Blood Cells (OCR A Level Biology)

• 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 of blood cells drawn from the field of view of a microscope observing a blood smear