B5 Growth and Development

Cell specialisation in animals
1. Cells of the same type are grouped as tissues
2. Organisms begin life as a zygote and divides through mitosis
3. Embryonic stem cells will produce any cell type in the body
4. Adult stem cells can differentiate into a limited number of cell types
5. Only genes are needed to enable the cell to function, as that type of cell is switched on.
Cell specialisation in plants
1. Xylem transports water and mineral salts
2. Phloem transports the products of photosynthesis
3. Cells in regions called meristems are unspecialised
  1. When meristem cells divide into two, the new cell produced can differentiate into different cell types.
4. Unlike animal cells plants keep growing for their whole lifetime
Plant clones
1. Pieces of plants that have plant cells and are used to produce clones are called cuttings
2. Cuttings can be used to produce new plants with the same desirable features as the plant
  1. Or to produce clones that are genetically identical to the parent plant
3. Root growth in cuttings is promoted by plant hormones
4. Another method is called tissue culture- a small piece of tissue, or a few cells are placed on agar jelly containing nutrients and plant hormones. Each will grow into a small plant
5. Plant hormones called auxins are included in the agar for tissue culture and in hormone rooting powder
  1. Auxins increase cell division and cell enlargement, promoting growth of the plant tissue
Plant growth and development
1. Plant growth and development is affected by the environment
2. Plants response to light is called phototropism
  1. Plants grow towards the light, so they are positively phototropic
3. If a plant is illuminated from one side:
  1. The auxin produced in the tip is distributed towards the shaded side, the auxin produces growth on the shaded side and therefore the shoot grows towards the light.
Cell Division
1. Mitosis
  1. Mitosis is the type of cell division that takes place when an organism grows and cells divide to repair tissues
  2. results in 2 daughter cells that are genetically identical
  3. Before mitosis, the DNA in each chromosome is copied. Each chromosome is now a double chromosome with two DNA molecules
  4. During Mitosis, each double chromosome separates so that two nuclei and two cells are produced
2. Meiosis
  1. Meiosis is the type of cell division used to produce gametes
  2. In humans, gametes contain half the number of chromosomes (23) as body cells (which contain 46 or 23 pairs)
  3. Produces 4 daughter cells with half the number of chromosomes
Chromosomes, genes and DNA
1. Chromosomes are made from a DNA molecule
2. DNA molecule is a double helix
3. There are four bases -A and T, G and C.
4. The order of the bases in a gene makes up the genetic code. This is the code that gives instructions for the assembly of a protein (the amino acids that are in the protein and the order in which they're arranged.
Protein synthesis
1. Protein synthesis occurs in the cytoplasm
2. Genes do not leave the nucleus, so in order to carry the genetic code to the cytoplasm, mRNA is produced in the nucleus, using DNA as the template.
3. Proteins are assembled on organelles in the cytoplasm called ribosomes
4. The number and sequence of amino acids determines the type of protein and its properties
  1. The sequence of amino acids in the protein is determined by the genetic code
  2. The bases work in threes to code for amino acids

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B5 Growth and Development

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