AS LEVEL- Biology- Basic components of living systems (Microscopes 1)

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  • Basic components of living systems (Microscopes 1)
    • Magnifiication- The number of times larger an image is compared to the actual size  of the image
      • Magnification = Image size/Actual size
    • Resolution- How well a microscope  distinguishes  between two points that are close together
    • Light  microscope
      • Has a lower resolution than electron microscopes so they are used to look at whole cells or tissues
      • Colour of specimen = Depends on stain
      • Magnification = Up to x2000
      • Size = Small
      • Sample preparation =  Simple
      • Cost = Cheap
      • Dead or Alive? Alive
      • Resolution = 200nm
      • Vacuum? No
      • Eyepiece Graticule-  *Has a scale on it  *Used to estimate the size of a specimen when viewed with a microscope.
      • Stage micrometer- *Glass slide with a scale on it *Used to calibrate the eyepiece graticule of a microscope
    • Microscopes are used to observe and investigate different types of cells + cell structrure in a range of eukaryotic organisms
    • Staining
      • *Increases contrast *Helps to differentiatebetween the different organelles
      • Iodine- *Used on plant cells *Interacts with starch
      • Negative Staining- *Repelled by the negatively charged cell components in the cytoplasm *Doesn't enter the cell leaving the cell unstained *Useful to see the number of cells *Won't be able to see organelles
      • Methylene Blue- *Used on animal cells *Positively charged stain so it's attracted to the negatively charged cell components in nucleus + cytoplasm
      • Differential staining- When multiple stains are used
        • *Makes different things show up *Different organelles/ cells/ organisms absorb different quanities of stain so they appear different
        • Gram Stain Technique- *Used to identigy whether bacteria are gram positive (thick cell wall) or gram nagative (thin cell wall) *Thick = purple *Thin = pink
        • Acid-Fast Technique- *Used to differentiatespecies of Mycobacterium from other bacteria *2 stains- carbol fuchsin + mythylene blue *Cells are washed with an acid- alcohol solution *Other bacteria are affected so they turn colourless


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