Lecture 2

• Hypothesis


  Tentative explanation that can be tested by further investigation
• Scientific Theory


  A well-supported explanation of observations
• Scientific Law


  A statement that summarises the relationship between variables
• Cell Theory


  All living organisms are composed of cells

  The cell is the basic unit of life

  Cells arise by division of pre-existing cells
• Eukaryotic Cell Size


  Around 10 - 100 µm
• Prokaryotic (Bacterial) Cell Size


  Around 1 - 10 µm
• Conversion 


  1µm = 10ˆ-6 m

  1nm = 10ˆ-9 m
• Brightfield Microscopy


  Used in cell biology lab

  Simple and inexpensive

  Stains can be used

  Limit of resolution - around 0.2µm (200nm)

  
• Resolution


  Measure of clarity of the image
• Fluorescence Microscopy


  Absorption of specific light wavelengths (colours) by specimen or fluorescent dyes

  Looking at light (colour) that is shining off the cell

  
• Confocal Microscopy


  3D fluorescence microscopy

  Optical sections

  Allows us to look deep inside cells and see what is going on (even when they are alive)

  Limited by using only light

  
• Electron Microscopy


  Limit of resolution - around 2nm (0.002µm)

  Electron beam instead of visible light (shorter wavelenth)

  Lenses are electromagnets

  See cell ultrastructure

  Image based on electrons

  Can't view living cells

  Two different type:

  • Transmission Electron Microscopy
  • Scanning Electron Microscopy
• Transmission Electron Microscopy (TEM)


  Very thin section

  Can see a 2D image of inside the cell

  
• Scanning Electron Microscopy


  Surface scanning

  3D surface view is seen