The tales of blood – PCK and TPACK

Shulman (1986) differentiates between content knowledge and pedagogical content knowledge (PCK).  It is true the teacher must be an expert in the content she wishes to teach but at the same time must also be an expert in how to teach that content.  This is where Shulman (1986) suggests PCK is, “…the most useful form of representation of those ideas, the most powerful analogies, illustrations, examples, explanations, and demonstrations…” (p. 9).  The ideas he speaks of are the content, the concepts, the specific learning outcomes outlined in the curriculum guides.  It is essentially not enough to know the stuff, but to know how to help students know that stuff that you know so well.

An example of PCK I have used in the past that has anecdotally worked well for me is the topic of blood types and blood transfusions, hence the title of this post :).

Blood types and transfusions shows up in the biology 30s Manitoba curriculum under the circulatory system.  It is a challenge for students to understand how we have 4 different blood types, and why getting certain red blood cells (RBCs) can be beneficial to a patient and why others can be catastrophic.  In order to help illustrate these ideas I have used the analogy of donuts. I did not come up with this analogy, simply found it online and borrowed it like any teachers with the best of intentions at heart.

Basically the analogy goes that RBCs are like donuts, some have A sprinkles, some have B sprinkles, some have A and B sprinkles and some have no sprinkles.  Sprinkles are analogous to antigens found poking out on the surface of these RBCs that help identify the type of they are either A, B, AB, or O.  The Rh sprinkle is tacked on after when students are comfortable with the A, B, AB, and O.

Then comes the challenging part of identifying correct versus wrong blood transfusions where students often get lost.  Here the presence of antibodies is explained and the Blood Typing Came from ( is used to help gamify transfusions and help the development of the concept in an engaging way.  I suppose this is where I use technology and essentially  I am using TPACK at this point in the lesson.

I enjoy teaching this lesson as I get to talk about donuts and the game is fun to play.



Shulman, Lee S. (1986). Those who understand: Knowledge growth in teaching.  Educational Researcher,  15,  2., pp. 4-14.

Blood Typing Game. ( Retrieved from:

One comment

  1. Vibhu,

    Thank you for sharing an excellent description of representation. The visual representation of donut is no doubt memorable for your students! I even found myself paying closer attention while reading about the donuts! A quotation found in Mishra and Koehler’s (2006) article came to mind while reading your post: “At the heart of PCK is the manner in which subject matter is transformed for teaching. This occurs when the teacher interprets the subject matter and finds different ways to represent it and make it accessible to learners (p.1021). This is exactly what you have accomplished through both examples that you have shared!

    Mishra, P., & Koehler, M. (2006). Technological pedagogical content knowledge: A framework for teacher knowledge. The Teachers College Record, 108(6), 1017-1054.

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