B5 Growth and Development

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  • Created by: emchown
  • Created on: 09-03-15 17:19
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  • B5
    • Group of specialised cells = tissue. Group of tisses = organ.
    • Mitosis
      • Process where cell divides to prodice 2 new identical cells,
      • Cells for growth and reapir and rplace old tissues
      • Fertilisation
        • Egg id fertilised by Sperm to produce a Zygote.
          • Zygote divides to form a cluster of cells called an Embryo.
        • Up to (and including) the 8 cell stage, cells are identical and unspecialised (Embryonic Stem Cells)
          • Zygote divides to form a cluster of cells called an Embryo.
          • @ 16 cell stage, most cells begin to specialise, form different types of tissue.
        • Although genes in the cells are the same, they are subtley diff.
          • @ 16 cell stage, most cells begin to specialise, form different types of tissue.
          • Differences define what functions the cells have.
        • Some cells stay unspecialised (Adult Stem Cells). Can become specialed at later stage but cannot become any type of cell
      • Mitosis and Growth
        • Can only take place when cells are ready to divide, so cells go through a cell cycle.
        • Cell Cycle
          • 1) Growth Stage (G1) - cell gets bigger, number of organelles increase.
          • 2) Synthesis Stage (S) - where DNA is copied
          • 3) - Very short growth stage (G2)
          • 4) Mitosis phase (M)
        • Both new cells need all DNA and organelles to function properly.
          • Number of organelles needs to increase and DNA has to be copied.
            • Chromosomes are copied when two strands of each DNA molecule seperate and new strands form along side.
    • Plant Meristems
      • Similar to stem cells in animals
      • Only cells inside of Meristems can divide repeatedly (mitotically active)
      • They are found in shoots and roots (apical - higher and longer) and stems (lateral - increased girth)
      • They are unspecialled and can develop into any kind of cell. eg. xylem, Phloem and organs
        • Xylem and Phloem
          • Xylem
            • Made from specialled cells.
            • Transports water and mineral salts from roots to stem and leaves
            • Helps replace water lost during transportationand photosynthesis
          • Phloem
            • Made from specialled cells
            • Transports dissolved food made by photosynthesis for respiration or storage
      • When a stems deliberately cut, hormones can be added that send messages to meristems to start to produce roots
        • It will grow into clone of parent plant
        • Main hormone used is Auxin
          • It affects cell division @ tip of shoot.
          • Just under tip, cells grow in presence of auxins
    • Phototropism
      • A response by a plant to light
      • Plants survival depends on photosynthesis
      • Plants will grow towards light source to be able to photosynthesise
      • How it works
        • Cells furthest away from the light source grpw more due to auxin being sensitive to light
        • Its produced at the shoot tip and migrates down the shoot
        • Light source shines at an angle - auxin facing the light moves to shaded side
        • Concentration of side furthest away from light increases
        • Cells there elongate and shot bends toward the light
        • Charles Darwin
          • Experiments to show role played by plant hormones produced in shoot tip
          • If tip of shoot removed or covered, shoot grows up as if light wasnt there
          • If covered by transparent cap, it grows towards the light
          • Cylinder around stem and tip exposed - grows towards light
          • Experiment proves it is a substance produced in tip that cause cells in shoot to grow
    • Meiosis
      • Only takes place in ovaries and testes
      • Produces gametes for sexual reproduction
      • Gametes contain half the no. of chromosomes of parent cell. Fuse together - full number
      • 1) Cell with 2 pairs of chromosomes
      • 2) Each chromosome replicates itself
      • 3) Chromosomes part an dmove to opposite sides with their 'copies'
      • 4) Cell divides for first time
      • 5) Copies seperate and second cell division takes place.
      • 6) Four gametes are now produced with half no. chromosomes
    • DNA
      • It's a nucleic acid, found in the nucleus and has a double helix form.
      • Structure was found out by Watson and Crick.
      • DNA molecule has bases connected together (rungs on a ladder).
        • The bases are always in pairs, A and T, G and C.
      • The bases are always in pairs, A and T, G and C.
      • Base Pairs
        • DNA stored in and never leaves the nucleus
        • It has a sequence of genes that code for protiens.
          • Protiens are made in the cytoplasm of a cell so there's a mechanism to transfer info in genes to cytoplasm
        • Protiens are made in the cytoplasm of a cell so there's a mechanism to transfer info in genes to cytoplasm
        • DNA molecules too large to leave cell
          • Relevant section of DNA 'unzipped'
            • Instructions copied onto mRNA which can pass through the nuclear membrane
              • Instructions are carried to the ribosomes in the cytoplasm which follow instructions to make specific protiens
        • Relevant section of DNA 'unzipped'
          • Instructions copied onto mRNA which can pass through the nuclear membrane
            • Instructions are carried to the ribosomes in the cytoplasm which follow instructions to make specific protiens
        • Order of bases determines what protien is made.
      • Gene Switching
        • A gene codes for one specific protien
        • All body cells contain exactly the same genes
        • All cells produce protiens for growth and respiration
          • Certain genes (making cell membrane and ribosomes) will be switched on in all cells
            • Genes that are not needed will be switched off
        • Certain genes (making cell membrane and ribosomes) will be switched on in all cells
          • Genes that are not needed will be switched off
        • When a stem cell become specialised, genes for proteins specific to new cell type will be switched on
        • Any gene in an embryonic stem cell could be switched on
    • Ethical Decisions
      • To produce large no. of stem cells, you need to clone cells from embryos.
      • Stem cells collected when embryos made up of 150 cells.
        • Rest of the embryo destroyed
      • Rest of the embryo destroyed
      • Unused embryos from IVF used for research
      • Should embryos be classed as people? Murder?
      • Left over from IVF - never grow into human?
      • Research carried out as long as consent from parents
      • Government regulates and makes laws on these matters.
    • Mammalian Cloning
      • Dolly the Sheep first to be cloned from adult skin cells
      • Illegal to clone human in this way
        • Dolly the Sheep first to be cloned from adult skin cells
      • Take specialised cell and reactivate inactive genes - making new specialised cell type
      • Gives potential to grow new tissue that is genetically the same as patient
      • Tissue will not be rejected by immune system of patient
      • Patient doesnt have to take expensive cocktail of drugs
      • Such drugs can affect patients immune system and can stop it fighting disease

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