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

Microscope Slide Preparation

  • 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

1.1-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

1.2-Common-Microscope-Stains-and-Uses-table

Drawing Cells

  • 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)

Exam Tip

When producing a biological drawing, it is vital that you only ever draw what you see and not what you think you see.To accurately reflect the size and proportions of structures you see under the microscope, you should get used to using the eyepiece graticule.

 

 

 

 

 

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