preparing biological samples for examination

• Cell


  The basic unit of life, which makes up all organisms
• Cells


  • Most organisms are multicellular and have cells that are specialised to do a particular job
  • Microscopes are needed to study cells in detail
• Monomers


  Smaller units from which larger molecules are made
• Polymers


  Molecules made from a large number of monomers joined together in a chain
• Micrometre (μm)


  The best unit to measure most cells
• Nanometre (nm)


  A smaller unit used to measure sub-cellular structures and organisms like viruses
• One metre can be broken down into millimetres, micrometres, and nanometres
• Standard form


  A system in which numbers are written as a number greater than 1 and less than 10 multiplied by a power of 10 which may be positive or negative
• Standard form numbers are written as: A × 10^n, where A is a number greater than one but less than 10, and n is the index or power, always in powers of 10
• Using standard form for large numbers

  • A population of 120,000,000 microorganisms could be written as 1.2 × 10^8
• Using standard form for small numbers

  • A red blood cell's diameter of 7 μm or 0.000007 m could be written as 7 × 10^-6 m
• Calculating the magnification of a cell


  1. Magnification = Measurement of cell in image / Actual size of cell

  2. Example: Magnification = 100 mm / 0.05 mm = 2000
• Sizes of most cells are given in micrometres (μm)
• Organisms are made up of cells
• Most organisms are multicellular and have cells that are specialised to do a particular job
• Microscopes are needed to study cells in detail
• Preparing biological samples for examination

  1. Place a small square or circle of thin glass called a coverslip over the specimen

  2. Use a mounted needle to hold the specimen in place as the coverslip is lowered

  3. Ensure no air bubbles are trapped underneath
• Most cells are colourless
• Stains


  Used to add contrast and stain specific cell structures or cell products
• Care must be taken when looking down the microscope if the illumination is too bright
• Care must be taken when using microscope stains
• Care must be taken when handling coverslips, microscope slides and mounted needles