B5 - Growth and Development

B5 - Growth and Development

1. DNA

   • DNA molecule has two strands coiled together in the shape of a double helix
   • DNA has four different bases which pair up as A-T and C-G
   • Making Proteins
     • DNA is found in the cell nucleus but it cant move out of the cell nucleus so a molecule of mRNA copies the DNA using the base pair rule. The molecule of mRNA moves out of the nucleus and joins with the ribosome in the cytoplasm. The job of the ribosome is to stick amino acids together in a chain to make a protein
       • Proteins are made by joining amino acids together in a particular order this order is determined by the order of bases in a gene that tells the cell what order to put the amino acids together. Each set of three bases is a code for one amino acid

2. Mitosis

   • in Mitosis two new cells are produced containing the same DNA they are genetically identical to each other and the parent cell
   • DNA replicates
     • DNA splits in half then bases pair up with the matching bases on the DNA this forms two DNA molecule identical to the original one
   • Stages in Mitosis
     • Chromosomes in the nucleus are copied
       • Chromosomes are pulled apart and move toward opposite ends
         • Chromosomes sepaerate
           • The cell divides producing two identical cells

3. Meiosis

   • Meiosis produces Gametes (sperm and eggs) which have half the normal number of chromosomes
   • Stages in Meiosis
     • The DNA replicates chromosomes make identical copies of each other
       • Similar chromosomes pair up and are then pulled apart so each cell has one copy of each chromosome
         • The chromosomes line up in the center of the cell and divide again
           • This produces four non identical gametes each with only a single set of chromosomes

4. Animal Development

   • Gene switching
     • All body cells in an organism contain the same genes, many genes in a particular cell may be 'switched off' (be made inactive) as the cell only produces the specific proteins it requires.
     • Stem cells are unspecialsed cells all of the genes in theses cells are switched on and can produce any type of specialised cell
   • Adult Stem cells
     • Adult stem cells are in certain places of the body like bone marrow they can only produce certain types of cells
     • Adult stem cells are used to cure some diseases like blood diseases
   • Embronic Stem cells
     • Embronic stem cells are unspecialsed cells in human embryos up to the 8 cell stage they can become any type of specialised cell
     • Embryonic stem cells can be made to differentiate into specific cells to replace faulty cell eg heart mucel cells for people with heart disease
   • Cloning
     • Cloning can be used to make stem cells
     • A nucleus from a body cell of the adult cell you are cloning is inserted into an empty egg cell the cell is then stimulated so that it forms a embryo. Embryonic stem cells can be extracted from the embryo and used to make any type of specialised cell

5. Plant Development

   • Meristems
     • Meristems are plant stem cells they are found in the areas of the plant that is growing like the shoots and roots
     • Meristems can produce any type of plant cell these cells can divide to generate any type of cell for as long as the plant lives. They do this so that if the plant is damaged it can form new tissue to form new organs
   • Cloning plants
     • Cuttings can be taken from an area of the plant that growing meristems cell which can differentiate into making any cell this means it can make a new plant which becomes a clone of the parent plant
     • Gardeners take cuttings form plants with desirable characteristics so they can have identical copies of the parent plant
     • Rooting powder is used to help make the cutting grow as it contains plant hormones that produce roots rapidly so the plant can start growing quikcly

6. Photorophism

   • Photorophism is a growth respons to the stmulus of light
   • Shoots are positively phototropic they grow towards the light. Plants need light for photosynthsis
   • Roots are negatively phtotropic they grow away form the light they do this so they can absorb water and nutrients from the soil
   • Auxins
     • Auxins are plant growth hormones that are contained at the tip of the shoot of the plant
     • Auxins diffuses down the stem and accumulate on the shaded side of the plant this makes the cells grow farster on the shaded side of the plant so the shoot bends towards the light