Activity: Observing Blood

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Human blood appears to be a red liquid to the naked eye, but under a microscope we can see that it contains four distinct elements:  
  • plasma
  • red blood cells
  • white blood cells
  • and platelets

The plasma is liquid part of blood, and is actually colorless. The red blood cells give blood its red color. White blood cells are interspersed in the sea of red blood cells and help fight infection. The platelets are fragments of red blood cells and function in clotting.

  • Compound light microscope like one of THESE.
  • pin
  • matchbook
  • band-aid
  • slides
  • coverslips

  1. First sterilize the pin by running it through a flame. (Ask an adult to supervise)  Next, poke your little finger quickly and lightly.  Squeeze your finger and place a drop of blood on a slide and cover with the coverslip. (Use a band-aid to prevent infection.)  You may wish to view the lab "Preparing a blood smear" for further information on preparing the slide.
  2. Place the slide on the microscope stage, and bring into focus on low power (100X). Adjust lighting and then switch into high power (400X).
  3. You should see hundreds of tiny red blood cells; there are billions circulating throughout our blood stream. Red blood cells contain no nucleus, which means they can't divide. Red blood cells are constantly produced by the bone marrow and the spleen. You should also be to find a few white blood cells. They are slightly larger than red blood cells, and have a nucleus. They resemble an amoeba and can contort their body in any way they like. White blood cells fight infection by consuming foreign bodies. The platelets are fragments of red blood cells and are very small.

The person whose blood was examined should then clean the slide.  Avoid coming into contact with another person's blood.

  • Which are bigger, red, or white blood cells?
  • What is the liquid part of the blood called?
  • What is the function of platelets?

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