microscopy

• cells are studied using...

  microscopes
• microscope


  device that produces magnified images of structures that are too small to see with the unaided eye
• how do light microscopes work?

  they use light and lenses to form an image of a specimen and magnify it
• light microscope diagram

  
• light microscope maximum resolution

  0.2µm
• light microscope maximum magnification

  x2000
• light microscope advantages


  - in colour

  - cheap

  - requires no training to use

  - small and portable

  - both dead and alive specimens can be viewed
• light microscope disadvantages


  - lower magnification

  - lower resolution

  - specimen may be disfigured during preparation to be viewed
• how do electron microscopes work?

  using a beam of electrons, an image of a specimen is formed
• electron microscope maximum resolution

  1nm
• electron microscope maximum magnification

  x 50,000,000
• electron microscope advantages


  - higher magnification

  - high resolution

  - used to enhance application in industrial/technological fields
• electron microscope disadvantages


  - not in colour

  - expensive

  - requires training to use

  - large and not portable

  - only dead specimens can be viewed

  - can only be used for viewing ultra-thin specimens
• km to m


  x1000
• m to mm


  x1000
• mm to µm


  x1000
• µm to nm


  x1000
• magnification =


  Image size/actual size
• magnification formula


  M=I/A
• magnification formula triangle

  
• microscopy practical


  1. cut a thin sample of onion with the scalpel and place it on the slide

  2. add a few drops of iodine

  3. carefully place a cover slip on top, avoiding air bubbles

  4. place the slide onto the stage

  5. select the lowest-powered objective lens

  6. use the coarse adjustment (/focus?) and then fine adjustment knob to focus your image

  7. if necessary, select a higher-powered objective lens and refocus
• stains can make subcellular structures...


  easier to see
• what is used as a stain in microscopy?

  iodine
• how does iodine make it easier to see subcellular structures?

  iodine binds to starch, making a blue-black colour - this gives colour to the epidermal cells, making them more readily visible and observable. the dark colour also provides good contrast, which allows other structures in the cell to be seen more easily
• a microscope observational drawing must...

  - be drawn with a sharp pencil

  - take up at least half of the available space

  - be drawn with clear, unbroken lines

  - not include any colouring or shading

  - have subcellular structures drawn in proportion if a cell is being drawn

  - have a title of what is being drawn

  - have the magnification that it was observed under included

  - have labelled features