microscopy and cell structure

• drawing diagrams rules

  -clear, single lines

  -no shading or colour

  -title

  -scale included

  -cells or tissues in correct proportions

  -label lines in pencil
• magnification


  the degree to which the size of an image is larger than the object itself
• resolution


  the degree to which it is possible to distinguish between two close objects as being separate. The higher the resolution, the greater the detail you can see
• animal cells are between 10-50μm (0.01 mm – 0.05 mm)
• plant cells are between 10-100μm (0.01 mm – 0.10 mm)
• bacterial cells are around 1 μm (0.001 mm)
• The nucleus is around 10 μm in diameter
• Mitochondria are 5-7 μm long
• Diameter of a ribosome – 18-22nm
• If the object is smaller than half the wavelength of radiation used to view it, the object cannot be see
• light microscopes

  -use lenses to focus rays of light to produce a clear image

  -different objective lenses give different levels of magnification

  -specimens must be cut very thinly

  -specimens must be stained to provide contrast
• electron microscopes

  -A beam of electrons is used to create the image, which overcomes the problem of poor resolution using light microscopes

  -When electrons are free from their nucleus they are very energetic and have a very short wavelength so EM are capable of much higher magnifications and better resolution than light microscopes

  -very large and expensive and need special training to use
• Transmission Electron Microscope


  -a beam of light is used to focus on the specimen

  -electrons pass through thinly cut specimen to produce a 2d image

  -magnification- 500,000 x

  -resolution-0.05-2nm
• the smaller the value for resolution, the better the resolution
• Scanning Electron Microscopes


  -electron beam is directed onto the specimen through a vacuum. condenser and objective lenses focus the beam

  -electrons bounce off the surface of the specimen and are sensed by a detector to produce a 3d image

  -mag- 100,000

  -res- 5-50nm
• Laser Scanning confocal microscopes


  -uses laser beams instead of beams of light

  -specimen must be tagged with fluorescent dye

  -laser beam is directed onto a beam splitter, which directs the beam onto the specimen which then emits the fluorescent dye.

  -pinhole just before the detector ensures a clear and sharp image
• advantaged of LSCM


  -produces clearer images than LM

  -can focus on objects at different depths- depth selectivity

  -multiple images can be layered to make a 3d image

  -high levels of contrast so can be easily identified