Science B5

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Science B5
2015-02-20 08:01:49
Science B5
Science B5
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  1. cells in multicellular organisms
    can be specialised to do particular jobs
  2. groups of specialised cells are called
  3. groups of tissues form
  4. a fertilised egg cell (zygote) divides by
    mitosis to form an embryo
  5. in a human embryo up to (and including) the eight cell stage
    all the cells are identical (embryonic stem cells) and could produce any type of cell required by the organism
  6. up to the 8 cell stage the cells are
  7. after the eight cell stage most of the embryo cells become
    specialised and form different types of tissue
  8. some cells (adult stem cells)
    remain unspecialised and can become specialised at a later stage to become many but not all types of cells required by the organism
  9. in plants only cells within special regions called meristems are
    mitotically active
  10. mitotically active means
    the act of mitosis
  11. mitosis
    cell division in all cells except sex cells
  12. new cells produced from plant meristems are
    unspecialised and can develop into any kind of plant cell
  13. unspecialised plant cells can become specialised to form
    different types of tissue (including xylem and phloem) within organs (including flowers- leaves- stems and roots)
  14. the presence of meristems (as sources of unspecialised cells)
    allows the production of clones of a plant from cuttings
  15. cloning may be done to reproduce a plant with
    desirable features
  16. a cut stem from a plant can
    develop roots and then grow into a complete plant which is a clone of the parent
  17. rooting can be promoted by
    the presence of plant hormones (auxins)
  18. the growth and development of plants is also affected by
    the environment (e.g. phototropism)
  19. Phototropism
    is the growth of organisms in response to light
  20. Auxins
    plant hormones that make some parts of a plant stem grow faster than others
  21. light destroys the auxin so
    growth near the light source slows down
  22. On the shaded side of the plant there is
    more auxin so growth on this side speeds up
  23. The result of phototropism is that
    the shoots and leaves are turned towards the light for photosynthesis
  24. Auxin is produced
    in the tip of growing shoots
  25. If the tips of plant shoots are removed
    they cannot produce auxin so phototropism cannot occur
  26. If the tips are covered
    light cannot break down the auxin so phototropism cannot then occur either
  27. cell division by mitosis produces
    two new cells that are genetically identical to each other and to the parent cell
  28. step 1 of cell growth
    numbers of organelles increase
  29. step 2 of cell growth
    the chromosomes are copied when the two strands of each DNA molecule separate and new strands form alongside them
  30. step 3- mitosis
    copies of the chromosomes separate
  31. step 4- mitosis
    the nucleus divides
  32. meiosis
    type of cell division that produces gametes
  33. gametes are
    sex cells (ovum and sperm)
  34. body cells have
    46 chromosomes
  35. gametes have
    23 chromosomes
  36. A fertilised egg cell has
    46 chromosomes (26 from sperm and 26 from ovum)
  37. Structure of DNA
    double helix
  38. both strands of the DNA molecule are made up of
    four different bases which always pair up in the same way
  39. A pairs with
  40. C pairs with
  41. A
  42. C
  43. T
  44. G
  45. the order of bases in a gene is the genetic code for
    the production of a protein
  46. every three bases codes for an
    amino acid
  47. an amino acid is the
    building block for a protein
  48. genetic code is in the
    cell nucleus of animal and plant cells
  49. proteins are produced in
    the cell cytoplasm
  50. genes do not leave the nucleus but a copy of the gene (messenger RNA)
    is produced to carry the genetic code to the cytoplasm
  51. although all body cells in an organism contain the same genes many genes in a particular cell are not active (switched off) because
    the cell only produces the specific proteins it needs
  52. in specialised cells only the genes
    needed for the cell can be switched on
  53. in embryonic stem cells
    any gene can be switched on during development to produce any type of specialised cell
  54. adult stem cells and embryonic stem cells have the potential to
    produce cells needed to replace damaged tissues
  55. ethical decisions need to be taken when using embryonic stem cells and
    this work is subject to Government regulation
  56. in carefully controlled conditions of mammalian cloning
    it is possible to reactivate (switch on) inactive genes in the nucleus of a body cell to form cells of all tissue types