OCR A Level Biology:复习笔记1.2.4 Drawing Cells From Blood Smears

Drawing Cells From Blood Smears

  • 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)

Blood smears

  • A blood smear is when a small amount of blood is spread on a glass microscope slide, stained and covered with a coverslip
  • The different blood cells can then be examined using a microscope
    • Red blood cells have no nuclei and a distinct biconcave shape
    • White blood cells have irregular shapes
    • Neutrophils have distinctive lobed nuclei
      • They make up roughly 70% of all white blood cells

       

    • Lymphocytes have very large nuclei that nearly occupy the entire cell

     

The different blood cells present in a blood smear

The lobed nucleus of a neutrophil

An example drawing of the cells observed (using a microscope) in a blood smear

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.You should be able to describe and interpret photomicrographs, electron micrographs and drawings of typical animal cells.

 

 

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