CIE A Level Biology复习笔记1.1.1 The Microscope in Cell Studies

• In order to observe cellular material in more detail, specimens can be prepared for viewing under a light microscope
• Samples need to be thin enough to allow light to pass through
• The type of preparation that is appropriate is dependent on the cellular material that needs to be viewed

Slide preparation methods table

• Samples sometimes need to be stained, as the cytosol and other cell structures may be transparent or difficult to distinguish
• To stain a slide the sample needs to be first air-dried and then heated by passing it through a Bunsen burner flame – this will allow the sample to be fixed to the slide and to take up the stain
• As with the type of preparation required, the type of stain used is dependent on what type of specimen is being used

Common microscope stains & uses table

• To record the observations seen under the microscope (or from photomicrographs taken) a labelled biological drawing is often made
• Biological drawings are line pictures which show specific features that have been observed when the specimen was viewed
• There are a number of rules/conventions that are followed when making a biological drawing

• The conventions are:
  • The drawing must have a title
  • The magnification under which the observations shown by the drawing are made must be recorded
  • A sharp HB pencil should be used (and a good eraser!)
  • Drawings should be on plain white paper
  • Lines should be clear, single lines (no thick shading)
  • No shading
  • The drawing should take up as much of the space on the page as possible
  • Well-defined structures should be drawn
  • The drawing should be made with proper proportions
  • Label lines should not cross or have arrowheads and should connect directly to the part of the drawing being labelled
  • Label lines should be kept to one side of the drawing (in parallel to the top of the page) and drawn with a ruler
• Drawings of cells are typically made when visualizing cells at a higher magnification power, whereas plan drawings are typically made of tissues viewed under lower magnifications (individual cells are never drawn in a plan diagram)