms X-Shaped chromosomes , both arms of the chromosome left and right
are the exact duplicate of another
The chromosomes are then lined up at the centre of the cell and cell fibres pull them
apart.…read more

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The way stem cells become specialised is called differentiation. After the 8th cell stage the
stem cells in the embryo start to differentiate. The embryo then begins to produce organs (
A group of tissue) and tissues ( group of specialised cells).…read more

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These tissues can then form together to form organs like the leaves , roots , stem and the
Clones Of Plant
A cutting from the plant is taken
The cutting will contain unspecialised cells which can differentiate to make any cell
From the cutting a whole identical parent plant can grow
Farmers take cuttings from plants with desirable characteristics to make clones.…read more


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