Halloween is approaching and the gore of blood is often a part of the scene. But how about turning your students on to the beauty of blood—the amazing beauty of how it accomplishes all it does?

In middle school, students often investigate the circulatory system and memorize the flow of blood from lungs to heart, to body, back to heart, and finally back to lungs. But how often do they investigate what this “fluid tissue” actually is and how it does all it does for us?

Red blood cells from http://sciencenow.sciencemag.org/feature/science_shots/images/ss_20051027_1.jpg

NYTimes.com recently published an article, The Wonders of Blood, in which blood’s various features are described. For example, the chemistry of blood is likened to sea water, a reference to the evolutionary history of multicellular organisms originating with a single-celled common ancestor living in sea water. Another feature of red blood cells is that they give up their nucleus and DNA in order to carry hemoglobin, the oxygen-binding part of red blood cells. A third feature of red blood cells is their squishing up in order to fit through the tiniest blood vessels in order to reach all 100 trillion or so cells of the human body. Their mantra could be No Cell Left Behind!

Additional features of blood include the three different kinds of blood cells. Besides red blood cells, there are white blood cells and platelets. And, like all other living cells, these cells react to stimuli. When an injury is incurred or an invader detected, these cells are signaled to take action. Another feature of blood is its ability to cleanse the body of things like ammonia. Blood does much more than simply travel through the circulatory system, exchanging oxygen for carbon dioxide.

Students are capable of understanding more than we sometimes challenge them to understand. The role of blood in the body is a perfect opportunity to allow students’ curiosity to take them to deeper understandings.

How to Turn This News Event into an Inquiry-Based, Standards-Related Science Lesson

The National Science Education Standards in life science states students should gain understanding in (1) structure and function in living systems, (2) regulation and behavior, and (3) diversity and adaptations of organisms. An exploration of blood touches on all three areas, depending on which you wish to emphasize.

Students probably do not conceive of blood as a tissue since it is liquid, not solid. Ask them what the definition of a tissue is — a collection of similar cells organized to perform a coordinated function. Ask them what blood is made of— cells and water. Do these cells work together to perform a function? Does that fit the definition of tissue? Where did we learn that tissues must be solid? You could connect to concepts in matter, such as solids suspended in a liquid, if students have had such discussions already.

Make explicit the overlap and connections from the system level of the circulatory system to the tissue and cellular level of blood. Though we teach students the hierarchical organization of living systems, we may inadvertently communicate that these levels are discrete. Such thinking will prevent students from understanding how the fundamental concept of homeostasis, reacting to stimuli at the cellular level, has important consequences at the system and organismal level.

Concepts in diversity and adaptations can be explored in comparing the blood of various phyla. We should be cautious of using the human system as the standard to which all other systems are compared for their sophistication. Rather, we should get students to think about the niche of the various organisms and how their particular blood works to help organisms accomplish their apparent role in their community and ecosystem. Further, students can think about selection pressures that may have contributed to the evolution of various systems, from the most primitive to the more recently derived.

Here are additional related resources from the National Science Digital Library Middle School Portal : Organ systems: Function, diversity and uniformity; and Sickle vs. Normal Cell; Cellular Service.

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